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Quantification of rill erosion using field measurements and remote sensing techniques Crudge, Steven 1987

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QUANTIFICATION OF RILL EROSION USING FIELD MEASUREMENTS AND REMOTE SENSING TECHNIQUES by STEVEN CRUDGE B . S C , York U n i v e r s i t y 1978 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES Department o f S o i l S c i e n c e We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 22, 1987 © Steven Crudge In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 ABSTRACT T h i s r e s e a r c h examines the use of remote sensing techniques to q u a n t i f y r i l l e r o s i o n i n two a g r i c u l t u r a l f i e l d s in the Lower F r a s e r V a l l e y . S o i l e r o s i o n d u r i n g the winter i s p a r t i c u l a r l y problematic i n some of the s l o p i n g s o i l s developed from l o e s s over g l a c i o - m a r i n e parent m a t e r i a l s . New techniques are needed to q u a n t i f y r i l l e r o s i o n on a t i m e l y b a s i s , and t h i s research focuses on.measuring the extent and r a t e of r i l l e r o s i o n from f i e l d and a e r i a l photograph measurements. A model which used r i l l measurements as input, was used to determine the r i l l plan a r e a s , r i l l volumes, and thus r i l l e r o s i o n r a t e s i n the t e s t a r e a . Using f i e l d r i l l o m e t e r measurements of r i l l s as input i n t o the model r e s u l t e d i n a 3 s o i l l o s s estimate of 49 m /ha/yr or 38.4 t/ha/yr f o r the t e s t s i t e . T h i s s o i l l o s s estimate i s deemed to be more r e l i a b l e than e r o s i o n p l o t and U n i v e r s a l S o i l Loss Equation estimates of s o i l l o s s f o r the t e s t a r e a . The r i l l volume and plan area of three main r i l l s , using three d i f f e r e n t r i l l measurement methods f o r input i n t o the model, were compared. Using f i e l d measuring tape measurements of r i l l s as input i n t o the model, r e s u l t e d i n a s o i l l o s s estimate which was 16 % g r e a t e r than the estimate from r i l l o m e t e r measurements. Using photo r i l l width measurements and an e s t i m a t i o n of r i l l depths and bottom widths from f i e l d data as model input, r e s u l t e d i n a s o i l l o s s estimate which was 22 % l e s s than the estimate from r i l l o m e t e r measurements. S p e c t r a l r e f l e c t i o n measurements made i n r i l l , i n t e r r i l l and d e p o s i t i o n a l areas were found to be s i g n i f i c a n t l y d i f f e r e n t , c o n f i r m i n g that r i l l e r o s i o n c o u l d be assessed in a q u a n t i t a t i v e manner using d i g i t a l image a n a l y s i s techniques. The s p e c t r a l s e p a r a t i o n was l a r g e l y due to d i f f e r e n c e s i n organic matter, s u r f a c e roughness and imaging geometry. The l a t t e r i s of p a r t i c u l a r importance i n c r e a t i n g darker shadowed r i l l s i d e s o p p o s i t e b r i g h t s u n - f a c i n g r i l l s i d e s w i t h i n a s i n g l e r i l l . A maximum l i k e l i h o o d c l a s s i f i e r , used as p a r t of the computer based image a n a l y s i s , determined the r i l l plan area f o r a sample area to be 9 % l e s s than the r i l l p l a n area obtained from the model using r i l l o m e t e r i n p u t . T h i s i n d i c a t e s the p o t e n t i a l of d i g i t a l a n a l y s i s to q u i c k l y determine the plan area of l a r g e r r i l l s . D i g i t a l e l e v a t i o n and moisture content data confirmed that the topographic shape of the f i e l d i s important in determining the s p a t i a l p a t t e r n of r i l l f ormation. The combination of such data with image a n a l y s i s and geographic i n f o r m a t i o n systems (GIS) have great p o t e n t i a l i n the t i m e l y q u a n t i f i c a t i o n of e r o s i o n i n the f u t u r e . i v TABLE OF CONTENTS Page ABSTRACT i i i TABLE OF CONTENTS V LIST OF PLATES v i i i LIST OF FIGURES v i i i LIST OF OVERLAYS ix LIST OF TABLES ix ACKNOWLEDGEMENTS x i I. INTRODUCTION 1 A. PROBLEMS AND AIMS 1 B. SITE DESCRIPTION 5 C. THE SITE EROSION PROBLEM 6 D. OVERVIEW OF THE STUDY DESIGN 9 11 . BACKGROUND 15 A. HARMFUL EFFECTS OF ACCELERATED EROSION 15 B. METHODS OF ASSESSMENT OF EROSION 17 C. SOIL REFLECTANCE 25 1. REFLECTANCE MEASUREMENTS 26 2. EFFECTS OF SOIL PROPERTIES ON REFLECTANCE 29 a. S o i l Moisture ' 30 b. Organic Matter 31 c. Surface C o n d i t i o n s 32 d. P a r t i c l e S i z e D i s t r i b u t i o n 34 e. Iron Oxide Content 35 3. THE EFFECT OF EROSION ON SOIL PROPERTIES WHICH AFFECT REFLECTANCE 35 a. S o i l P r o p e r t i e s 36 b. Removal of T o p s o i l 42 c. Shape of the S o i l Surface 43 D. USE OF GEOGRAPHIC INFORMATION SYSTEMS IN EROSION ASSESSMENT 44 v I I I . MATERIALS AND METHODS 52 A. STUDY GRID AND AERIAL PHOTOGRAPHY 52 B. SOIL REFLECTANCE AND PROPERTIES STUDY ( S e c t i o n 1) ..53 1. SOIL SPECTRAL MEASUREMENTS 53 2. SOIL PROPERTY ANALYSES 55 3. STATISTICAL ANALYSIS OF SOIL PROPERTIES AND REFLECTANCE DATA 56 C. SOIL LOSS ESTIMATES ( S e c t i o n s 2 & 3) 57 1. RILL VOLUME AND PLAN AREA MODEL 57 a. D e s c r i p t i o n of the Model 57 b. R i l l Measurements 58 2. CALIBRATION OF INPUT SOURCES USING THE 3 MAIN RILLS ( S e c t i o n 2) 59 3. SOIL LOSS ESTIMATES OF FIELD 2 ( S e c t i o n 3) 62 a. E s t i m a t i o n of R i l l Volume and Plan Area of a R e p r e s e n t a t i v e Area of F i e l d 2 Using 32 Randomly S e l e c t e d Sample Units..62 b. E r o s i o n P l o t E s t i m a t i o n of S o i l Loss ....64 c. U n i v e r s a l S o i l Loss Equation E s t i m a t i o n of S o i l Loss 65 D. DIGITAL ANALYSIS (S e c t i o n 4) 66 E. FORMATION OF THE' DIGITAL ELEVATION AND MOISTURE CONTENT MODELS ( S e c t i o n 5) 68 IV. RESULTS • 71 A. DATA ANALYSIS OF SOIL REFLECTANCE AND PROPERTIES (S e c t i o n 1) 71 1. VARIABILITY OF SOIL REFLECTANCE 71 2. REFLECTANCE DIFFERENCES BETWEEN RILL, INTERRILL AND DEPOSITION AREAS 74 a. F i e l d Data 74 b. Laboratory Data 77 c. Comparison of F i e l d & Laboratory Data 77 3. RELATIONSHIPS BETWEEN SOIL PROPERTIES AND REFLECTANCE 79 a. F i e l d R e f l e c t a n c e - S o i l Data R e l a t i o n s h i p s ..80 b. Laboratory R e f l e c t a n c e - S o i l Data R e l a t i o n s h i p s 83 c. Comparison of F i e l d & Laboratory Data 86 4. SUMMARY OF THE REFLECTANCE STUDY 87 B. SOIL LOSS ESTIMATES ( S e c t i o n s 2 & 3) 88 v i 1. CALIBRATION OF INPUT SOURCES OF THE RILL VOLUME AND PLAN AREA MODEL USING 3 MAIN RILLS ( S e c t i o n 2) 88 2. SOIL LOSS ESTIMATES OF FIELD 2 ( S e c t i o n 3) 95 a.- R i l l Model E s t i m a t i o n of S o i l L o s s of a R e p r e s e n t a t i v e Area of F i e l d 2 U s i n g 32 Randomly S e l e c t e d Sample U n i t s 95 i ) R i l l o m e t e r , Tape & Photo Data E s t i m a t e ..95 i i ) Tape Data E s t i m a t e 98 i i i ) Photo Data E s t i m a t e 99 i v ) Comparison of Model R e s u l t s from the R i l l o m e t e r , Tape & Photo Input Sources.100 b. E r o s i o n P l o t E s t i m a t e of S o i l L o s s 105 c. U n i v e r s a l S o i l L o s s E q u a t i o n E s t i m a t e of S o i l Loss 107 3. DIGITAL ANALYSIS ESTIMATES OF RILL PLAN AREA AND VOLUME FOR 3 SELECTED SAMPLE UNITS ( S e c t i o n 4) 110 4. DISCUSSION OF SOIL LOSS ESTIMATES 117 C. DIGITAL ELEVATION AND MOISTURE CONTENT MODELS 120 ( S e c t i o n 5) D. INTEGRATION OF RESULTS 127 V. CONCLUSIONS AND RECOMMENDATIONS 130 A. CONCLUSIONS 130 1. REFLECTANCE STUDY 130 2. RILL MODEL SOIL LOSS AND PLAN AREA ESTIMATES ..131 3. USLE AND EROSION PLOT SOIL LOSS ESTIMATES 132 4. DIGITAL IMAGE ANALYSIS PLAN AREA AND VOLUME ESTIMATES 133 5. USE OF THE SOIL LOSS ESTIMATION METHODS 134 6. DIGITAL ELEVATION AND MOISTURE CONTENT MAPS ...136 7. FUTURE DIRECTIONS 137 B. IMPLICATIONS OF SOIL LOSS AND RECOMMENDATIONS 137 LITERATURE CITED 140 APPENDICES 146 v i i L i s t of P l a t e s P l a t e Page 1. A e r i a l View of F i e l d 1 7 2. A e r i a l View of F i e l d 2 8 3. I n t e r r i l l S o i l Surface S t r u c t u r e 38 4. Breakdown of I n t e r r i l l S o i l Surface S t r u c t u r e 38 5. Smooth R i l l Bottom Surface 38 6. Smooth D e p o s i t i o n Area at Bottom of F i e l d 2 40 7. Smooth D e p o s i t i o n Area i n Topographic Low in the Middle of F i e l d 2 40 8. Specular R e f l e c t i o n from R i l l Bottoms 40 9. A e r i a l View of Specular R e f l e c t i o n from R i l l Bottoms .41 10. A e r i a l View of R i l l Bottoms i n P l a t e 9 With D i f f e r e n t Imaging Geometry 41 11. Increased Specular R e f l e c t i o n i n R i l l s Due to Increased Moisture Content 41 12. "Cos i " E f f e c t Observed on Snow Covered R i l l s 44 13. Colour Photocopy of Enlargement of F i e l d 2 and Sample U n i t s used i n the D i g i t a l A n a l y s i s 54 14. R i l l Measurement with a R i l l o m e t e r 61 15. Psuedo-Colour Image of the Maximum L i k l i h o o d C l a s s i f i c a t i o n of Sample Un i t 61 114 16. Psuedo-Colour Image of the Maximum L i k l i h o o d C l a s s i f i c a t i o n of Sample Un i t 77 114 17. Psuedo-Colour Image of the Maximum L i k l i h o o d C l a s s i f i c a t i o n of Sample U n i t 93 114 L i s t of F i g u r e s F i g u r e Page 1. Overview of Study Design 11 v i i i 2. Best F i t t i n g Q u a d r i l a t e r a l on R i l l P r o f i l e 61 3. Mean F i e l d R e f l e c t a n c e Values f o r R i l l , I n t e r r i l l and D e p o s i t i o n Areas 76 4. E l e v a t i o n P e r s p e c t i v e P l o t 122 5. Moisture Content P e r s p e c t i v e P l o t 123 L i s t of Overlays (In ^ e-r^b—on--ba-ek--e-o-ver) T i t l e O verlay Study G r i d 1 E l e v a t i o n Contour Map & Slope Gradient D i r e c t i o n Map f o r F i e l d 2 2 Moisture Contour Map, Slope Contour Map, & Rep r e s e n t a t i v e Area of F i e l d 2 and Sample U n i t s 3 L i s t of Tables Table Page 1. Data Sources Used f o r Each S e c t i o n of the Study 14 2. C o e f f i c i e n t s of V a r i a t i o n f o r R e f l e c t a n c e and S o i l P r o p e r t i e s 72 3. S i g n i f i c a n t D i f f e r e n c e s i n S o i l R e f l e c t a n c e s and P r o p e r t i e s Between R i l l , I n t e r r i l l and D e p o s i t i o n Areas i n F i e l d s 1 and 2 Combined 75 4. Means & Standard D e v i a t i o n s f o r R i l l , I n t e r r i l l and D e p o s i t i o n R e f l e c t a n c e and S o i l Property Values 76 5. Spearman's Rho Values f o r C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 1 81 6. Spearman's Rho Values f o r C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 2 81 7. Spearman's Rho Values f o r C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 1 I n t e r r i l l Areas 85 8. Spearman's Rho Values f o r C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 2 R i l l s 85 i x 9. Volumes and Plan Areas of the Three Main R i l l s and Percent D i f f e r e n c e From R i l l o m e t e r Derived Values ....90 10. Cumulative R i l l Segment E r r o r s For Tape and Photo Derived Volume and Plan Area 92 11. T o t a l Cumulative R i l l Segment E r r o r s and Percent of T o t a l R i l l o m e t e r D e r i v e d Values 93 12. Volumes of Sample U n i t s 96 13. Plan Areas of Sample U n i t s 97 14. Mean P i x e l Values of the Supervised C l a s s e s 111 15. Areas of Supervised C l a s s e s 112 16. R i l l Plan Area Estimates f o r Sample U n i t s 61, 77 & 93.112 17. R i l l Volume Estimates f o r Sample U n i t s 61, 77 & 93 ...115 18. S o i l Loss & Plan Area Estimates of the R i l l Model, U n i v e r s a l S o i l Loss Equation and E r o s i o n P l o t 118 x ACKNOWLEDGEMENTS The author wishes to thank Dr. Hans S c h r e i e r f o r h i s support and enthusiasm, and more i m p o r t a n t l y f o r being an e n j o y a b l e person to work under. Thanks are a l s o extended to the Department of S o i l Science l a b o r a t o r y t e c h n i c i a n s , f e l l o w graduate students, and f a c u l t y members. P a r t i a l funding f o r t h i s r e s e a r c h was pro v i d e d by the N a t u r a l Sciences and E n g i n e e r i n g Research C o u n c i l of Canada (NSERC). x i 1 Chapter I I n t r o d u c t i o n A. PROBLEMS AND AIMS " S o i l e r o s i o n may w e l l be the most underrated yet most damaging n a t u r a l resource problem of the 80's." T h i s q u o t a t i o n from a recent p u b l i c a t i o n by the Standing Senate Committee on A g r i c u l t u r e , F i s h e r i e s and F o r e s t r y (1986) i l l u s t r a t e s an i n c r e a s i n g concern with s o i l e r o s i o n , which can decrease a g r i c u l t u r a l p r o d u c t i v i t y and water q u a l i t y of water systems r e c e i v i n g the eroded sediment. Q u a n t i t a t i v e measurements of s o i l l o s s are necessary f o r an a c c u r a t e e s t i m a t i o n of the environmental and economic c o s t s a s s o c i a t e d with the d e t r i m e n t a l e f f e c t s of e r o s i o n . Accurate measurements of the causes and e f f e c t s of e r o s i o n w i l l allow f o r a g r e a t e r understanding of the e r o s i o n process which i n t u r n , w i l l l e a d to more acc u r a t e s o i l e r o s i o n p r e d i c t i o n models and a s s i s t i n determining a p p r o p r i a t e p r e v e n t a t i v e measures. In B r i t i s h Columbia, the Peace River D i s t r i c t and the Lower F r a s e r V a l l e y have experienced s i g n i f i c a n t s o i l l o s s e s due to water e r o s i o n (Science C o u n c i l of Canada 1986). The e r o s i o n a l processes of water movement on a h i l l s l o p e are i n t e r r i l l ( i n c l u d i n g r a i n s p l a s h and su r f a c e f l o w ) , r i l l , g u l l y and streambank e r o s i o n (Hudson 1981). 2 R i l l e r o s i o n i s the removal of s o i l by concentrated flow. I t i s important due to the volume of s o i l l o s t i n r i l l f ormation and the t r a n s p o r t a t i o n of s o i l detached i n i n t e r r i l l p rocesses by r i l l s . The volume of s o i l l o s s due to the a c t u a l r i l l formation v a r i e s with the tendency of a s o i l to be eroded by c o n c e n t r a t e d flow. S e v e r a l i n v e s t i g a t o r s have found that s u r f a c e s p o s s e s s i n g a tendency to r i l l produced s u b s t a n t i a l l y g r e a t e r t o t a l e r o s i o n than otherwise s i m i l a r s u r f a c e s l a c k i n g t h i s c h a r a c t e r i s t i c ( S o u l l i e r e and Toy 1986). The primary e r o s i v e f o r c e from the low energy, long d u r a t i o n type of r a i n f a l l found i n the P a c i f i c N.W. U n i t e d States comes from c o n c e n t r a t e d r i l l flow and can r e s u l t i n e x t e n s i v e r i l l development (Onstad and Young 1982). S i m i l a r c o n d i t i o n s e x i s t i n the Lower F r a s e r V a l l e y . Thus i t i s important to q u a n t i f y s o i l l o s s due to r i l l e r o s i o n i n t h i s area as i t can r e s u l t i n the l o s s of l a r g e amounts of s o i l . E r o s i o n i s very v a r i a b l e i n space and i n time. Remote sensing techniques provide s p a t i a l i n f o r m a t i o n and are w e l l s u i t e d f o r the e f f i c i e n t c o l l e c t i o n of multi-temporal data s e t s . Thus, remote sensing techniques can be u s e f u l i n p r o v i d i n g a data base f o r documenting the extent of s o i l e r o s i o n . Data c o l l e c t e d by remote sensing can be in a d i g i t a l form or can be converted from analog to d i g i t a l form. The e x i s t a n c e of the s p a t i a l data i n a d i g i t a l form allows f o r a wider range of a n a l y s e s . 3 Research i n t o the use of a e r i a l photographs i n the assessment of r i l l e r o s i o n i n the Palouse Region River Basin i n Washington State has been done ( F r a z i e r et a l . 1983). These r e s e a r c h e r s s t a t e that s p a t i a l r e l a t i o n s h i p s between c u l t i v a t i o n and e r o s i o n p a t t e r n s can only be viewed from above ground as only a p o r t i o n of any slope i s v i s i b l e from the ground. The s i g n i f i c a n c e of some p a t t e r n s i s not evident u n l e s s they are viewed from an a e r i a l p e r s p e c t i v e . They a l s o determined that r i l l measurement from a e r i a l photographs was f e a s i b l e ( F r a z i e r and McCool 1981). They found a minimum measurable r i l l width of 38 mm (ground d i s t a n c e ) on 1:2000 c o l o u r i n f r a r e d a e r i a l photographs using a 50 X pocket microscope. T h i s i n d i c a t e d the p o t e n t i a l f o r q u a n t i f i c a t i o n of r i l l e r o s i o n using a e r i a l imagery. The o v e r a l l purpose of t h i s study was to i n v e s t i g a t e the use of some remote sensing techniques i n the q u a n t i f i c a t i o n of r i l l e r o s i o n i n a c u l t i v a t e d f i e l d i n the Lower F r a s e r V a l l e y in S.W. B r i t i s h Columbia. The p e r i o d of a c t i v e e r o s i o n s t u d i e d was from f a l l 1984 to s p r i n g 1985. The study c o n s i s t s of f i v e main i n t e r r e l a t e d s e c t i o n s . The aim of the f i r s t s e c t i o n was to determine i f there are s i g n i f i c a n t d i f f e r e n c e s i n the s o i l r e f l e c t a n c e of r i l l , i n t e r r i l l and d e p o s i t i o n areas to f u r t h e r determine i f these areas are separable on a e r i a l photographs. A second aim was to determine the r e l a t i o n s h i p s between s o i l r e f l e c t a n c e and 4 c e r t a i n s e l e c t e d s o i l p r o p e r t i e s . The aim of s e c t i o n s 2 and 3 was to determine the p l a n area covered by r i l l s and the volume of s o i l l o s t due to r i l l f ormation using f i e l d and a e r i a l photograph r i l l measurements and a computer model. S e c t i o n 2 compared the r i l l volume and plan area estimates from three d i f f e r e n t r i l l model input sources. S e c t i o n 3 determined the r i l l volume and plan area of an area of the study f i e l d . T h i s s o i l l o s s was compared to s o i l l o s s c a l c u l a t e d from the U n i v e r s a l S o i l Loss Equation and e r o s i o n p l o t measurements. The f o u r t h s e c t i o n i n v o l v e d d i g i t i z a t i o n of the a e r i a l photograph and a n a l y s i s of the d i g i t i z e d image. A p o r t i o n of the image of the f i e l d was c l a s s i f i e d with respect to b r i g h t n e s s and the area of the c l a s s e s corresponding to the r i l l s was determined. The r i l l plan area determined from t h i s d i g i t a l c l a s s i f i c a t i o n was compared to the r i l l plan area determined from the f i e l d measurements and the computer model. In the f i f t h s e c t i o n , an e l e v a t i o n survey was done and a D i g i t a l E l e v a t i o n Model (DEM) was c r e a t e d . A d i g i t a l moisture content model was a l s o c r e a t e d . The output of both models was compared to the r i l l l o c a t i o n s observed on the a e r i a l photograph to i l l u s t r a t e the r e l a t i o n s h i p between e l e v a t i o n , f i e l d moisture content and r i l l development. 5 B. SITE DESCRIPTION Two f i e l d s l o c a t e d i n Matsqui M u n i c i p a l i t y i n the Lower Fr a s e r V a l l e y , B r i t i s h Columbia were chosen fo r the study. F i e l d 1 and F i e l d 2 were both used i n the i n i t i a l s o i l r e f l e c t a n c e / s o i l p r o p e r t i e s s e c t i o n of the study. F i e l d 2 was used f o r the remainder of the study. The f i e l d s are 2.5 km apart and are l o c a t e d i n u n d u l a t i n g to r o l l i n g t e r r a i n . The average slope of F i e l d 1 i s about 5-7 % and F i e l d 2 i s about 7-9 %. Both f i e l d s are complex s o i l u n i t s with the s o i l s having been c l a s s e d as Whatcom, Scat and N i c h o l s o n s o i l s e r i e s (Luttmerding 1980). These s o i l s are d e r i v e d from a r e l a t i v e l y t h i n l a y e r of a e o l i a n m a t e r i a l o v e r l y i n g g l a c i o - m a r i n e d e p o s i t s . The s o i l c o n s i s t s of 15 -30 cm s i l t loam with weak f i n e g r a n u l a r s t r u c t u r e o v e r l y i n g weakly s t r a t i f i e d s i l t loam or s i l t y c l a y loam. The t o p s o i l i n N i c h o l s o n s o i l s i s up to 25 cm t h i c k , while i n Whatcom s o i l s i t i s up to 50 cm t h i c k . Scat s o i l s d i f f e r from the others by being p o o r l y d r a i n e d . The Whatcom s o i l i s c l a s s e d as a L u v i s o l i c Humo-Ferric Podzol, the Nicholson s o i l i s a P o d z o l i c Gray L u v i s o l and the Scat s o i l i s an O r t h i c Humic G l e y s o l . A c c o r d i n g to the farmer, F i e l d 1 was c l e a r e d i n the e a r l y 1900's. F i e l d 2 had been i n pasture f o r 22 years before being c u l t i v a t e d and p l a n t e d to s t r a w b e r r i e s i n 1981. At the time of the study, from f a l l 1984 to s p r i n g 1985, F i e l d 1 was 6 f a l l o w while F i e l d 2 had been sown to ryegrass the p r e v i o u s f a l l . P l a t e s 1 and 2 are a e r i a l views of F i e l d s 1 and 2 re s p e c t i v e l y . C. THE SITE EROSION PROBLEM The annual r a i n f a l l i n the area i s q u i t e high and most occurs d u r i n g the f a l l and w i n t e r . R a i n f a l l from Oct to A p r i l i s about 1200 mm with i n t e n s i t i e s of 100 mm/day expected with a 2 year r e t u r n p e r i o d . Normal average monthly r a i n f a l l f o r the area f o r the months of Oct. to Feb. ranges from about 18 -20 cm. For the p e r i o d from Feb. to May i t ranges from about 10 - 17 cm and f o r the p e r i o d from May to Oct. i t ranges from about 4 - 1 0 cm. Thus, most of the e r o s i o n occurs i n t h i s area from Oct. to March. A number of f a c t o r s c o n t r i b u t e to the occurrence of c o n c e n t r a t e d flow and consequent r i l l f o rmation. The high f a l l and winter r a i n f a l l i n combination with the low storage c a p a c i t y of the t h i n t o p s o i l and the r e s t r i c t e d drainage of the impermeable s u b s o i l leads to s a t u r a t e d s o i l c o n d i t i o n s and f r e e water at the s u r f a c e . Under c o n d i t i o n s of l i m i t e d s o i l water storage, s a t u r a t i o n may occur w e l l below the minimum i n f i l t r a t i o n r a t e , p rovided that the r a i n f a l l input i s s u f f i c i e n t l y prolonged (Burt and Butcher 1985). Saturated s o i l c o n d i t i o n s are exacerbated i n F i e l d 2 by the long slope above the f i e l d , areas of t e l l u r i c seepage, leakage from a 7 PLATE 1. A e r i a l View of F i e l d 1. PLATE 2 . A e r i a l View o f F i e l d 2 . 9 r i g h t angle turn i n a drainage d i t c h , and drainage of water i n t o topographic lows i n the f i e l d . The occurrence of c o n c e n t r a t e d flow i s enhanced by the long slope l e n g t h s and e x i s t a n c e of two long topographic lows o r i e n t e d along the f a l l l i n e of the s l o p e . Surface flow d r a i n s i n t o these lows and down them to the f i e l d bottom. In F i e l d 1, furrows and t i r e t r a c k s have c o n t r i b u t e d to the occurrence of c o n c e n t r a t e d flow and r i l l f ormation. The steepness of the slope i n these f i e l d s i n c r e a s e s the amount of o v e r l a n d flow and the flow v e l o c i t y and thus the e r o s i v e power of the c o n c e n t r a t e d flow. The high s i l t content of the s o i l and l a c k of w e l l developed blocky s t r u c t u r e c o n t r i b u t e to the e r o d i b i l i t y of the s o i l . Ryegrass was p l a n t e d i n the p r e v i o u s f a l l i n F i e l d 2 i n an attempt to r e t a r d e r o s i o n . However, severe e r o s i o n o c c u r r e d before the c r o p was s u f f i c i e n t l y e s t a b l i s h e d . Much of the e r o s i o n in both f i e l d s o c c u r r e d d u r i n g a major r a i n f a l l event i n the f a l l of 1984. D. OVERVIEW OF THE STUDY DESIGN An overview of the study design i s presented i n a flow c h a r t format i n F i g u r e 1. The flow chart i l l u s t r a t e s the procedures used and the main purpose of each s e c t i o n of the study. S e c t i o n 1 of the study i n v e s t i g a t e s s o i l r e f l e c t a n c e 10 and s e l e c t e d s o i l p r o p e r t i e s to determine i f s i g n i f i c a n t d i f f e r e n c e s e x i s t among these i n r i l l , i n t e r r i l l and d e p o s i t i o n a r e a s . S p e c t r a l s e p a r a b i l i t y of the r i l l s from the surrounding area would pr o v i d e a b a s i s f o r the q u a n t i f i c a t i o n of r i l l e r o s i o n using d i r e c t measurements from remotely sensed images (eg. a e r i a l photographs) or d i g i t a l a n a l y s i s techniques. R e l a t i o n s h i p s between the s e l e c t e d s o i l p r o p e r t i e s and r e f l e c t a n c e are a l s o i n v e s t i g a t e d . Data from the l a b o r a t o r y a n a l y s i s of the s o i l samples a l s o p r o v i d e s input f o r the c a l c u l a t i o n of s o i l l o s s by the U n i v e r s a l S o i l Loss Equation. The r i l l volume and plan area model i s used to c a l c u l a t e these with 3 d i f f e r e n t input sources of r i l l measurements. These are r i l l o m e t e r and measuring tape measurements done i n the f i e l d , and photo measurements. The purpose of S e c t i o n 2 i s to c a l i b r a t e the 3 input sources used i n the r i l l volume and plan area model. That i s , the accuracy of r i l l volume and plan area estimates from (a) f i e l d tape r i l l measurement and (b) photo r i l l measurement input i n t o the model, r e l a t i v e to f i e l d r i l l o m e t e r r i l l measurement input i n t o the model are analysed. As the best p o t e n t i a l f o r the use of photo measurement f o r determining r i l l volume and plan area i s f o r l a r g e r r i l l s , t h i s c a l i b r a t i o n study i s done on the 3 main r i l l s i n f i e l d 2. These are r e f e r r e d to as R i l l 1, R i l l 2 and R i l l 3 (Overlay 1). OVERVIEW QF THE STUDY DESIGN RILL VOLUME i PLAN AREA MODEL Z X I COMPARISON OF RESULTS FROM RILLOMETER, MEASURING TAPE, ft PHOTO MEASUREMENT INPUTS RILL VOLUME t PLAN AREA OF AN AREA IN FIELD 2 EROSION PLOT ESTIMATION OF SOIL LOSS DIGITAL ANALYSIS RILL PLAN AREA OF A SAMPLE AREA COMPARISON OF RILL PLAN AREA USLE ESTIMATION OF SOIL LOSS COMPARISON OF SOIL LOSS RATES I EVALUATION OF REMOTE SENSING TECHNIQUES REFLECTANCE ft SOIL PROPERTIES OF RILL, INTERRILL I DEPOSITION AREAS DIGITAL ELEVATION I MOISTURE CONTENT MODELS DIFFERENCES BETWEEN RILL INTERRILL S DEPOSITION AREAS, REFLECTANCE-SOIL PROPERTIES RELATIONSHIPS 1 COMPARISON WITH AIR PHOTOS: ILLUSTRATE RELATIONSHIPS BETWEEN TOPOGRAPHY, MOISTURE I RILL PATTERN FIGURE 1. Overview of the Study Design. (Numbers i n d i c a t e d i f f e r e n t s e c t i o n s of the study as d e s c r i b e d i n the text) 12 In S e c t i o n 3, the r i l l model i s used to determine the t o t a l r i l l volume and p l a n area of a l a r g e , r e p r e s e n t a t i v e area of F i e l d 2 (Overlay 3). T h i s i s done by determining the t o t a l r i l l volume and r i l l plan area of 32 randomly s e l e c t e d 2 10 m sample u n i t s from the r e p r e s e n t a t i v e area of the f i e l d . The average r i l l volume and p l a n area of the sample u n i t s i s then used to c a l c u l a t e the r i l l volume/ha and p l a n area/ha f o r the r e p r e s e n t a t i v e area of the f i e l d . T h i s s o i l l o s s estimate (from the r i l l volume) i s compared to s o i l l o s s / h a estimates f o r the f i e l d determined by the U n i v e r s a l S o i l Loss Equation and e r o s i o n p l o t data. S e c t i o n 4 i n v e s t i g a t e s the use of d i g i t a l a n a l y s i s to a u t o m a t i c a l l y and q u i c k l y determine the plan area of r i l l s which are s p e c t r a l l y separable from the i n t e r r i l l a r e a. T h i s p a r t of the study i s performed on 3 of the above 32 sample u n i t s , sample u n i t s 61, 77 & 93. The 3 u n i t s chosen c o n t a i n p a r t of one of the main r i l l s , R i l l 3, and some smal l e r r i l l s . The p l a n area of the 3 u n i t s determined from computer c l a s s i f i c a t i o n i s compared to the plan area of the 3 u n i t s as determined from the r i l l model. R i l l volume was a l s o c a l c u l a t e d f o r the 3 u n i t s using the computer c l a s s i f i c a t i o n p lan area and an average r i l l depth f o r the 3 sample u n i t s determined from f i e l d measurements. T h i s i s a l s o compared to the r i l l model r e s u l t s . The purpose of S e c t i o n 5 i s to i n v e s t i g a t e the 13 r e l a t i o n s h i p s between topography, s o i l s u r f a c e moisture content and the r i l l e r o s i o n p a t t e r n using d i g i t a l e l e v a t i o n and moisture content maps and the a e r i a l photograph. Data from an e l e v a t i o n survey and s o i l sampling were used t o c r e a t e the d i g i t a l e l e v a t i o n and moisture content contour maps r e s p e c t i v e l y . From the e l e v a t i o n contour map, a slope g r a d i e n t contour map and a s u r f a c e water flow d i r e c t i o n map were c r e a t e d . P e r s p e c t i v e p l o t s of the f i e l d topography and s o i l moisture content were c r e a t e d to h e l p v i s u a l i z e the contour maps. These v a r i o u s output were compared to the a e r i a l photographs to i l l u s t r a t e the causes of accumulation of excess moisture, c o n c e n t r a t i o n of ove r l a n d flow and r i l l format i o n . Table 1 summarizes the main data sources used f o r each s e c t i o n of the study. 14 Table 1. Data Sources Used f o r Each S e c t i o n of the Study. S e c t i o n Data Source 1 . R e f l e c t a n c e & S o i l P r o p e r t i e s . S o i l R e f l e c t a n c e Measurements and S o i l P r o p e r t i e s of S o i l Samples from R i l l , I n t e r r i l l & D e p o s i t i o n Areas i n F i e l d s 1 & 2. 2. Comparison of Model R e s u l t s from R i l l o m e t e r , Measuring Tape & A i r Photo Inputs R i l l Measurements of the 3 Main R i l l s i n F i e l d 2 Using R i l l o m e t e r , Measuring Tape & Photo Measurements of R i l l s . 3. R i l l Volume ( S o i l Loss) and Plan Area of Re p r e s e n t a t i v e Area of F i e l d 2. R i l l o m e t e r , Tape & Photo R i l l Measurements of 32 Randomly S e l e c t e d 10 m Sample U n i t s from a R e p r e s e n t a t i v e Area of F i e l d 2. USLE S o i l Loss E s t i m a t i o n . S o i l Samples Laboratory Data (from S e c t i o n 1), E l e v a t i o n Survey Data, L i t e r a t u r e Data. E r o s i o n P l o t E s t i m a t i o n of S o i l Loss. P r e - e x i s t i n g Data From E r o s i o n P l o t on F i e l d 2. 4. D i g i t a l A n a l y s i s E s t i m a t i o n of R i l l Plan Area (& Volume). D i g i t a l Images of 3 Sample U n i t s S e l e c t e d from the above 32 Sample U n i t s . 5. D i g i t a l E l e v a t i o n & Moisture Content Models. E l e v a t i o n Survey, S o i l Samples from I n t e r r i l l Areas (moisture c o n t e n t s ) , A e r i a l Photograph. 15 Chapter II Background A. HARMFUL EFFECTS OF ACCELERATED EROSION Water and wind e r o s i o n are the most widespread s o i l d e g r a d a t i o n problems in Canada (Dumanski et a l . 1986). The main d e t r i m e n t a l e f f e c t of e r o s i o n i s a r e d u c t i o n i n crop p r o d u c t i v i t y . I t has been estimated that r i l l and sheet e r o s i o n i n the Palouse Region River Basin causes a r e d u c t i o n of average wheat y i e l d s of about 22 % ( F r a z i e r et a l . 1983). The economic c o s t of e r o s i o n i n B.C. has been estimated to be 10 m i l l i o n d o l l a r s (Science C o u n c i l of Canada 1986). I t has been estimated in Canada that e r o s i o n of one inch of s o i l can reduce wheat y i e l d s by 1.5 to 3.4 bushels/acre (SSCAFF 1986). Decreased p r o d u c t i v i t y r e s u l t s from the l o s s of s o i l as sediment in runoff and changes i n s o i l p r o p e r t i e s of the remaining s o i l . Loss of t o p s o i l r e s u l t s i n a t h i n n e r t o p s o i l which reduces the volume of f e r t i l e growth medium f o r p l a n t r o o t s . Numerous r e s e a r c h e r s have found that when the t o p s o i l i s removed, crop y i e l d s are reduced 20 to 75 % compared to check p l o t s (Spomer and P i e s t 1982). A c c e l e r a t e d l o s s of s o i l leads to an a c c e l e r a t e d e v o l u t i o n of the landscape such that the area a v a i l a b l e f o r c r o p p r o d u c t i o n i s reduced. That i s , g u l l y and r a v i n e growth i n t o a g r i c u l t u r a l f i e l d s can be a c c e l e r a t e d by l a r g e annual s o i l l o s s e s . Severe r i l l e r o s i o n 16 which develops a f t e r p l a n t i n g can a l s o reduce the area i n which p l a n t s can grow. As w e l l as complete removal of a p o r t i o n of the t o p s o i l , e r o s i o n r e s u l t s i n a decrease i n the f e r t i l i t y of the remaining s o i l . The s o r t i n g a c t i o n of water e r o s i o n removes a high p r o p o r t i o n of the c l a y and humus from the s o i l and leaves the l e s s p r o d u c t i v e c o a r s e r mineral f r a c t i o n behind (Troeh et a l . 1980). Much of s o i l f e r t i l i t y i s a s s o c i a t e d with c l a y and humus due to the p r o p e r t i e s that these c o n s t i t u e n t s impart to the s o i l . They are important as sources and storage s i t e s of n u t r i e n t s and c o n t r i b u t e to m a i n t a i n i n g other s o i l p r o p e r t i e s conducive to p l a n t growth. These i n c l u d e m i c r o b i a l a c t i v i t y , water h o l d i n g c a p a c i t y , b u f f e r i n g c a p a c i t y and s o i l s t r u c t u r e which a f f e c t s a e r a t i o n and p e r m e a b i l i t y . D e t r i m e n t a l e f f e c t s of the e r o s i o n process i n c l u d e the breakdown of s o i l s t r u c t u r e by r a i n d r o p impact and s u r f a c e flow, and the r e d u c t i o n of s u r f a c e i n f i l t r a b i l i t y by the formation of a s u r f a c e c r u s t . Thus, with res p e c t to s o i l f e r t i l i t y and the consequent crop p r o d u c t i o n , an eroded s o i l i s degraded c h e m i c a l l y , p h y s i c a l l y and b i o l o g i c a l l y . Another important d e t r i m e n t a l e f f e c t i s the r e d u c t i o n of water q u a l i t y i n h y d r a u l i c systems r e c e i v i n g the r u n o f f . Sediment lowers water q u a l i t y by t r a n s p o r t i n g adsorbed n u t i e n t s , heavy metals, p e s t i c i d e s and other t o x i c compounds from farmland to water bodies (Switzer-Howse and Coote 1984). E r o s i o n i s a major c o n t r i b u t o r to stream and r i v e r p o l l u t i o n 1 7 (SSCAFF 1984) as sediment from s u r f a c e e r o s i o n i s a major t r a n s p o r t v e h i c l e of n u t r i e n t s and p e s t i c i d e s ( F r e r e 1977). Research has shown that most of the n i t r o g e n and phosphorus di s c h a r g e d from c r o p l a n d i s a s s o c i a t e d with the eroded s o i l t r a n s p o r t e d by runoff ( A l b e r t s et a l . 1978). T h i s process r e s u l t s in an economic l o s s of f e r t i l i t y to the farmer and a d e t e r i o r a t i o n i n water q u a l i t y (Burwell 1977). N u t r i e n t s adsorbed to sediment can c o n t r i b u t e to e u t r o p h i c a t i o n while p e s t i c i d e s and heavy metals may cause t o x i c i t y problems. These e f f e c t s as w e l l as i n c r e a s e d t u r b i d i t y may d e s t r o y the a q u a t i c h a b i t a t . Increased sediment l o a d i n runoff may r e s u l t i n i n c r e a s e d sedimentation which decreases channel c a p a c i t y . These problems c o n t r i b u t e to the o f f s i t e economic c o s t s of e r o s i o n . I t i s very expensive to r e h a b i l i t a t e a e u t r o p h i c or t o x i c water body and i n c r e a s e d sedimentation can l e a d to i n c r e a s e d c o s t s from r e g u l a r c l e a n i n g of drainage and i r r i g a t i o n channels and dredging of harbours. T h i s o f f s i t e e f f e c t of e r o s i o n i s extremely widespread and c o n t r i b u t e s l a r g e l y to the o v e r a l l economic impact of e r o s i o n (Switzer-Howse and Coote 1984). B. METHODS OF ASSESSING EROSION It i s important to be able to assess the s e v e r i t y of e r o s i o n i n order to a s s i s t in the a l l o c a t i o n of funds f o r s o i l c o n s e r v a t i o n management and to determine the r e d u c t i o n 1 8 of e r o s i o n due to s o i l c o n s e r v a t i o n measures. The value of a method of assessment of e r o s i o n can be judged by the amount of i n f o r m a t i o n t h a t can be d e r i v e d from i t on damage to the environment and the p r e c i s i o n and accuracy of t h i s i n f o r m a t i o n . Q u a n t i t a t i v e methods are most u s e f u l in t h i s c o n t e x t . The amount of s o i l eroded over a given time p e r i o d , i f a c c u r a t e l y known, p r o v i d e s p r e c i s e i n f o r m a t i o n on the s e v e r i t y of e r o s i o n . The amount of s o i l eroded and knowledge of the c h a r a c t e r i s t i c s of the eroded sediment can be used as input to chemical t r a n s p o r t models. The r e s u l t s of these models c o u l d be used to help p r e d i c t economic l o s s e s due to l o s s of crop n u t r i e n t s or to p r e d i c t the decrease i n water q u a l i t y due to the a d d i t i o n of crop n u t r i e n t s or t o x i c chemicals. Assessment of e r o s i o n i s very d i f f i c u l t as e r o s i o n i s a l o c a l i z e d phenomenon, very i r r e g u l a r l y d i s t r i b u t e d i n space (De Boodt 1980) and time. Assessment of e r o s i o n can i n v o l v e (a) assessment of the f a c t o r s . which a f f e c t e r o s i o n and/or (b) assessment of a c t u a l e r o s i o n f e a t u r e s . The former method r e q u i r e s some p r e d i c t i v e c a p a b i l i t y of the degree of e r o s i o n which would r e s u l t from a given set of f a c t o r s . T h i s p r e d i c t i v e c a p a b i l i t y would be very u s e f u l i n determining the p o t e n t i a l change i n e r o s i o n r e s u l t i n g from a change in land use management. The assessment of e r o s i o n f e a t u r e s can be done at v a r i o u s l e v e l s of d e t a i l . 19 With an i n c r e a s e i n d e t a i l , g r e a t e r p r e c i s i o n i n r e p r e s e n t i n g the s e v e r i t y of e r o s i o n can be a c h i e v e d . The s c a l e of the e r o s i o n assessment l a r g e l y determines the l e v e l of d e t a i l i n v o l v e d . U s u a l l y , smaller s c a l e assessments use q u a l i t a t i v e methods while q u a n t i t a t i v e methods r e q u i r e a l a r g e r s c a l e . Some of the e r o s i o n assessment methods in use w i l l now be d i s c u s s e d . A r e l a t i v e l y simple method of assessment i s a v i s u a l examination of the landscape and s u b j e c t i v e d e l i n e a t i o n and ranking of areas i n t o d i f f e r e n t e r o s i o n c l a s s e s such as s l i g h t , moderate and severe. T h i s has o f t e n been done using a e r i a l photographs to map v i s i b l e e r o s i o n f e a t u r e s and/or e r o s i o n i n f l u e n c i n g f a c t o r s such as slope and v e g e t a t i o n cover. Mapping v i s i b l e e r o s i o n f e a t u r e s has i n v o l v e d mapping (a) l i n e a r e r o s i o n f e a t u r e s and/or (b) areas of d i f f e r e n t b r i g h t n e s s r e s u l t i n g from removal of t o p s o i l and subsequent exposure or mixing in of a s u b s o i l with a d i f f e r e n t r e f l e c t a n c e . The problem with mapping the l a t t e r i s that b r i g h t n e s s i s not always r e l a t e d to the e r o s i o n s t a t e i n the same manner. Bergsma (1974) found eroded toposequences where e r o s i o n a l areas had a l i g h t e r tone and d e p o s i t i o n a l areas had a darker tone as w e l l as the o p p o s i t e case. The b r i g h t n e s s w i l l depend on the amount of s o i l eroded, the r e f l e c t a n c e of the s u b s o i l and the c h a r a c t e r i s t i c s of the m a t e r i a l d e p o s i t e d , a l l of which may vary in d i f f e r e n t s i t u a t i o n s . The s u b j e c t i v e 20 i n t e r p r e t a t i o n of e r o s i o n f e a t u r e s , l i m i t s the c a t e g o r i z a t i o n of the s e v e r i t y of e r o s i o n i n t o very broad c a t e g o r i e s ( i . e . low p r e c i s i o n ) i f a reasonable degree of accuracy i s to be ob t a i n e d . A crude numerical assessment of e r o s i o n r i s k can be achieved u s i n g t h i s method by a s s i g n i n g a r a t i n g value to each land u n i t with respect t o e r o s i o n causing f a c t o r s and f e a t u r e s , and summing up the s c o r e s . While t h i s approach may i n c r e a s e the p r e c i s i o n of the method, the s u b j e c t i v e r a t i n g b r i n g s i n t o q u e s t i o n the accuracy of the method. Another approach has been to t r y to represent the s e v e r i t y of e r o s i o n by q u a n t i f y i n g the c h a r a c t e r i s t i c s of e r o s i o n f e a t u r e s . T h i s has i n c l u d e d determining the l e n g t h of l i n e a r e r o s i o n a l f e a t u r e s from a e r i a l photographs (Garland 1982). N o s s e i r (1980) c h a r a c t e r i z e d r i l l s , g u l l i e s and streams by t h e i r frequency, d e n s i t y and mean l e n g t h . While these s t a t i s t i c s do c h a r a c t e r i z e the l i n e a r e r o s i o n f e a t u r e s i n an area, i t has yet to be shown how w e l l they represent the a c t u a l amount of s o i l l o s t i n an a r e a . One of the most widely used methods i s sediment c o l l e c t i o n from p l o t s . Roel's (1985) paper i s a good c r i t i q u e on t h i s method. He p o i n t s out that a s i d e from measurement e r r o r s i n a p a r t i c u l a r p l o t , there are v a r i o u s sources of b i a s which must be taken i n t o account before p l o t data can be e x t r a p o l a t e d to land u n i t s i n a r e g i o n a l survey. Roels s t a t e s that e x t r a p o l a t i o n of p l o t r e s u l t s are condsidered to be 21 a p p l i c a b l e to a l l areas of s i m i l a r physiography ( s l o p e , aspect, cover, e r o s i o n f e a t u r e s ) , but that t h i s may lead to c o n s i d e r a b l e e r r o r s . The main reason i s due to the enormous s p a t i a l v a r i a b i l i t y i n s o i l l o s s and the small sampling percentage of p l o t s . T h i s problem i s i l l u s t r a t e d by F i e l d 2 ( P l a t e 2). Even when the e r o s i o n p a t t e r n i s known, i t would be d i f f i c u l t to pick the l o c a t i o n of one p l o t which would represent the average s o i l l o s s f o r the whole f i e l d . Roels s t a t e s that i f land u n i t s c o n t a i n only a small number of r i l l s , the best estimate of the t o t a l s o i l l o s s from each of these land u n i t s w i l l o b v i o u s l y be based on measurement of the r i l l e r o s i o n and sampling of the i n t e r r i l l and p r e - r i l l s u b p o p u l a t i o n s. He b e l i e v e s that there i s no sense in p e r s e v e r i n g e r o s i o n sampling s t u d i e s unless (very) l a r g e numbers of p l o t s and compared measurements ( i . e . those that w i l l reduce the variance) are used,and un l e s s g r e a t e r u n i f o r m i t y i s sought i n the areas under study. Another study on the v a r i a b i l i t y of r u n o f f f and s o i l l o s s from f a l l o w p l o t s (Wendt et a l . 1986) found that only minor amounts of observed v a r i a b i l i t y c o u l d be a t t r i b u t e d to any of s e v e r a l measured p l o t p r o p e r t i e s . E r o s i o n p l o t s have a p l o t l e n g t h which i s u s u a l l y s h o r t e r than the f i e l d whose s o i l l o s s they are supposed to r e p r e s e n t . T h i s s h o r t e r l e n g t h may l e a d to an i n a c c u r a t e r e p r e s e n t a t i o n of the s o i l l o s s of the f i e l d e s p e c i a l l y i n areas of abundant r i l l e r o s i o n . T h i s i s because 22 i t i s recog n i z e d that r i l l e r o s i o n v a r i e s with slope l e n g t h . A l s o , s u r f a c e water flow l i n e s are not always p a r a l l e l to the slope because of the i r r e g u l a r topography. Consequently, p l o t boundaries d i s t u r b the n a t u r a l course of the flow (Roels and Jonker 1983). E r o s i o n p i n s have been used to measure changes i n ground e l e v a t i o n due to s o i l l o s s . T h i s method has the disadvantage of being very time consuming and the presence of the p i n s may a f f e c t the e r o s i o n process. Again, unless the whole f i e l d i s measured, there must be s u f f i c i e n t sampling s i t e s to s t a t i s t i c a l l y v e r i f y e x t r a p o l a t i o n to the whole f i e l d . McCool (1981) has designed a r i l l o m e t e r to r e c o r d the c r o s s - s e c t i o n a l area of r i l l s , from which r i l l volume can be determined. The accuracy of t h i s method w i l l depend i n p a r t on the d i s t a n c e between the measurements down the r i l l . I f taken at d i s t a n c e s which are small r e l a t i v e to the d i s t a n c e s over which changes in r i l l shape occur, the volume measurements c o u l d be reasonably a c c u r a t e . T h i s method would be very time consuming i f there were many r i l l s i n the f i e l d and a l l were measured to determine t o t a l s o i l l o s s from r i l l s . However, a s u f f i c i e n t number of randomly s e l e c t e d areas of the f i e l d c o u l d be measured to a c c u r a t e l y represent the t o t a l s o i l l o s s from the f i e l d . T h i s method only i n c l u d e s s o i l l o s s from the formation of r i l l s and doesn't i n c l u d e i n t e r r i l l eroded s o i l . However some e r o s i o n models separate r i l l and i n t e r r i l l 23 e r o s i o n and t h i s method may be u s e f u l i n v a l i d a t i o n of the r i l l e r o s i o n part of e r o s i o n models. The change i n the s o i l s u r f a c e e l e v a t i o n due to e r o s i o n can a l s o be measured photogrammetrically. Thomas et a l . (1986) have i n v e s t i g a t e d the use of photogrammetry from a e r i a l photographs f o r q u a n t i f y i n g c o n c e n t r a t e d flow e r o s i o n . They have achieved a c c u r a c i e s of between + 13 and + 19 mm f o r e l e v a t i o n measurements and 55 mm f o r p l o t t e d contours, though they d i d not t r a n s l a t e these e r r o r s i n t o volume e r r o r s . These a c c u r a c i e s are s u f f i c i e n t f o r g u l l i e s and many r i l l s . With the use of s t a t e of the a r t equipment (such as a n a l y t i c a l s t e r e o p l o t t e r s ) and techniques, the accuracy can be improved. T h i s method may e v e n t u a l l y prove to be one of the most accurate and e f f i c i e n t e s t i m a t o r s of s o i l l o s s , however the equipment and t e c h n i c a l e x p e r t i s e necessary are not always a v a i l a b l e and are very expensive. E r o s i o n models attempt to n u m e r i c a l l y p r e d i c t s o i l l o s s . There are d e t e r m i n i s t i c , s t o c h a s t i c and parametric models. Most models i n e r o s i o n assessment are of the parametric grey-box type (Morgan 1979). They are based on d e f i n i n g the most important e r o s i o n f a c t o r s , measuring them, and using s t a t i s t i c a l techniques, r e l a t i n g them to measurements of s o i l l o s s . The most common of these type models i s the U n i v e r s a l S o i l Loss Equation (USLE). I t i s designed to p r e d i c t long-term average annual s o i l l o s s e s f o r 24 s p e c i f i c combinations of p h y s i c a l and management c o n d i t i o n s (Wischmeier 1976). There are problems which are inherent i n the design of the equation as w e l l as problems with misuse of the equation which are d i s c u s s e d by Wischmeier (1976). A l l e m p i r i c a l l y d e r i v e d equations i n v o l v e experimental e r r o r and p o t e n t i a l e s t i m a t i o n e r r o r due to the e f f e c t s of unmeasured v a r i a b l e s . A l s o , i n the USLE, there are some i n t e r a c t i o n s between v a r i a b l e s (eg. s o i l , topography and s u r f a c e c o n d i t i o n s ) that r e q u i r e f u r t h e r r e s e a r c h before t h e i r e f f e c t s can be i n c o r p o r a t e d i n t o the f a c t o r e v a l u a t i o n procedures (Wischmeier 1976). Probably the major misuses are inadequate accuracy of the f a c t o r v a l u e s used, and a p p l i c a t i o n of the equation to i n a p p r o p r i a t e s i t u a t i o n s . Use and l i m i t a t i o n s of the USLE are we l l documented i n many papers and books and w i l l not be d i s c u s s e d f u r t h e r here. Recently, much emphasis has been p l a c e d on the development of d e t e r m i n i s t i c models. These are based on the use of mathematical equations to d e s c r i b e the processes i n v o l v e d i n the model, t a k i n g i n t o account the laws of c o n s e r v a t i o n of mass and energy. The trend i n d e t e r m i n i s t i c models i s l i k e l y to be towards d i s t r i b u t e d parameter models which d i v i d e an area i n t o square planar segments and describe-both the temporal and s p a t i a l v a r i a t i o n s i n the e r o s i o n p r o c e s s . Due to the complexity of the e r o s i o n process, the models w i l l be very l a r g e and c o n s i s t of s e v e r a l submodels 25 such as h y d r o l o g i c , detachment and t r a n s p o r t / d e p o s i t i o n submodels. At present, most shallow flow t r a n s p o r t models are crude approximations of the a c t u a l e r o s i o n process ( D i l l a h a and Beasley 1983). With time, the models w i l l get more acc u r a t e , but a l s o more complex. The h y d r o l o g i c model by Rhodenburg et a l . (1986) i s a good example. As these r e s e a r c h e r s s t a t e , the c o l l e c t i o n of data f o r input i n t o t h i s model (and s i m i l a r l y complex models) r e q u i r e s an amount of work and equipment f a r exceeding that of e m p i r i c a l models (Bork and Rhodenburg 1986). A l s o , the lack of r e a d i l y a v a i l a b l e d e t e r m i n i s t i c models i n Canada and the lack of e x p e r t i s e i n t h e i r use discourages use of them. C. SOIL REFLECTANCE The r e f l e c t a n c e of the s o i l s u r f a c e i s a f f e c t e d by c e r t a i n s o i l p r o p e r t i e s . The s o i l p r o p e r t i e s which a f f e c t the r e f l e c t a n c e most are moisture content, organic matter content, s u r f a c e c o n d i t i o n (roughness), p a r t i c l e s i z e d i s t r i b u t i o n and i r o n oxide content. These p r o p e r t i e s , and thus the s o i l r e f l e c t a n c e , can be a f f e c t e d in v a r y i n g degrees by s o i l e r o s i o n . T h e r e f o r e , the s o i l r e f l e c t a n c e can be i n d i c a t i v e of the e f f e c t s of e r o s i o n in an area. In g e n e r a l , the r e f l e c t e d r a d i a t i o n from a s u r f a c e as de t e c t e d by a sensor with a given f i e l d of view and sensor aperture area i s a f u n c t i o n of the s p a t i a l and s p e c t r a l 26 d i s t r i b u t i o n of the i l l u m i n a t i o n , the imaging geometry, and the r e f l e c t i v i t y of the s u r f a c e m a t e r i a l . 1. REFLECTANCE MEASUREMENTS R e f l e c t i o n measurements of s u r f a c e s are taken i n the b e l i e f t hat the r e f l e c t a n c e measured i s r e p r e s e n t a t i v e of one or more s u r f a c e c h a r a c t e r i s t i c s which may be u s e f u l in a given a n a l y s i s . They u t i l i z e a source of i l l u m i n a t i o n and a sensor to d e t e c t the r e f l e c t e d r a d i a t i o n . R e f l e c t i o n measurements are taken i n the l a b , i n the f i e l d or from a e r i a l p l a t f o r m s . Each of these measurement s i t u a t i o n s may have t h e i r own s p e c i f i c set of parameters which a f f e c t the r e f l e c t a n c e measured from a given s u r f a c e . In the case of measurements o u t s i d e , the s p a t i a l and s p e c t r a l i l l u m i n a t i o n are a f f e c t e d by the sun p o s i t i o n , atmospheric e f f e c t s (e.g. atmospheric t r a n s m i s s i o n , path radiance) and r a d i a t i o n r e f l e c t e d from nearby s u r f a c e s (e.g. mountains). In the l a b s i t u a t i o n , the s p e c t r a l and s p a t i a l d i s t r i b u t i o n s are determined by the r a d i a t i o n source c h a r a c t e r i s t i c s . The imaging geometry i s d e f i n e d by the p o s i t i o n s of the r a d i a t i o n source and the sensor i n r e l a t i o n to the s u r f a c e . The b i d i r e c t i o n a l r e f l e c t a n c e d i s t r i b u t i o n f u n c t i o n (BRDF) int r o d u c e d by Nicodemus et a l . (1977), s p e c i f i e s the r e f l e c t a n c e from a s u r f a c e i n terms of both the i n c i d e n t and r e f l e c t e d beam geometry. The BRDF determines how b r i g h t a 27 given s u r f a c e w i l l appear with given viewing and i l l u m i n a t i o n d i r e c t i o n s . A Lambertian s u r f a c e i s an i d e a l i z e d s u r f a c e which appears e q u a l l y b r i g h t from any view angle ( p e r f e c t l y d i f f u s e r e f l e c t i o n ) . When such a surface i s i l l u m i n a t e d by a c o l l i m a t e d ( p o i n t ) source with i r r a d i a n c e E Q a r r i v i n g at an i n c i d e n t angle /, the radiance L r i s given by L r = p_ E 0 c ° s [ 1 ] where p i s the s u r f a c e albedo which i s an i n t r i n s i c p r o p e r t y of the s u r f a c e m a t e r i a l . The term cos / w i l l be determined by the sun azimuth angle and the slope of the s u r f a c e . When i l l u m i n a t e d by a h e m i s p h e r i c a l uniform source (e.g. un i f o r m l y d i s t r i b u t e d s k y l i g h t ) with radiance L Q over the v i s i b l e hemisphere, the radiance L r i s given by L r = p L (1 + cos e) [ 2 ] r o 2 where e i s the emergent angle of the l i g h t . Cos e depends on the s u r f a c e s l o p e . On a c l e a r day, most of the i l l u m i n a t i o n i s from the sun and thus the s u r f a c e radiance can be approximated by the f i r s t equation alone. Radiance of the su r f a c e i s thus c o n t r o l l e d by the i n c i d e n t angle of the i r r a d i a n c e and the albedo of the s u r f a c e m a t e r i a l . The in c i d e n c e angle i s c o n t r o l l e d by the sun p o s i t i o n and the 28 slope of the s u r f a c e . In a d d i t i o n to d i f f u s e r e f l e c t i o n , another source of s u r f a c e radiance i s s p e c u l a r r e f l e c t i o n . P e r f e c t s p e c u l a r r e f l e c t i o n i s r e f l e c t i o n i n which the i n c i d e n t angle and emergent angle are equal, and occurs on f l a t m i r r o r l i k e s u r f a c e s . T h i s type of r e f l e c t a n c e depends on the smoothness of the s u r f a c e but not on the i n t r i n s i c r e f l e c t i o n p r o p e r t i e s of the s u r f a c e m a t e r i a l ( i . e . the r e f l e c t e d spectrum equals the i n c i d e n t spectrum). Because of t h i s no i n f o r m a t i o n about the p r o p e r t i e s of the r e f l e c t i n g s u r f a c e (other than i t s smoothness) can be d e r i v e d from s p e c u l a r l y r e f l e c t e d l i g h t . Commonly, the a c t u a l r e f l e c t a n c e i s i n between pure s p e c u l a r r e f l e c t i o n and pure Lambertian ( d i f f u s e ) r e f l e c t i o n and i s a combination of both ( G o i l l o t 1980). U s u a l l y , f o r ground based measurements, a radiance measurement i s taken of a standard s u r f a c e (e.g. BaS04) which i s c o n s i d e r e d to be an approximation to an i d e a l , p e r f e c t l y r e f l e c t i n g , p e r f e c t l y d i f f u s i n g s u r f a c e i r r a d i a t e d i n the same way as the sample s u r f a c e . The r a t i o of the radiance of the sample s u r f a c e to the radiance of the standard s u r f a c e i s the r e f l e c t a n c e f a c t o r . For a standard which i s a p e r f e c t l y r e f l e c t i n g , p e r f e c t l y d i f f u s e r e f l e c t o r , t h e r e f l e c t a n c e f a c t o r i s equal to the albedo of the sample s u r f a c e . 29 2. EFFECTS OF SOIL PROPERTIES ON REFLECTANCE The p r o p e r t i e s of a s o i l s u r f a c e i n the f i e l d which most a f f e c t r e f l e c t i o n are moisture content, o r g a n i c matter content, s u r f a c e c o n d i t i o n (roughness), p a r t i c l e s i z e d i s t r i b u t i o n and i r o n oxide content. R e l a t i n g s o i l r e f l e c t i o n to s o i l p r o p e r t i e s i s complicated by the f a c t that many of the s o i l p r o p e r t i e s covary. S c h r e i e r (1977) s t a t e d that because of the i n t e r r e l a t i o n s h i p s between s o i l p r o p e r t i e s , i t i s d i f f i c u l t to d i s t i n g u i s h between the ones that are c a u s a t i v e with respect to s o i l r e f l e c t a n c e and the ones which are -c o r r e l a t e d to s p e c t r a l r e f l e c t a n c e merely by being a s s o c i a t e d with the c a u s a t i v e f a c t o r s . A given s o i l p r o p e r t y may have a d i f f e r e n t amount of i n f l u e n c e on the r e f l e c t a n c e i n d i f f e r e n t s o i l s depending on the r e l a t i v e values of the other s o i l p r o p e r t i e s which a f f e c t r e f l e c t a n c e . S c h r e i e r (1986), who found c o r r e l a t i o n s between % carbon, % i r o n and % sand content with s o i l r e f l e c t a n c e at c e r t a i n wavelengths, s t a t e s that these r e l a t i o n s h i p s are not u n i v e r s a l and are only a p p l i c a b l e on a s i t e s p e c i f i c b a s i s . He s t a t e s that s o i l r e f l e c t a n c e parameters can i n t e r a c t and thus obscure o v e r a l l r e l a t i o n s h i p s between i n d i v i d u a l parameters and r e f l e c t a n c e . In the study of s o i l s p e c t r a l c h a r a c t e r i s t i c s , two types of r e f l e c t a n c e curves are f r e q u e n t l y used. One type i s s o i l r e f l e c t a n c e versus wavelength, which can be used to i n v e s t i g a t e the c h a r a c t e r i s t i c v a r i a t i o n s i n a s o i l ' s 30 r e f l e c t a n c e values at d i f f e r e n t wavelengths ( s o i l s p e c t r a l c u r v e ) . The other type p l o t s s o i l r e f l e c t a n c e v a l u e s at an optimal wavelength band versus a p a r t i c u l a r s o i l p r o p e r t y . a. S o i l Moisture I t i s g e n e r a l l y observed that throughout the spectrum, s o i l s appear darker when wet than when dry. Stoner and Baumgardner (1981) and Stoner et a l . (1980) d e r i v e d f i v e s o i l s p e c t r a l curve forms from r e f l e c t a n c e measurements of more than 240 s o i l s e r i e s . The shape of the s o i l r e f l e c t a n c e curves i s a f f e c t e d by strong water a b s o r p t i o n bands at 1450 and 1970 nm., and o c c a s i o n a l l y by much weaker a b s o r p t i o n bands at 970, 1200, and 1770 nm. (Baumgardner et a l . 1985). I f the ge n e r a l shape of the s p e c t r a l r e f l e c t a n c e curve f o r a p a r t i c u l a r s o i l does not change with d i f f e r e n t moisture contents (other s o i l p r o p e r t i e s being unchanged), then the curve w i l l be c h a r a c t e r i s t i c of that p a r t i c u l a r s o i l at v a r i o u s moisture contents,and d i f f e r e n t s o i l types may be able t o be d i s t u i n g u i s h e d r e g a r d l e s s of moisture content. Obukhov and Orlov (1964) and Condit (1970) found that the shape of the r e f l e c t a n c e curves they s t u d i e d d i d not change upon wetting of the s o i l . More work needs to be done i n v o l v i n g c a r e f u l l y c o n t r o l l e d moisture t e n s i o n e q u i l i b r i a and s o i l moisture content i n r e f l e c t a n c e s t u d i e s (Baumgardner et a l . 1985). Some s t u d i e s have u t i l i z e d c o r r e l a t i o n and r e g r e s s i o n 31 of r e f l e c t a n c e with moisture content i n an attempt to q u a n t i f y the r e l a t i o n s h i p between the two s o i l p r o p e r t i e s . Peterson et a l (1979) found a l i n e a r r e l a t i o n s h i p between r e f l e c t a n c e and s o i l moisture content e q u i l i b r a t e d at v a r i o u s t e n s i o n s . He s t a t e d that the e f f e c t of s o i l moisture on r e f l e c t a n c e c o u l d be g e n e r a l i z e d i f the s o i l moisture content were expressed as s o i l t e n s i o n r a t h e r than percent dry weight of the s o i l . M o isture e f f e c t s on s o i l r e f l e c t a n c e i n the f i e l d i s important due to the l a r g e s p a t i a l and temporal v a r i a b i l i t y of moisture content i n the s o i l . C i h l a r and Pr o t z (1973) found that the range of r e f l e c t a n c e i s c o n s i d e r a b l y expanded i f the sur f a c e s o i l s c o n t a i n d i f f e r e n t amounts of moisture. They s t a t e that s p e c t r a l d i f f e r e n c e s between s o i l types i n c r e a s e when the moisture content d i f f e r s most between d i f f e r e n t s o i l types. b. Organic Matter S o i l organic matter content and the composition of the organic c o n s t i t u e n t s are known to have a str o n g i n f l u e n c e on s o i l r e f l e c t a n c e . I t has been g e n e r a l l y observed that as organic matter content i n c r e a s e s , s o i l r e f l e c t a n c e decreases throughout the 400 - 2500 nm wavelength range (Hoffer and Johannsen 1969). S e v e r a l s t u d i e s ( S c h r e i e r 1986 and 1977, Baumgardner et a l . 1970, Stoner and Baumgardner 1981) i n d i c a t e that organic matter contents gr e a t e r than 2 % play a dominant 32 r o l e i n determining s o i l r e f l e c t a n c e p r o p e r t i e s while organic matter contents of l e s s than 2 % are l e s s e f f e c t i v e i n masking the i n f l u e n c e on r e f l e c t a n c e of other s o i l c o n s t i t u e n t s (such as i r o n o x i d e ) . The decomposition s t a t e of the organic matter i n organic s o i l s has been observed to d r a s t i c a l l y a l t e r n o n v i s i b l e r e f l e c t a n c e , with g r e a t e r decomposition l e a d i n g to a decrease i n r e f l e c t a n c e (Baumgardner et a l . 1985). S e v e r a l s t u d i e s c i t e d i n a paper by Baumgardner et a l . (1985) suggest that the e f f e c t of organic matter on r e f l e c t a n c e i s g r e a t e r f o r wavelengths l e s s than 1200 nm Mathews et a l . (1973) found that with the d e s t r u c t i o n of o r g a n i c matter, the r e f l e c t a n c e i n c r e a s e d g r e a t l y from 400 to 600 nm, while i t a c t u a l l y decreased s l i g h t l y from 1500 to 2400 nm. c. Surface C o n d i t i o n s D i f f i c u l t i e s i n c h a r a c t e r i z i n g surface roughness has made the e f f e c t of s u r f a c e c o n d i t i o n one of the l e a s t understood areas of s o i l r e f l e c t a n c e (Baumgardner et a l . 1985). S c h r e i e r (1986) s t a t e s that s u r f a c e roughness has a s i g n i f i c a n t i n f l u e n c e on d e t a i l e d s p e c t r a l r e f l e c t a n c e measurements and suggests that l a s e r s might be used to measure s u r f a c e roughness. Many s o i l r e f l e c t a n c e s t u d i e s are done i n the l a b with crushed, s i e v e d to l e s s than 2 mm s o i l samples which may be a i r dry or wetted to a c e r t a i n t e n s i o n . I f wetted to a t e n s i o n which i s c h a r a c t e r i s t i c of f i e l d moisture content, 33 such samples have the same values f o r the s o i l p r o p e r t i e s as in the f i e l d except f o r s u r f a c e roughness which can be an important p r o p e r t y i n determining s o i l r e f l e c t a n c e . Surface roughness r e s u l t s mainly from s o i l s t r u c t u r e or recent t i l l a g e . C i p r a et a l . (1971) found that c r u s t e d s u r f a c e s had higher r e f l e c t a n c e i n the 430- 830 nm region than s o i l s u r f a c e s with the c r u s t broken. They a t t r i b u t e d t h i s to the rough s u r f a c e which would cause s c a t t e r i n g of l i g h t and an i n c r e a s e i n the area i n shadow. Coarse aggregates having an i r r e g u l a r shape form a complex s u r f a c e with a l a r g e number of i n t e r a g g r e g a t e spaces. As l i g h t f a l l s on such a s u r f a c e , most of the i n c i d e n t f l u x p e n etrates i n t o l i g h t t r a p s and i s completely e x t i n g u i s h e d there (Baumgardner et a l . 1985). Obukhov and Orlov (1964) found that s o i l s with w e l l d e f i n e d s t r u c t u r e i n the plow l a y e r r e f l e c t 15 - 20 % l e s s l i g h t energy than s t r u c t u r e l e s s s o i l s . The r e f l e c t a n c e of r e c e n t l y t i l l e d s o i l s u r f a c e s has been observed to vary with i l l u m i n a t i o n angle (Crown and Pawluk 1974, Coulson and Reynolds 1971). Smoother s o i l s u r f a c e s w i l l r e f l e c t a g r e a t e r amount of l i g h t as s p e c u l a r r e f l e c t a n c e . The p r o p o r t i o n of t h i s l i g h t d e t e c t e d by a sensor w i l l depend on the s o u r c e - s u r f a c e - s e n s o r geometry. Martin (1980) used c l o s e range photogrammetry to c h a r a c t e r i z e s o i l s u r f a c e roughness. He concluded that s o i l s u r f a c e 34 roughness may be a b l e to be c h a r a c t e r i z e d by o b serving the shadow e f f e c t from o b l i q u e i l l u m i n a t i o n and c a l i b r a t i n g i t to the photogrammetric data. M a r t i n ' s study i l l u s t r a t e s the importance of s u r f a c e roughness i n i n f l u e n c i n g r e f l e c t a n c e . d. P a r t i c l e S i z e D i s t r i b u t i o n Bowers and Hanks (1965) found an e x p o n e n t i a l i n c r e a s e i n r e f l e c t a n c e at a l l wavelengths between 400 and 1000 nm with d e c r e a s i n g p a r t i c l e s i z e of pure k a o l i n i t e . Averaged r e f l e c t a n c e s p e c t r a from a broad range of sandy s o i l s e x h i b i t the trend of i n c r e a s i n g r e f l e c t a n c e with d e c r e a s i n g p a r t i c l e s i z e p o s s i b l y due to a smoother s u r f a c e with fewer v o i d s to t r a p l i g h t (Baumgardner et a l . 1985). For a l a r g e number of rocks and m i n e r a l s , Hunt and S a l i s b u r y (1971) and Hunt et a l (1971) found that d e c r e a s i n g the p a r t i c l e s i z e i n c r e a s e d r e f l e c t a n c e at a l l wavelengths f o r s i l i c a t e and carbonate m i n e r a l s . Contrary to other s t u d i e s , they a l s o found that the r e f l e c t a n c e of oxides and s u l p h i d e s sometimes decreased with d e c r e a s i n g p a r t i c l e s i z e . T h i s phenomenom appeared to occur in m a t e r i a l s of very low r e f l e c t a n c e . A l s o c o n t r a r y to the s t u d i e s p r e v i o u s l y mentioned Gerberman and Neher (1979),in adding i n c r e a s i n g amounts of sand to a c l a y s o i l , found a l i n e a r i n c r e a s e i n r e f l e c t a n c e with i n c r e a s e s sand content f o r wavelengths i n the 540 to 860 nm range. Thus i t appears that s o i l p a r t i c l e s i z e and shape appear to i n f l u e n c e s o i l 35 , r e f l e c t a n c e i n v a r y i n g manners (Baumgardner et a l . 1985). The e f f e c t of the p a r t i c l e s i z e d i s t r i b u t i o n on r e f l e c t a n c e may be d i f f i c u l t to separate out i n a f i e l d measurement s i t u a t i o n as the p a r t i c l e s i z e d i s t r i b u t i o n may covary with o r g a n i c carbon and f i e l d moisture content, both of which g e n e r a l l y have a s t r o n g e r i n f l u e n c e on s o i l r e f l e c t a n c e i n the f i e l d . e. Iron Oxide Content T y p i c a l l y , the major a b s o r p t i o n bands f o r f e r r i c i r o n are at about 870 and 700 nm and f e r r o u s i r o n produces a band near 1000 nm (Baumgardner et a l . 1985). S o i l s higher i n i r o n c o n t e n t , e x h i b i t a broader a b s o r p t i o n band at 870 nm as compared to the narrow, yet d i s t i n c t band i n s o i l s of lower i r o n c o n t e n t . The shape of the s p e c t r a l curve can be s i g n i f i c a n t l y a f f e c t e d by the presence of i r o n . S c h r e i e r (1986 and 1977) found that the e f f e c t s of i r o n are l a r g e l y masked by the presence of o rganic matter of 2 % or more. The narrowness of the i n f r a r e d wavelength i r o n a b s o r p t i o n bands r e q u i r e very narrow band width sensors to be d e t e c t a b l e and thus allow f o r q u a n t i t a t i v e comparisons of r e f l e c t a n c e with i r o n oxide l e v e l s . 3. THE EFFECT OF EROSION ON SOIL PROPERTIES WHICH AFFECT REFLECTANCE E r o s i o n can a f f e c t the s o i l r e f l e c t a n c e i n three main 36 ways; (1) i t can a f f e c t the s o i l p r o p e r t i e s which a f f e c t s o i l r e f l e c t a n c e , (2) removal of s o i l can expose the s u b s o i l or r e s u l t i n mixing i n (upon c u l t i v a t i o n ) of a s u b s o i l of a d i f f e r e n t r e f l e c t a n c e or (3) i t can change the shape of the s o i l s u r f a c e and thus the imaging geometry. a. S o i l P r o p e r t i e s The e f f e c t s of e r o s i o n on the p a r t i c l e s i z e of s o i l i s not w e l l understood. S t u d i e s on the p a r t i c l e s i z e d i s t r i b u t i o n of eroded sediment have used d i f f e r e n t experimental designs, so comparison of the r e s u l t s i s d i f f i c u l t and the r e s u l t s are sometimes c o n t r a d i c t o r y . However, enrichment of the eroded sediment i n f i n e r p a r t i c l e s r e l a t i v e to the o r i g n a l s o i l matrix has been observed. I t has a l s o been observed that most of the c l a y i s eroded i n the form of aggregates and r e l a t i v e l y l i t t l e i s eroded as primary p a r t i c l e s (Young 1980). T h i s i s i n p a r t , of course, due to the f a c t that much of the c l a y i n the t o p s o i l complexes with organic matter to form aggregates. Except i n extremely sandy s o i l s a very c o n s i d e r a b l e p r o p o r t i o n of the org a n i c m a t e r i a l i s a s s c o c i a t e d with the i n o r g a n i c components (Greenland 1965). Thus many s o i l s which s u f f e r from e r o s i o n are d e p l e t e d i n c l a y and organic matter. D e p o s i t i o n s e l e c t i v e l y removes c o a r s e r p a r t i c l e s , i n c r e a s i n g the f r a c t i o n of f i n e s i n the sediment (Fos t e r et 37 a l . 1985). Thus many d e p o s i t i o n a l areas at slope bottoms are e n r i c h e d i n sand (and d e p l e t e d i n organic matter) r e l a t i v e to the o r i g i n a l matrix s o i l . However, i f the slope bottoms(or other areas i n the f i e l d ) are s u f f i c i e n t l y f l a t or c o n t a i n hollows, a good d e a l of c l a y and organic matter i n the runoff would be d e p o s i t e d and not t r a n s p o r t e d o f f the f i e l d . Breakdown of s u r f a c e s t r u c t u r e and formation of s u r f a c e c r u s t s are known to occur as a r e s u l t of r a i n drop impact and o v e r l a n d flow. In i n t e r r i l l areas, the s u r f a c e becomes g r a d u a l l y smoother as aggregates are broken down and eroded m a t e r i a l i s d e p o s i t e d between aggregates (De Ploey 1985). T h i s e f f e c t can be seen i n p i c t u r e s taken from i n t e r r i l l eroded areas i n F i e l d 1. The s o i l i n P l a t e 3 i s the l e a s t eroded and the aggregates are not as broken down, though some d e p o s i t i o n between the aggregates can be seen to decrease the s u r f a c e roughness. The l a r g e s t aggregates can be seen to c r e a t e the g r e a t e s t shadow area. P l a t e 4 ( c l o s e r to the f i e l d bottom) i l l u s t r a t e s an area i n which the s u r f a c e s t r u c t u r e i s more s e v e r e l y broken down and has more d e p o s i t i o n f i l l i n g the spaces between aggregates, thus c r e a t i n g a smoother su r f a c e and fewer shadows. I t i s i n t e r e s t i n g to note the l i n e a r p a t t e r n c r e a t e d by aggregate breakdown and p a r t i c l e t r a n s p o r t by water flowing down the f a l l l i n e . P l a t e 5 i l l u s t r a t e s the smoother r i l l bottom as compared to the adjacent i n t e r r i l l a r e a . The roughness of r i l l bottoms 38 PLATE 5. Smooth R i l l Bottom Surface 39 can be q u i t e v a r i a b l e depending on the stage of r i l l development and the presence of s t i c k s and stones in the s o i l which cause the r i l l bottom to erode unevenly. If t here i s s u f f i c i e n t d e p o s i t i o n i n an area to cover the e x i s t i n g s u r f a c e roughness, a smooth s u r f a c e r e s u l t s . P l a t e 6 i l l u s t r a t e s the d e p o s i t i o n a l area at the bottom of F i e l d 1 and P l a t e 7 i l l u s t r a t e s a d e p o s i t i o n a l area i n a t o p o g r a p h i c a l l y low area i n the middle of F i e l d 1. The smoother s u r f a c e s r e s u l t i n fewer shadows and l e s s s c a t t e r i n g of l i g h t . T h i s becomes e s p e c i a l l y important i n r e f l e c t a n c e measurements when the imaging geometry i s such that s p e c u l a r r e f l e c t a n c e can be r e c e i v e d by the sensor (when i=e). P l a t e 8 i l l u s t r a t e s the b r i g h t e r r i l l bottom as compared to the i n t e r r i l l area l a r g e l y due to the smoother s u r f a c e and thus the i n c r e a s e d specular r e f l e c t a n c e r e c e i v e d by the camera. The r i l l bottoms in P l a t e 9 appear b r i g h t e r than the same r i l l bottoms i n P l a t e 10 due to a d i f f e r e n t imaging geometry which r e s u l t e d i n more s p e c u l a r l y r e f l e c t e d l i g h t r e c e i v e d by the camera from the r i l l bottoms in P l a t e 9. There i s p o s s i b l y an i n t e r a c t i o n e f f e c t with surface roughness and f i e l d moisture content. While an i n c r e a s e i n f i e l d moisture content g e n e r a l l y decreases the r e f l e c t a n c e s f o r a rough s u r f a c e , f o r a smooth s u r f a c e , i f s u f f i c i e n t moisture i s present, i t may i n c r e a s e the r e f l e c t a n c e by c a u s i n g an i n c r e a s e i n s p e c u l a r r e f l e c t a n c e ( p r o v i d e d the PLATE 7. Smooth Deposition Area i n Topographic Low i n the Middle of F i e l d 1. PLATE 8. Specular Reflection from R i l l Bottoms. 41 PLATE 9. A e r i a l View of Specular Reflection From R i l l Bottoms. PLATE 10. A e r i a l View of R i l l Bottoms i n PLATE 9 With a D i f f e r e n t Imaging Geometry. PLATE 11. Increased Specular Reflection in R i l l s Due to Increased Moisture Content. 42 imaging geometry i s a p p r o p r i a t e f o r the sensor to r e c e i v e s p e c u l a r l y r e f l e c t e d l i g h t ) . P l a t e 11 demonstrates the high r e f l e c t a n c e of the wet, smooth r i l l bottoms (and some ponded water) due to the high amount of spec u l a r r e f l e c t i o n viewed. One can c o n j e c t u r e that as moisture content i n c r e a s e s s u f f i c i e n t l y , the water menisci between the s o i l p a r t i c l e s become f l a t t e r and c l o s e r to the tops of the p a r t i c l e s , thus r e s u l t i n g i n a g r e a t e r area a v a i l a b l e f o r s p e c u l a r r e f l e c t i o n . In summary, some d e p o s i t i o n a l areas w i l l be c o a r s e r t e x t u r e d with l e s s c l a y , organic matter and s u r f a c e s t r u c t u r e than uneroded or i n t e r r i l l eroded areas. Thus higher r e f l e c t a n c e w i l l be measured i n these d e p o s i t i o n a l areas e s p e c i a l l y i f the imaging geometry i s such that s p e c u l a r r e f l e c t i o n i s r e c e i v e d . R i l l bottoms w i l l a l s o tend to be smoother than i n t e r r i l l a reas. T h i s w i l l c o n t r i b u t e to higher r e f l e c t a n c e . F i e l d moisture content can be important i n a f f e c t i n g the r e f l e c t a n c e but i s l a r g e l y t o p o g r a p h i c a l l y c o n t r o l l e d and moisture content v a l u e s f o r r i l l , i n t e r r i l l and d e p o s i t i o n a l areas w i l l depend on the shape of the f i e l d . b. Removal of T o p s o i l Removal of t o p s o i l can r e s u l t i n exposure of a s u b s o i l with d i f f e r e n t r e f l e c t a n c e . T h i s c o u l d occur over time f o r a whole f i e l d or r e l a t i v e l y q u i c k l y where r i l l s and g u l l i e s have cut down i n t o the s u b s o i l . However even i f exposure of a 43 d i f f e r e n t r e f l e c t a n c e s u b s o i l doesn't occur, there c o u l d be enough t o p s o i l removed such that the s u b s o i l i s mixed i n upon c u l t i v a t i o n , thus changing the t o p s o i l p r o p e r t i e s and the r e f l e c t a n c e . c. Shape of the S o i l Surface The shape of r i l l s and g u l l i e s a f f e c t s the imaging geometry so as to make these f e a t u r e s more v i s i b l e (depending on the sun p o s i t i o n ) . The most obvious e f f e c t i s the presence of a shadow on one s i d e of the r i l l . The other s i d e of the r i l l f a ces the sun more d i r e c t l y than the adjacent ( i n t e r r i l l ) s o i l s u r f a c e . Thus the cos i term i n equation [1] i s l a r g e r and so i s the radiance of the r i l l s i d e as compared to the adjacent s o i l s u r f a c e . The shadow e f f e c t and the e f f e c t of more d i r e c t i n c i d e n t s u n l i g h t are very important and may dominate over a l l other s o i l f a c t o r s which a f f e c t r e f l e c t a n c e i n some cases, depending on the r i l l shape. In an a e r i a l view of F i e l d 2 ( P l a t e 2 ) , the r i l l bottoms can't be seen as the r i l l s tend to be "V" shaped and r e l a t i v e l y narrow and the s c a l e of the photograph i s not l a r g e enough. Here, the dark shadow and b r i g h t sun f a c i n g r i l l s i d e s (a r e s u l t of the imaging geometry) allow the r i l l s to be d i s t i n g u i s h e d . In an a e r i a l view of f i e l d 1 ( P l a t e 1 ) , the dark and b r i g h t r i l l s i d e s h e l p to d i s t i n g u i s h the r i l l s but the r i l l bottoms of the l a r g e r r i l l s are a l s o v i s i b l e . 44 T h i s i s due t o the w i d e r , f l a t t e r shape of t h e s e r i l l s and the l a r g e r s c a l e of the photograph. For the r i l l bottoms, the e f f e c t of imaging geometry does not dominate t h e r e f l e c t a n c e as much as t h e r i l l s i d e s and s o i l p r o p e r t i e s w i l l be more s i g n i f i c a n t i n d e t e r m i n i n g the r e f l e c t a n c e . The e f f e c t of imaging geometry i s i l l u s t r a t e d i n P l a t e 1 2 . Here, the snow p r e s e n t s a m a t e r i a l of u n i f o r m r e f l e c t a n c e and t h e v a r i a t i o n s i n l i g h t due t o the "cos /" e f f e c t a l o n e , can be seen t o d e l i n e a t e the r i l l p o s i t i o n s . PLATE 1 2 . "Cos i " E f f e c t Observed on Snow Covered R i l l s . D. Use of Geographic I n f o r m a t i o n Systems i n E r o s i o n  Assessment To a s s i s t i n the d e c i s i o n making p r o c e s s , r e s o u r c e managers must o f t e n s y n t h e s i z e l a r g e volumes of d i f f e r e n t 45 types of d a t a . The data may be ob t a i n e d from thematic maps, ground surveys and remotely sensed images. A c h a r a c t e r i s t i c of much of t h i s data i s that i t i s s p a t i a l l y o r i e n t e d . To s y n t h e s i z e t h i s s p a t i a l data manually i s te d i o u s and a n a l y t i c a l l y l i m i t i n g (SISI 1985). In order to a s s i s t i n the management of s p a t i a l data, geographic i n f o r m a t i o n systems have been developed. A geographic i n f o r m a t i o n system enables resource managers to e f f i c i e n t l y i n t e g r a t e and u t i l i z e l a r g e volumes of data and a v a r i e t y of data types i n t h e i r d e c i s i o n making p r o c e s s e s . A geographic i n f o r m a t i o n system (GIS) i s a computer hardware and software system designed to c o l l e c t , manage, analyze and d i s p l a y s p a t i a l l y r e f e r e n c e d data (Nystrom et a l . 1985). The GIS c r e a t e s a d i g i t a l data base c o n s i s t i n g of the v a r i o u s l a y e r s or themes of data entered i n t o the system. Each l a y e r i s a s p e c i a l form of geographic map f o r which each c a r t o g r a p h i c l o c a t i o n has only one thematic a t t r i b u t e . The v a r i e t y of mappable c h a r a c t e r i s t i c s a s s o c i a t e d with any given geographic l o c a t i o n are s t o r e d as a s e r i e s of these s p a t i a l l y r e g i s t e r e d computer compatible maps (SISI 1985). The s p a t i a l data of a thematic l a y e r i s s t o r e d i n the form of square g r i d u n i t s ( r a s t e r format) or i n the form of polygons of v a r i o u s s i z e s and shapes (vector format). The type of data that may be entered i n t o the system may be analog or d i g i t a l map and image data or t a b u l a r data. The essence of a GIS i s i t s 46 c a p a b i l i t y f o r m a n i p u l a t i n g and a n a l y z i n g data and producing output products t a i l o r e d to the needs of the user. For s u c c e s s f u l data a n a l y s i s the system user should have a thorough knowledge of the l a y e r s of data i n the system, the r e l a t i o n s h i p s among the l a y e r s and the a n a l y s i s c a p a b i l i t i e s of the GIS. The f u n c t i o n s of a GIS may be c h a r a c t e r i z e d as computer mapping, database management, s p a t i a l s t a t i s t i c s and c a r t o g r a p h i c modelling (SISI 1985). Some of the main o p e r a t i o n s a GIS i s capable of are r e c l a s s i f i c a t i o n of map c a t e g o r i e s , o v e r l a y i n g maps, map measurement and c h a r a c t e r i z a t i o n of c a r t o g r a p h i c neighbourhoods. R e c l a s s i f i c a t i o n i n v o l v e s the c r e a t i o n of a new map by a s s i g n i n g thematic val u e s to the c a t e g o r i e s of an e x i s t i n g map. In t h i s o p e r a t i o n , the same map u n i t boundaries are kept and i t may be thought of as a map i n t e r p r e t a t i o n . Overlay o p e r a t i o n s i n v o l v e the c r e a t i o n of a new map i n which the value a s s i g n e d to every p o i n t (or set of p o i n t s i n a category) i s a f u n c t i o n of the v a l u e s a s s o c i a t e d with that l o c a t i o n on two or more e x i s t i n g maps in the system. Map measurement can i n c l u d e measurement of l i n e a r or n o n - l i n e a r d i s t a n c e s , p erimeters and area. C h a r a c t e r i z a t i o n of c a r t o g r a p h i c neighbourhoods i n v o l v e s c r e a t i o n of a new map i n which the value a s s i g n e d to a l o c a t i o n i s computed as a f u n c t i o n of the v a l u e s w i t h i n a s p e c i f i e d d i s t a n c e and d i r e c t i o n around that l o c a t i o n on an e x i s t i n g map. 47 Ca r t o g r a p h i c modelling w i l l e v e n t u a l l y become one of the most powerful t o o l s a v a i l a b l e to resource managers to analyze s p a t i a l d a t a . C a r t o g r a p h i c m o d e l l i n g i n v o l v e s using q u a n t i t a t i v e values d e r i v e d from the data s t o r e d i n the thematic l a y e r s as input f o r v a r i a b l e s i n an a l g o r i t h m . Some of the o p e r a t i o n s above can be u s e f u l i n c a r t o g r a p h i c m o d e l l i n g . D i s t r i b u t e d parameter models which d i v i d e an area i n t o square planar segments are w e l l s u i t e d f o r use with a GIS with r a s t e r format. Large, complex models which c o n s i s t of s e v e r a l submodels c o u l d be e f f i c i e n t l y managed on the m u l t i -l a y e r storage and a n a l y s i s c a p a b i l i t i e s of a GIS. A GIS i s a powerful t o o l f o r the management and a n a l y s i s of s p a t i a l d a ta. Remote sensing systems are powerful t o o l s fo r the c o l l e c t i o n and c l a s s i f i c a t i o n of s p a t i a l data (Marble et a l . 1983). A GIS r e q u i r e s a source of s p a t i a l i n f o r m a t i o n and i s s t a t i c . Remote sensing techniques provide s p a t i a l i n f o r m a t i o n and are w e l l s u i t e d f o r the c o l l e c t i o n of m u l t i -temporal data s e t s . Many observers f e e l that the f u l l p o t e n t i a l of GIS and remote sensing techniques cannot be achieved u n t i l they are i n t e g r a t e d (Curran 1985). To achieve t h i s , the GIS should be i n t e g r a t e d with image a n a l y s i s software. The c h a r a c t e r i s t i c s of GIS and remote sensing techniques are w e l l s u i t e d to the monitoring and r e c o r d i n g of e r o s i o n and the assessment of e r o s i o n . The f a c t o r s which i n f l u e n c e the 48 r a t e of water e r o s i o n are r a i n f a l l , r u n o f f , s o i l , slope, p l a n t cover and presence or absence of c o n s e r v a t i o n measures (Morgan 1979). Each of these f a c t o r s v a r i e s i n d i v i d u a l l y in space and some vary over r e l a t i v e l y short time p e r i o d s . Thus e r o s i o n i s a complex process r e s u l t i n g from the i n t e r a c t i o n of many f a c t o r s , and v a r i e s i n time and space. A GIS allo w s f o r the e f f i c e n t r e p r e s e n t a t i o n of the s p a t i a l v a r i a b i l i t y of e r o s i o n . With the i n t e g r a t i o n of remotely sensed imagery, i t a l s o a l l o w s f o r r e p r e s e n t a t i o n of the temporal v a r i a b i l i t y i n e r o s i o n . As p r e v i o u s l y mentioned, assessment of e r o s i o n c o u l d i n v o l v e assessment of a c t u a l e r o s i o n f e a t u r e s or assessment of the f a c t o r s which a f f e c t e r o s i o n . A GIS allows f o r the r e p r e s e n t a t i o n of e r o s i o n f e a t u r e s through remotely sensed imagery. A GIS a l s o allows f o r the e f f i c i e n t r e p r e s e n t a t i o n of the s p a t i a l v a r i a b i l i t y of the f a c t o r s which a f f e c t e r o s i o n . In essence, a GIS i n combination with remotely sensed imagery and f i e l d c o l l e c t e d data a l l o w s f o r the i n t e g r a t i o n of a l l the in f o r m a t i o n r e l a t e d to e r o s i o n i n c l u d i n g a c t u a l e r o s i o n f e a t u r e s , the f a c t o r s a f f e c t i n g e r o s i o n and user d e f i n e d software to assess the e r o s i o n . The use of d i g i t a l imagery which c o n t a i n s e r o s i o n f e a t u r e s a l l o w s f o r grea t e r a n a l y t i c a l c a p a b i l i t y than p o s s i b l e with analog imagery. A n a l y s i s of e r o s i o n f e a t u r e s on imagery c o u l d i n c l u d e simple v i s u a l enhancements of the 49 f e a t u r e s to more s o p h i s t i c a t e d measurement o p e r a t i o n s , c l a s s i f i c a t i o n o p e r a t i o n s or even more s o p h i s t i c a t e d user designed a l g o r i t h m s f o r f e a t u r e e x t r a c t i o n and a n a l y s i s . The u t i l i t y of the imagery w i l l depend of course on the s e p a r a b i l i t y of the e r o s i o n f e a t u r e s from the landscape. A GIS c o u l d be used to assess e r o s i o n by a n a l y s i s of the f a c t o r s a f f e c t i n g e r o s i o n . A number of assessment procedures ranging from the simple to very complex c o u l d be used. An e r o s i o n r i s k map c o u l d be c r e a t e d by combining maps of the f a c t o r s which a f f e c t e r o s i o n and c r e a t i o n of s u b j e c t i v e user ranked e r o s i o n r i s k c a t e g o r i e s . T h i s procedure c o u l d be made s e m i - q u a n t i t a t i v e by a s s i g n i n g rank values to the c a t e g o r i e s on each i n d i v i d u a l e r o s i o n f a c t o r map and summing the maps. More s o p h i s t i c a t e d techniques c o u l d i n v o l v e c a r t o g r a p h i c m o d e l l i n g . A GIS has been used in c o n j u n c t i o n with remotely sensed imagery and the U n i v e r s a l S o i l Loss Equation to produce maps of the e r o s i o n c a u s i n g f a c t o r s of the equation and a map of s o i l l o s s ( P e l l e t i e r 1985). The values f o r the Crop P r o t e c t i o n F a c t o r of the equation were d e r i v e d from computer c l a s s i f i c a t i o n of remotely sensed images and ground survey data. The Slope Length and Slope Gradient f a c t o r s were d e r i v e d from a D i g i t a l E l e v a t i o n Model. I t should be noted that remotely sensed data cannot take the place of c o n v e n t i a l , d e t a i l e d ground surveys ( P e l l e t i e r 1985) but are u s e f u l t o o l s which can reduce the amount of f i e l d measurement. 50 S o p h i s t i c a t e d d i s t r i b u t e d parameter e r o s i o n models w i l l be w e l l s u i t e d f o r use with a GIS. Some models are d i v i d e d i n t o separate r i l l and i n t e r i l l components as d i f f e r e n t process a f f e c t the two types of e r o s i o n ( S o u l l i e r e and Toy 1986). Thus, these components w i l l have d i f f e r e n t model inputs and a l g o r i t h m s . In t u r n , each of these components w i l l c o n s i s t of a number of sub-models such as h y d r o l o g i c , detachment, t r a n s p o r t / d e p o s i t i o n sub-models. Depending on the complexity of the model, many s p a t i a l l y o r i e n t e d i n p u t s w i l l be r e q u i r e d . The m u l t i - l a y e r c a p a b i l i t y of the GIS i s w e l l s u i t e d to the storage and manipulation of the v a r i o u s l e v e l s of input and output of the d i f f e r e n t components of a complex e r o s i o n model. R e s u l t s from the model f o r d i f f e r e n t areas c o u l d be compared to imagery of the area to see how w e l l the model r e s u l t s r e f l e c t the a c t u a l e r o s i o n f e a t u r e s i n the area. A s t a t e of the a r t h y d r o l o g i c and a g r o e c o l o g i c a l model i l l u s t r a t e s these concepts (Bork and Rohdenburg 1986). I t c o n s i s t s of a DEM, a d i g i t a l Sediment & S o i l Model and a S o i l M oisture Data Processor. I t a l s o i n c l u d e s a Land Use Data Processor which processes and p r o v i d e s i n f o r m a t i o n from mapping and remote sensing data. An i n t e g r a l part of the h y d r o l o g i c submodel i s the DEM. The DEM can compute f o r each g r i d element r e l e v a n t morphographic parameters such as drainage d i r e c t i o n and slope, h o r i z o n t a l and v e r t i c a l c u r v a t u r e , s i z e and average slope of the drainage areas above 51 each g r i d element and the d i s t a n c e s from the water d i v i d e and the drainage channel. 52 Chapter III MATERIALS AND METHODS A. STUDY GRID AND AERIAL PHOTOGRAPHY 2 A p e r p e n d i c u l a r g r i d with 10 m spacing was i n s t a l l e d on the ground with wooden stakes to f a c i l i t a t e l o c a t i o n of r i l l s i n the f i e l d and on a e r i a l photographs, and f o r the e l e v a t i o n survey and formation of the d i g i t a l e l e v a t i o n model. T r a n s e c t s approximately p e r p e n d i c u l a r to the f a l l l i n e were p l a c e d 10 m apart at a f i x e d angle to a s i d e l i n e using a t h e o d o l i t e . S t a t i o n s were p l a c e d at 10 m i n t e r v a l s along the t r a n s e c t s by c h a i n i n g . An e l e v a t i o n survey of the s t a t i o n s was done using a rod and l e v e l . Benchmark 1 (BM 1) was ass i g n e d an e l e v a t i o n value of zero and a l l e l e v a t i o n s are r e l a t i v e to t h i s s t a t i o n . To f a c i l i t a t e l o c a t i o n of the g r i d on the a i r photos, .6 m square white boards were p l a c e d at known p o s i t i o n s on the g r i d and f l a g g i n g tape was pl a c e d along the t r a n s e c t s where they i n t e r s e c t e d 3 main r i l l s . The study g r i d i s i l l u s t r a t e d on Overlay 1. A l l o v e r l a y s were made to be p l a c e d over P l a t e 2. A Wild RC-10 metric camera with a 152 mm f o c a l l e n g t h l e n s and Kodak 2445 c o l o u r negative f i l m were used to take the a e r i a l photographs on A p r i l 6 1985. Paper co n t a c t c o l o u r p r i n t s were made from a 9 X 9 inch c o l o u r negative with a nominal s c a l e of 1:1500. In a d d i t i o n , enlargements of a 53 p o r t i o n of the a e r i a l photograph were done on duratrans which c o n s i s t s of an emulsion on a p l a s t i c t r a n s l u c e n t base and has b e t t e r r e s o l u t i o n than paper p r i n t s . The enlargements had a nominal s c a l e of 1:420. A c o l o u r photocopy of the enlar g e d photograph i s presented i n P l a t e 13. I t should be noted that the o r i g i n a l photograph from which measurements were made i s of much b e t t e r q u a l i t y . B. SOIL REFLECTANCE AND SOIL PROPERTIES STUDY ( S e c t i o n 1) 1. SOIL SPECTRAL MEASUREMENTS S o i l s u r f a c e r a d i a t i o n measurements were made of r i l l , i n t e r r i l l and d e p o s i t i o n areas i n both f i e l d s u s ing an Exotech Model 100A spectrometer with a 15° f i e l d of view from a height of approximately 1 m S p e c t r a l r a d i a t i o n measurements of the r i l l s were taken of the r i l l bottoms. R i l l s i d e s were avoided because of the e f f e c t s of a d i f f e r e n t source-sensor geometry f o r the r i l l s i d e s . S p e c t r a l r a d i a t i o n measurements were taken f o r 4 bandwidths; 500-600 nm, 600-700 nm, 700-800 nm and 800-1100 nm. F i e l d r e f l e c t a n c e measurements were taken i n March 1985. On both days, the sky was c l e a r except f o r a short p e r i o d of l i g h t haze d u r i n g F i e l d 2 measurements. S p e c t r a l r a d i a t i o n measurements were p e r i o d i c a l l y made of a standard s u r f a c e which was a board p a i n t e d with barium s u l p h a t e . S p e c t r a l r a d i a t i o n readings of the s o i l s u r f a c e are PLATE 13. C o l o u r Photocopy o f Enlargement o f A e r i a l Photograph o f F i e l d 2 and Sample U n i t s Used i n the D i g i t a l A n a l y s i s . 55 expressed as a p r o p o r t i o n of the standard s u r f a c e reading taken c l o s e s t i n time to the s o i l r e a d i n g . I f i t i s assumed that the standard s u r f a c e i s a good approximation to a p e r f e c t l y r e f l e c t i n g , p e r f e c t l y d i f f u s e s u r f a c e , then these p r o p o r t i o n s are approximately equal to the s o i l d i f f u s e r e f l e c t a n c e . Surface samples were taken at each f i e l d r e f l e c t a n c e l o c a t i o n . These were a i r d r i e d , crushed and s i e v e d to l e s s than 2 mm. S p e c t r a l r a d i a t i o n measurements of the samples were made i n the l a b o r a t o r y with a B a r r i n g e r HHRR Mark II s p e c t r a l radiometer with a 2° f i e l d of view approximately 50 cm above the sample. The a r t i f i c i a l l i g h t used to i l l u m i n a t e the samples i n the l a b o r a t o r y had a spectrum approximating that of d a y l i g h t . Again, the measurements were expressed as a p r o p o r t i o n of the standard s u r f a c e . The wavelength bands measured i n the l a b o r a t o r y were 20 nm wide with mean bandwidths of 870, 900, 1050, 1200, 1600, 2100, 2200, and 2350 nm. 2. SOIL PROPERTY ANALYSES S o i l samples were c o l l e c t e d at those l o c a t i o n s i n the f i e l d where the s p e c t r a l measurements were made. S o i l samples were a i r d r i e d , crushed and s i e v e d to < 2 mm. F o r t y -seven a d d i t i o n a l s u r f a c e samples from i n t e r r i l l areas were c o l l e c t e d f o r moisture content analyses f o r the d i g i t a l 56 moisture content model. F i e l d s o i l moisture content was determined g r a v i m e t r i c a l l y , by oven d r y i n g at 110° C. Clay content was determined using the hydrometer method (Day 1969). T o t a l sand, very f i n e sand and .1 — 2.0 mm sand f r a c t i o n s were determined by wet s i e v i n g . T o t a l carbon content was determined from a Leco Carbon Analyzer (Leco, 1959). 3. STATISTICAL ANALYSIS OF SOIL PROPERTIES AND REFLECTANCE  DATA The o b j e c t i v e s of the s t a t i s t i c a l a n a l y s i s were to (a) i n v e s t i g a t e the v a r i a b i l i t y of the data (b) determine i f s i g n i f i c a n t d i f f e r e n c e s e x i s t i n s o i l p r o p e r t i e s and r e f l e c t a n c e between r i l l , i n t e r r i l l and d e p o s i t i o n areas and (c) i n v e s t i g a t e the r e l a t i o n s h i p s between the s o i l p r o p e r t i e s and the r e f l e c t a n c e . V a r i o u s d e s c r i p t i v e s t a t i s t i c s were c a l c u l a t e d i n c l u d i n g the mean, v a r i a n c e , standard d e v i a t i o n , minimum, and maximum. The c o e f f i c i e n t of v a r i a t i o n ( C V . ) was determined to i n d i c a t e the v a r i a b i l i t y of the d ata. The % C V . i s d e f i n e d as: % C V . = Standard D e v i a t i o n X 100. Mean The Mann-Whitney U- t e s t ( S i e g a l 1959) was used to t e s t s i g n i f i c a n c e of d i f f e r e n c e s between r i l l , i n t e r r i l l and d e p o s i t i o n areas. I t i s a non-parametric t e s t and was chosen due to the lack of assumptions about the d i s t r i b u t i o n of the 57 data. The Spearman's Rho C o r r e l a t i o n C o e f f i c i e n t was used to i n d i c a t e the degree of c o r r e l a t i o n between the s o i l p r o p e r t i e s and the r e f l e c t a n c e data. I t i s a non-parametric c o r r e l a t i o n with minimal assumptions about the data. The Spearman's Rho values g i v e an i n d i c a t i o n of how w e l l the s o i l p r o p e r t i e s were r e l a t e d to the r e f l e c t a n c e values f o r the wavelength bands measured. C. SOIL LOSS ESTIMATES (Se c t i o n s 2 & 3) 1. RILL VOLUME AND PLAN AREA MODEL a. D e s c r i p t i o n of the Model In order to c a l c u l a t e the r i l l volume and plan area covered by the r i l l s , a q u a d r i l a t e r a l with p a r a l l e l top and bottom was chosen to represent the r i l l c r o s s - s e c t i o n a l shape. To s p e c i f y a given r i l l shape, the top width (Wt), bottom width (Wt), and depth (D) are r e q u i r e d . A computer program was w r i t t e n to c a l c u l a t e the volume and plan area between two r i l l c r o s s - s e c t i o n s a given d i s t a n c e a p a r t . The volumes and plan areas f o r these r i l l segments were then summed to determine the t o t a l volume and pla n area f o r the r i l l . The model r e s u l t s were checked by e n t e r i n g i n Wt, Wb, and D inputs of r i l l shapes whose volume and plan area c o u l d be e a s i l y c a l c u l a t e d by hand. A r e c t a n g u l a r shaped r i l l c r o s s - s e c t i o n (Wt=Wb) and an i n v e r t e d e q u i l a t e r a l t r i a n g l e r i l l c r o s s -58 s e c t i o n (Wb=0) were used f o r t h i s purpose. The Wt, Wb and D in p u t s were d e r i v e d from 3 sources; r i l l o m e t e r p r o f i l e s , measuring tape measurements and photo measurements. The model was a p p l i e d to the three main r i l l s i n the f i e l d to determine t h e i r volume and p l a n area and to check the accuracy of the r e s u l t s of the model from the tape and photo i n p u t s r e l a t i v e to the r e s u l t s from the r i l l o m e t e r i n p u t . The 2 model was a l s o a p p l i e d to 32 randomly s e l e c t e d 10 m sample u n i t s to determine the r i l l volume and plan area r e p r e s e n t a t i v e of a l a r g e area of F i e l d 2. The s o i l l o s s estimate from the model rep r e s e n t s the net s o i l l o s s due to the s o i l t r a n s p o r t e d o f f the f i e l d by c o n c e n t r a t e d flow. The model estimates of s o i l l o s s do not i n c l u d e i n t e r r i l l eroded s o i l or the s o i l moved downslope by the formation of di s c o n n e c t e d r i l l s . b. R i l l Measurements R i l l measurements i n the f i e l d were done using a r i l l o m e t e r (McCool 1979) and measuring tape on the same day the a e r i a l photographs were taken. R i l l o m e t e r measurements were taken every 5 m down the 3 main r i l l s . Tape measurements of the r i l l top width (Wt), bottom width (Wb) and depth (D) were made at the same l o c a t i o n s . In a d d i t i o n , tape measurements of Wt, Wb and D were made of every r i l l at the 59 p o i n t where they i n t e r s e c t e d the t r a n s e c t s and the d i s t a n c e from the nearest s t a t i o n was recorded. Wt was measured as the d i s t a n c e along the top of the r i l l from one r i l l edge to the o t h e r . Wb was measured at the approximate p o i n t where the r i l l s i d e s f l a t t e n e d out at the r i l l bottom. D was measured from the top of the r i l l used i n the Wt measurement to the r i l l bottom. Wt measurements were a l s o made from the a e r i a l photograph enlargements. The photographic s c a l e was determined f o r each t r a n s e c t by photo measurement of p o i n t s of known ground l o c a t i o n . A pocket comparator with 8 X m a g n i f i c a t i o n and a .1 mm d i v i s i o n s c a l e was used f o r the measurements. In order to develop some i n t e r p r e t i v e s k i l l i n p i c k i n g the r i l l edges, Wt measurements were made and then checked a g a i n s t ground measurements. For use as input i n t o the volume and plan area model, two Wt measurements were taken f o r each r i l l c r o s s -s e c t i o n and the average was taken. 2. CALIBRATION OF INPUT SOURCES USING THE 3 MAIN RILLS ( S e c t i o n 2) The r i l l volumes and plan areas of the 3 main r i l l s were c a l c u l a t e d from the r i l l o m e t e r p r o f i l e s i n the f o l l o w i n g manner. S l i d e s of the r i l l o m e t e r were p r o j e c t e d onto a p i e c e of paper, the r i l l p r o f i l e was t r a c e d and the r i l l edges ( i . e . Wt) were p i c k e d . The r i l l o m e t e r i s i l l u s t r a t e d i n P l a t e 14. 60 The r i l l o m e t e r has a measurement s c a l e so the s c a l e s of the t r a c i n g s c o u l d be c a l c u l a t e d . The r i l l was assumed to have a f l a t top which i s reasonable as topographic change over the width of a r i l l i s n e g l i g i b l e . The r i l l c r o s s - s e c t i o n s on the t r a c i n g s were then measured with a planimeter to determine the ar e a . Next, the best f i t t i n g q u a d r i l a t e r a l was t r a c e d over the r i l l c r o s s - s e c t i o n t r a c i n g to o b t a i n the Wt, Wb and D inputs f o r the model. T h i s i s i l l u s t r a t e d i n F i g u r e 2. The r i l l c r o s s - s e c t i o n areas c a l c u l a t e d using these inputs were checked to ensure that they were w i t h i n 5 % of the planimetered areas. For those that weren't, the Wb and D values were a d j u s t e d . For a few r i l l c r o s s - s e c t i o n s whose shape were not w e l l s u i t e d t o the model shape, Wt had to be a d j u s t e d as w e l l . The r i l l o m e t e r d e r i v e d r i l l volumes and plan areas are taken as the most ac c u r a t e estimate of the r i l l e r o s i o n . Tape measurements were a l s o used f o r the inputs i n t o the model. There were two s e t s of f i e l d measurements a v a i l a b l e f o r each of the three r i l l s ; one set taken every 5 m down the r i l l and one set taken every 10 m (where the t r a n s e c t s i n t e r s e c t e d ) . Where there were two s e t s of readings f o r one l o c a t i o n , the average of the two readings was used. Photo measurements were made as d e s c r i b e d to o b t a i n Wt inp u t s f o r the model. To o b t a i n the corresponding Wb and D inputs of the photo Wt measurements, the f o l l o w i n g procedure 61 FIGURE 2. T r a c i n g o f R i l l P r o f i l e from R i l l o m e t e r £ Best F i t t i n g Q u a d r i l a t e r a l 62 was f o l l o w e d . The average r a t i o s of Wt:Wb and Wt:D f o r the three main r i l l s were c a l c u l a t e d from the r i l l o m e t e r measurements. The average Wt:Wb r a t i o was .337 and the average Wt:D r a t i o was .249. For each Wt input value measured from the photo enlargement, corresponding Wb and D values were c a l c u l a t e d u sing these r a t i o s . The accuracy of the model r e s u l t s from the tape and photo measured inputs r e l a t i v e to the r e s u l t s from the r i l l o m e t e r i n puts were i n v e s t i g a t e d by comparing the r e s u l t s f o r the i n d i v i d u a l r i l l segments of each r i l l . 3. SOIL LOSS ESTIMATES OF FIELD 2 ( S e c t i o n 3) a. E s t i m a t i o n of R i l l Volume and Plan Area of a Repre s e n t a t i v e Area of F i e l d 2 Using 32 Randomly S e l e c t e d  Sample U n i t s An area of F i e l d 2 was chosen to demonstrate a p p l i c a t i o n of a technique to determine the s o i l l o s s from the f i e l d due to con c e n t r a t e d flow, i . e . r i l l f ormation. The area chosen i s l o c a t e d between t r a n s e c t s 4 and 13. T h i s area was 2 d i v i d e d i n t o 144 10 m u n i t s . T h i r t y - t w o sample u n i t s were chosen i n a s t r a t i f i e d random manner. From each block of 9 u n i t s two sample u n i t s were randomly chosen. T h i s represents a sample s i z e of about 22 % of the p o p u l a t i o n . In a study on sampling techniques f o r e s t i m a t i n g s o i l e r o s i o n , Roels and Jonker (1983) found that when the sample s i z e i s 10 % or more 63 of the p o p u l a t i o n , an i n c r e a s e i n the sample s i z e r e s u l t s i n o n l y a small i n c r e a s e i n the accuracy of the sample. Thus, the sample s i z e used here should be more than adequate to r e p r e s e n t the s o i l l o s s of the sample area. Roels and Jonker a l s o found that random sampling and s t r a t i f i e d random sampling y i e l d almost i d e n t i c a l standard e r r o r s . The sample u n i t s are i l l u s t r a t e d on Overlay 3. For each sample u n i t , four s e t s of input data were used f o r volume and plan area c a l c u l a t i o n . The f i r s t set of input, r e s u l t i n g i n the most accurate estimate, u t i l i z e d the r i l l o m e t e r data where a v a i l a b l e . Where r i l l o m e t e r data was not a v a i l a b l e , tape measurements were used where r i l l s i n t e r s e c t e d the t r a n s e c t s of the sample u n i t . For r i l l s which d i d not c r o s s both or e i t h e r of the t r a n s e c t s , mixed tape and photo or photo measurements alone were used r e s p e c t i v e l y . The second set of input used only tape data. The t h i r d and f o u r t h s e t s of input u t i l i z e d only photo measurements to o b t a i n Wt input v a l u e s . The t h i r d input set c o n s i s t e d of Wb and D v a l u e s obtained by the r a t i o method as p r e v i o u s l y d e s c r i b e d f o r the three main r i l l s . The f o u r t h input set u t i l i z e d photo Wt v a l u e s and average Wb and D v a l u e s a r r r i v e d at i n the f o l l o w i n g manner. Scattergrams of D vs. Wt and Wb vs. Wt were made. For each scattergram, the Wt values were v i s u a l l y d i v i d e d i n t o three groups such that v a r i a t i o n i n D and Wb v a l u e s were minimized f o r each group. Then f o r each group, 64 the average Wb and D value was c a l c u l a t e d . For Wb, the groups of Wt v a l u e s were; 0 - 3 4 cm, 35 - 95 cm, and > 95 cm with average Wb values f o r the groups of 12 cm, 20 cm, and 51 cm r e s p e c t i v e l y . For D, the groups of Wt values were; 0 -34 cm, 35 - 65 cm and > 65 cm with average D values f o r the groups of 9 cm, 13 cm and 19 cm r e s p e c t i v e l y . For each Wt val u e , the corresponding Wb and D v a l u e s were s e l e c t e d from the group c o n t a i n i n g that Wt v a l u e . b. E r o s i o n P l o t E s t i m a t i o n of S o i l Loss S o i l l o s s data was c o l l e c t e d from e r o s i o n p l o t s e s t a b l i s h e d by B.C. M i n i s t r y of A g r i c u l t u r e and Food personnel at the S.E. bottom of f i e l d 2 i n order to compare d r a i n e d vs. undrained c o n d i t i o n s . The p l o t s were monitored from Sept. 1983 to J u l y 1984 under f a l l r y egrass sown at about 130 kg/ha. The cumulative s o i l l o s s f o r t h i s p e r i o d was determined. Runoff was sampled by a Coshocton type runoff sampler designed to sample 1 % of runoff through a flume and was s t o r e d i n a b u r i e d 75 l i t r e c o n t a i n e r . Subsamples were c o l l e c t e d from the c o n t a i n e r . S o i l l o s s was determined from the weight of sediment i n the subsamples. The p l o t s were 4.57 m wide and 44.27 m long which i s twice the l e n g t h of the standard Wischmeier e r o s i o n p l o t . The slope g r a d i e n t of the p l o t s was 9 %. 65 c. U n i v e r s a l S o i l Loss Equation E s t i m a t i o n of S o i l Loss The U n i v e r s a l S o i l Loss Equation was used to determine the long term average annual s o i l l o s s from F i e l d 2. The equation i s : A = R x K x L x S x C x P where A = annual s o i l l o s s R = r a i n f a l l e r o s i v i t y f a c t o r K = s o i l e r o d i b i l i t y f a c t o r L = slope g r a d i e n t f a c t o r S = slope l e n g t h f a c t o r C = crop management f a c t o r P = c o n s e r v a t i o n p r a c t i c e f a c t o r . The r a i n f a l l e r o s i v i t y f a c t o r was determined f o r the f i e l d by i n t e r p o l a t i n g between i s o - e r o s i v i t y contour l i n e s on an e r o s i v i t y map of the Lower F r a s e r V a l l e y c o n t a i n e d i n an unpublished paper (Van Soest 1983). The Wischmeier Method f o r c a l c u l a t i n g e r o s i v i t y was used and data f o r ten years or more was used from the c l i m a t i c s t a t i o n s . The two nearest s t a t i o n s were l o c a t e d about 9 and 19 km on e i t h e r s i d e of the f i e l d . The s o i l e r o d i b i l i t y f a c t o r was c a l c u l a t e d from Wischmeier's S o i l E r o d i b i l i t y Nomograph (Hudson 1981). The inputs r e q u i r e d are; percent s i l t and very f i n e sand, percent sand, percent organic matter, s o i l s t r u c t u r e c l a s s and p e r m e a b i l i t y c l a s s . The mean s i l t , very f i n e sand and sand contents determined f o r F i e l d 2 by the hydrometer method and wet s i e v i n g were used. Percent organic matter was determined from the mean t o t a l carbon content of the f i e l d and a 66 c o n v e r s i o n f a c t o r of 1.724 which i s based on a carbon c o n c e n t r a t i o n i n s o i l o r g a n i c matter of 58 %. The s o i l s t r u c t u r e c l a s s was v i s u a l l y determined and the p e r m e a b i l i t y c l a s s was obtained from the s o i l survey of the area (Luttmerding 1981). The combined slope l e n g t h and g r a d i e n t f a c t o r was determined from a Wischmeier nomograph (Hudson 1981). Slope l e n g t h was determined from the e l e v a t i o n survey and a r e p r e s e n t a t i v e slope g r a d i e n t was determined from a slope g r a d i e n t contour map d e r i v e d from the DEM (Overlay 4). No work has been done i n the study area to develop a p p r o p r i a t e C f a c t o r values f o r the area. A C f a c t o r was determined f o r the area f o r ryegrass based on 1983 - 84 e r o s i o n p l o t d ata. However, the s i t u a t i o n f o r the 1984 - 85 season i s complicated by e r o s i o n o c c u r i n g before s u f f i c i e n t establishment of the crop had taken place and then f u r t h e r e r o s i o n o c c u r i n g a f t e r g r e a t e r development of c r o p growth. Thus a somewhat a r b i t r a r y value f o r the C f a c t o r had to be chosen fo r the f i e l d based on t h i s e r o s i o n h i s t o r y . No e r o s i o n c o n t r o l measures were taken f o r the f i e l d , so the P f a c t o r has a value of 1. D. D i g i t a l A n a l y s i s ( S e c t i o n 4) D i g i t a l images were produced from the photographic negative on an O p t r o n i c s C-4500 c o l o u r f i l m scanner. The 67 p i x e l s i z e chosen was 25 micro-metres which, given the nominal s c a l e of 1:1500, corresponds to a ground s p a t i a l r e s o l u t i o n of 2 3.75 cm . Blue, green and red f i l t e r s were used to produce blue, green and red images. Image a n a l y s i s was done on a Vax 11/780 based Raster Technology Model 25 image a n a l y s i s system. Three of the sample u n i t s chosen f o r the F i e l d 2 r i l l volume and plan area d e t e r m i n a t i o n were used f o r the d i g i t a l a n a l y s i s (sample u n i t s 61, 77 & 93 d e l i n e a t e d on P l a t e 13). A nearest neighbour and a maximum l i k e l i h o o d c l a s s i f i e r were used f o r s u p e r v i s e d c l a s s i f i c a t i o n s of the image i n t o i n t e r r i l l a reas, areas of r i l l shadow, and areas of sun f a c i n g r i l l s i d e s . The l a t t e r two areas were summed to o b t a i n the t o t a l r i l l p l an area f o r the sample u n i t . The red, blue and green images were a l l used i n the c l a s s i f i c a t i o n ( i e . a three dimensional c l a s s i f i c a t i o n ) . A t r a i n i n g set was chosen f o r each of the Jbhree c l a s s e s . The minimum t r a i n i n g set s i z e was 60 p i x e l s and the maximum was 92 p i x e l s . The same t r a i n i n g set was used f o r both of the s u p e r v i s e d c l a s s i f i e r s . The nearest neighbour c l a s s i f i e r used i s a minimum d i s t a n c e c l a s s i f i e r . I t c a l c u l a t e s a mean vecto r (average s p e c t r a l value) f o r each c l a s s and then a s s i g n s each p i x e l to the c l a s s whose mean v e c t o r i s the l e a s t d i s t a n c e from the p i x e l . T h i s type of c l a s s i f i e r c h a r a c t e r i z e s the mean of a c l a s s w e l l but does not take i n t o account the v a r i a n c e of the c l a s s . The maximum l i k e l i h o o d c l a s s i f i e r 68 a s s i g n s a given p i x e l to a c l a s s based on the a p r i o r i and c o n d i t i o n a l p r o b a b i l i t i e s of the c l a s s . The c o n d i t i o n a l p r o b a b i l i t y i s the p r o b a b i l i t y that a p i x e l belongs to a c e r t a i n c l a s s . I t i s d e r i v e d f o r each c l a s s from the t r a i n i n g s e t . The a p r i o r i p r o b a b i l i t y of a c l a s s i s the p r o b a b i l i t y that a p i x e l p i c k e d at random belongs to that c l a s s . A p r i o r i p r o b a b i l i t i e s were obtained from the c a l c u l a t i o n of plan area of the r i l l s from the volume and pl a n area model f o r these 3 sample u n i t s . The percentage area occupied by the r i l l was d i v i d e d e q u a l l y between the r i l l shadow and r i l l sun f a c i n g s i d e to o b t a i n the a p r i o r i p r o b a b i l i t i e s f o r the r i l l c l a s s e s . The maximum l i k e l i h o o d c l a s s i f i e r o f t e n gets b e t t e r r e s u l t s than the nearest neighbour c l a s s i f i e r as i t takes i n t o account both the mean and the v a r i a n c e of a c l a s s . However, i t does r e q u i r e more computer time. E. FORMATION OF DIGITAL ELEVATION & MOISTURE CONTENT MODELS (S e c t i o n 5) The t r a n s e c t s and s t a t i o n s were p l o t t e d on the 1:1500 a e r i a l photographs. F i r s t , known l o c a t i o n s (as i n d i c a t e d by the white boards and f l a g g i n g tape) were p l o t t e d . The int e r m e d i a t e s t a t i o n s were p l o t t e d a c c o r d i n g to the known (surveyed) d i s t a n c e between them, and the known s c a l e of each t r a n s e c t . The l o c a t i o n of many of these p l o t t e d s t a t i o n s were checked by the d i s t a n c e s from them to r i l l s v i s i b l e on the 69 a e r i a l photographs. The d i s t a n c e s of the s t a t i o n s from the r i l l s were known from the f i e l d r i l l measurement survey. The x,y l o c a t i o n s of the p l o t t e d s t a t i o n s were obtained by d i g i t i z i n g t h e i r l o c a t i o n s on a d i g i t i z i n g t a b l e t . The e l e v a t i o n s r e l a t i v e to the benchmark as c a l c u l a t e d from the ground e l e v a t i o n survey were then matched with the corres p o n d i n g x,y l o c a t i o n . From t h i s data, an e l e v a t i o n contour map and an e l e v a t i o n p e r s p e c t i v e p l o t were c r e a t e d using commercially a v a i l a b l e software (Golden Software 1985). The e l e v a t i o n contour map covers the area from t r a n s e c t 4 to t r a n s e c t 15. From the d i g i t a l e l e v a t i o n contour map, a contour map of slope g r a d i e n t was c r e a t e d using commercially a v a i l a b l e software (SISI 1985). A slope g r a d i e n t d i r e c t i o n map was a l s o c r e a t e d from the e l e v a t i o n contour map. The arrows on t h i s map represent the slope d i r e c t i o n as given by the normal to the e l e v a t i o n contour at a p a r t i c u l a r l o c a t i o n . The arrows i n d i c a t e the d i r e c t i o n of ov e r l a n d flow at that l o c a t i o n . The moisture content sample l o c a t i o n s were a l s o p l o t t e d on the a e r i a l photograph. These were d i g i t i z e d and the corres p o n d i n g f i e l d moisture contents were added. A moisture content contour map and p e r s p e c t i v e p l o t were c r e a t e d . The moisture content contour map covers the area from t r a n s e c t 4 to t r a n s e c t 13. The l o c a t i o n of the three main r i l l s i n the f i e l d were p l o t t e d onto the e l e v a t i o n and moisture content 70 p e r s p e c t i v e p l o t s to a s s i s t i n v i s u a l c o r r e l a t i o n between the two maps and the a e r i a l photograph. The o v e r l a y s and p e r s p e c t i v e p l o t s of e l e v a t i o n and moisture content were compared to each other and to the r i l l l o c a t i o n s on the a e r i a l photographs. Based on t h i s data and h i l l s l o p e hydrology i n f o r m a t i o n from the l i t e r a t u r e , i n t e r p r e t a t i o n s were made of topographic e f f e c t s on s o i l moisture and overland flow and the combined e f f e c t s of these on r i l l development. 71 Chapter IV R e s u l t s A. DATA ANALYSIS OF SOIL REFLECTANCE AND PROPERTIES 1. VARIABILITY OF SOIL REFLECTANCE The c o e f f i c i e n t s of v a r i a t i o n f o r s o i l r e f l e c t a n c e and f i e l d s o i l p r o p e r t i e s are l i s t e d i n Table 2. The f i r s t 8 wavelengths from 870 to 2350 nm are l a b o r a t o r y measured r e f l e c t a n c e s while the next 4 wavelengths from 500 to 1100 nm are f i e l d measured r e f l e c t a n c e s . Sand content was the most v a r i a b l e s o i l property measured with C.V.s of 85.2 % f o r the .1-2 mm sand f r a c t i o n , 45.3 % f o r the very f i n e sand f r a c t i o n and 70.1 % f o r t o t a l sand content. Moisture content was next i n v a r i a b i l i t y with a C V . of 40.6 %, followed by carbon content with a C.V. of 31.6 %, c l a y content with a C V . of 22.7 % and s i l t content with a C.V. of 17.9 %. The f i e l d r e f l e c t a n c e i s much more v a r i a b l e than the l a b o r a t o r y r e f l e c t a n c e . The c o e f f i c i e n t s of v a r i a t i o n f o r the l a b o r a t o r y r e f l e c t a n c e ( A l l Data, Table 2). vary from 5.4 to 12.7 % and f o r the f i e l d r e f l e c t a n c e vary from 37.0 to 48.9 %. T h i s i s due to (a) the e f f e c t of sur f a c e and s i t e c o n d i t i o n s i n the f i e l d and (b) more v a r i a b l e i l l u m i n a t i o n c o n d i t i o n s i n the f i e l d . 72 Table 2 C o e f f i c i e n t s of V a r i a t i o n f o r R e f l e c t a n c e and S o i l P r o p e r t i e s f o r A l l Data, F i e l d 1, F i e l d 2, I n t e r r i l l , R i l l and D e p o s i t i o n Areas. V a r i a b l e A l l Data (N=98) F i e l d 1 (N=67) F i e l d 2 (N=31) R i l l (N=31) I n t e r r i l l (N=43) Dep* n (N=18) 870 (nm) 9.3 5.5 10.9 12.5 5.2 6.7 900 8.1 5.6 9.6 10.7 4.6 5.9 1050 12.7 5.8 20.2 6.6 3.9 26.9 1200 6.9 5.8 8.6 6.8 4.8 6.8 1600 6.3 5.5 7.6 5.8 4.1 7.1 2100 5.6 4.5 7.6 6.1 4.0 5.3 2200 5.7 4.4 7.7 6.2 3.4 5.7 2350 5.4 4.1 7.4 5.9 3.2 5.5 500-600 46.4 36.0 40. 1 31.4 21.4 28.0 600-700 48.9 42.4 38.8 33.8 20.3 30.0 700-800 37.0 32.4 29.7 23.2 27.5 20.0 800-1100 38.8 34.2 39.5 34.5 26.6 16.3 Carbon 31.6 14.6 45. 1 33.3 11.5 49.5 Moisture 40.6 25.8 56.5 31.5 40.5 68.0 vf Sa 45.3 22.7 34. 1 43.9 32.0 32.8 1-2 mm Sa 85.2 47.7 48.7 73. 1 63.8 65.7 T o t a l Sa 70. 1 33.5 42. 1 60.7 51.3 55.6 S i l t 17.9 4.6 23.3 15.7 8.1 30.8 Clay 22.7 12.6 32.5 20. 1 1 1 .7 36.3 (a) Surface and S i t e C o n d i t i o n s : For the a i r d r i e d , crushed and s i e v e d s o i l samples, the main p r o p e r t i e s a f f e c t i n g the l a b o r a t o r y r e f l e c t a n c e are org a n i c matter content and the p a r t i c l e s i z e d i s t r i b u t i o n . V a r i a t i o n s i n these f a c t o r s are the main source of v a r i a t i o n i n the r e f l e c t a n c e . A l s o , the amount of < 2 mm aggregates remaining a f t e r c r u s h i n g and s i e v i n g may i n c r e a s e v a r i a b i l i t y . In a d d i t i o n to organic matter content and the p a r t i c l e s i z e d i s t r i b u t i o n , the f i e l d r e f l e c t a n c e s are a f f e c t e d by moisture content and s u r f a c e roughness which are both q u i t e v a r i a b l e . Although not 73 q u a n t i f i e d , i n both f i e l d s the i n t e r r i l l areas have the g r e a t e s t s u r f a c e roughness while r i l l and d e p o s i t i o n a l areas are r e l a t i v e l y smooth. The g r e a t e r v a r i a b l i l i t y of the f i e l d r e f l e c t a n c e s i n d i c a t e s the importance of these s i t e and s u r f a c e c o n d i t i o n s . (b) I l l u m i n a t i o n C o n d i t i o n s : Another source of v a r i a b i l i t y i n the f i e l d r e f l e c t a n c e i s the v a r i a b l e i l l u m i n a t i o n c o n d i t i o n s . I l l u m i n a t i o n w i l l change over time as the sun p o s i t i o n and atmospheric c o n d i t i o n s change. As the s o i l r e f l e c t a n c e v a l u e s are c a l c u l a t e d as a p r o p o r t i o n of the r e f l e c t a n c e readings from the standard r e f l e c t o r , v a r i a t i o n s i n i l l u m i n a t i o n are l a r g e l y removed from the data. However, readings from the standard r e f l e c t o r were not taken f o r every s o i l r e f l e c t a n c e r e a d i n g . Thus, because of v a r i a t i o n s i n i l l u m i n a t i o n between the standard r e f l e c t a n c e r eadings, e f f e c t s of v a r i a t i o n of i l l u m i n a t i o n are not n e c e s s a r i l y wholly removed from s o i l r e f l e c t a n c e r e a d i n g s . A l s o , as the sun angle changes, the amount of s p e c u l a r r e f l e c t i o n of a given (smooth) s u r f a c e w i l l change. However as the standard r e f l e c t o r i s mainly a d i f f u s e r e f l e c t o r , these v a r i a t i o n s i n s p e c u l a r r e f l e c t a n c e w i l l not be removed by c a l c u l a t i n g the s o i l r e f l e c t a n c e f a c t o r s as a p r o p o r t i o n of the standard r e f l e c t o r r e f l e c t a n c e v a l u e s . The i n t e r r i l l areas have the l e a s t v a r i a t i o n i n 74 p a r t i c l e s i z e and carbon content, and thus have the l e a s t v a r i a t i o n i n the l a b o r a t o r y r e f l e c t a n c e s . The s o i l p r o p e r t i e s of r i l l bottoms are a f u n c t i o n of both the m a t e r i a l removed from the r i l l bottom by water flow and the m a t e r i a l d e p o s i t e d when water flow slows or ceases. The shape of the r i l l bottom s u r f a c e i s o f t e n q u i t e v a r i a b l e due to s c o u r i n g by water flow. As a r e s u l t , r i l l samples have the most v a r i a b l e sand contents and g e n e r a l l y have the most v a r i a b l e f i e l d and l a b o r a t o r y r e f l e c t a n c e . 2. REFLECTANCE DIFFERENCES BETWEEN RILL, INTERRILL &  DEPOSITION AREAS a. F i e l d Data The primary goal of the r e f l e c t a n c e study was to determine i f the r e f l e c t a n c e s of r i l l , i n t e r r i l l and d e p o s i t i o n a l areas are s i g n i f i c a n t l y d i f f e r e n t . As can be seen from Table 3, s i g n i f i c a n t d i f f e r e n c e s were observed i n f i e l d r e f l e c t a n c e between r i l l , i n t e r r i l l and d e p o s i t i o n areas. The means and standard d e v i a t i o n s f o r r i l l , i n t e r r i l l and d e p o s i t i o n r e f l e c t a n c e and s o i l p r o p e r t i e s are l i s t e d i n Table 4. D e p o s i t i o n areas had the h i g h e s t r e f l e c t a n c e , f o l l o w e d by r i l l and then i n t e r r i l l a r e a s . The r e s u l t s demonstrate the f e a s i b i l i t y of s e p a r a t i n g these three d i f f e r e n t e r o s i o n s t a t e s on a i r b o r n e imagery. F i g u r e 3 shows the mean r e f l e c t a n c e f o r r i l l , i n t e r r i l l and d e p o s i t i o n areas f o r the data from F i e l d s 75 1 and 2 combined. Wavelength band 600-700 nm appears t o be the best f o r s e p a r a t i n g r i l l and i n t e r r i l l a r e a s , while band 700-800 nm appears best f o r s e p a r a t i n g r i l l and d e p o s i t i o n a l areas. A l l the bands appear e q u a l l y good f o r s e p a r a t i n g d e p o s i t i o n and i n t e r r i l l a r e a s . Table 3 S i g n i f i c a n t D i f f e r e n c e s (<*=.05) In S o i l R e f l e c t a n c e s and P r o p e r t i e s Between R i l l , I n t e r r i l l and D e p o s i t i o n Areas i n F i e l d s 1 and 2 Combined (N=94). I n t e r r i l l D e p o s i t i o n R i l l I n t e r r i l l 1050 (nm. ) 1200 carbon 21 00 vfSa 2350 .1-2 mm Sa 500-600 t o t a l Sa 600-700 S i l t 700-800 800-1100 1200 (nm. ) carbon 1600 carbon 2100 vfSa 2100 vf Sa 2200 .1-2 mm Sa 2200 ' .1-2 mm Sa 2350 t o t a l Sa 2350 t o t a l Sa 500-600 S i l t 500-600 S i l t 600-700 Clay 600-700 Clay 700-800 700-800 800-1100 800-1100 Table 4 Means & Standard D e v i a t i o n s f o r R i l l , I n t e r r i l l 76 and D e p o s i t i o n R e f l e c t a n c e & S o i l P r o p e r t i e s . R i l l I n t e r r i l l D e p o s i t i o n (N«43) (N* = 31) (N-18) V a r i a b l e Mean SD Mean SD Mean SD 870 nm 30.51 3.81 30.98 1 .61 30.39 2.03 900 nm 31 .97 3.43 32.72 1 .52 31.79 1.66 1050 nm 41.22 2.72 43.79 1.70 43.31 11.63 1200 nm 38.74 2.62 40.88 1.97 37.32 2.54 1600 nm 44.48 2.58 47.30 1.92 43.26 3.07 2100 nm 48.98 3.00 50.44 2.00 47.01 2.50 2200 nm 47.65 2.94 49.36 1.67 45.74 2.61 2350 nm 47.63 2.79 49.28 1.56 45.84 2.52 500-600 nm 5.95 1.87 3.46 .74 9.07 2.54 600-700 nm 8.73 2.95 4.74 .96 12.97 3.89 700-800 nm 10.66 2.52 7.10 1.95 15.36 3.01 800-1100 nm 13.44 4.64 9.54 2.54 19.45 3.18 Carbon 3.99 1.33 4.69 .56 2.95 1 .46 Moi s t u r e 29.43 9.28 27.66 1 1.20 24.02 16.33 vfSand 6.13 2.69 5.10 1.63 9.55 3.13 .1-2 mm Sand 13.96 10.21 8.23 5.25 25.87 16.99 T o t a l Sand 20.04 12.16 13.24 6.79 34.67 19.27 S i l t 65.65 10.33 71.51 5.76 54.81 16.86 Cl a y 14.31 2.88 15.25 1.79 10.52 3.82 24 500-600 600-700 700-800 800-1100 Wavelength (nm) R = R i l l I = I n t e r r i l l D=Deposition (Bars • +/- One Standard D e v i a t i o n ) FIGURE 3. Mean F i e l d R e f l e c t a n c e Values f o r R i l l , I n t e r r i l l & D e p o s i t i o n Areas. 77 b. Laboratory Data S i g n i f i c a n t r e f l e c t a n c e d i f f e r e n c e s between r i l l , i n t e r r i l l , and d e p o s i t i o n areas were a l s o found in the l a b o r a t o r y (Table 3). S i g n i f i c a n t r e f l e c t a n c e d i f f e r e n c e s occured between a l l three e r o s i o n s t a t e s f o r the 2100 and 2350 nm wavelength bands. Laboratory r e f l e c t a n c e f o r the d e p o s i t i o n areas was s i g n i f i c a n t l y d i f f e r e n t from the other two areas for the 2200 nm wavelength band while the i n t e r r i l l areas were s i g n i f i c a n t l y d i f f e r e n t from the other two areas f o r the 1200 nm wavelength band. Where s i g n i f i c a n t d i f f e r e n c e s d i d occur f o r the l a b o r a t o r y r e f l e c t a n c e , i n t e r r i l l samples had the highest r e f l e c t a n c e followed by r i l l and then d e p o s i t i o n samples. c. Comparison of F i e l d & Laboratory Data S i g n i f i c a n t d i f f e r e n c e s between r i l l , i n t e r r i l l and d e p o s i t i o n areas were found in both the f i e l d and l a b o r a t o r y r e f l e c t a n c e . The d i f f e r e n c e s i n the l a b o r a t o r y r e f l e c t a n c e were due mainly to the d i f f e r e n c e in s o i l p r o p e r t i e s between the r i l l , i n t e r r i l l and d e p o s i t i o n areas. The d i f f e r e n c e s i n the f i e l d r e f l e c t a n c e are due both to d i f f e r e n c e s i n s o i l p r o p e r t i e s and s i t e c o n d i t i o n s between r i l l , i n t e r r i l l and d e p o s i t i o n a r e a s . The main s i t e f a c t o r s which may a f f e c t s o i l r e f l e c t a n c e are s u r f a c e roughness and moisture content. It i s known that moisture content a f f e c t s r e f l e c t a n c e . However, 7 8 as seen from Table 3, there i s no s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e i n moisture content between r i l l , i n t e r r i l l and d e p o s i t i o n a r e a s . Thus i t i s l i k e l y that i t i s mainly s u r f a c e roughness t h a t i s r e s p o n s i b l e f o r the g r e a t e r s i g n i f i c a n t d i f f e r e n c e s i n f i e l d r e f l e c t a n c e compared to the l a b o r a t o r y r e f l e c t a n c e . D e p o s i t i o n areas are lowest in carbon content and g e n e r a l l y have the smoothest s u r f a c e . Due to these f a c t o r s , d e p o s i t i o n areas have the h i g h e s t f i e l d r e f l e c t a n c e . I n t e r r i l l areas have the h i g h e s t carbon content and the roughest s u r f a c e and thus have the lowest f i e l d r e f l e c t a n c e . Where s i g n i f i c a n t d i f f e r e n c e s occur i n the l a b o r a t o r y r e f l e c t a n c e (Table 3 ) , the i n t e r r i l l samples have the highest r e f l e c t a n c e and the d e p o s i t i o n samples have the lowest r e f l e c t a n c e (Table 4 ) , which i s opposite to the f i e l d r e f l e c t a n c e . The high sand, and low s i l t and c l a y content of the d e p o s i t i o n samples r e s u l t s i n a rougher m i c r o - s u r f a c e of the crushed and s i e v e d s o i l samples used f o r the l a b o r a t o r y r e f l e c t a n c e r e adings. Apparently, the decreased r e f l e c t a n c e due to t h i s rougher s u r f a c e dominates over any i n c r e a s e i n r e f l e c t a n c e due to the lower carbon content of the d e p o s i t i o n samples. Conversely, i n t e r r i l l samples have the lowest sand content and the highest s i l t content r e s u l t i n g i n a smoother s u r f a c e . T h i s causes an i n c r e a s e i n r e f l e c t a n c e which dominates over the decrease i n r e f l e c t a n c e due to the higher 79 carbon content of the i n t e r r i l l samples. Thus, in the l a b o r a t o r y r e f l e c t a n c e s , the d e p o s i t i o n samples have the lowest r e f l e c t a n c e and i n t e r r i l l samples have the h i g h e s t r e f l e c t a n c e . 3. RELATIONSHIPS BETWEEN SOIL PROPERTIES AND REFLECTANCE For the a i r d r i e d , crushed and s i e v e d s o i l samples, the main s o i l p r o p e r t i e s a f f e c t i n g r e f l e c t a n c e are organic matter content and the p a r t i c l e s i z e d i s t r i b u t i o n . A f a c t o r not accounted f o r i s the amount of <2 mm aggregates remaining a f t e r c r u s h i n g and s i e v i n g . T h i s may tend to p a r t i a l l y mask the e f f e c t s of organic matter content and p a r t i c l e s i z e d i s t r i b u t i o n on r e f l e c t a n c e . The c o r r e l a t i o n between carbon content and r e f l e c t a n c e i s p a r t i a l l y obscured by the f a c t that some of the carbon content i s due to p i e c e s of wood, r o o t s , e t c . which are not h i g h l y decomposed and w i l l not a f f e c t the r e f l e c t a n c e as much as more h i g h l y decomposed humus. The e f f e c t s of mineralogy on r e f l e c t a n c e have not been taken i n t o account in t h i s study. Some minimal x-ray d i f f r a c t i o n work on a few samples shows l i t t l e d i f f e r e n c e i n the c l a y mineralogy of r i l l , i n t e r r i l l and d e p o s i t i o n areas. The e f f e c t of mineralogy on r e f l e c t a n c e should not be important i n t h i s study because i t w i l l be masked by the e f f e c t of the high organic matter content on r e f l e c t a n c e . The systematic e f f e c t on r e f l e c t a n c e of a given s o i l 8 0 p r o p e r t y may not n e c e s s a r i l y appear in a s t a t i s t i c a l c o r r e l a t i o n as i t may be masked by the e f f e c t s on r e f l e c t a n c e of other s o i l p r o p e r t i e s . A l s o , i t i s o f t e n d i f f i c u l t to separate the s o i l p r o p e r t i e s ' e f f e c t s on r e f l e c t a n c e as many of the s o i l p r o p e r t i e s covary. a. F i e l d R e f l e c t a n c e - S o i l Data R e l a t i o n s h i p s The Spearman's Rho values f o r the c o r r e l a t i o n s f o r F i e l d 1 and F i e l d 2 data are l i s t e d i n Tables 5 and 6 r e s p e c t i v e l y . I n t e r r i l l areas have the lowest r e f l e c t a n c e mainly because they have the roughest s u r f a c e and the highest carbon content. D e p o s i t i o n areas have the h i g h e s t r e f l e c t a n c e mainly because they have a smoother s u r f a c e and the lowest carbon c o n t e n t s . The c o r r e l a t i o n s which occur are a consequence of t h i s s i t u a t i o n . The f i e l d r e f l e c t a n c e i s , i n g e n e r a l , n e g a t i v e l y c o r r e l a t e d with carbon content. T h i s c o r r e l a t i o n occurs p a r t l y due to the decrease in r e f l e c t a n c e caused by the carbon content. A c o n t r i b u t i n g f a c t o r i s the a s s o c i a t i o n of high carbon contents with the rough, low r e f l e c t a n c e s u r f a c e s i n the i n t e r r i l l areas and low carbon contents with the smoother, high r e f l e c t a n c e s u r f a c e s i n the d e p o s i t i o n a r e a s . F i e l d r e f l e c t a n c e i s p o s i t i v e l y c o r r e l a t e d with sand content. T h i s c o u l d occur because i n c r e a s e d sand content causes an i n c r e a s e i n r e f l e c t a n c e i n the f i e l d s i t u a t i o n . 81 Table 5 Spearman's Rho value s ( s i g n i f i c a n t at«»<=.05) For C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 1 (N=67). carbon moisture v f S a ,1-2mm Sa Sand S i l t C l a y 870 (nm.) .37 -.23 900 -.26 -.26 .43 1050 -.37 -.38 -.43 .49 1200 -.33 -.31 -.36 .40 1600 -.37 -.39 -.42 .47 2100 -.37 -.29 -.36 .42 • 2200 -.49 -.35 -.42 .46 2350 -.42 -.36 -.42 .47 500-600 -.40 .27 .49 .43 .49 -.28 -.37 600-700 -.38 .25 .45 .42 .47 -.28 -.32 700-800 -.40 .22 .46 .39 .45 -.24 -.38 800-1100 -.27 .40 .44 .33 .39 -.23 -.29 carbon X -.50 -.60 -.66 .38 .63 moisture X vfSa X .55 .73 -.50 -.50 .1-2 mm Sa X .95 -.80 -.50 t o t a l Sa X -.80 -.51 S i l t X Clay X Table 6 Spearman's Rho v a l u e s ( s i g n i f i c a n t at«*<=.05) For C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 2 (N=31). carbon moisture v f S a .1-2mm Sa Sa S i l t C lay 870 (nm.) -.42 -.32 .32 900 -.37 -.37 .37 1050 -.40 -.65 -.62 .65 .33 1200 .30 -.67 -.62 .72 1600 .32 -.29 -.70 -.65 .76 2100 .42 -.70 -.64 .76 2200 .42 -.30 -.72 -.67 .79 2350 .43 -.74 -.67 .79 500-600 -.57 -.32 .43 .62 .62 -.67 -.36 600-700 -.63 -.30 .51 .57 .61 -.63 -.38 700-800 -.46 .43 .58 .59 -.64 -.38 800-1100 -.30 .61 .65 .65 -.66 -.39 carbon X -.46 -.35 -.46 .45 .44 moisture X -.31 -.44 -.44 .44 vf S a X .56 .72 -.64 -.63 .1-2 mm Sa • X .96 -.94 -.61 t o t a l Sa X -.97 -.69 S i l t X .55 Cl a y X 82 Geberman and Neher (1979) found an i n c r e a s e i n r e f l e c t a n c e with the a d d i t i o n of i n c r e a s i n g amounts of sand to c l a y . However, i t may be at l e a s t p a r t l y due to the f a c t that high sand contents are a s s o c i a t e d with d e p o s i t i o n areas which have high r e f l e c t a n c e due to having low carbon contents and a smoother s u r f a c e . In other words, the e f f e c t s on r e f l e c t a n c e of these two l a t t e r p r o p e r t i e s may mask the e f f e c t of sand content on the r e f l e c t a n c e . An a d d i t i o n a l f a c t o r i s that the sand content i n F i e l d 2 i s n e g a t i v e l y c o r r e l a t e d with f i e l d moisture content. A lower moisture content with i n c r e a s i n g amounts of sand would a l s o tend to i n c r e a s e the r e f l e c t a n c e and c o n t r i b u t e to a p o s i t i v e c o r r e l a t i o n between sand content and f i e l d r e f l e c t a n c e . A n egative c o r r e l a t i o n e x i s t s between s i l t content and f i e l d r e f l e c t a n c e . S i l t content i s p o s i t i v e l y c o r r e l a t e d with carbon content i n both F i e l d s 1 and 2, and p o s i t i v e l y c o r r e l a t e d with moisture content i n F i e l d 2. Both carbon and moisture content are n e g a t i v e l y c o r r e l a t e d with r e f l e c t a n c e . Thus, a higher s i l t content i s a s s o c i a t e d with higher carbon and moisture contents, and consequently, lower f i e l d r e f l e c t a n c e . Another c o n t r i b u t i n g f a c t o r i s t h a t d e p o s i t i o n areas have the lowest s i l t c ontent. The smooth s u r f a c e of these areas tend to i n c r e a s e r e f l e c t a n c e and c o n t r i b u t e to the negative c o r r e l a t i o n of r e f l e c t a n c e with s i l t c ontent. Clay content i s n e g a t i v e l y c o r r e l a t e d with f i e l d 83 r e f l e c t a n c e . The reasons are the same as f o r the s i l t c o ntent, the only d i f f e r e n c e being that c l a y i s not c o r r e l a t e d with f i e l d moisture content f o r the F i e l d 2 data s e t . F i e l d 1 has a p o s i t i v e c o r r e l a t i o n between f i e l d r e f l e c t a n c e and moisture content as the d e p o s i t i o n areas have the h i g h e s t r e f l e c t a n c e and h i g h e s t moisture content i n the f i e l d r e l a t i v e to the other areas. F i e l d 2 has a negative c o r r e l a t i o n between f i e l d r e f l e c t a n c e and moisture content as the d e p o s i t i o n areas have the h i g h e s t r e f l e c t a n c e and the lowest moisture content r e l a t i v e to the other areas i n the f i e l d . The moisture content of the d e p o s i t i o n area at the bottom of F i e l d 1 i s h i g h because the slope g r a d i e n t decreases and t h e r e f o r e water flow decreases and the water content i s h i g h e r . In F i e l d 2, the slope g r a d i e n t i s more or l e s s constant to the edge of the r a v i n e so there i s l e s s moisture b u i l d u p . b. Laboratory R e f l e c t a n c e - S o i l Data R e l a t i o n s h i p s In both f i e l d s , there i s g e n e r a l l y a negative c o r r e l a t i o n between l a b o r a t o r y r e f l e c t a n c e and sand content and a p o s i t i v e c o r r e l a t i o n between l a b o r a t o r y r e f l e c t a n c e and s i l t content. Higher sand content and lower s i l t content r e s u l t i n a rougher s u r f a c e of the crushed and s i e v e d s o i l samples used i n the l a b o r a t o r y r e f l e c t a n c e study. T h i s r e s u l t s i n decreased r e f l e c t a n c e f o r i n c r e a s i n g amounts of sand and decreasing. 84 amounts of s i l t . The only c o r r e l a t i o n between l a b o r a t o r y r e f l e c t a n c e and carbon content occurs f o r wavelength bands 870 and 900 nm i n the- F i e l d 2 data. Thus the e f f e c t of carbon content on the l a b o r a t o r y r e f l e c t a n c e must be masked by other f a c t o r s such as the e f f e c t of sand content. C o r r e l a t i o n s were a l s o done on subsets of the data. These i n c l u d e d the r i l l , i n t e r r i l l and d e p o s i t i o n subsets f o r each f i e l d . Negative c o r r e l a t i o n s occured between carbon content and a l l l a b o r a t o r y r e f l e c t a n c e wavelength bands f o r F i e l d 1 i n t e r r i l l samples (Table 7) and F i e l d 2 r i l l samples (Table 8). In these data s e t s , the e f f e c t of carbon content on the r e f l e c t a n c e i s not masked. I t i s not masked in the F i e l d 1 i n t e r r i l l data set probably because of the high carbon content (5.1%) and low sand content (9.9 %) of these samples. Although l e s s apparent f o r the F i e l d 2 r i l l samples, the negative c o r r e l a t i o n between carbon content and l a b o r a t o r y r e f l e c t a n c e may occur d e s p i t e a lower carbon content (2.7 %) because of .the high v a r i a b i l i t y of the carbon content (C.V.=49.3 % ) . The absence of c o r r e l a t i o n between l a b o r a t o r y r e f l e c t a n c e and carbon content i n the F i e l d 1 and F i e l d 2 data, and the decrease i n the Spearman's Rho values with i n c r e a s i n g wavelength seem to support the l i t e r a t u r e f i n d i n g s that the s h o r t e r wavelength bands (< 1200 nm.) are best f o r d e t e c t i n g carbon content. The e f f e c t of c l a y on l a b o r a t o r y r e f l e c t a n c e i s a l s o 85 Table 7 Spearman's Rho valu e s ( s i g n i f i c a n t at »<=.05) For C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 1 I n t e r r i l l Areas (N=26). 870 (nm.) 900 1050 1200 1600 2100 2200 2350 500-600 600-700 700-800 800-1100 carbon moi s t u r e v f S a .1-2 mm Sa t o t a l Sa S i l t C l a y carbon moisture vfSa 1-2mm Sa Sa S i l t Clay -.65 -.49 -.59 -.46 -.59 .35 -.50 -.58 * -.45 -.55 .37 -.36 -.48 .36 -.49 .35 -.51 .39 -.46 .47 -.48 -.39 ^.38 .37 -.37 -.35 .45 -.37 .49 -.38 .59 .82 -.45 X .92 -.64 X -.32 -.53 X -.50 X Table 8 Spearman's Rho valu e s ( s i g n i f i c a n t at«»<=.05) f o r C o r r e l a t i o n s Between S o i l R e f l e c t a n c e and P r o p e r t i e s f o r F i e l d 2 R i l l s (N=15). carbon moisture vfSa ,1-2mm Sa Sa S i l t C l a y 870 (nm.) -.77 900 -.76 1050 -.53 .47 -.56 -.51 .58 1200 -.54 . -.51 -.48 .55 1600 -.51 .48 -.53 -.49 .55 2100 -.45 .55 -.61 -.56 .61 2200 -.45 .52 -.62 -.56 .63 2350 -.49 .51 -.61 -.55 .61 500-600 -.45 600-700 -.55 -.61 .56 .46 700-800 800-1100 -.55 .66 .52 .60 -.61 carbon X moisture X -.44 -.80 -.78 .73 vf S a X .56 -.53 .1-2 mm Sa X .96 -.94 -.45 t o t a l Sa X -.97 -.55 S i l t X C l a y X 86 l a r g e l y masked f o r the F i e l d 1 and F i e l d 2 d a t a . However, a negative c o r r e l a t i o n with l a b o r a t o r y r e f l e c t a n c e i s apparent i n the F i e l d 1 i n t e r r i l l data subset and occurs f o r the wavelength bands 870 to 1600 nm. The negative c o r r e l a t i o n i s l i k e l y due to the a s s o c i a t i o n of carbon with the c l a y and thus an i n c r e a s e i n c l a y content r e s u l t s i n a decrease i n the l a b o r a t o r y r e f l e c t a n c e . The c o r r e l a t i o n may be apparent i n t h i s case due to a combination of the high carbon content (5.1 % ) , lower sand content (9.9 %) and higher c l a y content (15.81 %) of these samples. P o s i t i v e c o r r e l a t i o n s occur for F i e l d 2 data between l a b o r a t o r y r e f l e c t a n c e of a i r dry samples and f i e l d moisture content. The reason f o r t h i s i s probably that the l a b o r a t o r y r e f l e c t a n c e i s n e g a t i v e l y c o r r e l a t e d with sand content and sand content i s n e g a t i v e l y c o r r e l a t e d with moisture content i n the f i e l d . Thus an i n c r e a s e i n moisture content i n the f i e l d i s a s s o c i a t e d with a decrease i n sand content and decreased sand content r e s u l t s i n an i n c r e a s e i n l a b o r a t o r y r e f l e c t a n c e . c. Comparison of F i e l d and Laboratory Data Sand content i s p o s i t i v e l y c o r r e l a t e d with f i e l d r e f l e c t a n c e and n e g a t i v e l y c o r r e l a t e d with l a b o r a t o r y r e f l e c t a n c e . The exact o p p o s i t e trend was found f o r s i l t content and r e f l e c t a n c e . Carbon content i s n e g a t i v e l y 87 c o r r e l a t e d with f i e l d r e f l e c t a n c e and i t s e f f e c t on l a b o r a t o r y r e f l e c t a n c e i s masked f o r the F i e l d 1 data s e t . Clay content i s n e g a t i v e l y c o r r e l a t e d with f i e l d r e f l e c t a n c e and i t s e f f e c t on l a b o r a t o r y r e f l e c t a n c e i s l a r g e l y masked. The c o n t r a d i c t i o n s and v a r i a t i o n s i n the e f f e c t of a given s o i l p r o p e r t y on r e f l e c t a n c e i n d i f f e r e n t s i t u a t i o n s i l l u s t r a t e s the importance of the i n t e r a c t i o n of the d i f f e r e n t s o i l p r o p e r t i e s ' e f f e c t s on r e f l e c t a n c e . A l s o apparent i s the d i f f i c u l t y of s e p a r a t i n g e f f e c t s on r e f l e c t a n c e of a given s o i l p r o p e r t y due to co v a r i a n c e of s o i l p r o p e r t i e s . Thus i t may be necessary to develop s i t e s p e c i f i c r e l a t i o n s h i p s between s o i l p r o p e r t i e s and r e f l e c t a n c e . I f more u n i v e r s a l s o i l p r o p e r t y - r e f l e c t a n c e r e l a t i o n s h i p s are d e s i r e d , then r e f l e c t a n c e s t u d i e s must i n c l u d e a wide range of s o i l and s i t e c o n d i t i o n s . In a d d i t i o n , c o r r e l a t i o n a n a l y s i s was done between f i e l d and l a b o r a t o r y r e f l e c t a n c e , and the n a t u r a l l o g of the s o i l p r o p e r t i e s ' v a l u e s . A l s o , c o r r e l a t i o n a n a l y s i s was done on the s o i l p r o p e r t i e s ' values and a l l p o s s i b l e r a t i o s of the f i e l d r e f l e c t a n c e . There were no changes i n the c o r r e l a t i o n trends i n t h i s transformed data compared to the untransformed d a t a . 4. Summary of the R e f l e c t a n c e Study The l a b o r a t o r y r e f l e c t a n c e study shows s i g n i f i c a n t 88 d i f f e r e n c e s between the r i l l , i n t e r r i l l and d e p o s i t i o n areas due to d i f f e r e n c e s i n s o i l p r o p e r t i e s . D i f f e r e n c e s i n f i e l d r e f l e c t a n c e between the three e r o s i o n s t a t e s occur due to d i f f e r e n c e s i n s i t e c o n d i t i o n s and s o i l p r o p e r t i e s . Based on these r e s u l t s , r i l l , i n t e r r i l l and d e p o s i t i o n areas should be separable on a e r i a l imagery of s u f f i c i e n t s c a l e due to r e f l e c t a n c e d i f f e r e n c e s a r i s i n g from s o i l p r o p e r t y and s i t e d i f f e r e n c e s . An a d d i t i o n a l f a c t o r which w i l l a f f e c t the r e f l e c t a n c e and i n c r e a s e the s e p a r a b i l i t y of r i l l s from the other areas i s the s o u r c e - s u r f a c e geometry. One side of the r i l l s w i l l have l i t t l e r e f l e c t a n c e due to shadow and the other s i d e w i l l have i n c r e a s e d r e f l e c t a n c e due to the sun angle being more d i r e c t than on the more l e v e l i n t e r r i l l and d e p o s i t i o n areas. T h i s e f f e c t i s demonstrated i n P l a t e 12. B. SOIL LOSS ESTIMATES (S e c t i o n s 2 & 3) 1. CALIBRATION OF INPUT SOURCES OF THE RILL VOLUME AND  PLAN AREA MODEL USING 3 MAIN RILLS ( S e c t i o n 2) The t o t a l r i l l o m e t e r d e r i v e d volume ( i . e . the t o t a l 3 3 s o i l l o s s ) of r i l l one i s 5.29 m , from r i l l two i s 3.94 m , 3 3 and from r i l l three i s 8.16 m f o r a t o t a l of 17.39 m . Using a measured bulk d e n s i t y of the Ap ho r i z o n of 784 kg/m , the t o t a l s o i l l o s s from these three r i l l s i s 13.63 tonnes. The 2 t o t a l r i l l o m e t e r d e r i v e d plan area of r i l l one i s 60.20 m , of 89 2 2 r i l l two i s 44.13 m , and of r i l l t hree i s 57.10 m f o r a t o t a l of 161.43 m2. The r i l l o m e t e r d e r i v e d Wt, Wb and D inputs f o r the three r i l l s were v a r i e d to observe the e f f e c t s on the volume and plan area c a l c u l a t e d . Using a r e c t a n g u l a r r i l l shape ( i . e . Wb = Wt) overestimated the r i l l volumes by 30 - 35 %. Decreasing Wt by 10 % r e s u l t e d i n a 7 % decrease i n volume and a 10 % decrease i n i n plan area. Decreasing Wb by 10 % r e s u l t e d i n a 2 - 3 % decrease i n volume while d e c r e a s i n g the depth by 10 % r e s u l t e d i n a 9 - 10 % decrease in volume. T h i s i n d i c a t e s that f o r the volume d e t e r m i n a t i o n , the Wt and D inputs are more c r i t i c a l than the Wb v a l u e . Decreasing a l l of Wt, Wb, and D f o r r i l l s two and three by 10 % r e s u l t e d i n a decrease in the volume of about 18 %. Thus a s i g n i f i c a n t e r r o r i n volume c o u l d occur with a 10 % e r r o r i n a l l three of the inp u t s i f the e r r o r s are i n the same d i r e c t i o n ( i . e . a l l are l e s s e r or g r e a t e r than the a c t u a l r i l l d imensions). For each r i l l segment volume c a l c u l a t i o n , two Wt, two Wb and two D value s are r e q u i r e d . Measurement e r r o r s of these which are i n oppo s i t e d i r e c t i o n s w i l l p a r t i a l l y compensate f o r each other i n the volume c a l c u l a t i o n of an i n d i v i d u a l segment. Thus the e r r o r i n the volume c a l c u l a t i o n w i l l l i k e l y be l e s s than the maximum p o s s i b l e e r r o r which c o u l d occur i f the measurement e r r o r s are a l l i n the same d i r e c t i o n . The volumes and plan areas c a l c u l a t e d by the model from 90 r i l l o m e t e r , tape and photo measurements f o r each r i l l are l i s t e d i n Table 9. A l s o l i s t e d i n Table 9, i n brackets beside the f i e l d and photo d e r i v e d volumes and plan areas, i s the percent d i f f e r e n c e of the value from the r i l l o m e t e r d e r i v e d 3 v a l u e . The t o t a l tape d e r i v e d volume i s 20.16 m which i s 16 % g r e a t e r than the r i l l o m e t e r d e r i v e d volume. The tape 2 d e r i v e d p l a n area i s 146.65 m which i s 9 % l e s s than the r i l l o m e t e r d e r i v e d p l a n area. R e l a t i v e to the r i l l o m e t e r d e r i v e d Wt values, the tape Wt v a l u e s were s m a l l e r f o r 72 % of the r i l l c r o s s - s e c t i o n s which r e s u l t e d i n a smaller t o t a l p lan area. However, tape Wb v a l u e s were g r e a t e r than r i l l o m e t e r v a l u e s f o r 53 % of the c r o s s - s e c t i o n s and tape D v a l u e s were gr e a t e r f o r 97 % of the c r o s s - s e c t i o n s which r e s u l t e d i n a l a r g e r tape d e r i v e d r i l l volume. Table 9 Volumes and Plan Areas of the Three Main R i l l s and Percent D i f f e r e n c e From R i l l o m e t e r Derived Values R i l l o m e t e r Tape Photo Data Data Data R i l l One 5.29 5.77 (+9 %) 4. 78 (-10 %) Volume R i l l Two 3.94 5.08 (+23 %) 2. 73 (-31 %) R i l l Three 8.16 9.31 (+14 %) 6. 13 (-25 %) (m J) T o t a l 17.39 20.16 (+16 %) 1 3 .64 (-22 %) R i l l One 60.20 54.10 (-10 %) 53 .45 (-1 1 %) Plan R i l l Two 44. 1 3 40.25 (-9 %) 37 .38 (-15 %) Area R i l l Three 57. 10 52.30 (-8 %) 55 .00 (-4 %) (m ) T o t a l 161.43 146.65 (-9 %) 1 45 .83 (-10 %) 91 The t o t a l photo d e r i v e d volume i s 13.64 m which i s 22 % l e s s than the r i l l o m e t e r d e r i v e d volume. The photo d e r i v e d 2 plan area i s 145.83 m which i s 10 % l e s s than the r i l l o m e t e r d e r i v e d plan area. R e l a t i v e to the r i l l o m e t e r d e r i v e d Wt val u e s , photo Wt values were l e s s e r 70 % of the time, Wb values were l e s s e r 62 % of the time and D values were l e s s e r 66 % of the time. Thus, the photo d e r i v e d r i l l volume and plan area were smal l e r than the r i l l o m e t e r d e r i v e d v a l u e s . To f u r t h e r i n v e s t i g a t e the accuracy of the tape and photo measurement r e s u l t s , the volumes and plan areas from the r i l l o m e t e r , tape and photo measurements were compared f o r the i n d i v i d u a l segments of each r i l l . For each segment, the d i f f e r e n c e s between tape and photo d e r i v e d volume and plan area, vs. the r i l l o m e t e r d e r i v e d volume and plan area were c a l c u l a t e d . Then the abs o l u t e value of the d i f f e r e n c e s of a l l the segments i n a r i l l were summed to ob t a i n a cumulative d i f f e r e n c e , i . e . t o t a l segment e r r o r , f o r th a t r i l l . For each r i l l , the t o t a l segment e r r o r , the mean segment e r r o r , the standard d e v i a t i o n of the segment e r r o r and the minimum and maximum segment e r r o r of the segments i n the r i l l were c a l c u l a t e d (Table 10). The t o t a l cumulative segment e r r o r f o r each r i l l and the percent that t h i s e r r o r i s of the t o t a l r i l l o m e t e r d e r i v e d value f o r that r i l l are l i s t e d i n Table 11 for volumes and plan a r e a s . The percent e r r o r i n both volume 92 and p l a n area i s q u i t e v a r i a b l e amongst the three r i l l s . The cumulative segment e r r o r s i n the tape d e r i v e d volume f o r a l l three r i l l s i s 25 % of the t o t a l r i l l o m e t e r d e r i v e d volume. For the photo d e r i v e d volumes, the cumulative segment e r r o r f o r a l l three r i l l s amounts to 31 % of the t o t a l r i l l o m e t e r d e r i v e d volume. Cumulative e r r o r s i n the tape d e r i v e d plan area amount to 20 % of the t o t a l r i l l o m e t e r d e r i v e d p l a n area and f o r the photo d e r i v e d plan area amount to 13 % of the t o t a l r i l l o m e t e r d e r i v e d p l a n area. Table 10 Cumulative R i l l Segment E r r o r s f o r Tape and Photo Derived Volume and Plan Area T o t a l Mean 2 S.D. Min. Max. Tape Derived R i l l One 1 .36 .124 .192 .01 .28 Volume R i l l Two 1 .55 .172 .195 .05 .32 R i l l Three 1 .39 . 1 54 .202 .03 .37 ( n T ) Tape Derived R i l l One 10.96 .996 1 .47 .16 2.40 Plan R i l l Two 14.90 .729 1 .53 .08 2.65 Area R i l l Three 6.16 .684 .849 .10 1 .47 (m 2) Photo Derived R i l l One 1.12 .051 .070 0.0 .13 Volume R i l l Two 1 .23 .068 .137 0.0 .25 o R i l l Three 3.03 .168 .248 .02 .46 Photo De r i v e d R i l l One 8.35 .380 .627 .02 1.15 Plan R i l l Two 7.54 .419 .581 .07 1.15 Area R i l l Three 4.76 .264 .479 0.0 0.80 (m 2) 93 Table 11 T o t a l Cumulative R i l l Segment E r r o r s and Percent of T o t a l R i l l o m e t e r D e r i v e d Values (Table 9) Tape Data Photo Data Volume R i l l One _ R i l l Two (m ) R i l l Three T o t a l 1.36 (26 %) 1.55 (39 %) 1.39 (17 %) 4.30 (25 %) 1.12 (21 %) 1 .23 (31 %) 3.03 (37 %) 5.38 (31 %) Plan R i l l One Area R i l l Two ~ R i l l Three (m 2) T o t a l 10.96 (18 %) 14.90 (34 %) 6.16 (11 %) 32.02 (20 %) 8.35 (14 %) 7.54 (17 %) 4.76 (8 %) 20.56 (13 %) In comparing the e r r o r s c a l c u l a t e d on a per segment b a s i s (Table 11) vs. those c a l c u l a t e d from the t o t a l volume and plan areas of each r i l l (Table 9), i t i s observed that the former are l a r g e r . T h i s i s because i n a given r i l l , some of the segment e r r o r s i n the r i l l are p o s i t i v e while others are n e g a t i v e . In summing the v a l u e s of the i n d i v i d u a l segments i n a r i l l to o b t a i n the t o t a l volume and plan area of the r i l l , t h ere i s p a r t i a l c a n c e l l a t i o n of the e r r o r . Thus, the a c t u a l e r r o r s per segment which occured were g r e a t e r than i n d i c a t e d by the t o t a l r i l l volumes and plan areas. For the tape d e r i v e d volumes and plan areas, the e r r o r s based on the cumulative segment e r r o r s vary from 17 to 39 % and 6 to 18 % r e s p e c t i v e l y . These e r r o r s are due to the g r e a t e r d i s t a n c e between the tape measurements than r i l l o m e t e r 94 measurements and the v a r i a t i o n between tape vs. r i l l o m e t e r Wt, Wb and D v a l u e s . D i f f e r e n c e s i n Wt values between r i l l o m e t e r and tape measurements are due to d i f f e r e n t i n t e r p r e t a t i o n s of where the r i l l edges a r e . T h i s was exacerbated i n t h i s p a r t i c u l a r f i e l d by the f a c t t h at some e r o s i o n occured, then grass grew on t h i s eroded area, then the main p a r t of the r i l l eroded. D i f f e r e n c e s i n depth occured as the tape depth measurements were from the top of the r i l l to the bottom while r i l l o m e t e r depth measurements were from the top of the r i l l to the bottom segment of the best f i t t i n g q u a d r i l a t e r a l which was u s u a l l y above the a c t u a l r i l l bottom. A l s o , r i l l o m e t e r Wb value s were of the best f i t t i n g q u a d r i l a t e r a l while tape va l u e s were a s u b j e c t i v e i n t e r p r e t a t i o n of the r i l l bottom as the a c t u a l r i l l bottom was u s u s a l l y not f l a t . Thus s i g n i f i c a n t e r r o r s can occur i n f i e l d measurements without some s p e c i f i c c r i t e r i a on how to choose the p a r t s of the r i l l f o r measurement. For the photo d e r i v e d volumes and plan areas, the e r r o r s based on the cumulative segment e r r o r s vary from 21 to 38 % and 8 to 17 % r e s p e c t i v e l y . These e r r o r s a r i s e from e r r o r s in Wt values measured from the photograph and e r r o r s i n Wb and D a r i s i n g from e r r o r s i n Wt and the use of Wt:Wb and Wt:D r a t i o s to o b t a i n Wb and D v a l u e s . E r r o r s i n measuring Wt from the photos arose from two sources: m i s i n t e r p r e t a t i o n of the l o c a t i o n of the r i l l edges 95 and e r r o r s i n measurement of the i n t e r p r e t e d r i l l edges. The former e r r o r d i d not occur too o f t e n but d i d sometimes r e s u l t i n l a r g e e r r o r s i n Wt. E r r o r s i n Wt measurements were o f t e n d i m i n i s h e d by the averaging of two Wt measurements to o b t a i n the Wt f o r input i n t o the model. As the s c a l e was determined fo r each t r a n s e c t , there was n e g l i g i b l e e r r o r i n Wt from the s c a l e f a c t o r . 2. SOIL LOSS ESTIMATES OF FIELD 2 ( S e c t i o n 3) a. R i l l Model E s t i m a t i o n of S o i l Loss of a Re p r e s e n t a t i v e Area  of F i e l d 2 Using 32 Randomly S e l e c t e d Sample U n i t s The sample u n i t volume and plan area estimates f o r a l l input sources are l i s t e d i n Tables 12 and 13 r e s p e c t i v e l y , i ) R i l l o m e t e r , Tape and Photo Data Estimate The best estimate of the s o i l l o s s from r i l l formation i n the sample u n i t s u t i l i z e s the r i l l o m e t e r measurements. T h i s w i l l be r e f e r r e d to as the r i l l o m e t e r estimate. However some of the sample u n i t s c o ntained r i l l s other than those measured with the r i l l o m e t e r so tape measurements were used f o r these r i l l s where p o s s i b l e . Other r i l l s d i d not i n t e r s e c t both or e i t h e r of the t r a n s e c t s so mixed tape and photo or photo measurements alone had to be used. The t o t a l volume of r i l l s 3 in the 32 sample u n i t s i s 15.53 m . Of t h i s amount 45 % was c a l c u l a t e d from r i l l o m e t e r measurements, 42 % from tape measurements, 12 % from mixed tape and photo measurements, and 96 Table 12 Volumes of Sample U n i t s (S.U.) S.U. # of T o t a l R i l l o m e t e r Tape Photo- Photo-R i l l s R i l l Est imate Estimate r a t i o ave. W Length Estimate Estima (m) (m ) (m 3) (m 3) (m 3) 6 0 0 0 0 0 0 8 2 1 1.7 .244 .396 . 168 .255 1 2 1 10.4 .329 .329 .291 .381 1 4 3 20.0 .313 .320 .308 .392 21 0 0 0 0 0 0 24 2 13.5 .502 .697 .388 .499 31 0 0 0 0 0 0 36 0 0 0 0 0 0 40 2 11.1 .689 .547 .626 .671 42 0 0 0 0 0 0 50 6 53.6 .999 1 .059 .795 1 .044 53 3 18.6 .142 .142 .174 .276 56 2 12.1 .349 .550 .262 .341 61 1 10.3 .816 1 .029 .581 .529 68 5 26.9 .963 .745 .856 .946 69 3 24.5 .181 .160 .266 .445 76 6 47.3 2.513 2.545 1 .748 1 .663 77 3 19.2 .954 .926 .803 .729 82 4 33.2 .604 .621 .624 .753 88 5 22.0 .622 1 .000 .371 .527 93 4 33.9 1 .463 1 .702 .951 1 .060 94 3 22.2 .994 1 .059 .655 .665 100 7 45.4 1 .528 1 .399 1 .227 1 .278 105 0 0 0 0 0 0 1 12 0 0 0 0 0 0 1 1 6 5 35.0 .721 .713 .855 .971 121 0 0 0 0 0 0 123 3 11.3 .094 .099 .159 .188 130 0 0 0 0 0 0 1 32 3 16.2 .353 .394 .331 .391 136 3 7.3 .160 .234 .307 .266 138 0 0 0 0 0 0 T o t . 76 505.7 15.53 16.67 12.75 14.27 97 Table 13 Plan Areas of Sample U n i t s (S.U.) S.U. # of R i l l s T o t a l R i l l Length (m) R i l l o m e t e r Estimate (m 2) Tape Estimate (m 2) Photo Estimat (m 2) 6 0 0 0 0 0 8 2 1 1.7 3.283 3.633 3.269 12 1 10.4 3.588 3.588 3.744 14 3 20.0 4.938 4.972 4.910 21 0 0 0 0 0 24 2 13.5 5.457 5.664 5.481 31 0 0 0 0 0 36 0 0 0 0 0 40 2 11.1 7.303 4.683 6.037 42 0 0 0 0 0 50 6 53.6 13.338 13.975 13.725 53 3 18.6 2.903 2.903 3.891 56 2 12.1 4.883 4.409 4. 186 61 1 10.3 5.768 5.768 6. 180 68 5 26.9 10.460 8.116 9.981 69 3 24.5 4.283 4.283 5. 183 76 6 47.3 18.534 18.694 18.106 77 3 19.2 8.334 7.594 8.260 82 4 33.2 9.535 9.053 8.628 88 5 22.0 7.802 8.774 6.624 93 4 33.9 11.999 12.528 12.028 94 3 22.2 9.076 9.628 7.713 100 7 45.4 17.852 1 5.259 15.846 105 0 0 0 0 0 1 12 0 0 0 0 0 1 16 5 35.0 11.375 9.958 11.632 121 0 0 0 0 0 123 3 11.3 2.614 2.679 2.758 1 30 0 0 0 0 0 132 3 16.2 3.909 3.969 4.703 136 3 7.3 2.484 2.970 2.917 138 0 0 0 0 0 Tot. 76 505.7 169.72 163.10 165.86 98 1 % from photo measurements. The average volume per sample 3 u n i t i s .49 m . Given that the randomly s e l e c t e d 32 sample u n i t s are r e p r e s e n t a t i v e of the 144 u n i t s of the sample area, 3 t h i s amounts to 70.56 m of s o i l l o s t from the 1.44 ha area. 3 T h i s i s e q u i v a l e n t to a s o i l l o s s of 49 m per ha (38.4 t/ h a ) . The l a r g e s t r i l l depth measured was 36 cm For the 144 ha 3 sample area, t h i s depth of s o i l has a volume of 5184 m . 3 Thus, the s o i l l o s s of 49 m /ha i s .95 % of the s o i l in the sample area down to the depth of e r o s i o n . The r i l l o m e t e r estimate of plan area covered by the r i l l s 2 i s 169.67 m . Of t h i s amount, 39 % was d e r i v e d from r i l l o m e t e r data, 42% from tape data, 17 % from mixed tape and f i e l d data and 2 % from photo data. The average p l a n area per 2 . 2 sample u n i t i s 5.3 m . T h i s amounts to 768.96 m covered by 2 r i l l s i n the sample a r e a . T h i s i s e q u i v a l e n t to 534 m /ha which i s 5.3 % of the a r e a . i i ) Tape Data Estimate The t o t a l r i l l volume f o r the sample u n i t s estimated 3 from tape measurements was 16.67 m which i s e q u i v a l e n t to a 3 s o i l l o s s of 52.1 m /ha (40.8 t/ha) f o r the sample a r e a . T h i s i s 1 % of the s o i l volume of the sample area down to the depth of e r o s i o n . The tape estimate i s 6.3 % gr e a t e r than the r i l l o m e t e r estimate. The r i l l plan area estimate using the tape data was 2 2 163.10 m which i s e q u i v a l e n t to a pl a n area of 510 m /ha f o r 99 the sample area. T h i s i s 3.9 % l e s s than the r i l l o m e t e r est imate. i i i ) Photo Data Estimate The t o t a l volume of the sample u n i t s d e r i v e d from photo 3 measurements and r a t i o s of Wt:Wb and Wt:D i s 12.75 m which 3 i s e q u i v a l e n t to a s o i l l o s s of 39.8 m /ha (31.2 t/ha) f o r the sample a r e a . T h i s i s 18 % l e s s than the r i l l o m e t e r e s t i m a t e . The t o t a l p l a n area determined by photomeasurement i s 165.86 2 2 m which i s e q u i v a l e n t to a pla n area of 518 m /ha f o r the sample a r e a . T h i s i s 2 % gr e a t e r than the r i l l o m e t e r e s t i m a t e . The t o t a l volume of the sample u n i t s d e r i v e d from photo measurement and average Wt and average D values i s 14.27 3 3 m which i s e q u i v a l e n t to a s o i l l o s s of 44.6 m /ha (35.0 t/ha) f o r the sample area. T h i s i s 9 % l e s s than the r i l l o m e t e r estimate. The use of average Wb and D values with photo estimated Wt values appears to give a b e t t e r e s t i m a t i o n of r i l l volume than the use of the average r a t i o s of Wt:Wb and Wt:D. T h i s occurs due to gr e a t e r c a n c e l l a t i o n of the p o s i t i v e and negative e r r o r s i n summing the sample u n i t values d e r i v e d from average Wb and D values than i n summing the r a t i o d e r i v e d v a l u e s . For each i n d i v i d u a l sample u n i t , the d i f f e r e n c e between both photo estimates vs. the r i l l o m e t e r estimate was c a l c u l a t e d and then the ab s o l u t e value of the d i f f e r e n c e s of a l l the sample u n i t s were summed to ob t a i n the t o t a l cumulative sample u n i t e r r o r . For both photo estimates, the 100 t o t a l cumulative sample u n i t e r r o r amounted to 24 % of the t o t a l r i l l o m e t e r d e r i v e d volume est i m a t e . An estimate of r i l l volume was a l s o made using the photo estimate of plan area and an average r i l l depth of 9 cm c a l c u l a t e d from the f i e l d measurements. T h i s g i v e s a r i l l 3 volume estimate of 14.7 m which i s 5 % l e s s than the r i l l o m e t e r e stimate. i v ) Comparison of Model R e s u l t s from the R i l l o m e t e r , Tape &  Photo Input Sources The most accurate estimate of s o i l l o s s i s the estimate which i n c l u d e s the r i l l o m e t e r measurements. The r i l l o m e t e r estimate of the s o i l l o s t due to r i l l formation i n the sample area was 38.4 t/ha. I t i s d i f f i c u l t to estimate the accuracy of t h i s e s t i m a t e . F o r t y two percent of t h i s estimate was d e r i v e d from tape measurements. There are no corresponding r i l l o m e t e r measurements to check these tape measurements. The volume c a l c u l a t i o n s of the three main r i l l s showed that r e l a t i v e to the r i l l o m e t e r measurements, the average e r r o r i n the tape d e r i v e d r i l l segment volumes was approximately 25 % (Table 11) but p a r t i a l c a n c e l l a t i o n of p o s i t i v e and negative e r r o r s i n summing the segments l e d to a decreased e r r o r i n the t o t a l volume estimate. In t h i s case, i t i s l i k e l y that again both underestimation and o v e r e s t i m a t i o n e r r o r s occured f o r the r i l l volume e s t i m a t i o n s from the tape data. Thus, there was l i k e l y p a r t i a l c a n c e l l a t i o n of e r r o r s i n summing the r i l l s of 101 the sample u n i t s to determine the t o t a l r i l l volume f o r the sample a r e a . T h e r e f o r e , the e r r o r i n the tape p o r t i o n of t h i s estimate i s l i k e l y l e s s than 25 %. A 25 % e r r o r i n 42 % of the data would r e s u l t i n a t o t a l e r r o r of 25 % X 42 % = 10.5 %. Thus using tape data i n p l a c e of r i l l o m e t e r data f o r p a r t of the estimate probably r e s u l t s i n an e r r o r of l e s s than 10 %. The f i e l d and photo estimates of r i l l volume and plan area are f a i r l y c l o s e to the r i l l o m e t e r e s t i m a t e s . T h i s i s due i n p a r t to c a n c e l l a t i o n of p o s i t i v e and negative e r r o r s i n summing the sample u n i t s to o b t a i n the t o t a l volume and plan area. I t i s not p o s s i b l e to p r e d i c t the accuracy of tape or photo measurements i n the det e r m i n a t i o n of volume or plan area i n f u t u r e a p p l i c a t i o n s of the method as the accuracy i s dependent i n p a r t on how w e l l p o s i t i v e and negative e r r o r s i n the volume and plan area of r i l l segments c a n c e l each other i n summation to determine the t o t a l volume and plan area. Each source of input data f o r the model has advantages and disadvantages. The r i l l o m e t e r measurements were the most accurate f o r determining r i l l c r o s s - s e c t i o n dimensions and thus the volume and plan area of the r i l l s . However, the r i l l o m e t e r f i e l d measurements and the d e r i v a t i o n of r i l l dimensions from the r i l l o m e t e r p r o f i l e were the most time consuming input source. The tape measurements were much qui c k e r and c o u l d be input d i r e c t l y i n t o the model. While not 102 as a c c u r a t e , the t o t a l r i l l volume and plan area c a l c u l a t e d from the tape measurements were r e l a t i v e l y c l o s e to the r i l l o m e t e r e stimate. The p a r t i c u l a r tape measurements made i n c o n j u n c t i o n with the model r i l l shape used are b e t t e r s u i t e d to more f l a t bottomed r i l l s such as are found i n F i e l d 1. The Wb measurement i s d i f f i c u l t when the r i l l s have a rounded bottom. I t i s thus d e s i r a b l e to produce a r i l l c r o s s -s e c t i o n a l area measurement which has the accuracy of r i l l o m e t e r measurements, the quickness of the tape measurements and which can be a p p l i e d to any r i l l shape. T h i s c o u l d be achieved by the use of a simple p r o f i l o m e t e r and a camera, and a m o d i f i c a t i o n of the r i l l volume program. Photographic p r i n t s taken of r i l l p r o f i l e s down the r i l l would be q u i c k l y d i g i t i z e d or measured with a planimeter and the r i l l c r o s s - s e c t i o n a l area determined. The model would c a l c u l a t e the r i l l volume d i r e c t l y from the r i l l c r o s s -s e c t i o n a l areas. Thus, f i e l d measurements would i n v o l v e only t a k i n g p i c t u r e s and the r i l l c r o s s - s e c t i o n a l areas c o u l d be input i n t o the model immediately upon r e t u r n from the f i e l d . T h i s technique has the p o t e n t i a l to be accurate and r e l a t i v e l y f a s t . A s i m i l a r but q u i c k e r method would be to use a video camera i n s t e a d of a s t i l l camera. The r i l l p r o f i l e c o u l d then be d i r e c t l y t r a c e d from a video monitor with a l i g h t pen and the r i l l c r o s s - s e c t i o n a l area a c c u r a t e l y c a l c u l a t e d from t h i s t r a c i n g a u t o m a t i c a l l y by the computer. 103 The photo e s t i m a t i o n of plan area was very c l o s e to the r i l l o m e t e r e s t i m a t e . Thus, the g r e a t e s t source of e r r o r i n the photo volume estimate was from e r r o r i n the e s t i m a t i o n of Wb and D. The photo method can provide a good e s t i m a t i o n of plan area, but trades o f f reduced accuracy i n the e s t i m a t i o n of volume with reduced f i e l d measurements of Wb and D. With the photo method, s o i l l o s s f o r a l a r g e r area c o u l d be assessed i n l e s s time, but with l e s s accuracy. A l s o , the metric q u a l i t y a e r i a l photographs are expensive to o b t a i n . In view of the p r e v i o u s d i s c u s s i o n , i t can be s t a t e d that the d i f f e r e n t methods would be most a p p r o p r i a t e f o r d i f f e r e n t o b j e c t i v e s . For r o u t i n e , f a i r l y a c c urate s o i l l o s s e s t i m a t i o n , the use of randomly s e l e c t e d sample u n i t s of a chosen s i z e i s recommended. More experimentation i s needed to determine what i s the minimum percentage of a f i e l d that should be sampled i n order to o b t a i n a r e l i a b l e s o i l l o s s e s t i m a t i o n f o r the whole f i e l d . The sample u n i t s would be d e l i n e a t e d i n the f i e l d with f l a g g i n g tape. D i s t a n c e s of r i l l s from the s i d e of the sample u n i t s and r i l l c r o s s -s e c t i o n a l areas would be measured along t r a n s e c t s . Spacing between t r a n s e c t s would depend on the v a r i a b i l i t y of r i l l s i z e and the accuracy d e s i r e d . For each measurement, r i l l c r o s s -s e c t i o n a l area would be measured as recommended above. A 35 mm a e r i a l photograph of the f i e l d and/or i n d i v i d u a l sample 104 u n i t s , would be taken of the f i e l d with a b a l l o o n mounted camera or from an u l t r a l i g h t or smal l plane. The photo would provide a sy n o p t i c view of the e r o s i o n p a t t e r n and would a s s i s t i n matching the f i e l d measurements to the c o r r e c t r i l l s . A simpler a l t e r n a t i v e would be to r e c o r d the r i l l measurements down each r i l l i n the sample u n i t and av o i d using a e r i a l photographs. However, i n s i t u a t i o n s with l a r g e r sample u n i t s and dense r i l l i n g p a t t e r n s , t h i s might be q u i t e a b i t more time consuming than u s i n g t r a n s e c t s , and no photographic r e c o r d i s produced. In any case, the r i l l c r o s s - s e c t i o n a l areas would be d i r e c t l y input i n t o the model to c a l c u l a t e r i l l volume. For reconnaisance work i n v o l v i n g l a r g e r areas and l e s s r e q u i r e d accuracy, l a r g e s c a l e m e t r i c q u a l i t y a e r i a l photographs c o u l d be used. T h i s method would be a p p l i c a b l e to f i e l d s with l a r g e r r i l l s and the a p p r o p r i a t e image geometry. R i l l Wt measurements would be made from the photographs to ob t a i n an e s t i m a t i o n of r i l l plan area. With a few f i e l d measurements to estimate Wb and D and the model, a l e s s accurate but reasonable e s t i m a t i o n of r i l l volume c o u l d be made. For very quick, rough reconnaisance work, the photographs c o u l d be d i g i t i z e d and c l a s s i f i e d to o b t a i n an e s t i m a t i o n of r i l l plan area. R i l l volume c o u l d be estimated by using an average r i l l depth f o r the f i e l d though, as shown, the r e s u l t would overestimate r i l l volume. 105 Another a l t e r n a t i v e not s t u d i e d here but with much p o t e n t i a l i s to measure the r i l l volumes photogrammetrically though t h i s can be very expensive. b. E r o s i o n P l o t Estimate of S o i l Loss E r o s i o n p l o t data w i l l vary from year to year depending on the r a i n f a l l p a t t e r n f o r a p a r t i c u l a r year. Thus, s o i l l o s s d e t e r m i n a t i o n s f o r a s p e c i f i c area are most meaningful when r e p o r t e d as an average over a s e v e r a l year p e r i o d which w i l l average out y e a r l y v a r i a t i o n s i n r a i n f a l l . E x t r a p o l a t i n g one year's s o i l l o s s data to other years should be done with t h i s i n mind. A q u e s t i o n which must be r a i s e d i s , how r e p r e s e n t a t i v e i s the e r o s i o n p l o t s o i l l o s s values of the average s o i l l o s s of the whole f i e l d ? The slope of the e r o s i o n p l o t s was determined from a slope g r a d i e n t contour map to be r e p r e s e n t a t i v e of the slope of the f i e l d . Two main f a c t o r s a f f e c t the r e l i a b i l i t y of e x t r a p o l a t i n g the e r o s i o n p l o t estimate to the whole f i e l d . These are the r e s t r i c t e d l e n g t h of the p l o t and the l o c a t i o n of the p l o t in r e l a t i o n to the topographic shape of the f i e l d s u r f a c e . From the D.E.M. and the a i r photo, i t i s apparent that the m a j o r i t y of the r i l l s are found i n two main topographic lows o r i e n t e d down the f a l l l i n e . T h i s i s due i n l a r g e part to the f u n n e l l i n g of water i n t o the lows and the r e s u l t a n t e r o s i v e concentrated flow. 106 The e r o s i o n p l o t i s l o c a t e d on a t o p o g r a p h i c a l l y high r i d g e r e l a t i v e to these lows. Su r f a c e runoff and t e l l u r i c seepage tends to d r a i n to one s i d e or other of the p l o t l o c a t i o n due the the topographic shape of the f i e l d . Thus, r i l l s tend not to form i n t h i s area. T h i s i s confirmed by a e r i a l photographs taken of the f i e l d i n the s p r i n g of 1986. At t h i s time, the e r o s i o n p l o t had been removed and no r i l l s were present at the p l o t l o c a t i o n . The p l o t l e n g t h was twice the l e n g t h of standard p l o t s which i s presumed to be an attempt to r e f l e c t the longer f i e l d slopes and allow f o r r i l l formation more r e p r e s e n t a t i v e of the f i e l d . However, the f i e l d l e n g t h i s 120 m and t h i s c o n t r i b u t e s very s i g n i f i c a n t l y to the e x t e n s i v e r i l l development. For these reasons, the e r o s i o n p l o t data may underestimate the s o i l l o s s of the f i e l d . Given these c a u t i o n s , the e r o s i o n p l o t s o i l l o s s under ryegrass cover fo r the p e r i o d of Sept. 1983 to J u l y 1984 was 26.7 t/ha. About 88 % of t h i s s o i l l o s s o c c u r r e d from Nov. 1 '83 to Feb. 31 '84. As l i t t l e e r o s i o n would have o c c u r r e d d u r i n g the year o u t s i d e the p e r i o d of monitoring, t h i s s o i l l o s s value can be c o n s i d e r e d to represent most of the s o i l l o s s i n that year. E r o s i o n p l o t data was a l s o a v a i l a b l e f o r a r a s p b e r r y crop cover p l a n t e d i n h o r i z o n t a l rows f o r the 1982-83 season. From Dec. '82 to A p r i l '83, the cumulative s o i l l o s s was about 40 t/ha. T h i s p e r i o d does not i n c l u d e the r e l a t i v e l y h i g h 107 r a i n f a l l months of Sept. and Oct. and thus the a c t u a l s o i l l o s s f o r that winter i s probably a l i t t l e more than t h i s . T h i s value c o u l d be c o n s i d e r e d a minimum e s t i m a t i o n of the s o i l l o s s under s t r a w b e r r i e s f o r that season. c. U n i v e r s a l S o i l Loss Equation Estimate of S o i l Loss The r a i n f a l l e r o s i v i t y f a c t o r as obtained from the e r o s i v i t y map (Van Soest 1983) f o r F i e l d 2 was 63. The f o l l o w i n g values were used to determine the s o i l e r o d i b i l i t y f a c t o r from the Wischmeier nomograph. A mean s i l t content of 53 % and a mean very f i n e sand content of 9 % were used, g i v i n g a t o t a l f o r the two s i z e f r a c t i o n s of 62 %. The mean .1 - 2.0 mm sand content used was 26 %. The mean carbon content of f i e l d two was 2.9 %. Assuming a l l the carbon to be organic i n nature and using a c o n v e r s i o n f a c t o r of 1.724, the mean org a n i c matter content was determined to be 4.9 %. However, the maximum organic matter content which can be used i n determining the e r o d i b i l i t y by t h i s method i s 4 %, so t h i s value was used. The s o i l s t r u c t u r e was f i n e g r a n u l a r which puts i t i n s t r u c t u r e c l a s s two. Perviousness, as taken from the s o i l survey report f o r the area, v a r i e s from poor f o r Scat s o i l s and from poor to moderate f o r Whatcom s o i l s . Thus the perviousness c l a s s chosen was c l a s s 4, slow to moderate. Using these values, the s o i l e r o d i b i l i t y f a c t o r was determined to be .32. 1 0 8 The combined slope l e n g t h - g r a d i e n t f a c t o r was determined from the Wischmeier topographic f a c t o r nomograph (Hudson 1980). Slope l e n g t h i s the h o r i z o n t a l d i s t a n c e downslope from the p o i n t where o v e r l a n d flow o r i g i n a t e s t o where the r u n o f f e n t e r s a waterway or to where the slope decreases and d e p o s i t i o n occurs (Troeh et a l . 1980). In t h i s f i e l d , r unoff occurs at the top of the f i e l d and d e p o s i t i o n at the very bottom. Ther e f o r e the whole l e n g t h of the f i e l d was used. The slope l e n g t h used was 120 m and a value of 9 % was used f o r the slope g r a d i e n t . Using these v a l u e s , the LS f a c t o r f o r the f i e l d was determined to be 2.2. I d e a l l y , l o c a l l y d e r i v e d C values should be used as v a l u e s of C f o r s p e c i f i c crops d i f f e r with r a i n f a l l p a t t e r n and p l a n t i n g dates. In t h i s case as no C v a l u e s were a v a i l a b l e f o r t h i s area, the e r o s i o n p l o t data was used to c a l c u l a t e a C value f o r r y e g r a s s and h o r i z o n t a l l y p l a n t e d s t r a w b e r r i e s . The p o t e n t i a l e r o s i o n of a s p e c i f i c f i e l d without c r o p cover or c o n s e r v a t i o n p r a c t i c e s i s represented by the p o r t i o n of the equation which i n c l u d e s the R,K,L and S f a c t o r s . Using the f a c t o r values c a l c u l a t e d above the p o t e n t i a l s o i l l o s s f o r t h i s f i e l d i s 44 t o n s / a c r e or 98 tonnes/ha. A C f a c t o r f o r r y e g r a s s was c a l c u l a t e d by d i v i d i n g the s o i l l o s s from the r y e g r a s s covered e r o s i o n p l o t s (26.7 t/ha) by the p o t e n t i a l s o i l l o s s (98 t / h a ) . C a l c u l a t i n g a C f a c t o r value i n t h i s manner assumes that the e r o s i v i t y f a c t o r 109 value f o r that p a r t i c u l a r year of e r o s i o n p l o t m o n i t o r i n g , was the same as the long term average e r o s i v i t y v alue of 63 and that the e r o s i o n p l o t s o i l l o s s v alue was r e p r e s e n t a t i v e of the s o i l l o s s f o r the f i e l d . For the r y e g r a s s , a C f a c t o r value of .27 was c a l c u l a t e d . T h i s value r e p r e s e n t s the percentage decrease i n s o i l l o s s on the e r o s i o n p l o t s i n 1983-84 due to the ryegrass cover. A C f a c t o r f o r s t r a w b e r r i e s was c a l c u l a t e d by d i v i d i n g the s o i l l o s s from the strawberry covered e r o s i o n p l o t s (40 t/ha) by the p o t e n t i a l s o i l l o s s (98 t / h a ) . The C f a c t o r value f o r s t r a w b e r r i e s determined i n t h i s manner i s .41. However, the above c a l c u l a t e d C f a c t o r value fo r r y e g r a s s cannot be used to c a l c u l a t e the s o i l l o s s f o r the year of the study (1984-85) f o r the f o l l o w i n g reason. In the year of the study a cover crop of f a l l ryegrass was sown i n an attempt to r e t a r d e r o s i o n . However, t h i s p a r t i c u l a r crop d i d not get s u f f i c i e n t l y w e l l e s t a b l i s h e d before severe e r o s i o n had o c c u r r e d . Late establishment of a crop has an important e f f e c t on the amount of p r o t e c t i o n p rovided by the c r o p cover. Roose (1977) r e p o r t s a crop cover of r a p i d development or e a r l y p l a n t i n g i n W. A f r i c a to have a C f a c t o r v alue of .01 to .1 while a c r o p cover of slow development or l a t e p l a n t i n g has a C f a c t o r value of .3 to .8. Much of the r i l l development in the year of the study was i n i t i a t e d i n one l a r g e r a i n f a l l event i n the f a l l . Crop growth was patchy and remained r e l a t i v e l y sparse i n some a r e a s . D e s p i t e these f a c t s , the 110 ryegrass cover would have r e t a r d e d e r o s i o n somewhat. Due to t h i s more complex s i t u a t i o n , l i t e r a t u r e values or the c a l c u l a t e d value of C cannot j u s t i f i a b l y be used. A p p l y i n g the USLE to s i t u a t i o n s f o r which i t s f a c t o r values cannot be determined from e x i s t i n g data with a c c e p t a b l e accuracy i s a misuse of the equation (wischmeier 1977). There are no a v a i l a b l e C f a c t o r values a p p r o p r i a t e f o r t h i s p a r t i c u l a r s i t u a t i o n and no procedure to determine one. T h e r e f o r e , a range of C f a c t o r values of .5 - .7 i s estimated and used i n the equation with the a p p r o p r i a t e s k e p t i c i s m . . As no s p e c i a l e r o s i o n c o n t r o l p r a c t i c e s were employed, a P f a c t o r value of 1 was used. S u b s t i t u t i n g these f a c t o r v a l u e s i n t o the U.S.L.E. r e s u l t s i n an estimated long term, average annual s o i l l o s s f o r the. s p e c i f i e d c o n d i t i o n s of 22 to 31 tons/acre or 49 to 69 tonnes/ha. 3. DIGITAL ANALYSIS ESTIMATES OF RILL PLAN AREA AND VOLUME  FOR 3 SELECTED SAMPLE UNITS ( S e c t i o n 4) Sample u n i t s 61, 77 and 93 were used f o r the d i g i t a l a n a l y s i s . The mean p i x e l values f o r the r i l l shadow, r i l l s u n - f a c i n g and i n t e r r i l l c l a s s e s are l i s t e d i n Table 14. As expected, the r i l l shadow s i d e has the lowest mean values, the su n - f a c i n g r i l l s i d e has the highest mean values and the i n t e r r i l l area has intermediate v a l u e s . 111 Table 14. Mean P i x e l Values of the Supervised C l a s s e s . Sample Unit R i l l Shadow I n t e r r i l l R i l l Sun-F a c i n g R G B R G B R G B 61 77 93 69 68 36 78 74 38 79 75 39 114 110 52 114 106 51 106 103 49 137 122 56 125 111 52 129 114 53 The area of each c l a s s f o r both s u p e r v i s e d c l a s s i f i e r s i s l i s t e d i n Table 15. The r i l l p l a n area f o r the three sample u n i t s estimated from the r i l l o m e t e r and photo measurements and the d i g i t a l c l a s s i f i c a t i o n s are l i s t e d i n Table 16. I t can be seen that the nearest neighbour c l a s s i f i e r overestimates the t o t a l r i l l area s i g n i f i c a n t l y . T h i s was due to e r r o r s of commission f o r the r i l l sun f a c i n g c l a s s which occurred because of the l a c k of s e p a r a t i o n of the p i x e l values between the r i l l sun f a c i n g s i d e and the l i g h t e r c o l o u r e d bare s o i l i n the i n t e r r i l l a r eas. As a r e s u l t some of the b r i g h t e r bare s o i l i n the i n t e r r i l l area gets c l a s s e d as r i l l s u n - f a c i n g s i d e . As can be seen on the enlargement ( P l a t e 13), the r i l l s u n - f a c i n g s i d e has areas b r i g h t e r than the i n t e r r i l l bare s o i l areas and a l s o areas which are not b r i g h t e r . T h i s i s due to v a r i a t i o n s i n the angle of the r i l l s i d e to the sun, v a r i a t i o n s i n the f l a t n e s s of the r i l l s i d e and v a r i a t i o n s in the amount of the r i l l s i d e v i s i b l e to the camera. Some of 1 12 the l e s s b r i g h t areas of the r i l l s u n - f a c i n g s i d e s were c l a s s e d as i n t e r r i l l a r e a s . Some of the darker i n t e r r i l l bare s o i l areas get m i s c l a s s i f i e d as r i l l shadow areas as do some of the shadows present i n the grass cover. M i s c l a s s i f i c a t i o n of i n t e r r i l l bare s o i l would of course have been l e s s of a problem with g r e a t e r v e g e t a t i o n cover. Table 15. Areas of Supervised C l a s s e s (% of t o t a l ) . C l a s s i f i e r Sample R i l l R i l l Sun- T o t a l I n t e r r i l l Unit Shadow Fac i n g R i l l 61 1 .6 13.5 15.1 84.9 Nearest 77 3.5 29.3 32.8 67. 1 Neighbour 93 3.9 28.5 32.4 67.6 61 1 .6 1 .8 3.4 96.6 Maximum 77 4.2 2.1 8.4 93.7 L i k l i h o o d 93 4.1 7.9 12.0 88.0 Table 16. R i l l Plan Area Estimates (m ) f o r Sample U n i t s 61 , 77 & 93. Sample U n i t D i g i t a l C l a s s ' n R i l l Model Estimates N.N. Max. L i k . R i l l o m e t e r A e r i a l Photo 61 15.1 3.4 5.8 6.2 77 32.8 8.4 8.3 8.3 93 32.4 12.0 12.0 12.0 T o t a l 80.3 23.8 26. 1 26.5 It can a l s o be seen from Table 16 that the maximum l i k e l i h o o d c l a s s i f i e r c l a s s i f i e d the t o t a l r i l l area much more a c c u r a t e l y , r e l a t i v e to the model d e r i v e d plan area, than the 113 nearest neighbour c l a s s i f i e r . While there i s a f a i r l y l a r g e e r r o r f o r sample u n i t 61, the maximum l i k e l i h o o d c l a s s i f i e r p l an area estimate i s very a c c u r a t e f o r the other two sample u n i t s . O v e r a l l , the t o t a l maximum l i k e l i h o o d plan area f o r the three u n i t s i s 8.8 % l e s s than the r i l l o m e t e r e s t i m a t e . The g r e a t e r accuracy of the maximum l i k e l i h o o d c l a s s i f i e r i s due mainly to a much more ac c u r a t e c l a s s i f i c a t i o n of the r i l l s u n - f a c i n g area. The more ac c u r a t e c l a s s i f i c a t i o n i s l a r g e l y due to the use of the a p r i o r i p r o b a b i l i t i e s . In a c t u a l p r a c t i c e , these would not be known as they were i n t h i s case. However, an estimate of them c o u l d be made from the remotely sensed imagery. I t should be noted that here we are examining the map accuracy of the c l a s s i f i e r s and not the c l a s s i f i c a t i o n a ccuracy. A psuedo-colour image of the maximum l i k e l i h o o d c l a s s i f i e d images f o r each sample u n i t i s presented i n P l a t e s 15, 16 and 17. I t can be seen that although there are some e r r o r s of omission and commission, o v e r a l l the maximum l i k e l i h o o d c l a s s i f i e r d i d a reasonably good job, e s p e c i a l l y fo r Sample U n i t s 61 & 77. There were more e r r o r s of omission & commision i n the c l a s s i f i c a t i o n of Sample Unit 93 though these e r r o r s compensated f o r each other, r e s u l t i n g i n an accu r a t e e s t i m a t i o n of plan area f o r the u n i t . The maximum l i k e l i h o o d c l a s s i f i e r was a l s o a p p l i e d to sample u n i t 93 using the red, green and blue images in separate c l a s s i f i c a t i o n s . None of the r e s u l t s of r i l l p l an 114 PLATE 15. Psuedo-Colour Image of Maximum Likelihood C l a s s i f i c a t i o n of Sample Unit 61. Red = R i l l Shadow Side Blue = R i l l Sun-Facing Side Green = I n t e r r i l l Area PLATE 16. Psuedo-Colour Image of Maximum Likelihood C l a s s i f i c a t i o n of Sample Unit 77. PLATE 17. Psuedo-Colour Image of Maximum Likelihood C l a s s i f i c a t i o n of Sample Unit 93. 1 15 area were as good as the r e s u l t s u s i n g a l l three images i n the c l a s s i f i c a t i o n . Of the three image c l a s s i f i c a t i o n s , the red image r e s u l t e d i n the best e s t i m a t i o n of r i l l plan area with a r i l l p l an area f o r the sample u n i t of 10.8 %. The green image r e s u l t e d i n a r i l l plan area of 9.1 %, while the blue image r e s u l t e d i n a r i l l plan area of 6.1 %. An estimate of the r i l l volume of the three sample u n i t s was made from the maximum l i k e l i h o o d c l a s s i f i e d p l a n area and the average r i l l depth of the three sample u n i t s of 16 cm. The r e s u l t s are compared to the r i l l o m e t e r estimate i n Table 17. The r i l l volume f o r sample u n i t 61 i s underestimated r e l a t i v e to the r i l l o m e t e r estimate due to the plan area estimate being too low. R i l l volume i s overestimated i n the other two sample u n i t s mainly because m u l t i p l y i n g the plan area by an average depth assumes a r e c t a n g u l a r (Wt = Wb) r i l l shape, which has been shown to overestimate r i l l volume. 3 Table 17 R i l l Volume Estimates (m ) f o r Sample U n i t s 61, 77 & 93 Sample U n i t Maximum L i k e l i h o o d C l a s s i f i e r R i l l Model Estimate from R i l l o m e t e r Input T o t a l 61 77 93 .54 1 .34 1 .92 3.80 .82 .95 1 .46 3.23 These r e s u l t s i n d i c a t e that f o r at l e a s t some f i e l d s , the 1 1 6 plan area covered by g u l l i e s and l a r g e r r i l l s can be estimated very q u i c k l y by computer c l a s s i f i c a t i o n . These f i e l d s would be those which have the a p p r o p r i a t e sun-surface-sensor geometry r e s u l t i n g i n r i l l shadow and b r i g h t e r sun f a c i n g r i l l s i d e s which can be s p e c t r a l l y separated from i n t e r r i l l a r e a s . The accuracy of e s t i m a t i n g r i l l p l a n area by t h i s r e l a t i v e l y simple image a n a l y s i s c o u l d be improved. Larger t r a i n i n g s e t s and s e p a r a t i n g the i n t e r r i l l c l a s s i n t o i n t e r r i l l v e g e t a t i o n and bare s o i l c l a s s e s may improve the r e s u l t s of the nearest neighbour c l a s s i f i c a t i o n . Operations such as edge d e t e c t i o n and enhancement may h e l p i n i s o l a t i n g r i l l s from the i n t e r r i l l a r e a . The l a r g e s t improvements however, would l i k e l y r e s u l t from an expert systems approach. T h i s approach would use knowledge of the process of r i l l e r o s i o n to produce a l g o r i t h m s which would i n c r e a s e the accuracy of the plan area e s t i m a t i o n . For i n s t a n c e , i t i s known that the r i l l s are r e l a t i v e l y continuous, l i n e a r f e a t u r e s which are g e n e r a l l y o r i e n t e d downslope ( i . e . i n a c e r t a i n d i r e c t i o n range). Algorithms based on t h i s knowledge cou l d be a p p l i e d to the c l a s s i f i e d image. These a l g o r i t h m s may r e q u i r e a s p e c i f i e d c o n t i n u i t y and c o n t i g u i t y f o r the p i x e l s to belong to a r i l l c l a s s . A d i r e c t i o n a l g r a d i e n t f i l t e r which only passes l i n e a r f e a t u r e s which are w i t h i n a s p e c i f i e d d i r e c t i o n range c o u l d a l s o i n c r e a s e accuracy. In order to d e p i c t r i l l s s m a l l e r than g u l l i e s and the 117 l a r g e s t r i l l s , a very l a r g e s c a l e and very small p i x e l s i z e s was r e q u i r e d . T h i s leads to the problem of the images c o n t a i n i n g very l a r g e amounts of data and thus l a r g e amounts of computer memory are r e q u i r e d . T h i s i s expensive and s u f f i c i e n t memory may not be a v a i l a b l e i n a given system. For 2 i n s t a n c e , to cover the 14,400 m area o u t l i n e d i n Overlay 3 with 25 micrometre p i x e l r e s o l u t i o n would r e q u i r e 10,240,00 p i x e l s . At 8 b i t s / p i x e l , t h i s r e p r e s e n t s 81,920,000 b i t s of in f o r m a t i o n f o r one image plane. For r e s o l u t i o n of only g u l l i e s and the l a r g e s t r i l l s , a l a r g e r p i x e l s i z e c o u l d be used. However, with the advent of o p t i c a l d i s k technology which allows f o r a much gr e a t e r amount of data storage, the problem of having adequate memory w i l l become l e s s i n the near f u t u r e . 4. DISCUSSION OF SOIL LOSS ESTIMATES The s o i l l o s s estimates from the d i f f e r e n t methods are l i s t e d i n Table 18. Only the r i l l volume model p r o v i d e s an estimate of the plan area covered by the r i l l s . The methods' r e s u l t s cannot be d i r e c t l y compared as the methods were designed f o r d i f f e r e n t purposes or a p p l i e d to d i f f e r e n t c o n d i t i o n s . The r i l l model was designed to c a l c u l a t e r i l l volume and thus the s o i l l o s s from r i l l f ormation. However, as most of the e r o s i o n o c c c u r i n g i n t h i s f i e l d i s r i l l e r o s i o n , the s o i l l o s s from r i l l e r o s i o n should be f a i r l y c l o s e to the t o t a l ( r i l l + i n t e r r i l l ) s o i l l o s s . The best 118 estimate of s o i l l o s s from the model i s 38.4 t/ha which i s .95 % of the volume of s o i l down to the depth of e r o s i o n (36 cm). The f i e l d measurements f o r the r i l l volume c a l c u l a t i o n were done on A p r i l 6, 1985. Thus the r i l l volume estimate of s o i l l o s s can be c o n s i d e r e d to be the s o i l l o s s f o r the f a l l / w i n t e r p e r i o d . As the m a j o r i t y , i f not a l l , of r i l l formation occurs d u r i n g t h i s p e r i o d , t h i s value can be c o n s i d e r e d to i n c l u d e most of the s o i l l o s s due to r i l l formation f o r the year p e r i o d ending on the date of f i e l d measurement. Table 18. S o i l Loss & Plan Area Estimates of the R i l l Model, U n i v e r s a l S o i l Loss Equation and E r o s i o n P l o t . S o i l Loss Plan By volume (m 3/ha) % of s o i l volume to max. depth of e r o s i o n (36 cm) By weight (t/ha) Area (m 2) Model R i l l o m e t e r Tape Photo: A B 49.0 52.1 44.6 39.8 .95 1 .00 .68 .60 38.4 40.8 35.0 31.2 534 510 518 518 USLE 62.5-88.0 1 .20 - 1.70 49 - 69 X E r o s i o n P l o t 34. 1 .57 26.7 X Photo A: photo estimate uses average Wb & D values Photo B: photo estimate uses average r a t i o s of Wt:Wb & Wt:D The U n i v e r a l S o i l Loss Equation was designed to estimate the long term average annual s o i l l o s s f o r a f i e l d under s p e c i f i c crop cover. In t h i s case, the r e l i a b i l i t y of the s o i l 1 19 l o s s value i s l i m i t e d mostly by the lack of a r e l i a b l e C f a c t o r . Thus, at best, only a range of s o i l l o s s c o u l d reasonably be c a l c u l a t e d u sing the USLE i n t h i s s i t u a t i o n . Use of i n a c c u r a t e f a c t o r values i s one of the main sources of misuse of the USLE (Wischmeier 1976). Another l i m i t a t i o n of the USLE i n t h i s case i s that i t does not a c c u r a t e l y estimate e r o s i o n by con c e n t r a t e d flow ( F o s t e r 1982). T h i s i s because the USLE was d e r i v e d mainly from data from e r o s i o n p l o t s which were only 22.6 m long. However, r i l l formation w i l l be r e l a t i v e l y g r e a t e r i n slopes longer than 22.6 m and thus the e r o s i o n p l o t data w i l l l i k e l y underestimate s o i l l o s s from longer slopes which s u f f e r s i g n i f i c a n t r i l l e r o s i o n . The USLE e s t i m a t i o n of s o i l l o s s of 49 - 69 t/ha i s l a r g e r than the r i l l model est i m a t e . T h i s c o u l d be due to one or more of the f o l l o w i n g reasons; (a) the USLE estimates t o t a l s o i l l o s s and thus should be g r e a t e r , (b) the year of the study had l e s s e r r a i n f a l l e r o s i v i t y than the long term average e r o s i v i t y used i n the equation and (c) the C f a c t o r chosen f o r the USLE was too high. Lack of r e l i a b l e C f a c t o r s w i l l be a problem i n using the USLE f o r many i f not most l o c a t i o n s i n Canada. The author deems the r i l l model estimate to be more r e l i a b l e f o r the study f i e l d as i t was obtained from d i r e c t r i l l measurement while the USLE i s a p r e d i c t i v e equation based on u n r e l i a b l e input ( i . e . the C f a c t o r v a l u e ) . The r i l l model estimate i s s i g n i f i c a n t l y higher than the 1 20 ryegrass covered e r o s i o n p l o t s o i l l o s s estimate of the prev i o u s year. Both estimates r e f l e c t d i f f e r e n t c o n d i t i o n s . The main reason the r i l l e stimate i s higher i s due to the development of a s i g n i f i c a n t amount of r i l l e r o s i o n i n the f i e l d p r i o r to s u f f i c i e n t development of the ryegrass crop and the patchy growth of the crop i n the year of the study. T h i s i l l u s t r a t e s the importance of a w e l l e s t a b l i s h e d cover crop i n the p r e v e n t i o n of e r o s i o n . I t i s not known how much d i f f e r e n c e i n the two s o i l l o s s estimates i s due to d i f f e r e n t r a i n f a l l e r o s i v i t i e s f o r the two d i f f e r e n t y e a r s . A l s o , e x t r a p o l a t i o n of the p l o t r e s u l t s to the whole f i e l d i s q u e s t i o n a b l e due to the p l o t l o c a t i o n s which don't r e f l e c t the e f f e c t s of the topographic shape of the f i e l d and the short p l o t l e n g t h r e l a t i v e to the l e n g t h of the f i e l d . A s o i l l o s s estimate from the image a n a l y s i s was only done f o r three sample u n i t s and t h e r e f o r e t h i s technique can not be compared. The r e s u l t s with the three sample u n i t s i n d i c a t e a reasonable estimate of plan area can be obtained though r i l l volume i s overestimated when c a l c u l a t e d by using an average r i l l depth. C. D i g i t a l E l e v a t i o n and Moisture Content Models ( S e c t i o n 5) The e l e v a t i o n and moisture content contour maps are i l l u s t r a t e d on Overlays 1 and 2 r e s p e c t i v e l y . The e l e v a t i o n and moisture content p e r s p e c t i v e p l o t s are i l l u s t r a t e d i n 121 F i g u r e s 4 and 5 r e s p e c t i v e l y . The three main r i l l s have been superimposed on these f i g u r e s . The e l e v a t i o n p e r s p e c t i v e p l o t has been d i s p l a y e d at approximately 15 times v e r t i c a l exaggeration to i l l u s t r a t e the more s u b t l e l a t e r a l changes i n the topography. The main topographic highs and lows have been o u t l i n e d on the e l e v a t i o n contour map and can be observed on the e l e v a t i o n p e r s p e c t i v e p l o t . The slope g r a d i e n t d i r e c t i o n map i s i l l u s t r a t e d i n Overlay 3. Moisture content i s very v a r i a b l e over time and space. As the moisture content map was d e r i v e d from 47 sample l o c a t i o n s i t should be viewed as i n d i c a t i n g g eneral trends i n moisture content d i s t r i b u t i o n at the time of sampling (March 1985). The primary e r o s i v e f o r c e i n r i l l e r o s i o n i s conc e n t r a t e d flow which r e s u l t s from excess water on a s l o p i n g s o i l s u r f a c e . From the moisture content contour map i t i s apparent that the moisture content i n the f i e l d was very unevenly d i s t r i b u t e d . These areas of higher moisture content are seen on the a e r i a l photograph to have a darker c o l o u r . I t i s a l s o apparent that the m a j o r i t y of r i l l s are i n i t i a t e d i n or j u s t below these higher moisture content zones. T h i s i s expected as these zones w i l l be the f i r s t to become s a t u r a t e d and cause o v e r l a n d flow. In g e n e r a l , the higher moisture content areas are p r i m a r i l y a s s o c i a t e d with topographic lows or r e g i o n a l areas. The topographic highs g e n e r a l l y have lower moisture contents. 122 R i l l 1 R i l l 2 R i l l 3 FIGURE Elevation Perspective Plot 123 FIGURE 5. Moisture Perspective Plot 124 Broad a s s o c i a t i o n s between moisture content and topography are apparent. However, a c o r r e l a t i o n a n a l y s i s of the moisture contents with e l e v a t i o n and with slope g r a d i e n t showed no s t a t i s t i c a l s i g n i f i c a n c e . T h i s i s not s u r p r i s i n g as there are many f a c t o r s which a f f e c t the moisture content at the s u r f a c e at a p a r t i c u l a r l o c a t i o n i n a f i e l d . Simple topographic i n d i c i e s are inadequate to c o r r e l a t e w e l l with moisture content. Burt and Butcher (1985) s t a t e that s o i l moisture c o n d i t i o n s at a given p o i n t cannot be estimated s o l e l y on the b a s i s of known values of topography and mean slope wetness. The g e n e r a l d i s t r i b u t i o n of s o i l moisture a l s o needs to be i n c o r p o r a t e d i n a s o i l moisture content model. They a l s o s t a t e however, that broad a s s o c i a t i o n s between topographic p o s i t i o n and s o i l wetness have been observed. H i l l s l o p e hollows favour convergence of s o i l water f l o w i n g i n t o the hollow l e a d i n g to accumulation of s o i l water. S o i l s a t u r a t i o n i s encouraged on low g r a d i e n t s l o p e s where runoff i s l i m i t e d by a low h y d r a u l i c g r a d i e n t . Where slope g r a d i e n t s become reduced at the foot of a h i l l s l o p e , the e f f e c t of low g r a d i e n t i s augmented by water d r a i n i n g from above. The high moisture content area at the top of r i l l one i s l i k e l y c o n t r i b u t e d to by leakage and subsurface flow from the drainage d i t c h immediately above i t . A l s o from the e l e v a t i o n and slope contour maps i t i s observed that t h i s wet area i s l o c a t e d where the slope l e v e l s out to a f a i r l y f l a t a r e a. Excess 125 moisture i n the wetter areas i s c o n t r i b u t e d to by subsurface flow from the slope above t h i s f i e l d and by l a t e r a l subsurface flow from the t o p o g r a p h i c a l l y high areas to the lower a r e a s . The presence of a l a y e r of r e s t r i c t e d p e r m e a b i l i t y at depth such as occurs i n the study f i e l d w i l l promote l a t e r a l flow of water on the h i l l s l o p e (Burt and Butcher 1986). Accumulation of water w i l l l e a d to subsurface r u n o f f . Where s o i l water storage i s exceeded, s a t u r a t i o n - excess overland flow i s generated. The r e s u l t s of the study by Burt and Butcher (1986) i n d i c a t e d that upslope drainage area i s a more important c o n t r o l of the d i s t r i b u t i o n of s o i l moisture than contour c u r v a t u r e at l e a s t f o r t h e i r study s i t e . In the study f i e l d of t h i s t h e s i s i t i s apparent from the slope g r a d i e n t d i r e c t i o n map that the g r e a t e s t area i s dr a i n e d through the bottoms of the two topographic lows. However, these areas are not the wettest i n the f i e l d . T h i s i s p a r t i a l l y because the l a r g e number of r i l l s found i n these lows are e f f i c i e n t i n t r a n s p o r t i n g water o f f the f i e l d . Once formed, r i l l s change the hydrology of a h i l l s l o p e ( S o u l l i e r e and Toy 1986). I t i s apparent that the m a j o r i t y of the r i l l s are i n i t i a t e d i n or below the areas of higher moisture content. The slope g r a d i e n t d i r e c t i o n map i l l u s t r a t e s that the l o c a t i o n of the r i l l s c o i n c i d e s with the d i r e c t i o n of overland flow of s a t u r a t i o n - e x c e s s water. Concentrated flow down the 126 topographic lows i s the main e r o s i v e energy source i n t h i s f i e l d . A s l i g h t topographic high i n the middle of the bottom pa r t of the south topographic low can be seen on the e l e v a t i o n contour map. T h i s s l i g h t high w i l l funnel o v e r l a n d flow to e i t h e r s i d e of i t . I t can be seen from the moisture content contour map and from the a e r i a l photograph that t h i s s l i g h t y higher area i s d r i e r than the area immediately above i t and that there are few or no r i l l s on i t . While simple topographic i n d i c e s cannot p r e d i c t moisture content, simple i n t e r p r e t a t i o n s of e l e v a t i o n and moisture content maps along with a e r i a l photographs which show r i l l l o c a t i o n s can be u s e f u l i n r e l a t i n g r i l l formation to the topography and hydrology i n a p a r t i c u l a r f i e l d . T h i s c o u l d be very u s e f u l i n plann i n g c o n s e r v a t i o n measures such as the use of grassed waterways. With a s t a t e of the a r t G.I.S. with s u f f i c i e n t data and a p p r o p r i a t e a l g o r i t h m s , a more d e t a i l e d q u a n t i t a t i v e approach c o u l d be used. At present d i g i t a l maps of environmental f a c t o r s r e l e v a n t to e r o s i o n can be analysed with the h e l p of a G.I.S. to in c r e a s e understanding of the er o s i o n process i n general or i n a p a r t i c u l a r f i e l d . Such f a c t o r s may i n c l u d e e l e v a t i o n , moisture content, s o i l p r o p e r t i e s , s o i l t h i c k n e s s e t c . Other maps which w i l l h e lp analyze the e r o s i o n processes i n a f i e l d can be d e r i v e d from the b a s i c maps. For i n s t a n c e from the e l e v a t i o n map s e v e r a l u s e f u l maps c o u l d be d e r i v e d . These i n c l u d e slope g r a d i e n t , 127 slope c o n v e x i t y , d i s t a n c e from the d i v i d e , o v e r l a n d flow f l o w l i n e s , and upslope area of drainage through a p a r t i c u l a r l o c a t i o n . E v e n t u a l l y s o p h i s t i c a t e d models w i l l be developed which are a b l e to p r e d i c t the hydrology of a f i e l d and the sediment eroded from the f i e l d . In summary, the high amount of r a i n f a l l , the l i m i t e d storage c a p a c i t y of the t h i n t o p s o i l and the r e l a t i v e l y impermeable s u b s o i l are main causes of excess moisture. Comparison of the outputs from the d i g i t a l e l e v a t i o n and moisture content models with the a i r photos i l l u s t r a t e d the importance of the topographic shape of the f i e l d i n e x p l a i n i n g the s p a t i a l d i s t r i b u t i o n of r i l l i n g in t h i s p a r t i c u l a r f i e l d by a l l o w i n g easy comparison of the r i l l p a t t e r n to the d i s t r i b u t i o n of excess moisture and the o v e r l a n d flow p a t t e r n . The r i l l s were found to develop l a r g e l y i n two long topographic lows o r i e n t e d down the f a l l l i n e and were i n i t i a t e d i n or j u s t below zones of high moisture content. R e l a t i v e l y s u b t l e changes i n topography were observed to have important e f f e c t s on moisture d i s t r i b u t i o n and overland flow p a t t e r n . Other f a c t o r s a f f e c t i n g the formation of r i l l s such as leakage from d i t c h e s and the presence of furrows were observed. D. I n t e g r a t i o n of the R e s u l t s The most e f f i c i e n t l i n k between the d i f f e r e n t techniques 128 f o r g a t h e r i n g and a n a l y s i n g i n f o r m a t i o n about e r o s i o n i s the Geographic Information System. The f i e l d r e f l e c t a n c e study has demonstrated the p o t e n t i a l f o r s e p a r a t i n g r i l l s from the surrounding area on remotely sensed imagery. T h i s i s p o s s i b l e due to d i f f e r e n c e s between r i l l s and the surrounding area i n s o i l and s i t e p r o p e r t i e s and imaging geometries. Thus, remotely sensed imagery of r i l l s can be used as a data input source f o r e r o s i o n a n a l y s i s with a GIS i n c o n j u n c t i o n with an image a n a l y s i s system. There i s p o t e n t i a l f o r o b t a i n i n g r i l l dimensions such as r i l l l e n gth and widths of l a r g e r r i l l s f o r input i n t o a r i l l volume model s i m i l a r to the one used i n t h i s t h e s i s . T h i s c o u l d be i n t e g r a t e d with f i e l d measured r i l l data by the a s s i g n i n g of f i e l d measured r i l l a t t r i b u t e v a l u e s to the a p p r o p r i a t e p o i n t s i n an o v e r l a y . Other d i g i t a l a n a l y s es such as the one demonstrated here f o r c l a s s i f i c a t i o n and d e t e r m i n a t i o n of r i l l plan area c o u l d be performed. The imagery c o u l d a l s o be used f o r v i s u a l i n t e r p r e t a t i o n or to a s s i s t i n the l o c a t i o n of f i e l d c o l l e c t e d r i l l data. As w e l l as p o i n t format, data c o l l e c t e d of e r o s i o n r e l a t e d environmental v a r i a b l e s can be input and manipulated i n the form of maps. E l e v a t i o n and moisture content are two important v a r i a b l e s i n v o l v e d i n the e r o s i o n p r o c e s s . As demonstrated here, r e p r e s e n t a t i o n of these as w e l l as other r e l e v a n t v a r i a b l e s i n the form of d i g i t a l maps allows f o r a 129 wide range of a n a l y t i c a l procedures f o r the i n t e r p r e t a t i o n of e r o s i o n d ata. Data from these maps c o u l d be used i n s o i l l o s s e s t i m a t i o n models. The techniques f o r a n a l y s i s - o f e r o s i o n used i n t h i s t h e s i s demonstrate the p o t e n t i a l u t i l i t y of them as components in an i n t e g r a t e d e r o s i o n data c o l l e c t i o n and a n a l y s i s system c o n s i s t i n g of a GIS and an image a n a l y s i s system. The system c o u l d be very f l e x i b l e i n a l l o w i n g f o r v a r y i n g l e v e l s of s o p h i s t i c a t i o n i n the type of data c o l l e c t e d and s t o r e d , the a n a l y s e s performed on the data, and the output of the r e s u l t s . 130 Chapter V A. CONCLUSIONS 1. REFLECTANCE STUDY S i g n i f i c a n t r e f l e c t a n c e d i f f e r e n c e s occurred between the r i l l , i n t e r r i l l and d e p o s i t i o n areas due to d i f f e r e n c e s i n s o i l and s i t e p r o p e r t i e s . D e p o s i t i o n areas had the h i g h e s t f i e l d r e f l e c t a n c e mainly because they had the lowest carbon contents and the smoothest s u r f a c e . I n t e r r i l l areas had the lowest f i e l d r e f l e c t a n c e mainly because they had the highest carbon content and the roughest s u r f a c e . The most important f a c t o r c o n t r i b u t i n g to the s p e c t r a l s e p a r a b i l i t y of r i l l s from the surrounding area i s probably the e f f e c t of s o u r c e - s u r f a c e -sensor geometry. With c e r t a i n geometries, one s i d e of the r i l l s w i l l be dark due to being i n shadow and the other s i d e w i l l be b r i g h t e r than the surrounding area due to a more d i r e c t angle of i n c i d e n t s u n l i g h t . The s p e c t r a l s e p a r a b i l i t y of r i l l s from the surrounding area p r o v i d e s a b a s i s f o r the q u a n t i f i c a t i o n of e r o s i o n using remotely sensed images. In t h i s study, t h i s approach was i n v e s t i g a t e d by d i r e c t hard copy measurement of r i l l dimensions and by d i g i t a l image a n a l y s i s . The e f f e c t of a given s o i l p r o p e r t y on s o i l r e f l e c t a n c e was found to be v a r i a b l e and c o u l d be masked by the e f f e c t s on r e f l e c t a n c e of other s o i l and s i t e p r o p e r t i e s . Covariance of 131 s o i l p r o p e r t i e s made i t impossible to separate the e f f e c t s on s o i l r e f l e c t a n c e of c e r t a i n s o i l p r o p e r t i e s i n some cases. 2. RILL MODEL SOIL LOSS AND PLAN AREA ESTIMATES The best estimate of s o i l l o s s due to r i l l formation was 3 49 m /ha (38.4 t/ha) as determined from the r i l l volume and plan area model u t i l i z i n g r i l l o m e t e r i n p u t . The plan area 2 covered by the r i l l s was 534 m /ha or 5.34 % of the area. Using the tape measurements of r i l l dimensions as input r e s u l t e d i n a s o i l l o s s value of 52.1 m /ha (40.8 t/ha) which i s 6 % more than the best e s t i m a t e . The r i l l p l an area was 510 m /ha which i s 4 % l e s s than the best e s t i m a t e . Using photo measurements and two d i f f e r e n t methods of e s t i m a t i o n of r i l l depths and bottom widths as model input r e s u l t e d i n s o i l l o s s e stimates of 44.6 m 3/ha (35.0 t/ha) and 39.8 m 3/ha (31.2 t/ha) which are 9 and 19 % l e s s than the best estimate r e s p e c t i v e l y . R i l l plan area c a l c u l a t e d from photomeasurement input was 518 m /ha which i s 3 % l e s s than the best e s t i m a t e . An i n v e s t i g a t i o n i n t o the accuracy of the tape and photo measurement inputs r e l a t i v e to the best estimate u t i l i z i n g r i l l o m e t e r data f o r three main r i l l s was done. I t showed that the average e r r o r of the tape and photo estimates f o r i n d i v i d u a l r i l l segments was g e n e r a l l y higher than r e p o r t e d above f o r the t o t a l r i l l volume and plan area e s t i m a t e s . T h i s was due to p a r t i a l c a n c e l l a t i o n of e r r o r s 132 of over and underestimation of r i l l volume and plan area of i n d i v i d u a l r i l l segments i n summing the r i l l segments to determine the t o t a l r i l l volume and plan area. The r i l l volume and p l a n area d e r i v e d from the tape and photo measurements were not as accurate as the r e s u l t s d e r i v e d from the r i l l o m e t e r measurements. However, they are accurate enough to pr o v i d e a l t e r n a t i v e methods where the accuracy requirements are not as high and a q u i c k e r s o i l l o s s estimate i s d e s i r e d . 3. USLE & EROSION PLOT SOIL LOSS ESTIMATES The USLE s o i l l o s s estimate was 62.5 - 88.0 m /ha (49 -69 t/ha) which i s 28 to 82 % more than the s o i l l o s s estimated from the r i l l model u t i l i z i n g r i l l o m e t e r i n p u t . The USLE s o i l l o s s estimate would be expected to be more than the r i l l model estimate as the r i l l model only c a l c u l a t e s s o i l l o s s due to r i l l e r o s i o n . The USLE estimate, while i t seems to be about the r i g h t magnitude, i s u n r e l i a b l e i n t h i s case mainly due to the u n a v a i l a b i l i t y of a r e l i a b l e C f a c t o r value or a method to determine one f o r the s i t u a t i o n encountered i n the year of the study ( i . e . l a t e and patchy development of the cover c r o p ) . The lac k of r e l i a b l e C f a c t o r values f o r many areas i s an important drawback i n using the USLE. The e r o s i o n p l o t s o i l l o s s estimate f o r the year previous 133 3 to the r i l l model study was 34.1 m /ha (26.7 t/ha) which i s 30 % l e s s than the r i l l model est i m a t e . The e r o s i o n p l o t estimate i s much lower than the r i l l model estimate because in the year of the r i l l model study, a s i g n i f i c a n t amount of r i l l e r o s i o n o c c u r r e d p r i o r to s u f f i c i e n t establishment of the ryegrass crop. T h i s combined with patchy growth i n the year of the r i l l model study allowed much more s o i l to be eroded than would have occured with a w e l l e s t a b l i s h e d cover crop. T h i s i l l u s t r a t e s the importance of a w e l l e s t a b l i s h e d crop cover i n the p r e v e n t i o n of e r o s i o n . 4. DIGITAL IMAGE ANALYSIS PLAN AREA AND VOLUME ESTIMATES The r i l l p l an area of three sample u n i t s estimated by computer c l a s s i f i c a t i o n of the d i g i t a l image with a maximum l i k l i h o o d c l a s s i f i e r was 9 % l e s s than the best r i l l model estimate u s i n g the r i l l o m e t e r i n p u t . T h i s r e s u l t i n d i c a t e s that f o r at l e a s t some areas, the plan area covered by g u l l i e s and l a r g e r r i l l s can be q u i c k l y estimated. These areas are those which have the a p p r o p r i a t e sun-surface-sensor geometry r e s u l t i n g i n r i l l shadow and b r i g h t e r sun-facing r i l l s i d e s which can be s p e c t r a l l y separated from i n t e r r i l l a r eas. E s t i m a t i o n of r i l l area c o u l d be improved by consequent a p p l i c a t i o n of a l g o r i t h m s which u t i l i z e knowledge of the form of r i l l s . As w e l l as p l a n area other r i l l measurements such as r i l l l e n g t h and width may be p o s s i b l e . 134 An e s t i m a t i o n of volume of the three u n i t s was made using the plan area r e s u l t i n g from image c l a s s i f i c a t i o n with the maximum l i k l i h o o d c l a s s i f i e r and an average r i l l depth f o r the three sample u n i t s obtained from f i e l d measurements. The r e s u l t overestimated r i l l volume by 18 % r e l a t i v e to the best r i l l model est i m a t e . T h i s overestimate was p r i m a r i l y due to the use of the average depth which assumes a r e c t a n g u l a r r i l l c r o s s - s e c t i o n a l shape and thus overestimates the r i l l volume. 5. USE OF THE SOIL LOSS ESTIMATION METHODS None of the s o i l l o s s e s t i m a t i o n methods are a p p l i c a b l e to a l l s i t u a t i o n s . Where r i l l e r o s i o n i s predominant, a m o d i f i e d r i l l volume method as p r e v i o u s l y d e s c r i b e d i n the the t h e s i s i s recommended f o r r o u t i n e s o i l l o s s e s t i m a t i o n . Compared to e r o s i o n p l o t s , i t i s a r e l a t i v e l y quick procedure done at the end of the e r o s i o n season. E r o s i o n p l o t s r e q u i r e a l o t of time and work to set up and monitor them. A l s o , there are q u e s t i o n s about the accuracy of e r o s i o n p l o t e s timates i n areas with s i g n i f i c a n t r i l l e r o s i o n on f i e l d s which are much longer than the e r o s i o n p l o t s . Roels (1985) q u e s t i o n s the r e l i a b i l i t y of e x t r a p o l a t i n g e r o s i o n p l o t r e s u l t s to l a r g e r areas. The l o c a t i o n of the e r o s i o n p l o t i n the study f i e l d was seen to r e - e n f o r c e Roels' arguments as i t d i d not r e f l e c t the very important e f f e c t of the topographic shape of the f i e l d on r i l l f o rmation. E r o s i o n p l o t s are most 135 a p p r o p r i a t e f o r comparing d i f f e r e n t treatments of p l o t s adjacent to each other. P l o t s adjacent to each other w i l l have the same p h y s i c a l parameters, and thus d i f f e r e n t management treatments can be compared on adjacent p l o t s eventhough the p l o t s may not be r e p r e s e n t a t i v e of a l a r g e area around the p l o t l o c a t i o n s . The l i m i t a t i o n s of the USLE are e x t e n s i v e ( F o s t e r 1982). It does not a c c u r a t e l y estimate e r o s i o n by c o n c e n t r a t e d flow ( F o s t e r 1982) and i s thus not w e l l s u i t e d to areas with a s i g n i f i c a n t amount of r i l l e r o s i o n . Another important l i m i t a t i o n i n using the USLE as i l l u s t r a t e d i n t h i s t h e s i s i s the l a c k of r e l i a b l e C f a c t o r values f o r many, i f not most, areas i n Canada. Thus, use of the r i l l volume method of s o i l l o s s e s t i m a t i o n i s p r e f e r r e d f o r areas with s i g n i f i c a n t r i l l e r o s i o n . I t i s the only method which a l s o p r o v i d e s i n f o r m a t i o n on the plan area covered by r i l l s . For s o i l l o s s e s t i m a t i o n work of a reconnaisance nature in areas with s i g n i f i c a n t r i l l e r o s i o n , the use of l a r g e s c a l e remotely sensed imagery i s recommended where the a p p r o p r i a t e image geometry allows f o r s p e c t r a l s e p a r a b i l i t y of the r i l l s from i n t e r r i l l and d e p o s i t i o n areas. Using r i l l measurements from the images reduces the amount of f i e l d measurements necessary. Larger areas can be covered more q u i c k l y though accuracy i s reduced. D i g i t a l image c l a s s i f i c a t i o n i s recommended f o r very quick estimates of plan area, e s p e c i a l l y 1 36 i f i t i s used i n c o n j u n c t i o n with subsequent a p p l i c a t i o n of al g o r i t h m s which u t i l i z e knowledge of r i l l form. 6. DIGITAL ELEVATION AND MOISTURE CONTENT MAPS The high r a i n f a l l , the l i m i t e d storage c a p a c i t y of the t h i n t o p s o i l , the r e l a t i v e l y impermeable s u b s o i l , leakage from drainage d i t c h e s , and the topography of the f i e l d i n t e r a c t e d to cause areas of excess moisture i n the f i e l d . Comparison of the outputs from the d i g i t a l e l e v a t i o n and moisture content maps with the a i r photos i l l u s t r a t e d the importance of the topographic shape of the f i e l d i n e x p l a i n i n g the s p a t i a l d i s t r i b u t i o n of r i l l i n g i n t h i s p a r t i c u l a r f i e l d by a l l o w i n g easy comparison of the r i l l p a t t e r n to the d i s t r i b u t i o n of excess moisture and the ov e r l a n d flow p a t t e r n . The r i l l s developed mostly i n two long topographic lows o r i e n t e d down the f a l l l i n e and were i n i t i a t e d i n or j u s t below areas of high moisture content. Areas of high moisture were c o n t r i b u t e d to by .downslope subsurface flow from the long slope above the f i e l d and w i t h i n the f i e l d , and l a t e r a l subsurface flow from topographic highs w i t h i n the f i e l d . A l s o , a s i g n i f i c a n t decrease i n the gr a d i e n t of the f i e l d at one l o c a t i o n c o n t r i b u t e d to an accumulation of moisture. The shape of the f i e l d was seen to concentrate the overland flow i n t o and down the two main topographic lows r e s u l t i n g i n the formation of the m a j o r i t y of the r i l l s i n these l o c a t i o n s . 1 37 7. Future D i r e c t i o n s The p o t e n t i a l of using remotely sensed images and d i g i t a l maps to a s s i s t i n the study of the processes and e f f e c t s of r i l l e r o s i o n has been demonstrated. A Geographic Information System in c o n j u n c t i o n with an image a n a l y s i s system i s w e l l s u i t e d to analyse t h i s s p a t i a l l y v a r i a b l e d ata. Such a system p r o v i d e s a s u i t a b l e environment f o r the use of a l g o r i t h m s designed f o r the a n a l y s i s of e r o s i o n . These c o u l d i n v o l v e d i s t r i b u t e d parameter p r e d i c t i o n models, or a l g o r i t h m s designed f o r measurement of r i l l e r o s i o n from remotely sensed images, p o s s i b l y i n t e g r a t e d with some f i e l d measurements. These techniques w i l l become more p r a c t i c a l as computer memory and other technology becomes l e s s expensive and more r e a d i l y a v a i l a b l e . B. I m p l i c a t i o n s of S o i l Loss and Recommendations 3 The r i l l e r o s i o n estimate of 49 m /ha (38.4 t/ha) i s severe e r o s i o n . T h i s value i s c l o s e to the annual s o i l l o s s of 45 t/ha estimated f o r the most e r o s i v e p a r t of the Palouse R i v e r Basin which has s i m i l a r r i l l e r o s i o n problems. I t has been estimated that e r o s i o n i n the Palouse River Basin has reduced wheat y i e l d s by 22 % ( F r a z i e r et a l 1983). With no remedial measures, s o i l l o s s w i l l c ontinue on t h i s f i e l d at a high r a t e and the r a v i n e at the slope bottom 1 38 w i l l "grow" up the topographic lows as i t has on e i t h e r s i d e of the f i e l d . E v e n t u a l l y , t h i s w i l l negate any a g r i c u l t u r a l land use. In the meantime, s o i l f e r t i l i t y w i l l be reduced as the t o p s o i l becomes i n c r e a s i n g l y t h i n n e r . Each year r i l l s w i l l occupy a p o r t i o n of the s u r f a c e area, reducing the area a v a i l a b l e f o r crop p r o d u c t i o n . I t may be best that t h i s l a n d be l e f t i n dense cover v e g e t a t i o n such as p a s t u r e . I f more i n t e n s i v e crop p r o d u c t i o n i s to be done, remedial measures should be taken. I f a winter cover crop i s to be p l a n t e d , i t should be sown in time to be w e l l e s t a b l i s h e d and provide s u f f i c i e n t cover before the higher r a i n f a l l autumn months a r r i v e . The f o l l o w i n g recommendations are wider i n scope and importance. While they do not f o l l o w d i r e c t l y from the r e s u l t s of the study, they were a r r i v e d at from the review of l i t e r a t u r e on e r o s i o n . Compared to the United S t a t e s , Canada has l i t t l e i n the way of a permanent government or p r i v a t e i n f r a s t r u c t u r e to deal s p e c i f i c a l l y with s o i l and water c o n s e r v a t i o n . Given that there i s an i n c r e a s i n g r e a l i z a t i o n of the e x i s t a n c e of s i g n i f i c a n t economic l o s s e s r e s u l t i n g from e r o s i o n , a p p r o p r i a t e a c t i o n s must be taken. Both the Standing Senate Committee in A g r i c u l t u r e , F i s h e r i e s & F o r e s t r y (1986) and the Science C o u n c i l of Canada (1986) have recommended i n c r e a s e d s o i l and water c o n s e r v a t i o n r e s e a r c h , and technology t r a n s f e r to the farmers. To s u c c e s s f u l l y 1 39 achieve these o b j e c t i v e s r e q u i r e s the c r e a t i o n of a n a t i o n a l s o i l and water c o n s e r v a t i o n p o l i c y and a governmental i n f r a s t r u c t u r e to a d m i n i s t e r t h i s p o l i c y . F e d e r a l and p r o v i n c i a l s o i l and water c o n s e r v a t i o n i n f r a s t r u c t u r e s should c o n s i s t of agencies to a d m i n i s t e r p o l i c y , c a r r y out r e s e a r c h and most imp o r t a n t l y to t r a n s f e r r e s e a r c h f i n d i n g s from the s c i e n t i s t s to farmers i n the form of p r a c t i c a l farm management techniques. 140 L i t e r a t u r e C i t e d A l b e r t s , E. E., Schuman G. E. and R. E. B u r w e l l . 1978. Seasonal runoff of n i t r o g e n and phosphorus from M i s s o u r i V a l l e y l o e s s watersheds. J . E n v i r o n . Qual. 7:203-208. Baumgardner, M. F., L. F. S i l v a , L. L. B i e h l , and E. R. Stoner. 1985. R e f l e c t a n c e p r o p e r t i e s of s o i l s . Advances i n Agronomy. 38:1-44. Bergsma, E. 1974. S o i l e r o s i o n sequences on a e r i a l photographs. I.T.C. J o u r n a l 1974-1:342-376. Bork, H. R. and H. Rohdenburg. 1986. 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S o i l R e f l e c t a n c e and Laboratory A n a l y s i s Data Labo r a t o r y R e f l e c t a n c e samp1e D f i e l d RID 870 '% 900 54 1050 % 1200 % 1600 % S C 1 1 .0 1 .0 30 .2 32 .4 42 .3 39 .9 45 .4 sc 2 1 .0 1 .0 28 . 3 29 .7 38 .7 36 .6 41 .5 sc 3 1 .0 1 .0 28 .5 29 .8 39 . 1 37 . 1 42 .6 sc 4 1 .0 1 .0 27 .5 29 .7 39 .7 37 .5 43 .6 sc 5 1 .0 1 .0 26 .9 28 .7 38 .2 36 .3 42 . 1 sc 6 1 .0 1 .0 27 .2 29 .0 38 .6 36 .4 42 .2 sc 7 1 .0 1 .0 29 .9 31 .5 39 .7 38 .4 43 .2 sc 8 1 .0 1 .0 30 .2 31 .8 42 .0 39 .5 45 . 1 sc 9 1 .0 1 .0 27 .6 29 .6 39 .2 37. .6 43 .7 sc 10 1 .0 1 .0' 29 . 3 30 .8 40 . 1 37 .8 43 .3 sc 1 1 1 .o 1 .0 26 .6 28 .3 38 .6 36 .2 42 .3 sc 12 1 .0 1 .0 25 .9 27 .8 37 .3 35 .0 40 .9 sc 13 1 .0 1 .0 27 .4 28 .4 38 .9 36 .5 42 .3 sc 14 1 .0 1 .0 27 .7 29 .2 39 . 3 37 .2 44 .0 sc 15 1 .0 1 .0 30 .7 32 .6 43 . 1 40 .2 45 .7 sc 16 1 .0 1 .o 26 .5 27 .9 36 .2 33 .9 39 . 1 sc 17 1 .0 1 .0 30 .4 31 .9 43 . 1 39 .4 46 .5 sc 18 1 .0 1 .0 27 .6 29 . 1 40, .8 37 . 1 44 .0 sc 19 1 .0 1 .0 29 .8 31 .3 42. .2 39 .9 46 .2 sc 20 1 .0 1 .0 27 . 1 28 .5 37 .4 35 .0 40 .2 sc 21 1 .0 1 .0 29 .5 31 .8 44 .8 41 . 1 48, .4 sc 22 1 .o 1 .0 29 .6 31 .8 43 . 1 40 .0 46 .4 sc 23 1 .0 1 .0 29 .5 30 .8 41 , . 1 38 . 1 45, .0 sc 24 1 .0 1 .0 30 . 1 31 .5 43 .4 40 .3 47, . 1 sc 25 1 .0 1 .0 29 .2 30 .8 41 . .6 38 2 44 , 9 sc 26 1 .0 1 .0 29 .5 31 .6 42 .7 39 .7 46 .2 S C 27 1 .0 1 .0 29 .5 31 .4 42 .6 39. .2 45, .9 sc 28 1 .0 1 .0 29 . 3 31 . 1 42 .6 39 .2 46 .7 S C 29 1 .0 2 .0 33 .3 34 .5 44 .9 42 .5 48 .4 sc 30 1 .0 2 .0 33 .7 35 .3 46 8 44. .8 50, .9 sc 31 1 .0 2 -O 32 .8 34 .4 45 7 43. . 1 49 .7 sc 32 1 .0 2 .0 30. 9 32. .0 43. 8 40. 8 47, .6 S C 33 1 .0 2 .0 30 .5 32 .5 44 . 0 40. .4 48 . 1 sc 34 1 .0 2 .0 31 . 6 33 .9 45. , 1 42. O 48 . 7 sc 35 1 .0 2 .0 30 .8 33 . 1 44 . 3 41 . 2 47, .3 sc 36 1 .0 2 .0 32 . 0 33. 8 46. ,0 42 . .7 49. 0 sc 37 1 .0 2 .0 33. ,2 35. 2 46. 3 43. 1 49. 1 sc 38 1 .0 2 .0 29. 5 31 . 4 42. 1 39. 3 45. 6 sc 39 1 .0 2 .0 30. .3 31 . 5 42 . 3 39. 0 45. 9 sc 40 1 .0 2 .0 32 6 34 .7 45. .4 42 . .4 49 7 sc 41 1 .0 2 .0 30. 8 32 . , 3 44 . , 1 41 . 0 48. 2 sc 42 1 .0 2 .0 32 . 0 32. 9 44. 6 41 . 2 47. .8 S C 43 1 .0 2. .0 32. 9 34 . 3 46. 0 43 . 1 49. .4 S C 44 1 .0 2 .0 29. 4 31 . 6 42 . 4 39. 5 45. 5 S C 45 1 .0 2 . 0 29. 1 31 . 0 42 . 3 38. 4 44. 3 sc 46 1 .0 2 .0 31 . 1 33. 0 44. 5 41 . 7 48 . 3 S C 47 1 .0 2. .0 27. 8 29. 2 38. 2 35. 0 40. 8 sc 48 1 .0 2 .0 29. .5 31 . 6 43. 4 39. 8 46 . 2 S C 49 1 .0 2 .0 29. 1 31 . 3 43. 1 39. 4 46. 4 sc 50 1 .o 2 . 0 29. 0 31 . 4 42 . 8 39. 2 46. 2 sc 51 1 .0 2. .0 29. 8 31 . 6 43. 5 40. 3 47. 5 sc 53 1 .0 2 ,0 29. 4 31 . 6 44. 0 40. 0 47. 7 sc 54 1 .0 2 .0 29. 3 31 . 0 42. 5 38. 1 46. , 1 S C 55 1 o 2 .0 29. 0 31 . O 43. 0 39. 0 47 . 6 S C 56 1 .0 3 .0 29. 9 31 . 9 42. 0 37. 9 45. 9 S C 57 1, .0 3. .0 29. 1 30. 5 40. 4 36. 6 43 . 9 S C 58 1 .0 3. .0 29: 5 31 . 2 41 . 6 37 . 6 45. 4 148 sc 59 1 .0 3 .0 29 . 1 30 .9 39 .6 36 .5 43 .6 sc 60 1 .0 3 .0 27 .7 29 .9 41 .2 37 .0 44 . .4 sc 61 1 .0 3 .0 29 . 1 31 . 2 41 .9 38 .0 45 . 5 S C 62 1 .0 3 .0 29 .9 31 .8 . 42 .3 38 .5 46 . 1 sc 63 1 .o 4 .0 3 1 , . 3 32 . 1 42 .3 39 .3 45 .9 S C 64 1 .0 4 .0 29 . 1 30 .9 41 . 1 37 .7 44 . .6 sc 65 1 .0 4 .0 30 . 1 32 .3 43 . 1 39 .5 47 .0 sc 66 1 .0 4 .0 29 .3 31 .0 41 .9 38 . 1 45 .5 sc 67 1 .0 4 .0 30 .4 32 .3 42 .0 39 .0 45. .5 S C 68 1 .0 4 .0 26 .2 28 .0 38 .5 34. .3 41 , .8 sc 69 2 .0 1 .0 28 .7 30 .4 39 .7 36 .8 43 . 4 sc 70 2 .0 3 .0 30. .2 31 .6 41 . 1 38 .2 44 .5 sc 7 1 2 .0 1 .0 28 .4 30 .3 37 .3 35 .0 40, .2 sc 73 2 .0 1 .0 30. .3 32. . 1 41 .9 38 .7 45. . 1 S C 74 2 .0 1 .0 29 .3 31 .0 37 .4 34 .6 39 .7 S C 75 2 .0 1 .0 26. .9 28 .6 37 .6 36 .0 41 . 8 S C 76 2 .0 1 .0 39 . 1 39 .9 46 .4 43 . 7 48 .7 sc 77 2 .0 1 .0 37 .9 38 .9 45 . 1 42 .8 47 . 4 S C 78 2 .0 1 .0 37 . 6 39 .4 48 .0 45 .4 51 . 0 S C 79 2 .0 3 .0 27 .6 28 .2 89 .4 31 . 4 34 . 2 S C 80 2 .0 1 .0 32 .5 33 .7 42 .8 40. .6 46 5 S C 81 2 .0 1 .0 39 .9 40 .4 44 .6 42 .3 46 .8 S C 82 2 .0 3 .0 34 . 6 35 . 1 41 . 1 39 .0 43 .4 sc 83 2 .0 3 .0 33 .0 34 .0 40. .7 39. .0 43. . 3 sc 8 4 2 .0 1 .0 33. . 3 34 . 4 4 2 .5 4 0 . .5 45 .6 sc 85 2 .0 1 .0 40. .0 40. .2 4 4 .9 43 .2 46 6 sc 87 2 .0 1 .0 37 .3 35 .6 42 .0 39 .6 43 .7 sc 89 2 .0 1 .0 31 . 8 33 .0 41 . 1 38 .8 43 .4 sc 90 2 .0 3 .0 29. .5 30 .6 35 .8 33 .8 37 , .7 S C 91 2 .0 3 .0 27. .9 29 .0 37 .3 35 .6 40. .4 sc 92 2 .o 1 .0 36 1 36 9 4 4 . .0 4 2 .5 47 . O sc 93 2 .0 3 .0 33 . 1 34 .2 40. .8 39. .5 43. 7 sc 96 2 .0 2 .0 32 . .9 35 O 45 .0 43 .2 48 .6 S C 97 2 .0 2 .0 31 . 8 33 .6 44 . 1 42 .7 46 .6 S C 98 2 .0 2 .0 -2 . ,0 -2 .0 -2 O -2 .0 -2 .0 S C 99 2 .0 3 .0 31 . 2 33 . 1 41 . 7 40, .4 45. 2 s d O O 2 .o 2 .0 31 . 5 33. . 1 42. .5 41 .2 45 .9 sc101 2 .0 2 .0 32. 8 34 .0 43. .4 41 .6 46 . .8 S C 1 0 2 2 .0 2 .0 32 . 6 33. .6 43 8 42 . .5 48 . . 3 S C 1 0 3 2 .0 3 .0 33. , 1 34 . 1 42 .5 40 8 45. 8 SC104 2 .0 3 .0 30. 8 32. . 1 40 .5 32 .9 43 .2 S C 1 0 6 2 .0 3 .0 31 . 8 32. 8 39 .7 39 . 1 4 2 .5 S C 1 0 7 2 o 2 .0 30. 2 3 1 . 7 41 . 4 40. .0 45. 3 S C 1 0 8 2 .0 1 .0 31 . 8 33, .2 42. . 1 40. .9 45 .6 RID: l = R i l l 2 = I n t e r r i l l 3=Deposition 4 = P a r t i a l l y Eroded ( R i l l ) Laboratory R e f l e c t a n c e F i e l d R e f l e c t a n c e 149 sample 2100 % 2200 2350% .5 - .6 .6 - .7 .7 - .8 .8-1.1 sc 1 51 .7 50 .7 50 .3 4 .9 6 .7 10. .2 12. .9 sc 2 47 .8 46 .5 46 .7 5 .4 7 .6 10 .8 13 .8 sc 3 47 .9 46 .9 46 .8 5 .7 7 .7 10 .8 12 .8 sc 4 48 .6 47 .6 47 .2 5 .2 7 .3 10. .8 14, .4 sc 5 46 .6 44 .6 44 .7 5 .9 7 .5 9. .4 12 . 1 sc 6 47 .4 46 .0 45 .9 4 . 1 5 .9 9 .3 12 . 1 sc 7 47 .6 46 .0 46 .0 6 . 1 10 .0 11 . .5 1 1 .2 sc 8 50 .3 49 .0 48 .7 5 .8 8 .9 11 .3 15 .7 sc 9 48 .4 47 .2 47 .2 6 .8 9 .2 14 .5 16 .7 sc 10 47 .2 46 .0 46 .2 4 .6 7 . 1 10 . 3 13 .7 sc 11 46 .6 45 .5 45 .5 6 .4 8 .8 10 .9 15 .6 sc 12 44 .3 43 .5 44 . 1 4 .0 4 .8 6 .3 10, .7 sc 13 47 . 1 45 .9 46 .4 4 .4 5 .9 8 . 2 7 . 1 sc 14 48 . 1 46 .6 46 .8 3 .6 4 .8 7 .2 9 .3 sc 15 49 .0 48 .0 48 .0 5 .4 7 .3 9 .9 12 .9 sc 16 42 .4 41 . 1 41 .4 5 . 1 6 .9 10 .0 12 .8 sc 17 50 .2 48 .9 48 .7 4 .9 6 .6 10 .3 13 .3 sc 18 48 .4 47 . 1 47 .2 7 .0 12 .2 10 .7 16 .7 sc 19 49 .2 48 .0 48 .4 5 .7 6 .4 12 .2 18 .2 sc 20 44 .6 43 .8 44 . 1 4 .3 6 .2 7. .2 1 1 .6 sc 21 51 . 1 50. .2 50 .2 3 .3 4 .2 6 .4 8 .7 sc 22 50 .4 49 .2 49 .3 4 .0 6 .3 8 .9 1 1 .3 sc 23 48 .6 47 .3 47 .4 4 .2 6 .0 9 .4 12 .7 sc 24 50 .5 49 .3 49 .3 5 .9 8 .O 10 .6 12 .7 sc 25 48 .6 47 .5 47 . 7 5 .3 8 .0 9 .3 12 .2 sc 26 49 .4 48 .2 48 .4 6 . 1 9 .3 12. .3 16 .8 sc 27 50 .0 48 .6 48 .7 6 .7 9 .3 10. .4 14 .7 sc 28 50 .2 49 .0 48 .9 9 .0 13 .7 15 .3 20. .0 sc 29 51 .2 50, . 1 50 .3 4 .0 4 .9 7 .5 8 .9 sc 30 53 .6 52 .0 51 .9 3 .6 5 .2 7 .6 9 .5 sc 31 52 .2 50 .9 50 .8 3 .7 5 . 1 7 .7 10 . 3 sc 32 50 .7 49 .4 49 .2 3 .4 4 .5 6 .8 8 .4 sc 33 51 . 4 50 .2 50 . 1 3 . 1 4 .4 6 .O 8 .4 sc 34 52. .0 50 .8 50 . 3 2 .9 4 .0 5 .6 7 .9 sc 35 50 .4 49 .0 48 .9 3 .5 4 .9 6 .8 9 .0 sc 36 53 .2 52. .0 51 .7 4 .6 6 .0 8 .7 10 .5 sc 37 52. ,0 50, .9 50 .4 3 . 1 4 .2 6 .7 8 .9 sc 38 50 .2 49 .0 48 .9 2 .7 4 .2 5. .9 8 .7 sc 39 48 .5 47, . 3 47 .2 2 . 2 2 .9 5. O 6 .4 sc 40 52 . 5 51 , .2 50 9 3 .3 4 .0 6 .9 8 .6 sc 41 51 . 2 49. .9 49 .7 2 .9 4 . 1 5. .7 8 .9 sc 42 50. .4 49 . 1 49 .3 3 . 1 4 .2 6 .2 8 .2 sc 43 52 . 6 51 . 2 51 .3 3 .3 4 .4 6 4 7 .8 sc 44 48. .5 47 . 2 47 .3 3. .0 4 .6 6. 6 8 .9 sc 45 48 . 0 46. .7 47. . 1 3 .4 4 . 9 6. 8 9 .4 sc 46 51 . 4 50. 3 50. .4 3 . 3 4 .5 6 .3 7 .7 sc 47 45. 2 44 . 4 45. .0 3 .5 4 .6 6 .5 8 .6 sc 48 49. 9 48 8 49 .3 2 .9 4 .2 5 9 8 .7 sc 49 49. 8 48 . 6 48 .5 2 .7 3 ,8 5. .6 8 .7 sc 50 48. 9 47 . 8 47. .5 3 . 1 3 .8 7 . 1 9 . 1 sc 51 51 . 2 49. 9 49 7 2 .8 4 .4 6. 4 9 . 1 sc 53 45. 2 49. 5 49 7 3 .7 5 .5 7. 2 10. .5 sc 54 49. 8 48 .4 48 .5 3 .7 4 . 2 6. 9 9. .5 sc 55 51 . 4 50. . 1 50. .3 3 .3 4 9 6 .7 10. .7 sc 56 49 . 5 48 . 3 48. 8 9 .3 15 . 1 17. .3 24 .0 sc 57 48. 2 46 8 47 . 0 8 .7 14 .0 15 .0 24 .0 sc 58 49. 2 47 . 9 48 . 3 8. .3 12, .6 13 . 3 17 .3 sc 59 46. 9 45. 4 46. 2 6. .7 12. .0 14. 7 21 . 3 sc 60 47 . , 1 46. 0 46. 2 7. . 3 11 . .4 14 . 3 20. O sc 61 46. 9 46. 6 46 9 5. 0 5 .8 8. 0 12 7 sc 62 47 . 9 47 .2 47 .3 6 .5 7 .3 11 . 6 16 .4 sc 63 50. 1 48. .8 48 9 4 .3 5. .6 7 .6 9. .5 sc 64 48. 2 46 7 46. .7 3 .9 5 .2 6 . 9 8 .7 sc 65 49. 8 48 4 48. 4 5. .2 7. .2 9. 6 12, . 3 sc 66 48. 9 47. 9 47. 8 3. .8 5 . 1 6. 9 9. .3 150 sc 67 49. .4 47 , 9 47 . 7 3 9 5 . 7 7. 8 9. .5 sc 68 47. .3 46. .3 46. ,4 2. .4 3. 0 4 . 2 6. .4 sc 69 4 8 . 0 46. 5 46 . 6 6 .4 9 4 12. 8 1 8 . 8 SC 70 48. ,5 4 7 2 46. 5 10. . 1 13. 3 16. .0 22. .4 sc 71 44. . 1 42 . .6 4 2 . 5 14 . .0 17 . ,4 20. 0 29. .4 sc 73 49 .0 47. .5 47 . 5 6. .3 6. ,4 12. 6 11 . 7 sc 74 42. 9 41 . .2 41 . .4 6 .0 8. 8 11 . 6 13. ,4 S C 75 4 7 .3 46. .3 4 5 . 9 6 .0 8. .5 11 . 6 13 , 8 S C 76 54 . .7 53. .0 52. 5 5. .6 9. 2 9. ,5 2. 8 S C 77 54. 2 53. .0 52. 8 7. .6 9. 2 13. .7 3, .4 sc 78 57. .9 56. .0 55. 8 6 .0 7. .5 11 . 6 3. . 1 sc 79 39 6 37 .9 38. .5 14 .4 18 9 19 5 15 .7 sc 80 52 .6 51 , .0 50. .5 3 .9 8 .0 9. .0 1 1 , .0 sc 81 53. .2 51 , .4 50. 9 9 .7 14 . 7 14 . .5 17 . .3 sc 82 48 .6 46 .6 46. .4 10 .8 16. .0 17 . .0 20 .0 sc 83 48 .3 47 .0 46. 7 9 .7 15. .6 15 5 18. .4 sc 84 50. .7 49 .3 48. 8 5 . 7 12 . 0 10. 0 14. .9 sc 85 52. .3 50 .7 50. 7 4 .9 10. .7 8 5 12 . 2 sc 87 48 .4 46 .6 46. 9 8 .4 16 9 13. .5 18. .0 sc 89 4 7 .8 46 .6 46 6 7 .7 1 1 . .6 9 .5 15. .3 sc 90 42 .9 41 .0 41 . . 1 14 .9 21 . .3 21 . .0 22 .4 sc 91 4 5 .2 44 . 3 44 . .4 8 .6 12, .8 18 . .6 22 .9 sc 92 51 .0 49 . 5 4 9 . 1 6 .0 9 .3 14 , .3 20 .6 sc 93 47 .3 45 .8 45. . 7 9 .3 12 .2 15 .7 20. .0 sc 96 52 .2 50 .9 50, . 3 6 .0 7 .5 16, .0 20 .0 sc 9 7 51 .3 4 9 .8 4 9 . .4 5 .2 6 . 3 10 . 3 14 .7 S C 98 -2 .0 -2 .0 -2 .0 4 .3 6 .4 9 .3 14 . 1 sc 99 49 . 1 47 .9 47 . .7 8 .9 15 .8 16 . 1 20 .0 sc100 4 9 .0 48 . 1 4 8 . 1 3 .4 6 .4 7 .6 10 .2 sc101 50 . 1 49 .0 4 8 .7 3 .4 3 .5 6 .0 6 .9 S C 1 0 2 51 .8 50 . 1 4 9 .8 3 .6 5 . 3 6 .5 8 .2 sc103 4 9 .0 4 7 .6 4 7 .6 6 .9 10 .0 12 .9 17 . 1 S C 1 0 4 46 .6 45 . 1 45. .0 10 .5 1 1 .2 16 .8 15 .5 S C 1 0 6 45 .4 44 .7 44 .8 7 .4 8 . 1 13 .2 20 .0 S C 1 0 7 4 8 .2 47 .0 4 6 .5 -2 .0 -2 .0 -2 .0 -2 .0 S C 1 0 8 48 .8 47 . 1 47 , . 1 8 .0 1 1 .8 10 .9 12 .9 S o i l P r o p e r t i e s sample % C S C 1 4.8 S C 2 4.5 sc 3 4.9 sc 4 5.2 sc 5 5.0 sc 6 5.4 sc 7 3.8 sc 8 4.6 sc 9 5.1 sc 10 5.3 sc 11 5.2 sc 12 5.2 sc 13 4.4 sc 14 4.7 S C 15 3.9 sc 16 3.7 sc 17 4.6 sc 18 4.9 S C 19 3.5 sc 20 4.2 sc 21 4.8 sc 22 5.3 sc 23 4.6 sc 24 5.0 sc 25 4.8 sc 26 4.5 sc 27 5.2 S C 28 5.3 sc 29 4.7 sc 30 4.8 S C 31 5.0 sc 32 5.0 sc 33 5.2 S C 34 5.3 sc 35 5.0 sc 36 4.8 sc 37 4.8 sc 38 5.7 sc 39 5.0 S C 40 4.8 sc 41 5.2 sc 42 4.5 sc 43 4.5 sc 44 5.0 sc 45 4.8 S C 46 4.9 sc 47 5.4 sc 48 5.6 S C 49 5.9 sc 50 5.6 MC % % vfS 30 .4 4 .9 44 .4 4 .2 28 .0 5 .0 27 .2 4 . 1 27 .5 4 .6 17 .5 4 .9 15 .6 5 .8 31 .5 5 .3 36 .4 4 . 1 32 .5 4 . 1 35 .8 5 .4 37 .6 4 .8 19 .7 4 . 7 33 .2 4 . 7 31 . 2 4 . 6 29 . 1 4. 8 35. .5 4 7 33. . 1 4 . 5 34. .0 7 .7 36. 9 6. 0 36 9 4 . 6 35. .5 4. 0 37 . 1 5. .0 34. .9 4. .4 41 . .5 5. 5 45. 6 5. 1 39. 9 5. 0 48. 8 4. 2 25. 3 4 . 3 15. 7 3. 7 30. 0 4 . 3 16. 4 4 . 3 29. 1 4 . 8 31 . 1 4. 4 15. 8 6. 8 30. 4 3. 9 23. 7 5. 1 44. 0 3. 5 21 . 4 4. 7 39. 9 4. 3 37 . 5 3. 9 32. 1 4 . 3 35. 4 3. 8 29. 5 5. 0 33. 1 5. 1 29. 6 4. 3 23. 4 4. 6 39. 9 3. 9 27. 8 3. 9 15. 7 4. 5 1-2mmS % S 8 .3 13 .2 6 .6 10 .8 7 .9 12 .9 6 .2 10 .2 6 .0 10 .6 7 .3 12 .2 6 .6 12 .3 7 .2 12 .4 6 . 1 10 .2 5 .7 9 .8 10 .0 15 .4 7 .7 12 .4 10 . 3 14 .9 8 .5 13 .2 6. . 1 12. .7 21 .2 25 9 7 . 9 1 1 .O 7 , .5 12. .0 14 .9 22. .5 17. .5 23. .5 10. .0 14 . 6 6. 4 10. .4 9. .0 14. .0 6. 9 1 1 . .2 10. 5 16. .0 14. 3 19. .4 9. 8 14. .8 7. .4 11 . .6 6. .6 10 .9 4 . 9 8 5 5 0 9. .3 5. 1 9 .4 5. . 1 9. 9 5. 7 10. 1 6. 8 11 . 6 5. . 1 8. 6 12. 8 17. .9 4 . ,7 8. 3 8. O 12 . 6 4 . 8 9. 1 4 . 8 8. 7 6. 6 10. 9 5. 9 9. 7 5. 3 10. 2 6. 3 11 . 3 5. 0 9. 3 5. 8 10. 4 4. 7 8. 6 3. 6 7. 4 4 . 5 9. 0 SI % Cl 73 .3 13 .5 72 .9 16 .3 70 .8 16 .3 73 .0 16 .8 72 .6 16 .8 71 .0 16 .8 72 .7 15 .0 71 .6 16 .0 73 .8 16 .0 76 .0 14 .2 69 .0 15 .6 69 .5 18 . 1 69 . 1 16 .0 71 . .2 15. .6 73. , 1 14. .2 61 .2 12 .9 74 . 2 14 8 71 . .2 16. 8 65. .3 12. .2 63 8 12. 7 70 .7 14 . 7 72. 8 16 . 8 69. .2 16 .8 72. .0 16 8 69. .8 14 . 2 66 .4 14, .2 71 . .0 14 .2 71 , . 1 17 .3 75. .6 13 .5 74. .7 16 .8 76 .0 14 , .7 74. .3 16 3 73. .3 16 8 74. 4 15 , 5 74 . 2 14 , .2 77. 2 14 , .2 68 . 7 13. .5 72. .9 18 . 8 70. 6 16. 8 75. 4 15. .5 73. 7 17. .6 75. 4 13. 7 76. . 1 14. .2 73. 0 16. 8 71 . 9 16. 8 73. 9 16. 8 75. 3 14. 3 74 . 6 16. 8 75. 8 16. 8 74 . 2 16. 8 152 s c 51 5 .6 33 .5 3 .9 5 .3 9 .3 74 .7 16 .0 s c 53 5 .2 45 .7 3 .8 5 . 1 8 .9 74 .3 16. .8 sc 54 5 .5 41 .6 4 .3 5 .4 9 .7 76 .0 14 .3 s c 55 4 .9 50 .5 3 .5 4. .4 7 .9 75 .3 16 8 s c 56 3 .4 37 .3 6 .4 6 .4 12 , .9 76 .9 10 2 s c 57 2 .9 31 . 1 8 .8 11 .8 20, .6 69 .7 9. 7 s c 58 3 .9 41 .6 7 .3 6 .5 13 .8 74 .5 11 . 7 s c 59 1 .9 32 .2 6 .3 15, .3 21 .6 68. .2 10 2 sc 60 6 .2 46 .4 5 .3 2 .4 7 .7 77 .0 15. 3 sc 61 4 .8 43 .2 5 .6 4 .7 10 .3 73 .7 16 .0 s c 62 4 .6 43 .0 9 .2 5 .9 15 . 1 72 .0 12. 9 s c 63 4 .4 35 8 5 O 8 8 13, .8 72 . O 14 . 2 SC 64 4 . 5 27, .9 4. .2 17 , .8 22. .0 63 8 14 . 2 sc 65 5. .3 32 .4 4, .3 6 . 5 10. 8 74 .5 14 . 7 s c 66 5 . 1 31 . 1 4 .8 5 . , 7 10. .5 72 7 16 . 8 s c 67 3. 8 32 7 5. .8 15. , 1 20 8 67. 5 1 1 . 7s c 68 5. 6 19, .7 4 . 0 5. 5 9. 5 73. .7 16 . 8 s c 69 3. 7 24 . 5 9 5 19 . 1 28. .5 58 O 13. 5 SC 70 4. 0 19. 6 7. .3 40. 0 34. 1 52 .4 13 . 5 SC 71 2 . 5 1 1 . . 1 8. 9 35 . 3 44 . . 1 44 . 2 1 1 . 7sc 73 3 1 20. 9 9. .4 26. 2 35. .6 50, .2 14 . 2 s c 74 3. 6 13. 1 7. .3 56. 8 64 . 1 28 2 7. 7 sc 75 6. 0 34 . 5 4 . 9 11 . ,4 16 3 60, . 3 23. 4 s c 76 1 .7 27 .2 4 .4 12 .8 17 .2 66 .5 16 .3 s c 77 2 . 1 29 .2 2 . 3 6 .4 8 .7 80 .9 10 .4 sc 78 2 .7 31 .9 2 .5 5 . 2 7 . 7 79 . 1 13. .2 SC 79 1 . 7 6 . 1 6 .3 26 .5 32 .8 47 .9 19. .3 SC 80 3 .9 26 .0 7 .9 17 .6 25 .4 62 .9 11 .7 s c 81 0 .6 19 .0 13 .9 16 .7 30 .6 57 .7 11 . 7 s c 82 0 .9 1 1 .7 12 .9 42 .9 55 .8 37 .0 7 .2 s c 83 2 . 1 1 1 .8 1 1 .5 40 . 3 51 .8 40 .5 7 .7 s c 84 2 .7 23 .0 12 .2 26 . 1 38 .3 52 .0 9 .7 SC 85 1 .7 18 . 1 9 .6 21 .5 31 . 1 57 .2 11 . 7 s c 87 0. .8 -2 .0 1 1 .7 26 O 37 .7 50 .6 11 .7 sc 89 2 .9 11 .9 9 . 1 19 .6 28 .7 59 .6 1 1 .7 s c 90 0 .8 51 .4 14 .2 57 .5 71 .7 24 .4 3 .9 s c 91 3 .3 12 .0 13 .6 32 . 1 45 .6 43 .4 11 .0 s c 92 1 .7 19 .9 12 .0 30 .9 42 .9 49 .4 7 .7 SC 93 1 .5 5 .6 13 .8 42 .2 55 .9 36 .4 7 . 7 s c 96 4 .2 24 .0 8 .5 17 .2 25 .7 61 .3 13 .0 sc 97 3 .9 26 .6 7 .2 17 .5 24 .7 62 . 3 13 O s c 98 4, .0 23 .0 7 .7 19 .0 26 .7 59 .8 13 .5 s c 99 3 .0 10 .9 9 .2 22 .4 31 .6 59 .2 9 .2 S d O O 4 . 0 10 .5 8 .3 17 .5 25 .8 61 .2 13 .0 sc101 3. .5 23 .2 6 .9 16 .8 23 .7 62 .0 14 .3 sc102 4 . 4 2 .4 7 .7 17 . 1 24 .7 64 .8 10 . 5 sc103 3 9 12. .4 13 .0 31 . 9 44 .8 48 .5 6 .7 S C 1 0 4 1 .6 6 .4 12 .3 44 , .6 56 .9 36 .4 6 .7 SC106 2 .6 9 .6 8 .9 32 .3 41 . 1 48 .4 10 .5 sc107 4 .7 5 .0 9 .0 19 . 1 28 .0 57 .0 15 .0 sc108 3 .5 17 .7 7 .5 27 O 34 .6 53 .6 1 1 .8 153 APPENDIX I I  R i l l Volume and P l a n Area Program 1 REAL L 2 INTEGER RN 3 READ(5,1) NR 4 1 FORMAT(13) 5 DIMENSION WT(40),WB(40).D(40).L0C(40),XSA(40),V0L(40).PA(40) 6 +,R(40),RA(40) 7 T0TV0L=0.0 8 TOTPA=0.0 9 TOTXSA=0.0 10 DO 5 K=1,NR 1 1 RTVOL=0.0 12 RTXSA=0.0 13 RTPA=0.0 14 TOTL=0.0 15 VPS=0.0 16 PAPS=0.0 17 XSAPS=0.0 18 READ(5,9) RN.NM.L 19 9 FORMAT(13,1X.I3.1X.F5.2) 20 WRITE(6,12) 21 12 FORMAT(' ' . ' TRANSECT ' ,3X , 'WT ' ,4X , 'WB' ,5X , 'D ' , 3X , 'WT /WB' ,2X , 22 + 'X .S .AREA' .1X . 'WT/D ' ,1X , 'PLAN A R E A ' , 2 X , ' V O L . ' ) 23 DO 2 I=1,NM 24 READC5. 1 1 ) LOC(I),WT(I),WB(I ) ,D(I ) 25 1 1 FORMAT(14,1X.F4.2,1X.F4.2,1X.F4.2) 25.5 RA(I)=WT(I)/D(I) 26 2 R(I)=WT(I)/WB(I) 27 d=NM-1 28 DO 3 1 = 1 ,d 29 A=(WT(I+1)-WT(I))/L 30 B=(WB(I+1)-WB(I))/L 31 C=(D(I+1)-D(I))/L 32 E=A+3*B 33 F=WB(I)+WT(I) 34 G=D(I )*E+C*F 35 VOL(I ) = (C*E*L**3) /6+(G*L**2) /6+(D( I ) *F*L) /2 36 PA(I)=L*(WT(I)+(WT(I+1)-WT(I))/2) 37 XSA(I)=D(I)*(WB(I)+(WT(I)-WB(I))/2) 38 WRITE(6,14) LOC(I) .WT(I ) .WB(I) ,D( I ) ,R( I ) .XSA(I) .RA(I ) . 39 +PA(I ) ,VOL(I) 40 14 FORMAT(' ' , 3X , I 4 .2X ,F5 .2 .1X .F5 .2 ,1X .F5 .2 .2X ,F4 .1 ,6X . 41 +F5 .4 .F4 .1 ,2X,F5 .2 ,4X,F5 .2 ) 42 RTXSA=RTXSA+XSA(I) 43 RTVOL=RTVOL+VOL(I) 44 3 RTPA=RTPA+PA(I ) 45 XSA(NM)=D(NM)*(WB(NM)+(WT(NM)-WB(NM))/2) 46 RTXSA=RTXSA+XSA(NM) 47 T0TL=(NM-1)*L 48 VPS=RTVOL/TOTL 49 PAPS*RTPA/TOTL 50 XSAPS=RTXSA/TOTL 51 WRITE(6.22) LOC(NM).WT(NM).WB(NM),D(NM),R(NM),XSA(NM),RA(NM) 52 22 FORMAT(' ' , 3X , I 4 . 2X .F5 .2 .1X .F5 .2 .1X ,F5 .2 .2X ,F4 .1 .6X .F5 .4 .F4 .1 ) 53 17 WRITE(6.18) RN.RTVOL 54 18 FORMATC '.'VOLUME OF R I L L ' . 1 2 , ' = ' , F 7 . 3 ) 55 WRITE(6.19) RN.RTPA 56 19 FORMAT(' ' . ' P L A N AREA OF R I L L ' , 1 2 , ' = ' , F 7 . 3 ) 57 WRITE(6,24) RN.RTXSA 154 58 24 FORMATC ' , ' X . S . AREA OF R ILL ' .12 . ' = ' ,F7.3) 59 WRITE(6.26) RN.VPS 60 26 FORMAT(' ' . ' V O L . / M . OF R ILL ' ,12 , ' = ' ,F7.3) 61 WRITE(6,27) RN.PAPS 62 27 FORMAT(' ' , ' P L A N AREA/M. OF R I L L ' , 12. '•=' .F7.3) 65 WRITE(6,29) RN.TOTL 66 29 FORMAT(' ' . 'LENGTH OF R I L L ' , 1 2 . ' = ' ,F7.3) 67 WRITE(6,23) 68 23 FORMATC ' , ' ') 69 TOTXSA=TOTXSA+RTXSA 70 TOTVOL=TOTVOL+RTVOL 71 5 TOTPA=TOTPA+RTPA 72 WRITE(6.20) TOTVOL 73 20 FORMAT(' ' . 'TOTAL RILL VDLUME=',F9 .3 .1X , 'CU.M. 74 WRITE(6,21) TOTPA 75 21 FORMATC ' . 'TOTAL RILL PLAN AREA=' ,F9 .3 ,1X . 'SO 76 WRITEC6.25) TOTXSA 77 25 FORMATC ' . 'TOTAL RILL X . S . AREA=' ,F7 .3 ,1X . 'SO 78 STOP 79 END (This program was w r i t t e n f o r p e r s o n a l use and thus no attempt a t proper documentation was made) 

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