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A study of manganese (III) oxidation of hindered phenols Poh, Bo Long 1972

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)3253 HYDROLOGIC PROPERTIES AND WATER • BALANCE OF THE FOREST FLOOR OF A CANADIAN WEST COAST WATERSHED by ANDRE P. PLAMONDON B.S.F., U n i v e r s i t e L a v a l , 1968 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY ( F o r e s t Hydrology - Biometeorology) in the Department of Forestry We accept t h i s t h e s i s as conforming to the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA J u n e , 1972 - p o ^ d does ^  4 * i d In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y a v a i l a b l e f o r reference and study. I further agree that permission for extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or* by his representatives. It i s under-stood that copying or p u b l i c a t i o n of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Forestry The University of B r i t i s h Columbia Vancouver 8, Canada i ABSTRACT The importance of the forest f l o o r i n the prevention of erosion has been well established; however, i t s r o l e i n the control of the amount and timing of water y i e l d and i n plant growth has been only p a r t i a l l y investigated. The need to determine the role of the forest f l o o r i n watershed hydro-logy i s e s p e c i a l l y important where i t i s several centimeters thick as i n the humid, steeply sloping forests of the Canadian West Coast. The objective of t h i s study was to q u a n t i t a t i v e l y describe the processes c o n t r o l l i n g the amount of water absorbed by the forest f l o o r during p r e c i p i t a t i o n and the amount of water l o s t by drainage, evaporation, and t r a n s p i r a t i o n . In addition, a survey of the s p a t i a l v a r i a t i o n of the depth and the physical and hydrologic properties of the forest f l o o r was undertaken. Chapter I. Depth of forest f l o o r and a l t i t u d e , slope, aspect, and forest basal area were systematically measured over four representative areas within a Coast Mountain water-shed. Multiple regression was used to develop an equation that predicts the average forest f l o o r depth of a small plot from physiographic f a c t o r s . Bulk density, saturation capacity and f i e l d moisture capacity were determined i n the laboratory from samples c o l l e c t e d i n the f i e l d . Bulk density was not re l a t e d to depth or to the physiographic f a c t o r s . Saturation i i and f i e l d moisture capacities were l i n e a r l y r e l a t e d to the forest f l o o r depth. Chapter II. Estimates of the evaporation from the forest f l o o r using the energy balance method were compared with measurements made by a small, s e n s i t i v e weighing lysimeter. Evaporation was well estimated by the net ra d i a t i o n minus the s o i l heat f l u x , i n d i c a t i n g a small, downward,sensible heat f l u x . Results suggest that the s i m i l a r i t y p r i n c i p l e was not applicable under the canopy. For much of the time, evaporation from the forest f l o o r was a c a p i l l a r y flow l i m i t e d , rather than an energy limited, process. Chapter III. The r o l e of the forest f l o o r i n water-shed hydrology was investigated by measuring the components of i t s water balance on a 30° slope and by determining i t s water retention and hydraulic conductivity c h a r a c t e r i s t i c s i n the laboratory. The hydraulic conductivity varied by about three orders of magnitude over a range of matric potentials between -0.01 and -0.1 bars. When the forest f l o o r had reached i t s maximum water content during r a i n f a l l , the drainage rate through the matrix accounted for approximately 0.5% of the r a i n f a l l rate. The amount of water absorbed during r a i n f a l l was la r g e l y a function of the i n i t i a l water content and hydraulic conductivity. I t appears that the forest f l o o r contributes to delayed storm-i i i f l o w , s t o r e s a s i g n i f i c a n t amount o f a v a i l a b l e water f o r p l a n t s , does not s i g n i f i c a n t l y c o n t r i b u t e t o base flo w , o r a f f e c t streamflow peaks. Chapter IV. The procedures p r e v i o u s l y used to measure the h y d r a u l i c c o n d u c t i v i t y c h a r a c t e r i s t i c s o f porous m a t e r i a l are b r i e f l y reviewed. A simple steady-s t a t e method o f measuring the h y d r a u l i c c o n d u c t i v i t y o f an u n d i s t u r b e d sample o f f o r e s t f l o o r m a t e r i a l i n the l a b o r a t o r y i s d e s c r i b e d . The main f e a t u r e s o f the method are t h a t the water i s a p p l i e d at a constant r a t e at the top o f the sample by a chromatography micropump w h i l e the water content w i t h i n the sample i s c o n t r o l l e d by hanging a v a r i a b l e - l e n g t h water column from a porous p l a t e at the bottom o f the f o r e s t f l o o r c o r e . An advantage o f the method i s t h a t a s m a l l m a t r i c p o t e n t i a l g r a d i e n t can be maintained i n the sample by a d j u s t i n g the l e n g t h o f the hanging water column. i v TABLE OF CONTENTS Page ABSTRACT i LIST OF TABLES v i i i LIST OF FIGURES - ix ACKNOWLEDGEMENTS x l i i Introduction 1 Lit e r a t u r e Cited 3 CHAPTER I - GENERAL SURVEY OF SOME PHYSICAL AND HYDROLOGIC CHARACTERISTICS OF THE FOREST FLOOR 6 Introduction 6 F i e l d Design and Procedures 7 Laboratory Procedures 12 Results and Discussion 1*+ a) Physical c h a r a c t e r i s t i c s 14 Forest f l o o r depth and influencing parameters 15 Forest f l o o r depth, weight, and bulk density r e l a t i o n s h i p s 19 D i s t r i b u t i o n of forest f l o o r depth.. 22 b) Hydrologic c h a r a c t e r i s t i c s 25 Saturation capacity 30 F i e l d moisture capacity 33 V Page Conclusion... L i t e r a t u r e Cited... CHAPTER II - ENERGY BALANCE METHOD FOR ESTIMATING EVAPORATION FROM THE FOREST FLOOR 38 Introduction 39 Theory HO Experimental Site and Measurements 4 2 Results and Discussion 45 Energy balance 45 Bowen r a t i o and s i m i l a r i t y 4 7 Aerodynamic method 52 Turbulence under the canopy 54 Evaporation and s o i l moisture 59 Conclusion 59 Lit e r a t u r e Cited 60 CHAPTER III - THE ROLE OF HYDROLOGIC PROPERTIES OF THE FOREST FLOOR IN WATERSHED HYDROLOGY 6 3 Introduction 64 Theory 6 5 Experimental Site and Methods 6 9 Results and Discussion 76 Water retention c h a r a c t e r i s t i c s . 76 Hydraulic conductivity c h a r a c t e r i s t i c s . . 78 Water balance of the forest f l o o r during p r e c i p i t a t i o n 80 v i Page Water balance of the forest f l o o r during drying periods 85 Seasonal d i s t r i b u t i o n of water content i n the forest f l o o r 88 Implications for plant growth 94 Implications for watershed hydrology 94 Conclusion 96 Lit e r a t u r e Cited 9 8 CHAPTER IV - LABORATORY MEASUREMENTS OF HYDRAULIC CONDUCTIVITY CHARACTERISTICS OF THE FOREST FLOOR . . 99 Introduction 99 Review of Procedures Used Previously 100 Methods and Results 105 Lite r a t u r e Cited 10 8 APPENDIX I - L i s t of the plot numbers i n Chapter I by area I l l APPENDIX II - Tabulation by plots of the average depths of humus and t o t a l forest f l o o r with t h e i r respective standard deviations, and of the biophysical c h a r a c t e r i s t i c s (Chapter I ) . . . 112 APPENDIX III - L i s t i n g of sample c h a r a c t e r i s t i c s by p l o t f o r Chapter I. Four samples were co l l e c t e d i n each p l o t 115 v i i Page APPENDIX IV - Time trends of t o t a l water p o t e n t i a l p r o f i l e s f or the forest f l o o r during three drying periods 120 APPENDIX V - Drainage, evaporation, t r a n s p i r a t i o n , and t o t a l water depletion -rates f o r the forest f l o o r f o r a drying period 124 APPENDIX vi. - Volumetric water contents at the time of n e g l i g i b l e drainage and at a matric p o t e n t i a l of -15 bars 126 v i i i LIST OF TABLES Table Page Chapter I 1 Plot frequency d i s t r i b u t i o n by classes of biophysical features 11 2 Forest f l o o r physical c h a r a c t e r i s t i c s 15 3 Ground cover by study areas 16 4 C o e f f i c i e n t s of c o r r e l a t i o n between forest f l o o r depth and influencing parameters 18 5 Average and confidence l i m i t s of f i e l d moisture and saturation capacities 30 CHAPTER II 3 -3 1 Volumetric water content cm cm and evaporation rates for the forest f l o o r (mm day - 1) 49 2 Analysis of temperature and wind speed data under the canopy by 30 sec mean values over s i x 26-min periods on 10 August 1971 57 CHAPTER III 1 Water balance components during r a i n f a l l . The data are for periods during which the p r e c i p i t a t i o n i n t e n s i t y , matric p o t e n t i a l , and t o t a l p o t e n t i a l gradient were r e l a t i v e -l y constant 84 i x LIST OF FIGURES F i g u r e Page Chapter I 1 L o c a t i o n o f the p l o t s w i t h i n Seymour Water-shed 9 2 R e l a t i o n o f f o r e s t f l o o r depth to i n f l u e n c i n g parameters 20 3 R e l a t i o n o f f o r e s t f l o o r oven-dry weight to f o r e s t f l o o r depth 21 4 R e l a t i o n between bu lk d e n s i t y and f o r e s t f l o o r depth 23 5 Frequency d i s t r i b u t i o n s o f humus and f o r e s t f l o o r depths i n Areas 1, 2, 3 and 4 24 6 D e t a i l e d map o f f o r e s t f l o o r depth i n P l o t A (Seymour Watershed) 26 7 D e t a i l e d map o f f o r e s t f l o o r depth i n P l o t B (Seymour Watershed) 27 8 Frequency d i s t r i b u t i o n s o f humus and f o r e s t f l o o r depths w i t h i n P l o t s A and B 29 9 R e l a t i o n between s a t u r a t i o n c a p a c i t y , exp re s s -ed i n cen t imete r s o f water ,and f o r e s t f l o o r depth 31 10 R e l a t i o n between f i e l d mois ture c a p a c i t y expressed i n cen t imete r s o f water and f o r e s t f l o o r depth 34 X Figure Page Chapter II 1 Measured and calculated energy balance components f o r a wet (1 August, 19 70) and a dry (9 August, 1971) day 46 2 Temperature and vapour pressure d i f f e r -ences between 20 and 110 cm above the forest f l o o r 48 3 Mean temperature differences for periods of 2 min between 2 0 and 110 cm above the forest f l o o r measured with aspirated and unaspirated thermocouples 51 4 Half hourly values of eddy d i f f u s i v i t y f o r water vapour versus mean wind speed at 110 cm above the forest f l o o r 53 5 Daily lysimeter evaporation rate versus volumetric water content of s o i l between 0 and 5 cm 6 0 Chapter III 1 Cross-section of s o i l on land with slope angle a, showing two-dimensional coordinate system and flow vectors 67 2 Typ i c a l forest f l o o r p r o f i l e and bulk densities of the L, F, and H horizons 70 x i F i g u r e Page 3 Water r e t e n t i o n c h a r a c t e r i s t i c s of the f o r e s t f l o o r at 1, 2, 6, 10, and 14-cm depths . 77 4 H y d r a u l i c c o n d u c t i v i t y as a f u n c t i o n o f the m a t r i c p o t e n t i a l f o r the F (0 t o 8-cm depth) and H (8 to 17-cm depth) h o r i z o n s . The measurement e r r o r s i n h y d r a u l i c c o n d u c t i v i t i e s of 100, 1, 0.01 cm day 1 are approximately + 1.0, ± 0.07, and + 0.003 cm d a y - 1 r e s p e c t i v e -!y 79 5 Changes o f t o t a l water p o t e n t i a l w i t h time and depth f o r the f o r e s t f l o o r d u r i n g r a i n f a l l ... 81 6 V o l u m e t r i c water content at the 2, 6, 9, and 16-cm depths and t o t a l water content o f the f o r e s t f l o o r d u r i n g r a i n f a l l 83 7 Drainage, e v a p o r a t i o n , t r a n s p i r a t i o n , and t o t a l water d e p l e t i o n r a t e s f o r the f o r e s t f l o o r d u r i n g a d r y i n g p e r i o d i n September... .86 8 Drainage, e v a p o r a t i o n , t r a n s p i r a t i o n , and t o t a l water d e p l e t i o n r a t e s f o r the f o r e s t f l o o r d u r i n g a d r y i n g p e r i o d i n October 87 9 V o l u m e t r i c water content o f the F and H h o r i z o n s as a f u n c t i o n of time. The t o t a l water content and r a i n f a l l are a l s o p l o t t e d 89 x i i Figure 10 Page Chapter IV 1 Relationship between the minimum water content before r a i n f a l l and the maximum increase of water content during r a i n -f a l l f o r a 17-cm thick forest f l o o r on a 30°slope. The volumetric water content 3 -3 at saturation was 0.8 8 cm cm . The 1:1 l i n e was f i t t e d by eye to the data.. 9 3 Diagram of the apparatus used to measure hydraulic conductivity c h a r a c t e r i s t i c s of the forest f l o o r material i n the laboratory.106 ACKNOWLEDGEMENTS The author i s indebted to Dr. B.C. Goodell, Professor of Forest Hydrology, Faculty of Forestry and to Dr. T.A. Black, Assistant Professor of Biometeorology, Department of S o i l Science f o r t h e i r guidance and encouragement during a l l phases of t h i s study. Special thanks are due to Mr. J. Walters, Director of the U.B.C. Research Forest and to the Greater Vancouver Water Board f o r t h e i r cooperation during the f i e l d phase of t h i s study. Sincere thanks goes to Dr. J. DeVries for his w i l l i n g cooperation during the laboratory phase of t h i s research. I wish to extend my thanks to Drs. T. B a l l a r d , P. Haddock, and A. Kozak f o r t h e i r h e l p f u l l c r i t i c i s m s during the writing phase of t h i s t h e s i s . Many thanks to the S o i l Science and Forestry s t a f f f o r t h e i r assistance. The required funds were made avail a b l e through grants from the National Research Council of Canada and the Canada Department of the Environment (NCWRR). Je remercie tres specialement mon epouse pour avoir mis sa competence de secr e t a i r e a ma d i s p o s i t i o n et plus encore pour sa patience et son support moral durant ma c a r r i e r e d'etudiant. INTRODUCTION The r o l e of the forest f l o o r i n watershed hydrology has long been a controversial subject of study. Early i n t h i s century, Henri (1904) investigated the absorption of water by l e a f l i t t e r . Studies of broader scope followed, notably one by Lowdermilk (1930) i n which the e f f e c t s of forest l i t t e r on erosion, runoff and percolation were examined through comparison between plots covered and not covered by forest l i t t e r . The r e s u l t s were, however, only q u a l i t a t i v e . S t i c k e l (1931), as reported by Kittredge (1948) using c o r r e l a t i o n analysis } found that the evaporation rate from the forest f l o o r was the single most important fa c t o r i n f l u e n c i n g i t s moisture content. In more recent years,several quantitative studies of water r e l a t i o n s h i p s of the forest f l o o r have been undertaken but none have attempted the comprehensive and quantitative evaluation of the processes c o n t r o l l i n g the amount of water absorbed during p r e c i p i t a t i o n and the amount of water l o s t by drainage, evaporation, and t r a n s p i r a t i o n ( B a l c i , 1964; Bernard, 1963; Blow, 1955; Broadfoot, 1953; C u r t i s , 1960; Kittredge, 1948; Helvey and P a t r i c , 1965; Helvey, 1964; Mader and L u l l , 1968; Metz, 1958; Molchanov, 1963; Place, 1950; Rowe, 1955; Rutter, 1966; Semago and Nash, 1962; Trimble and Lull,1956). Such a comprehensive study of the hydrologic r o l e of a thick forest f l o o r on steeply sloping land i s the object-ive of t h i s study. The study was comprised of four parts: ( i ) a survey of the s p a t i a l v a r i a b i l i t y of some hydro-l o g i c and physical properties of the forest f l o o r over a mountainous watershed, near Vancouver, B.C. Depth, bulk density, and water retention capacity of the forest f l o o r were determined f o r biophyei-c a l l y d i f f e r e n t areas of the watershed. The r e s u l t s are reported i n Chapt. 1. ( i i ) the development and t e s t i n g of methods of estimating evaporation from the forest f l o o r . The study was c a r r i e d out i n a Douglas f i r plantation on the University of B r i t i s h Columbia Research Forest at Haney, B.C. under well define boundary conditions. Values of the evaporation calculated by the energy balance and aerodynamic methods were compared with that measured by a small, weighing lysimeter. These r e s u l t s are reported i n Chapt. 2. ( i i i ) the measurement of the water balance components of the forest f l o o r on a 30° slope i n Seymour Watershed during natural wetting and drying periods. I t was attempted to explain the magnitude of the water storage, drainage, and evaporation components of the water balance by a better knowledge of the water retention and conductivity properties of the forest - 3 -f l o o r . The r e s u l t s of t h i s study are reported i n Chapt. 3. (iv) the laboratory measurement of the conductivity c h a r a c t e r i s t i c s of the forest f l o o r . These c h a r a c t e r i s t i c s are p a r t i c u l a r l y d i f f i c u l t to determine f o r the forest f l o o r material. The method of measurement i s described i n Chapt. 4. Li t e r a t u r e Cited , BALCI, A.N. 1964. Physical, chemical, and hydrological properties of c e r t a i n Western Washington forest f l o o r types. Unpub. PhD. Thesis. Wash. State Univ. BERNARD, J.M. 196 3. Forest f l o o r moisture capacity of the New Jersey pine barrens. Ecology 44: 574-576. BLOW, F.E. 1955. Quantity and hydrologic c h a r a c t e r i s t i c s of l i t t e r upon upland oak forests i n eastern Tennessee. Jour. Forestry 53: 190-195. BR0ADF00T, W.M. 195 3. Moisture i n hardwood forest f l o o r . U.S. Forest Serv. S.E. Forestry Note 85, l p . CURTIS, W.R. 1960. Moisture storage by l e a f l i t t e r . U.S. Forest Serv. Lake State Tech. Note 577, 2pp. KITTREDGE, J . 194 8. Forest influences. 349pp. MacGraw-H i l l , N.Y. HELVEY, J.D., and J.H. PATRIC. 196 5. Canopy and l i t t e r i n t erception of r a i n f a l l by hardwoods of eastern United States. Water Resources Res. 1: 19 3^206. - 4 -HELVEY, J.D. 1964. R a i n f a l l interception by hardwood forest l i t t e r i n the southern Appalachian. U.S. Forest Serv, Res. Paper SE-8, 9pp. HENRI, E. 19 04. Faculte d'imbibition de l a couverture morte. Revue des Eaux et Forets 43: 353-361. LOWDERMILK, W.C. 19 30. Influence of forest l i t t e r on run-off, percolation, and s o i l erosion. J. Forestry 28: 474-491. MADER, D.L. and H.W. LULL. 196 8. Depth, weight, and water storage of the forest f l o o r i n white pine stands i n Massachusetts. U.S. Forest Serv. Res. Paper NE-109, 35pp. METZ, L.J. 1958. Moisture held i n pine l i t t e r . J . Forestry 56: 36. MOLCHANOV, A.A. 196 3. The hydrological r o l e of fo r e s t s . Translated from Russian I s r a e l program fo r s c i e n t i f i c t r a n s l a t i o n 400pp. PLACE, I.CM. 1950. Comparative moisture regimes of humus and rotten wood. Can Dept. Res. Develop. Forest Res. Div. S i l v . Leaf1. 37. ROWE, P.B. 1955. Ef f e c t s of the forest f l o o r on di s p o s i t i o n of r a i n f a l l i n pine stands. Jour. Forestry 53: 342-348. RUTTER, A.J. 1966. Studies on the water r e l a t i o n of Pinus s y l v e s t r i s i n plantation conditions. IV Direct - 5 -observations on the rates of t r a n s p i r a t i o n , evaporation of intercepted water, and evaporation from the s o i l surface. J . Appl. Ecol. 3: 393-405. SEMAGO, W.T. and A.J. NASH. 1962. Interception of p r e c i p i t a t i o n by a hardwood forest f l o o r i n the Missouri Ozarks. Univ. Missouri Agr. Expt. Sta. Res. B u l l . 796, 31pp. TRIMBLE, G.R., J r . , and H.W. LULL. 1956. The r o l e of forest humus i n watershed management i n New England. U.S. Forest Serv. NE. Sta. Paper 85, 34pp. - 6 -GENERAL SURVEY OF SOME PHYSICAL AND HYDROLOGIC. CHARACTERISTICS OF THE FOREST FLOOR A b s t r a c t . Depth o f f o r e s t f l o o r and a l t i t u d e , s l o p e , a s p e c t , and f o r e s t b a s a l a r e a were s y s t e m a t i c a l l y measured o v e r f o u r r e p r e s e n t a t i v e a r e a s w i t h i n a Coast M o u n t a i n w a t e r s h e d . M u l t i p l e r e g r e s s i o n was used t o d e v e l o p an e q u a t i o n t h a t p r e d i c t s t h e average f o r e s t f l o o r d e p th o f a s m a l l p l o t from p h y s i o g r a p h i c f a c t o r s . B u l k d e n s i t y , s a t u r a t i o n c a p a c i t y and f i e l d m o i s t u r e c a p a c i t y were d e t e r m i n e d i n t h e l a b o r a t o r y from samples c o l l e c t e d i n t h e f i e l d . B u l k d e n s i t y was n o t r e l a t e d t o d e p t h o r t o t h e p h y s i o g r a p h i c f a c t o r s . S a t u r a t i o n and f i e l d m o i s t u r e c a p a c i t i e s were l i n e a r -l y r e l a t e d t o t h e f o r e s t f l o o r d e p t h . I n t r o d u c t i o n The f o r e s t f l o o r component o f t h e f o r e s t e cosystem s e r v e s i m p o r t a n t f u n c t i o n s i n n u t r i e n t c y c l i n g , t r e e r e g e n e r a t i o n , and s o i l b i o l o g y , and i n f l u e n c e s many h y d r o -l o g i c c h a r a c t e r i s t i c s o f f o r e s t l a n d s . I t i n s u l a t e s t h e m i n e r a l s o i l from extremes o f t e m p e r a t u r e and o f f e r s m e c h a n i c a l p r o t e c t i o n from e r o s i o n a l f o r c e s . I t s w a t e r h o l d i n g c a p a c i t y may be i m p o r t a n t i n d e l a y i n g peak f l o w . Knowledge o f t h e d e p t h , s p a t i a l d i s t r i b u t i o n , and p h y s i c a l and h y d r o l o g i c p r o p e r t i e s o f t h e f o r e s t f l o o r i s necessary for the sound management of forested watersheds. It i s impossible to f u l l y understand the hydrologic changes associated with land management without knowledge of the r o l e of the forest f l o o r layer i n the s o i l - plant -atmosphere system. The f i r s t set of objectives of t h i s reconnaissance survey was: to measure the depth and the bulk density of the forest f l o o r ; to explore the s p a t i a l v a r i a t i o n of i t s depth; and to determine the c o r r e l a t i o n of depth with some e a s i l y recognizable, inf l u e n c i n g parameters. The second set of objectives was: to determine the e f f e c t s of environmental factors on the amounts of water held at f i e l d moisture capacity and saturation capacity, and to f i n d out i f these amounts could be predicted from knowledge of the forest f l o o r depth. An equation predicting the amount of water held by the f o r e s t f l o o r would make possible extrapolation from a detailed p l o t study to a lar g e r area. F i e l d Design and Procedures The survey was c a r r i e d out within the Seymour River Basin which stretches northward 20 miles (32.2 km) from i t s mouth i n Burrard I n l e t . The catchment i s a t y p i c a l U-shaped v a l l e y 2 2 of the Coast Mountain Range. Its area i s 69.5 mi (18 0 km ) of which 30% i s covered by mature timber, 10% by immature timber, 27% by scrub, 18% by alpine vegetation, and 15% by s l i d e s , rocks, water, and swamps. - 8 -The survey was not s t a t i s t i c a l l y designed to estimate the variance of the physical or hydrologic c h a r a c t e r i s t i c s of the forest f l o o r , but to quickly determine what subsequent investigations w i l l be necessary for assessment of the r o l e of the forest f l o o r i n the hydro-logy of a Coast Mountain watershed. I f knowledge from d e t a i l e d , plot studies of forest f l o o r c h a r a c t e r i s t i c s can be safel y extrapolated, t h i s type of approach would be highly e f f i c i e n t . On the other hand, i f the hydrologic c h a r a c t e r i s t i c s of the forest f l o o r vary too much s p a t i a l l y , sampling of actual moisture content over a watershed may be necessary to supplement de t a i l e d studies on sample p l o t s . Two sampling areas were picked on each side of the v a l l e y , at d i f f e r e n t distances from the I n l e t , for system-a t i c study of f o r e s t f l o o r depth under overmature timber stands ( F i g . 1). A l l areas were within the Coastal, Western Hemlock, Biogeoclimatic Zone of B r i t i s h Columbia (Krajina, 1965). This zone corresponds to the South P a c i f i c Coast Region (C.2) described by Rowe (1959). In each area a transect l i n e was run more or less perpendicularly to the r i v e r from the v a l l e y bottom to the 2,500 feet (762 m) contour l e v e l . On the v a l l e y bottom a plot was established every 200 feet (61 m) of horizon-t a l distance, whereas on the steep sides of the v a l l e y a plo t was established at every 400 feet (121.9 m) of a l t i t u d e . For more intensive study of Area 1, four supplementary transects were run up to an a l t i t u d e of 1,000 feet (304.8 m). - 9 -Figure 1. Location of the plots within Seymour watershed. - 10 -A t o t a l of 60 plots were thus established i n d i f f e r e n t areas, and over ranges of a l t i t u d e s and exposures. Table 1 shows the number of plots by study areas and factors assumed to influence forest f l o o r depth. Within each plot the forest f l o o r depth was system-a t i c a l l y measured along a l i n e passing through the plot center and running at 4 5° to the main transect l i n e . Twenty depth measurements were taken at one foot i n t e r v a l s on each side of the center. Any measurable layer of humus on logs and stones was included. The forest f l o o r was not separated into L, F, and H horizons as the separation between F and H would have been a r b i t r a r y . The t o t a l depth of organic material exclusive of i d e n t i f i a b l e rotten wood was c l a s s i f i e d as humus. The thickness of rotten wood was recorded separately. Three parameters of depth were thus obtained: depth of humus, depth of rotten wood, and t o t a l depth of forest f l o o r (humus plus rotten wood). Logs and undecomposed branches l y i n g on the top of the l i t t e r were not included i n the depth measurements. Calculation of average depth and volume of each component, and also c a l c u l a t i o n of the percentage of t o t a l f o rest f l o o r volume that rotten wood represents were thus possible. Four types of s o i l cover were recognized: humus, rotten wood, undecomposed logs and branches, and stones. - 11 -Table 1. Plot frequency d i s t r i b u t i o n by classes of biophysical features. Influencing Classes Frequency parameters (No. of plots i n each class) AREA 1 38 2 7 3 8 4 7 ALTITUDE 7 01 - 10 00 f t 26 1001 - 1300 f t 15 1301 - 1600 f t 5 1601 - 1900 f t . 5 1901 - 2200 f t 5. 2201 - 2500 f t 4 SLOPE 0 - 1 0 degree 14 11 - 20 degree 15 21 - 30 degree 15 31 - 40 degree 10 HI - 50 degree 6 ORIENTATION N 2 NE 5 E 33 SE 4 S 5 SW 3 S 8 BASAL AREA 1 - 8 0 sq.ft/acre 2 of forest 81 - 160 sq.ft/acre 19 161 - 240 sq.ft/acre 18 241 - 320 sq.ft/acre 10 321 - 400 sq.ft/acre 6 401 - 480 sq.ft/acre 5 RADIATION 0.186 2 2 INDEX 0.2561 - 0.2893 4 0.3713 1 0.4092 - 0.4185 41 0.4690 1 0.5301 - 0.5447 7 0.5860 - 0.5912 4 - 12 -The f r a c t i o n a l area covered by each type was estimated o i n each plo t by means of four 10 square foot (0.9 29 m ) g r i d s . A c i r c u l a r sample of f o r e s t f l o o r 15 cm i n diameter was c o l l e c t e d from each of four points systematically located about the p l o t center. To investigate more i n t e n s i v e l y the v a r i a b i l i t y of forest f l o o r depth and hydrologic properties, two p l o t s , each 20 by 20 feet (6.1 m) i n size were established. One of these, to be c a l l e d Plot A, was located i n Area 1, the other, Plot B, i n Area 3 ( F i g . 1). On these, depths of humus and rotten wood were measured at intersections of a one foot g r i d and the p o s i t i o n of each tree was recorded. This information was l a t e r used to map the forest f l o o r depth and tree l o c a t i o n s . Twenty-five samples were also c o l l e c t e d from each plot at the intersections of a 5 square foot g r i d f o r v a r i a b i l i t y studies of oven-dry weight, bulk density, saturation capacity, and f i e l d moisture capacity. To avoid confusion i n the text, these two plots w i l l be r e f e r r e d to as Plot A and Plot B whereas the non-specified plots w i l l be from the transects. Laboratory Procedures Each sample c o l l e c t e d i n the f i e l d was brought to the laboratory f o r determination of the bulk density, the f i e l d moisture capacity, and the saturation capacity. The bulk density was obtained by d i v i d i n g the oven-dry weight of the sample by volume at the f i e l d moisture content. - 13 -F i e l d moisture capacity has been defined as the amount of moisture held by s o i l a f t e r i t has been saturated i n the f i e l d , covered to prevent evaporation, and allowed to drain f o r 24 hrs. A more r e a l i s t i c d e f i n i t i o n of f i e l d moisture capacity i s the amount of moisture held a f t e r the rate of drainage has m a t e r i a l l y decreased. This i s a function of the unsaturated hydraulic conductivity of the material which i n turn i s a function of the matric p o t e n t i a l . In conformance with B a l c i (1964), a matric p o t e n t i a l of -100 cm of water was applied, and the water content measured at equilibrium was considered to be the f i e l d moisture capacity. Since the thickness of the forest f l o o r samples ranged from 1 to 30 cm the centers of the samples were used as reference levels ( i . e . zero gravimetric u o t a n t i a l ) . The procedure f o r determining saturation capacity was to support the sample on a layer of cheesecloth over the bottom end of an open c y l i n d e r , completely immerse i t i n water fo r 4 8 hrs, then suspend i t i n a i r f o r 10 min to allow free drainage before weighing. Another variable reported i n the l i t e r a t u r e i s the e f f e c t i v e saturation capacity which has been defined by B a l c i (1964) as the maximum amount of water held during r a i n f a l l . B a l c i determined the e f f e c t i v e saturation capacity i n the laboratory under simulated " r a i n f a l l by holding a forest -floor sample on a porous plate under a - I n -constant matric p o t e n t i a l of -100 cm of water. With such a system, the resistance of the plate to water flow causes the p a t r i c p o t e n t i a l at the bottom of the sample to be somewhat higher than -100 cm of water. In the f i e l d , under natural r a i n f a l l conditions, the matric p o t e n t i a l at the mineral s o i l - forest f l o o r interface would be higher than -100 cm of water and would also d i f f e r with r a i n f a l l i n t e n s i t y . Since f i e l d conditions are not r e a d i l y reproduce-able i n the laboratory the author believes that recognition of e f f e c t i v e saturation capacity as a s p e c i f i c s o i l character-i s t i c should not be encouraged. The water held i s i n fac t a function of the average hydraulic conductivity of the material which i s a more exact c h a r a c t e r i s t i c . The importance and a p p l i c a t i o n of hydraulic conductivity, as well as the f i e l d measurements of forest f l o o r water content under high i n t e n s i t i e s of r a i n f a l l , w i l l be reported i n Chapter 3. Results and Discussion a) Physical c h a r a c t e r i s t i c s Humus and t o t a l forest f l o o r depth for each plot of the transects of Areas 1 to 4 are reported i n Appendix I I . Averages of physical c h a r a c t e r i s t i c s of the forest f l o o r , as based on transect data, are presented i n Table 2 with t h e i r respective confidence l i m i t s (95%). Over the surveyed areas, the plot averages of forest f l o o r depth ranged from 3 cm to 4 5 cm. Sixty-three percent of forest f l o o r volume was humus; the remaining volume, 37% was rotten wood. The areal extent of each of four types of ground cover - 15 -Table 2. Forest f l o o r physical c h a r a c t e r i s t i c s CHARACTERISTICS AREA Humus depth (cm) Forest f l o o r depth (cm) Bulk density (g cm ) 1 2 3 4 1 2 3 4 AVERAGES and 95-percent Confidence l i m i t s 6,6 + 0.35 11.6 ± 1.20 8.3 + 0.76 17.8 + 2.09 11.9 ± 0.65 16.3 + 1.62 12.7 + 1.26 25.5 ± 2.55 N A l l (1-4) 0.147 ± 0.007 1520 280 320 280 1520 280 320 280 240 N= Number of observations i s presented i n Table 3. It can be seen that the areal extent of the ground surface, into which water cannot i n f i l t r a t e (e.g. log and stone) i s very l i m i t e d . Forest floor depth and influencing parameters. Simple regression equations were calculated r e l a t i n g the t o t a l f o r e s t f l o o r depth (DF), and the humus depth (DH) to - 16 -a l t i t u d e , slope, basal area, r a d i a t i o n index, and the distance northward from Burrard Inlet (Table 4). These variables were assumed to be the most important, r e a d i l y measurable, biophysical parameters correlated with f o r e s t f l o o r depth i n mountainous watersheds. Table 3. Ground cover by study areas. Ground cover (%) Area Humus Rotten wood 1 Log 1 Stone 1 83.3 6.4 4.9 5.4 2 87.7 3.9 1.9 6.4 3 94.1 2.5 0.4 3.0 4 86.9 5.3 7.3 0.6 No over-layer of humus. The a l t i t u d e i s an index of temperature which a f f e c t s decomposition of l i t t e r , and may also a f f e c t l i t t e r production. The angle of the slope may a f f e c t the decomposi-t i o n rate by influencing th© amount of energy avai l a b l e and the water regime of a s i t e . The basal area i s related to the age and stocking of the stand which a f f e c t the amount of l i t t e r - 17 -f a l l i n g each year. Basal area i s also related to canopy density which influences the rad i a t i o n input to the forest f l o o r . (In overmature stands l i t t e r f a l l i s perhaps more independent of the basal area). The distance from the Inlet probably serves as an index of sunshine duration, r a i n f a l l i n t e n s i t y , and temperature, since i t was observed that clouds and r a i n occured more often towards the head of the catchment. The r a d i a t i o n index i s an e f f i c i e n t and convenient parameter for expressing the combined ef f e c t s of the slope and aspect of a s i t e on the p o t e n t i a l solar energy input to the s i t e . In turn, i t should be an index to the rate of organic matter decay and thus to the depth of for e s t f l o o r . I t i s the r a t i o of the annual p o t e n t i a l solar beam r a d i a t i o n (atmosphere attenuation = 0) on the surface to the annual p o t e n t i a l solar beam i r r a d i a t i o n on a surface always normal to the solar beam (Frank et at., 1966). The l a t t e r i s simply the solar constant times the duration of sunshine f o r the year. The annual p o t e n t i a l r a d i a t i o n t o t a l on a surface i s equal to the solar constant times the cosine of the angle of incidence times the po t e n t i a l duration of sunshine on the surface. The incidence angle for a t e r r e s t r i a l surface depends i n turn on f i v e independent v a r i a b l e s ; t e r r e s t r i a l l a t i t u d e , time of day, time of year, surface slope, and surface - 18 -or i e n t a t i o n . Therefore the r a d i a t i o n index includes e f f e c t s of the parameters of both slope and aspect. Table 4. C o e f f i c i e n t s of c o r r e l a t i o n between forest f l o o r depth and influencing parameters. Correlation c o e f f i c i e n t Independent variables Excluding Including rotten wood rotten wood DH DF ALT (Alt i t u d e feet) 0.538** 0.253* SLP (Slope degree) 0 .591** 0.128 ns 2 BAR (Basal area feet ) 0.318* 0.244 ns DIS (Distance miles) 0.505** 0 .454** RAD (Radiation index) -0.488** -0.557** N = 60 ns = non s i g n i f i c a n t * S i g n i f i c a n t at the 5% l e v e l ** S i g n i f i c a n t at the 1% l e v e l . Radiation index, the best single v a r i a b l e , explains about 30% of forest f l o o r depth v a r i a t i o n . The negative c o r r e l a t i o n with t h i s variable r e f l e c t s i t s e f f e c t on decomposition rate of the organic matter. The r e l a t i o n s h i p s between depth and several influencing factors were calculated by multiple regression. The equations that were best with respect to both ease of measurement of - 19 -the independent variables and the s i g n i f i c a n c e of the c o r r e l a t i o n c o e f f i c i e n t s were: DH = 13.19 - 21.7 * RAD + 0.000339 * DIS * ALT R = .751 DF = 26.31 - 38.3 * RAD + 0.000282 * DIS * ALT R = .661 In these equations the r a d i a t i o n index i s as given by Frank et ai.(1966). The distance and a l t i t u d e were re s p e c t i v e l y i n miles and i n feet. The two equations account f o r 56 and 44% of the v a r i a b i l i t i e s of DH and DF r e s p e c t i v e l y . Figure 2 shows the predicting surface with the 95% confidence l i m i t s . The low percentage of v a r i a t i o n accounted f o r indicates that some important factors have not been included i n the model. Past events such as flood, w i n d f a l l , and f i r e may have much e f f e c t on forest f l o o r depth but such e f f e c t s could not be measured. Rotten wood depth, which i s included i n DF, i s probably influenced by past w i n d f a l l events. That f i r e may have been i n f l u e n t i a l i s indicated by the observed presence of charcoal on Areas 1, and 3. The average forest f l o o r thickness on these two areas i s l e s s . The p r e d i c t i v e equations must be used with caution as the basic data were not c o l l e c t e d at random. Forest floor depth, weight, and bulk density relationships. Regression analysis was used to predict the oven-dry weight of the f o r e s t f l o o r i n grams per square centimeter (W) from i t s depth ( F i g . 3). The confidence l i m i t s were not computed since the variance of W about the regression l i n e i s not homogeneous. - 20 ~ • F i g u r e 2. R e l a t i o n o f f o r e s t , f l o o r depth (DF) to . i n f l u e n c i n g parameters. - 21 -F i g u r e 3. R e l a t i o n o f f o r e s t f l o o r o v e n - d r y w e i g h t t o f o r e s t f l o o r d e p t h . - 2 2 -As based on sampling along transects, bulk density i s not correlated with depth ( F i g . 4 ) . I t was also found that bulk density was not s i g n i f i c a n t l y correlated with any of the environmental parameters measured. The v a r i a t i o n of the bulk density around the mean i s large because roots, rotten wood, or mineral matter may be included i n the sample. These inclusions cause greater variations at shallower depths as they then represent a high percentage of the t o t a l weight. The i n s e r t of Figure 4 shows the r e l a t i o n s h i p between the bulk density and depth of samples taken within the two r e l a t i v e l y uniform Plots A and B. It indicates that the average bulk density of the forest f l o o r was independent of the depth i n Plot B, whereas i t s i g n i f i c a n t l y ( 9 5 % l e v e l ) decreased with depth i n Plot A. This i s explained by the fact that on Plot A several samples were taken from the thick and loose l i t t e r layer around tree bases. Distribution of forest floor depth. The frequency d i s t r i b u t i o n of humus and t o t a l f o rest f l o o r depths (humus plus rotten wood) are presented by study areas i n Figure 5. In t h i s figure each cross or dot represents the r e l a t i v e frequency of each class of 2 cm depth. Zero depth i s a separate c l a s s . The cumulative frequencies are also plotted i n the same fi g u r e . For example the percentage of the area covered by forest - 2 3 -fx UJ 5 0-4 o o Ul rx o < HO 2 I-u. o SD « 01 ui a TRANSECT DATA N = 240 OO I 8 12 16 20 24 FOREST FLOOR DEPTH (cm) 28 32 Figure 4. Relation between bulk density and fo r e s t f l o o r depth. - 24 -20 10 i « 5 o 5 o S20 15 -£ 5 o i 0 2 2 0 10 5 -i 1 1 1 1 1 1 1 1 1 r . SEYMOUR WATERSHED 1969 I \ CUMULATIVE.\ ; - 8 ' \ x— AVERAGE DEPTH (cm) .V HUMUS 9 0 If— x,x"-~ FOREST FLOOR « — « 140 y\ N = 300 ••v..\ Are0 3 \.-''<?x .?>.X—«—"* / C U M U L A T I V E ^ ^ ->k'^~' \ ,•' AVERAGE DEPTH (cm) / \ / \ HUMUS 6-5 x « / / * \ . \ FOREST FLOOR « — * 120 * < ! t » ^ - , v . N = I520 Areo I V . . . - - . \ « x ^ x / " I I I | _ i ~ i -i.''— >--r-»—.i-4-0 4 8 12 16 20 24 28 32 36 40 DEPTH (cm) —I 1 1 I 1 1 1 i 1 1 r AVERAGE DEPTH (cm) SEYMOUR WATERSHED 1969 HUMUS • 170 FOREST FLOOR x—x25-5 " " " N = 300 ! \ - ' ' \ - ' ' " ^CUMULATIVE Area 4 ^/ ^ - « - ^ CUMULATIVE AVERAGE DEPTH (cm) HUMUS 11-5 > , , FOREST FLOOR » — x 160 /T-?*^ \ I \ A N ' 2 8 0 j'J>^  Area 2 * ^'^Ni? '~"~?--^ « 0 4 8 12 16 20 24 28 32 36 40 DEPTH (cm) 100 75 50 5s o 25 UJ o UJ o £ 100 > - 75 50 25 100 75 50 -25 S 0 a. 75 => S u H50 25 Figure 5. Frequency d i s t r i b u t i o n s of humus and for e s t f l o o r depths i n Areas 1, 2, 3 and 4. - 25 -f l o o r less than 3 cm thick i n Area 1 i s 25%. I f a s p e c i f i c depth of forest f l o o r i s recognized as a f f e c t i n g tree regeneration, s i t e hydrology, or forest f u e l supply, such frequency d i s t r i b u t i o n s provide useful estimates of the surface area having a c r i t i c a l depth of forest f l o o r ( F f o l l i o t t et al., 1968). Forest f l o o r depths were examined i n d e t a i l over Plots A and B (Fig. 6 and 7). In general the depth of the for e s t f l o o r increases sharply at the base of each tree. However, the accumulation of debris i s very variable around any one tree and the organic layer depth does not smoothly decrease with distance away from the trunk to increase again midway between 2 trees. The depth i s very unpredictable and i s as much influenced by t e r r a i n depressions as by the trees. The heterogeneity of the forest f l o o r depth i s further a f f e c t -ed by decaying wood which i s randomly d i s t r i b u t e d . The frequency d i s t r i b u t i o n s of humus and forest f l o o r depths f o r Plots A and B are shown i n Figure 8. The d i s t r i b u t i o n on Plot A, Area 1 i s appreciably d i f f e r e n t from that on Area 1 i t s e l f ( F i g . 5). S i m i l a r l y the d i s t r i b u t i o n on Plot B d i f f e r s from that on Area 3. This exemplifies the heterogeneity of these forest f l o o r c h a r a c t e r i s t i c s , b) Hydrologic c h a r a c t e r i s t i c s Saturation c a p a c i t i e s , and f i e l d moisture capacities determined - 26 -DISTANCE Cm) Figure 6 Detailed map of forest f l o o r depth i n Plot A (Seymour V/atershed) - 27 -DISTANCE (m) Figure 7 . Detailed map of forest f l o o r depth i n Plot B . (Seymour Watershed) - 29 -i r —i 1 i i 1 SEYMOUR WATERSHED 1969 1 r 20 - CUMULATIVE • 100 - 5 o z 0 Ul o 2 0 -15 -AVERAGE DEPTH (cm) HUMUS 9-6 FOREST FLOOR i—* 14 4 N = 388 75 50 VI--"'"' ^ i - " " " " * 1 " ^ C U M U 10 • LATIVE //// w .'/ // V v • ' / . » Plot A X / \ « — - » (within area I) AVERAGE DEPTH (cm) HUMUS 81 FOREST FLOOR « — * I I 0 N = 4I5 25 o z U l o 0 jjj IOO £ 75 J S O 50 25 8 12 16 20 24 28 32 36 40 OEPTH (cm) Figure 8. Frequency d i s t r i b u t i o n s o f humus and f o r e s t f l o o r depths w i t h i n P l o t s A and B . - 30 -from the forest f l o o r samples c o l l e c t e d i n the transect plots are l i s t e d i n Appendix I I I . Table 5 presents for a l l transects the averages and the confidence l i m i t s of f i e l d moisture and saturation c a p a c i t i e s . The samples c o l l e c t e d i n the f i e l d excluded rotten wood as much as possible, the l a t t e r being the object of another study. Table 5. Average and confidence l i m i t s of f i e l d moisture and saturation c a p a c i t i e s . N = 24 0 WATER CONTENT % of dry cm of % of Cha r a c t e r i s t i c s weight water volume F i e l d moisture capacity 214 ± 8 2.2+0.2 3 1 + 3 Saturation 453 +17 4.5+0.3 6 7 + 5 capacity Saturation capacity. Simple regression of the saturation capacity i n centimeters of water on forest f l o o r depth explains 79% of the v a r i a t i o n ( F i g . 9a). The lea s t squares l i n e intercepts the y-axis at 0.76 cm. B a l c i (1964), using the same method to determine the saturation capacity, reported an intercept at 0.70 cm. The author believes that these p o s i t i v e intercepts were mainly due to the technique used. - 31 -F i g u r e 9. R e l a t i o n between s a t u r a t i o n c a p a c i t y , expressed i n cen t ime te r s o f water and f o r e s t f l o o r dep th . - 32 -Two systematic errors are associated with t h i s technique. At equilibrium the average matric p o t e n t i a l of a sample suspended i n a i r approximates h a l f (negative) i t s t o t a l depth, assuming that there i s no water entrapped within the sample and that the matric p o t e n t i a l at the bottom of the sample i s zero. Thus the equilibrium matric p o t e n t i a l of a sample increases (negatively) with i t s depth and consequently i t s average volumetric water content would tend to decrease with an increase i n depth. The amount of water draining out i s a function of the shape of the water retention c h a r a c t e r i s t i c s of the forest f l o o r material. The data show that the volumetric water content at saturation capacity decreased s i g n i f i c a n t l y ( 9 5 % l e v e l ) with an increase of forest f l o o r depth. The slope of the regression l i n e i s then smaller than i t should be. A second source of error i s the adherence of water to the walls of the container. Error from t h i s source should also depress the slope of the regression by causing a r e l a t i v e l y greater over-estimate of saturation capacities of the thinner samples. A conditioned regression passing through the o r i g i n was found s t a t i s t i c a l l y s i g n i f i c a n t l y ( 9 5 % l e v e l ) d i f f e r e n t from the o r i g i n a l model (F i g . 9 a ) . I l l u s t r a t i o n of the s p a t i a l uniformity of the saturation capacity as a function of depth i s given by comparison of F i g . 9a with Fig, 9b. There i s no s t a t i s t i c -- 33 -a l l y s i g n i f i c a n t (95% l e v e l ) difference between the slopes and the l e v e l s of those two regression l i n e s . Thus there i s no i n d i c a t i o n that saturation capacity i s influenced by environmental f a c t o r s . The r e s i d u a l variance about the transect data l i n e i s s i g n i f i c a n t l y (95% l e v e l ) greater than the r e s i d u a l variance about the Plot B l i n e . This i s p r i n c i p a l l y due to the scatter i n the upper part of the transect data l i n e . Saturation capacity, determined as described e a r l i e r , i s not a h y d r o l o g i c a l l y useful parameter on sloping land. As 3 - 3 w i l l be shown in Chapt. 3, It exceeds by about 0.20 cm cm the volumetric water content of the forest f l o o r during high i n t e n s i t y r a i n f a l l (0.5 cm/hr for 5 h r s ) . However, saturation capacity i s very easy to measure and may be useful i n the comparison of d i f f e r e n t areas. The volumetric water content of i n d i v i d u a l samples can be calculated from F i g . 9 by d i v i d i n g i t s water content at saturation by i t s t o t a l depth. Field moisture capacity. The water content i n centimeters at a matric p o t e n t i a l -100 cm of water was regressed against forest f l o o r depths (Fig. 10a). Depth explains 84% of the v a r i a b i l i t y as compared with 79% of the v a r i a b i l i t y of saturation capacity. The r e s i d u a l variances of the two curves are s i g n i f i c a n t l y d i f f e r e n t (95% l e v e l ) . Both parameters were evaluated on the same samples. The \ - 34 -1 I 1 I SEYMOUR WATERSHEO — i 1 1 — 1969 1 - 6 1 1 1 F .-0-19I + 0 301 1 OF - 4 _r>0949 r 2-09OO ."^ N'25 -- 2 (b) Plot 8 (o) Tronjacl dolo -/ I i i * ) 4 8 12 16 95-percent confidence limit* " t OF-20" 6 0 4 , 0 1 8 -F - 4 r D F , 2 '0-48S0I2 * . •1-97 tO 08 -N • 240 . . S E-£ * 0-634 ....\r^-' f '-O 137 + 0309 X DF . ;•:-•§• I*.: •.. : .• '• r»0 9l7 r 2»OB4l -> i i i 1 » ! I O 4 8 12 16 20 24 2B 32 FOREST FLOOR DEPTH (cm) Figure 10. Relation between f i e l d moisture capacity^ expressed i n centimeters of water }and f o r e s t f l o o r depth. - 35 -difference i n the c o e f f i c i e n t s of determination i s a t t r i b u t e d to the more rigorous technique used i n measurements of f i e l d moisture capacity. Figure 10b shows the v a r i a t i o n of the f i e l d moisture capacity with depth within Plot B . About 10% of the v a r i a t i o n of f i e l d moisture capacity with depth i s not explained even though the samples were c o l l e c t e d the same day within a 100 square feet area. No s i g n i f i c a n t differences (95% l e v e l ) were found between curves a and b. The volumetric water content of i n d i v i d u a l samples can be calculated from F i g . 10 by d i v i d i n g i t s water content at f i e l d moisture capacity by i t s t o t a l depth. Useful information was provided by using transect data to regress the volumetric water content at f i e l d moisture capacity on the forest f l o o r depth. It was found that there was no s i g n i f i c a n t c o r r e l a t i o n between the two v a r i a b l e s . This indicates the p o s s i b i l i t y of extrapolating the data from a plo t to a large area. From the above f i n d i n g , which says that the f i e l d moisture capacity of the forest f l o o r was the same a l l over the study area, i t i s expected that one retention curve w i l l be representative of the whole area. Samples from three s i t e s were used to determine the volumetric water content at tensions of 60, 80 and 100 cm of water. Among the three s i t e s , the difference - 36 -did not exceed the experimental error. Conclusion On the watershed studied, the average forest f l o o r depth of a small plo t can be predicted with an accuracy of about 30% (95% l e v e l ) through use of influencing factors r e a d i l y evaluated from a topographic map. Knowing the depth of the forest f l o o r at one point, the saturation capacity at t h i s point can be estimated within ± 2.2 cm of water (95% l e v e l ) . S i m i l a r l y , the f i e l d moisture capacity of any forest f l o o r sample can be estimated within + 1.2 cm (95% l e v e l ) . These confidence i n t e r v a l s of i n d i v i d u a l observ-ations were determined for forest f l o o r thickness ranging from 0 to 30 cm. Since the hydrologic c h a r a c t e r i s t i c s of the forest f l o o r are s i m i l a r over d i f f e r e n t physiographic features i t appears possible to estimate the e f f e c t s of the f o r e s t f l o o r on the hydrologic response of t h i s watershed. Li t e r a t u r e Cited BALCI, A.N. 1964. Physical, chemical, and hydrological properties of c e r t a i n Western Washington forest f l o o r types. Unpub. PhD. Thesis Wash. State Univ. FRANK, E.C. and R. LEE. 1966. Potential s o l a r beam i r r a d i a t i o n on slopes. U.S.D.A. Forest Serv. Res. Paper RM-18. - 37 -KRAJINA, V.J. 1965. Biogeoclimatic zones and c l a s s i f i c -a tion of B r i t i s h Columbia Ecol. of Western N.A. 1: 1-17. ROWE, J.S. 1959. F o r e s t r e g i o n s of Canada. Dept. Northern A f f a i r s and N a t i o n a l Resources, F o r e s t r y Branch, B u l l . 123. - 38 -ENERGY BALANCE METHOD FOR ESTIMATING EVAPORATION FROM THE FOREST FLOOR1 Abstract. Estimates of the evaporation from the forest f l o o r using the energy balance method were compared with measurements made by a small, sensitive,weighing l y s i -meter. Evaporation was well estimated by the net ra d i a t i o n minus the s o i l heat f l u x , i n d i c a t i n g a small, downward, sensible heat f l u x . Results suggest that the s i m i l a r i t y p r i n c i p l e was not applicable under the canopy. For much of the time, evaporation from the forest f l o o r was a c a p i l l a r y flow l i m i t e d , rather than an energy lim i t e d , process. This chapter was submitted as a paper to Canadian Journal of Forest Research. - 3 9 -Introduction Forest hydrologists speculate about the influence of the surface organic l a y e r of the forest on the amount and timing of water y i e l d , e s p e c i a l l y where t h i s layer may be several centimeters t h i c k , as i n the c o o l , humid forests of the west coast of B r i t i s h Columbia. Knowledge of the water balance of the f o r e s t f l o o r i s e s s e n t i a l to a s o l u t i o n of t h i s problem, and i s also required i n moisture index models (Turner, 1966) used f o r prescribed burning programs. U n t i l now the evaporation from the forest f l o o r has been commonly estimated e i t h e r by per i o d i c gravimetric sampling (Helvey, 1964; Mader et a l . , 1968) or by p e r i o d i c a l l y weighing a sample contained i n a screen-bottomed box (Helvey et al. , 1965) or i n a tray (Semago et al. , 1962, Rutter, 1966). These methods, although simple and inexpensive, are subject to serious sampling e r r o r and are not accurate enough to y i e l d short period estimates of evaporation. Large,sensitive weighing lysimeters have provided accurate evaporation rates under most a g r i c u l t u r a l conditions (Fritschen, 1966) but . they..are i m p r a c t i c a l i n mountainous, forested areas. The micrometeorological methods, on the other hand have the advantages of measuring evaporation over short time i n t e r v a l s without di s t u r b i n g the environment and providing information on the nature of the processes (Tanner, 1967). - 40 -Very few micrometeorological measurements of evaporation under a canopy have been reported i n the l i t e r a t u r e . 3aumgartner (1956), using the energy balance technique,estimated the evaporation from the forest f l o o r to be somewhat smaller than 0.5 mm/day. Denmead (1964) reported that the evaporation rate one meter above the ground under a pine plantation at 1145 AEST i n May, 1963, was 0.014 mrrt/hr (see his f i g . 2). Black et al. } (1970) estimated the evaporation under a snap bean canopy by using the l i m i t i n g value of e i t h e r the a b i l i t y of the s o i l to conduct water to the surface or the energy a v a i l a b l e f o r evaporation. The evaporation from a s o i l surface can be estimated by e i t h e r one of the three micrometeorological methods energy balance, aerodynamic, and eddy c o r r e l a t i o n . The research described here was undertaken to assess the usefulness of the aerodynamic and the energy balance approaches to estimating evaporation from the forest f l o o r . In a d d i t i o n , evaporation measurements were made during drying periods to determine to what degree the evaporation from the f o r e s t f l o o r i s an energy or c a p i l l a r y flow l i m i t e d process. Theory The energy balance at the forest f l o o r surface of a uniform, closed canopy fo r e s t of i n f i n i t e - e x t e n t i s - U l -R = LE + H + G (1) n where R i s the net r a d i a t i o n flux at the forest f l o o r n surface, LE i s the lat e n t heat f l u x , H i s the sensible heat f l u x , and G i s the s o i l heat f l u x . This assumes that h o r i z o n t a l l y advected heat i s zero. 3oth R and G n are r e l a t i v e l y easy to measure. The problem i n using (1) to estimate LE i s how to measure K. One of two s i m p l i f y i n g assumptions can be made at t h i s point: f i r s t , that the d i f f u s i v i t i e s f o r latent and sensible heat t r a n s f e r within the biomass are equal (K = K, ) H v h or second, that sensible heat t r a n s f e r from the canopy to the forest f l o o r surface i s n e g l i g i b l e because of the occurrence of a strong temperature inversion during most of the day. With the f i r s t assumption (1) becomes the f a m i l i a r energy balance/Bowen r a t i o equation LE = (R - G ) / ( l + B) ( 2 ) n where B i s the Bowen r a t i o (B = yAT/Ae), y i s the psychrometric constant, AT and Ae are r e s p e c t i v e l y the dry bulb temperature difference and the vapour pressure di f f e r e n c e between two heights. With the second assumption (1) becomes LE - R - G ( 3 ) n ' ~ The formal transport equation f o r water vapour expressed i n f i n i t e form i s LE = (pc /y)K vAe/Az (4) _ 42 _ where K v i s the eddy d i f f u s i v i t y f o r water vapour,. Ae/Az i s the vapour pressure gradient, p i s the density of a i r , and c i s the s p e c i f i c heat of a i r . A more p r a c t i c a l form P of equation (4) i s the simple aerodynamic expression: LE = CUAe (5) where, U i s the wind speed measured at a singl e height, Ae i s the vapour pressure d i f f e r e n c e between two heights, and C i s a constant which i s a function of the s i t e geometry (Tanner, 1967). The f i r s t objective of t h i s study was to determine the v a l i d i t y of the above assumptions by use of a small, weighing lvsimeter. The second objective was to assess the usefulness of the aerodynamic method i n estimating evaporation under the canopy. Experimental Site and Measurements The study was c a r r i e d out i n the summers of 1970 and 1971 at the U n i v e r s i t y of B r i t i s h Columbia Research Forest, 4 8 km east of Vancouver. The average summer p r e c i p i t a t i o n i s 25.4 cm which i s 11% of the annual p r e c i p i t a t i o n ( G r i f f i t h , 1963). The s i t e was an 11-year old Douglas f i r p l a n t a t i o n with a 2 m x 2 m tree spacing. The trees were 8.2 m h i g h ; the .canopy was closed and had a well defined base 2.5 m above the forest f l o o r . There was no understory vegetation. The topography was f l a t to gently r o l l i n g . - 4 3 -S u n f l e c k i n g o f the f l o o r was r e l a t i v e l y u n i f o r m . The f o r e s t f l o o r was a 1.5 cm t h i c k , l i t t e r l a y e r w i t h an - 3 average b u l k d e n s i t y o f 0.036 gm cm . The m i n e r a l s o i l beneath the f o r e s t f l o o r was Cap i l ano g r a v e l l y sandy loam c o n t a i n i n g 14% o r g a n i c n a t t e r by weight i n the top 7 cm. Net r a d i a t i o n was measured c o n t i n u o u s l y w i t h a Swi s s t eco l i n e a r net r ad iome te r 1 m long to o b t a i n s p a t i a l l y and t e m p o r a l l y i n t e g r a t e d v a l u e . Four s o i l heat f l u x p l a t e s connected i n s e r i e s were l o c a t e d d i a g o n a l l y ac ross one t r e e i n t e r s p a c e a t 5 cm below the f o r e s t f l o o r s u r f a c e . S o i l heat f l u x i n the top 5 cm was determined by c a l o r i m e t r y ; the temperature was measured w i t h 2 i n t e g r a t i n g d iode- thermometers . The heat c a p a c i t y was c a l c u l a t e d from tw ice d a i l y measurements o f s o i l water con ten t i n the 0-5 cm dep th . S o i l heat f l u x and temperatures were sampled twice h o u r l y . In 1971 the net r ad iome te r and the heat f l u x p l a t e s were i n s t a l l e d 2 meters away from the 1970 l o c a t i o n . E v a p o r a t i o n was measured w i t h a s imple w e i g h i n g l y s i m e t e r c o n s i s t i n g of", a 7.5 cm deep by 14.6 cm diameter, i n s u l a t e d , a c r y l i c c y l i n d e r c o n t a i n i n g a s o i l c o r e . A core .was c a r e f u l l y cut each morning between 0500 and 0700 h r s . The l y s i m e t e r was p l a c e d i n a ho l e w i t h the c o r e ' s su r face f l u s h w i t h the f o r e s t f l o o r . Weights were r ecorded every _ 44 -4 hours with a r e s o l u t i o n equivalent to a 0.00G mm depth of water. The sunflecking pattern on the lysimeter surface was not noticeably d i f f e r e n t from that on the adjacent f l o o r . The lysimeter was made deep enough to prevent water shortage within the core and consequent underestimates of evaporation. Moisture sampling of the s o i l . c o r e at the end of 24 hours showed moisture p r o f i l e s v i r t u a l l y the same as those of the adjacent s o i l . The wind v e l o c i t y was measured at 20 and 110 cm above the forest f l o o r with Thornthwaite, sensitive, cup anemometers. V.'et and dry bulb gradients between 20 and 110 cm above the for e s t f l o o r were measured with shielded, aspirated, 26-gauge thermocouples, mounted on a r o t a t i n g apparatus which interchanged top and bottom sensors every 15 minutes (Sargeant and Tanner, 1967). V/et and dry bulb di f f e r e n c e measurements had an accuracy of 0.01 C. Both dry and wet bulb gradients were c o n t i n u a l l y recorded. Further measurements of ho r i z o n t a l and v e r t i c a l temperature gradients, and temperature f l u c t u a t i o n s under the canopy were made with fine wire, unaspirated thermocouples. The thermocouple junctions were made by butt welding 0.001-diameter copper and cons f a n f a n wires- and were painted with high r e f l e c t a n c e paint^'. The a i r temperature f l u c t u a t i o n s 2 Suggested by-G..W. • T h u r t e l l i n a personnal communication. - 4 5 -were measured with the f i n e wire thermocouples of which one junction sensed the actual a i r temperature and the-other the temperature of a shielded brass block. : The block had a thermal time constant of 2 minutes and contained a diode thermometer. Thermocouple signals v 7 e r e recorded on a s t r i p chart recorder. Results and Discussion The t y p i c a l dry weather conditions of south western B r i t i s h Columbia prevailed during the measurement periods. Only 2.5% of the d a i l y shortwave r a d i a t i o n above the canopy reached the f o r e s t f l o o r . The d a i l y net r a d i a t i o n at the f l o o r was 5% of i t s counterpart above the canopy. The volumetric s o i l moisture content of the top 5 cm ranged from 0.28 to 0.18 cm3', era"3 i n 1970. and from 0.08 to 0.06 cm3 -_ 3 cm . i n 1971. Energy balance. F i g . 1 presents the d i u r n a l trends of the energy balance components f o r 2 c l e a r days. The sensible heat was calculated as the r e s i d u a l i n equation (1). The large f l u c t u a t i o n s i n H are the r e s u l t of the combined errors i n measuring R , G and LE. The upper and lower parts of the figure compare the evaporation rates under the same net r a d i a t i o n f l u x but d i f f e r e n t s o i l moisture conditions. It shows that under d r i e r s o i l conditions the energy not used to evaporate water was - ns -Figure 1. Measured and calculated energy balance components for a wet (1 August, 1970) and a dry (9 August, 1971) day. - 47 -conducted i n t o the s o i l . The s o i l heat f l u x changed from 3 c a l c m - 2 d a y - 1 i n 1970 to 13 c a l c m - 2 d a y - 1 i n 1971. A i r temperatures under the canopy were on the average 5°C h i g h e r i n 1971 than i n 1970. The l a g i n the e v a p o r a t i o n measured by the l y s i m e t e r i s a t t r i b u t a b l e to the s l i g h t l y d i f f e r e n t thermal regime between i t and the und i s tu rbed s o i l (B lack et al. , 1968) . The r e s u l t s o f F i g . 1 were reproduced on s e v e r a l occas ions w i t h d i f f e r e n t s o i l cores i n the l y s i m e t e r . Temperature and vapour p ressure d i f f e r e n c e s between 20 and 110 cm are shown i n F i g . 2. Temperature i n v e r s i o n s d u r i n g the p e r i o d s o f s tudy occu r red d u r i n g both the dayt ime and n i g h t t i m e . The l a r g e p o s i t i v e daytime temperature g r a d i e n t s suggest c o n d i t i o n s o f s t r o n g s t a b i l i t y . The s m a l l i n p u t o f s e n s i b l e heat from the canopy to the f o r e s t f l o o r i n d i c a t e d i n F i g . 1 i s t h e r e f o r e expec ted . T h i s lends suppor t t o the assumption o f n e g l i g i b l e s e n s i b l e heat f l u x to the f o r e s t f l o o r as expressed i n equa t ion ( 3 ) . The nega t i ve vapour p ressure g r a d i e n t s show tha t e v a p o r a t i o n o c c u r r e d at a l l t i m e s . A l though n i g h t t i m e condensa t ion d i d not occu r under the canopy i t was observed w i t h i n the canopy. Bowen ratio and similarity. H a l f h o u r l y Bowen r a t i o s used i n equa t ion (2) were c a l c u l a t e d from the da ta shown i n F i g . 2 . In Table 1, e v a p o r a t i o n r a t e s c a l c u l a t e d from equat ions (2) and (3) are compared w i t h those measured by the l y s i m e t e r . - 48 -i i ' i • i 1 1 1 i r -16 -• 1 1 • 1 • 1 i ; i i > • 0 4 6 12 16 20 24 HOURS POT Figure 2. Temperature and vapour pressure differences between 20 and 110 cm above the forest f l o o r . - 49 -TABLE 1. V o l u m e t r i c water content cm cm and e v a p o r a t i o n r a t e s f o r the f o r e s t f l o o r (mm day ^ ) . Energy balance V o l u m e t r i c e s t i m a t e s Date water content L y s i m e t e r Eq. (2) Eq.. (3) 1 August 1970 0.28 0.31 0.48 0.25 10 August 1970 0.18 0.26 0.43 0.21 9 August 1971 0.08 0.14 0.25 0.12. 10 August 1971 0.07 0 . l l -- 0.10 11 August 1971 0.07 0.14 - - 0. H - 50 -E q u a t i o n (3) s l i g h t l y underes t imates the e v a p o r a t i o n r a t e whereas equa t ion (2) ove res t ima tes by a f a c t o r o f 1.5 to 2 . 5 . These r e s u l t s s t r o n g l y suggest t h a t the s i m i l a r i t y assumption (K = K, ) does not apply beneath - v n ~ the canopy. Eddy d i f f u s i v i t i e s f o r water vapour C^v) es t ima ted from the l y s i m e t e r e v a p o r a t i o n r a t e s and the vapour p re s su re g r a d i e n t s f o r the a f te rnoon hours ranged 2 - 1 2 from 30 to 60 cm sec i n 1970, and from 18 to 50 cm sec 1 i n 1971. From the c a l c u l a t e d s e n s i b l e heat f l u x e s of. F i g . 1 and the temperature g rad ien t s , e s t imates o f a f t e rnoon va lue s o f the eddy d i f f u s i v i t y f o r s e n s i b l e heat 2 -1 (K, ) v a r i e d between 5 and 5 0 cm sec . S ince rl was n u s u a l l y ve ry s m a l l , and had h i g h percentages Of e r r o r , these"va lues o f 'cannot be cons idered h i g h l y r e l i a b l e . C a l c u l a t i o n s i n d i c a t e d t h a t a d v e c t i o n was n e g l i g i b l y s m a l l compared to the v e r t i c a l energy f l u x e s used i n equa t ions (2) and ( 3 ) . The p o s s i b i l i t y o f the a s p i r a t e d thermocouple sensors d i s t u r b i n g the temperature and the vapour p r e s su re s t r u c t u r e under the canopy was i n v e s t i g a t e d . Temperature d i f f e r e n c e s measured by the unaspir-ated, f i n e w i r e thermocouples were i n good agreement w i t h the temperature d i f f e r e n c e s measured by the a s p i r a t e d thermocouple ( F i g . 3 ) . T h i s i n d i c a t e s t ha t the a s p i r a t e d thermocouple p r o v i d e d a good es t ima te o f AT under the - 51 -o.e to 0.7 z o t-o o z 0.6 r> III ~ 3 o U EN _ l 0. 0.5 tr o UJ o u. o u. o o s cc 0.4 Ul rr => THE AT o 0.3 cc UJ UJ 1-CL < EM PIR 0.2 »-UNAS 0.1 1 1 1 U.B.C RESEARCH FOREST T 1 1 1 0 HANEY, B.C. o • DOUGLAS FIR 2M * 2M SPACING 6 2 M HIGH o PLANTED 1959 o / o Y o / o o / ° ^ 1=1 LINE 0 / o /o o 0 o 0 / 0 / 0 o 12 AUGUST 1971 (1038 - 1144 ) • / ° -1 I 1 1 _ i I i i I.I 0.2 0.3 0.4 0.5 0.6 0.7 TEMPERATURE DIFFERENCE (C) (ASPIRATED THERMOCOUPLE JUNCTIONS) Figure 3 . Mean temperature differences f o r periods of 2 min between 2 0 and 1 1 0 cm above the fo r e s t f l o o r measured with aspirated and unaspirated thermocouples. - 52 -canopy. However, large r e l a t i v e errors occur i n the c a l c u l a t i o n of LE from (2) (Fuchs and Tanner, 1970). During the afternoon the Bowen ratios, which ranged from -0.6 to -0.9,could possibly have been i n error by 17 to 4 5%. The r e l a t i v e error of the Bowen r a t i o estimate increases as i t s values approach -1.0. The inaccuracy of the Bowen r a t i o method causes a maximum error of about 30 to 59% i n estimating afternoon values of LE,assuming that R and G are accurate to 5%. n Aerodynamic Method. Values of C i n equation (5) were calcula t e d from the lysimeter evaporation rate and the vapour pressure d i f f e r e n c e between 20 and 110 cm above the forest f l o o r . Considerable v a r i a b i l i t y i n C were found which indicated that the transport process was not a simple function of U and Ae. In order that equation (5) be used, C must be established to be only a function of s i t e geometry i . e . independent of wind speed. In other 'words, for C to be a constant, the eddy d i f f u s i v i t y f o r water vapour K y must be a l i n e a r function of U. In F i g . 4 the eddy d i f f u s i v i t i e s f o r water vapour C^ v) ca l c u l a t e d from the lysimeter evaporation rates and the vapour pressure gradients are plotted against the wind v e l o c i t y measured at 110 cm above the surface. No simple r e l a t i o n s h i p e x i s t s between the two v a r i a b l e s , therefore the simple aerodynamic method appears to be u n r e l i a b l e i n estimating LE from the forest f l o o r . - 53 -60 U.B.C. RESEARCH FOREST HANEY, B.C. DOUGLAS FIR 211 I 2M SPACING 8.2 M HIGH PLANTED 1959 O o 50 e u O 4 0 < >-o o o I G o e 9 AUGUST 1971 HOURS O 0 - 4 4 - 8 8 - 1 2 12 - 16 16 - 2 0 2 0 - 2 3 • x 30 o > 20 10 0 20 40 60 80 100 120 MO 160 EDDY DIFFUSIVITY FOR WATER VAPOUR (cm* sec" 1 ) ure 4 . H a l f h o u r l y v a l u e s o f eddy d i f f u s i v i t y f o r water vapour versus mean wind speed a t 110 cm above the f o r e s t f l o o r . - 54. -Turbulence under the Canopy. In o r d e r to d e s c r i b e the degree o f s t a b i l i t y under the canopy, R i c h a r d s o n numbers were c a l c u l a t e d . A f t e r n o o n v a l u e s ranged from 0.02 t o 5, w h i l e a t n i g h t , a l t h o u g h the wind speed g r a d i e n t s were d i f f i c u l t t o measure, Richardson numbers were e s t i m a t e d to range from 1 to 20. Smoke s t u d i e s i n d i c a t e d t h a t some t u r b u l e n t mixing o c c u r r e d under the canopy. R i c h a r d s o n numbers r a n g i n g from 0.1 t o 0.5 under corn 2.2 m h i g h were r e p o r t e d by D r u i l h e t et al. (1971). From l a b o r a t o r y and f i e l d s t u d i e s i t has been found t h a t t u r b u l e n c e s t a r t s t o decay a t approximately R i = 0.10 (Oke, 1970). The complete decay o f t u r b u l e n c e mixing t h e o r e t i c a l l y o c c u r s between R i = 0.2 and Ri = 0.3 (Uebb , 1965; Oke, 1970). I t was r e p o r t e d by Oke (1970) t h a t a l t h o u g h complete c e s s a t i o n of t u r b u l e n c e does not o c c u r , v e r t i c a l t r a n s p o r t remains n e g l i g i b l y s m a l l at R i = 0.3. The magnitudes o f the R i c h a r d s o n numbers i n these s t u d i e s were f o r s t a b l e c o n d i t i o n s - e x t e n d i n g high.above the s u r f a c e as compared w i t h the s i z e of the a s p e r i t i e s . Under these c o n d i t i o n s the t u r b u l e n c e can be due t o such p r o c e s s e s as g r a v i t y waves o r k a t a b a t i c d r i f t ( V / i i n - N i e l s e n , 1965). Our study d e a l s w i t h an e n t i r e l y d i f f e r e n t s i t u a t i o n i n which the atmosphere above the f o r e s t i s t u r b u l e n t d u r i n g most of the day. - 55 -• Eddies of turbulent motion are caused by the e f f e c t s of e i t h e r thermal buoyancy or mean wind shear, or both. In order to f i n d out i f turbulent motion resulted from the r i s i n g of a i r c e l l s warmed by sunflecks on the f o r e s t f l o o r , temperature differences between sunflecks and shaded areas v;ere measured near the surface with fi n e wire thermocouples. The sunflecks ranged from 10 to 30 cm i n diameter. One thermocouple junction was kept within the center t h i r d of a p a r t i c u l a r sunfleck while the other thermocouple junction (50 cm away) was kept i n shade. At 0.5 cm above the l i t t e r surface the average h o r i z o n t a l temperature differences were les s than 0.5 C f o r any one minute period. Differences of 1 C f o r shorter time i n t e r v a l s were recorded. At 2 cm above the surface the temperature differences were smaller than 0.2 C while the 15 minute average temperature differences were less than 0.05 C. It would appear that because the sunflecks moved r a p i d l y across the surf ace, there "was-not enough •• time f o r l o c a l heating of the a i r near the f o r e s t f l o o r . I t i s concluded that the e f f e c t of buoyancy near the f o r e s t f l o o r was not the f a c t o r causing turbulent motion under the canopy. In view of the observed turbulence under the canopy shown by the smoke releases, other-mechanisms"of turbulent transfer must be considered. I t has been suggested that the mixing - 56 -under the canopy i s primarily caused by the turbulent a i r currents above the forest (Denmead, 1964; Valendik, (1964). Analyses of turbulence spectra by A l l e n (1968) show that turbulence under the canopy i s associated with large scale eddies. He also reported that the period between large gusts was about 21 seconds for wind speeds of 100 cm sec""1 under a lar c h canopy. I f turbulent transport within and beneath the canopy i s due to penetration of wind gusts from above the canopy, then two r e s u l t i n g e f f e c t s can be hypothesized. F i r s t , i f these gusts transport warm a i r from the canopy to the forest f l o o r , t h e r e should be a p o s i t i v e c o r r e l a t i o n between wind speed and a i r temperature. Second, i f an increase i n wind speed below the canopy r e s u l t s i n increased turbulence and consequently, decreased v e r t i c a l temperature gradients, then there should be a negative c o r r e l a t i o n between wind speed and temperature gradient. Horizontal wind speed, a i r temperature, and v e r t i c a l temperature gradients beneath the canopy were measured on several c l e a r days i n order to te s t these two hypotheses. The means, standard deviations, s, and c o r r e l a t i o n c o e f f i c i e n t s , r , f o r an afternoon period are shown i n Table 2. In two of the s i x periods a s i g n i f i c a n t c o r r e l a t i o n between the wind speed and the a i r temperature indicates that wind gusts transported - 57 -TABLE 2. Analysis of temperature and wind speed data under the canopy using 30 sec mean values over s i x 26-min periods on 10 August 1971. The bar denotes the 26-min time average. Periods 1336 -1400 1418 -1442 1442 -1506 1518 -1542 1542 -1606 1946 -2010 U (cm sec""'") 38.9 40.9 43.3 40 . 5 36.2 32 . 6 10.6 13.1 13.3 12.5 11.6 11. 8 T (C) 27. 23 27.89 28.15 28.48 28 .16 28. 31 0. 35 0.57 0.65 0 . 59 0.47 0.68 AT (C m""1) 0.60 ' 0.68 0.60 0 . 81 0.65 0 . 89 S A T 0.25 0 . 39 0. 32 0.42 0 .25 0 . 36 r u , AT 0. 33* -0 . 20 0.04 0.16 -0 . 3 8* 0.25 r u , T 0. 33* 0.03 -0 .18 0.21 0.06 0 . 38--* S i g n i f i c a n t at 95% l e v e l some s e n s i b l e h e a t from th e canopy t o t h e f o r e s t f l o o r . The c o r r e l a t i o n c o e f f i c i e n t s between wind speed and t e m p e r a t u r e g r a d i e n t s do n o t show any s y s t e m a t i c t r e n d . I n o r d e r t o f u l l y d e s c r i b e t u r b u l e n t t r a n s p o r t under t h e c a n o p y , t h e o r i g i n , f r e q u e n c y , and s i z e o f t u r b u l e n t e d d i e s must be known. Evaporation and Soil Moisture. E v a p o r a t i o n from s o i l i s l i m i t e d e i t h e r by t h e energy a v a i l a b l e a t t h e s o i l s u r f a c e o r by t h e c a p i l l a r y f l o w o f w a t e r t o the s u r f a c e , T o d e t e r m i n e w h i c h -of t h e s e l i m i t e d e v a p o r a t i o n from- t h e f o r e s t f l o o r , t h e l y s i m e t e r e v a p o r a t i o n r a t e s f o r sunny days were p l o t t e d a g a i n s t t h e v o l u m e t r i c w a t e r c o n t e n t o f t h e t o p 5 cm o f s o i l ( F i g . 5 ) . These r e s u l t s s u g g e s t t h a t d u r i n g e x t e n s i v e d r y i n g p e r i o d s i n s o u t h w e s t e r n 3 r i t i s h C o l u m b i a , t h e r e a r e s e v e r a l days d u r i n g w h i c h t h e s o i l w a t e r l i m i t s e v a p o r a t i o n even though o n l y 5% o f t h e n e t r a d i a t i o n r e a c h e s t h e f o r e s t f l o o r . C o n c l u s i o n s The e n e rgy b a l a n c e o f t h e f o r e s t f l o o r d i f f e r e d c o n s i d e r a b l y between wet and d r y s o i l c o n d i t i o n s . The r e d u c t i o n o f s o i l m o i s t u r e c o n t e n t r e s u l t e d i n a d e c r e a s e i n t h e e v a p o r a t i o n r a t e and an i n c r e a s e i n t h e s o i l h e a t f l u x . A s i m p l e h o u r l y e s t i m a t e o f e v a p o r a t i o n i s g i v e n by (R - G). The s t r o n g t e m p e r a t u r e i n v e r s i o n s p r e v a i l i n g u nder th e canopy appeared - 59. -0.3 fc 0.2 • < or o o. < > 0.1 -or ui >-_i 1 1 1 U.B.C RESEARCH FOREST HANEY, B.C. DOUGLAS FIR 2M x 2M SPACING 8.2 M HIGH PLANTED 1959 0 o 1970 • 1971 NET RADIATION AT THE FOREST FLOOR • 0.3 mm d o y " 1 (WATER EQUIVALENT) 0 0.1 0.2 VOLUMETRIC WATER CONTENT (cm-3 cm"3) 0.3 Figure 5. Daily lysimeter evaporation rate versus volumetric water content of s o i l between 0 and 5 cm. - 60 -to l i m i t the downward movement of sensible heat. A bett e r estimate of evaporation v/ould be given by (R - G - H). thi s would necessitate the d i r e c t measurement of the sensible heat. A better understanding of turbulent transport under the canopy requires high r e s o l u t i o n measurements of the three dimensional turbulence spectra. At volumetric water contents of the s o i l surface (0-5 cm) smaller than about" 3 - 3 0.35 cm cm i t would appear that the evaporation rate from the forest f l o o r surface was li m i t e d by the a b i l i t y of the s o i l t.o conduct water to the surface. L i t e r a t u r e Cited BAUMGARTNER, A. 1956. Investigations of the heat- and water-economy of a young f o r e s t . Translation No. 3760. Melbourne (1953). BLACK, T.A., G. W. THURTELL and C.B. TANNER. 1968. Hydraulic l o a d - c e l l lysimeter, construction, c a l i b r a t i o n and t e s t s . S o i l S c i . Soc. Am. Proc. 32(5): 623-629. BLACK, T.A., C.B. TANNER and W.R. GARDNER. 1970. Evapotranspiration from a snap bean crop. Agron. J . 62: 66-69. DENMEAD, O.T. 196U. Evaporation sources and apparent d i f f u s i v i t i e s i n a f o r e s t canopy. J . of Appl. Meteorol. 3: 383-389. - 61 -DRUILHET, A., A. PERRIER, J. FONTAN and J.L. LAURENT. 1971. Analysis of turbulent transfers i n vegetation: use of thoron for measuring the d i f f u s i v i t y p r o f i l e s . Boundary-Layer Meteorology 2: 17 3-187. FRITSCHEN, L.J. 1966. Evapotranspiration rates of f i e l d crops determined by the Bowen r a t i o method. Agron. J. 58: 339-342. GRIFFITH, B.G. 1968. Phenology, growth, and flower and cone production of 154 Douglas f i r trees on the University Forest as influenced by climate and f e r t i l i z e r , 1957-1967. U.B.C. Faculty of Forestry, B u l l . No. 6, 7 0 pp. HELVEY, J.D. and J.H. PATRIC. 1965. Canopy and l i t t e r i n t erception of r a i n f a l l by hardwoods of eastern United States. Water Resources Res. 1: 193-206. HELVEY, J.D. 1964. R a i n f a l l interception by hardwood forest l i t t e r i n the southern Appalachian. U.S. Forest Serv. Res. Paper SE-8. MADER, D.L. and LULL, H.W. 196 8. Depth, weight, and water storage of the forest f l o o r i n white pine stands i n Massachusetts. U.S.D.A. For. Serv. Res. Paper NE-109. OKE, T.R. 19 70. Turbulent transport near the ground i n stable conditions. J. Appl. Meteorol. 9: 778-786. - 6 2 RUTTER, A.J. 1966. Studies on the water r e l a t i o n s of Pinus sylvestvis i n plantation conditions. IV. Direct observations on the rates of t r a n s p i r a t i o n , evaporation of intercepted water, and evaporation from the s o i l surface. J . Appl. Ecol. 3: 393-405. SARGEANT, D.H. and C.B. TANNER. 1957. A simple apparatus f o r Bowen r a t i o determinations. J. Appl. Meteorol. 6: 414-413. SEMAGO, W.T. and A.J. NASH. 1962. Interception of p r e c i p i t a t i o n by a hardwood forest f l o o r i n the Missouri Ozarks. Univ. Missouri Agr. Expt. Sta. Res. B u l l . 796. TANNER, C.B. 196 7. Measurement of evapotranspiration. In R.M. Hagan (ed.) I r r i g a t i o n of A g r i c u l t u r a l Lands. Agronomy 11: 534-555. TURNER, J.A. 1966. The stored moisture index/A guide to slash burning. B.C. Forest Service, Protection D i v i s i o n , V i c t o r i a , B.C. VALENDIK, E.N. 1964. The penetration and transformation of wind i n pine f o r e s t s . Can. Dept. For. Translation 71F. WEBB, E.K. 1965. A e r i a l microclimate. Meteorol. Monographs 6: 27-53. WIIN-NIELSEN, A. 1965. On the propagation of gravity waves i n a hydrostatic compressible f l u i d with v e r t i c a l wind shear. T e l l u s 17: 306-320. - 63 -THE ROLE OF HYDROLOGIC PROPERTIES OF THE FOREST FLOOR IN WATERSHED HYDROLOGY1 Abstract. The r o l e of the forest f l o o r i n watershed hydrology was investigated by measuring the components of i t s water balance on a 30° slope and by determining i t s water retention and hydraulic conductivity c h a r a c t e r i s t i c s i n the laboratory. The hydraulic conductivity varied by about four orders of magnitude over a range of matric potentials between -0.003 and -0.08 bars. When the forest f l o o r had reached i t s maximum water content during r a i n f a l l , the drainage This chapter was presented as a paper at the National Symposium on Watersheds in Transition sponsored by the American Water Resources Association and Colorado State University at Fort C o l l i n s , Colorado, on June 19-21, 1972 . - 6»* -rate through the matrix accounted f o r approximately 0.5% of the r a i n f a l l r a t e . The amount of water absorbed during r a i n f a l l was l a r g e l y a function of the i n i t i a l water content and hydraulic conductivity of the f o r e s t f l o o r . I t appears that the forest f l o o r contributes to delayed stormflow, stores a s i g n i f i c a n t amount of av a i l a b l e water f o r plants, does not s i g n i f i c a n t l y contribute to base flow or a f f e c t steamflow peaks. Introduction The f o r e s t f l o o r plays a major r o l e i n the hydrology of sloping forest lands. One of i t s more important functions i s to s h i e l d the mineral s o i l from raindrop impacts which dislodge s o i l p a r t i c l e s to cause the clogging of s o i l pores and reduction of water i n f i l t r a t i o n into the mineral s o i l . It also r e t a i n s considerable water and detains water when the r a i n f a l l i n t e n s i t y exceeds the i n f i l t r a t i o n capacity of the mineral s o i l . These two aspects of the r o l e of the fo r e s t f l o o r are b e n e f i c i a l to the well regulated y i e l d of high q u a l i t y water. They are p a r t i c u l a r l y important i n the West Coast fo r e s t s of B r i t i s h Columbia where the fo r e s t f l o o r may - 65 -be many centimeters t h i c k , where f a l l and winter rains are prolonged, and summers are dry. Q u a l i t a t i v e l y the r o l e of the forest f l o o r was recognized as early as 1930 (Lowdermilk, 1930) but quanti t a t i v e information on forest f l o o r s such as those of the Canadian West Coast i s s t i l l l a c k i n g , as i s knowledge of the water conducting c h a r a c t e r i s t i c s of these organic p r o f i l e s . T y p i c a l forest f l o o r s on the West Coast are on sloping, rather than on f l a t , land. This adds complexity to t h e i r hydrologic r o l e . The purpose of the research reported i n t h i s paper was to elucidate the hydrologic r o l e of the fo r e s t f l o o r by a laboratory study of i t s water retention and conductivity properties and a f i e l d study of i t s water balance under conditions of sloping land and natural cycles of wetting and drying. Theory The flow of water through an i s o t r o p i c porous medium can be c a l c u l a t e d by the three-dimensional form of the Darcy equation: -*• Q = -kViJ. (1) -*• where Q i s the volume flow of water per unit c r o s s - s e c t i o n a l - 6 6 -are per unit time; k i s the hydraulic conductivity, which i s a function of s o i l water content; and 7^ i s the p o t e n t i a l gradient vector. In s o i l s with n e g l i g i b l e osmotic D o t e n t i a l , the p o t e n t i a l i s given by i|» = ip + 4< , ^ g m where 4» i s the g r a v i t a t i o n a l p o t e n t i a l and u> i s the g " m . matric p o t e n t i a l . In ani s o t r o p i c s o i l s , k must be considered a tensor rather than a s c a l a r as i n (1) (Liakopoulos, 1965; Zaslavski and Rogowski, 1969). The coordinate system used i n the following discussion i s shown i n F i g . 1. I f cross-slope flow (along the y'. axis) i s n e g l i g i b l e , the flow of water i n sloping s o i l can be considered to be two-dimensional ( F i g . 1). Further-more, assuming that the p r i n c i p a l axes ( d i r e c t i o n s i n which the flow and the p o t e n t i a l gradient coincide, Childs , 1969) are p a r a l l e l to the x' and z' axes, (1) can be rewritten as: - * • - » - -*-Q = -(k ,34//8x'i + k ,3ip/3z' k) (2) where k , and k r are the hydraulic c o n d u c t i v i t i e s f o r the x 1 and z' d i r e c t i o n s r e s p e c t i v e l y and are d i f f e r e n t i n a n i s o t r o p i c s o i l s , 3^/3x' and 34>/Sz' are the hydraulic gradients i n the x' and z' d i r e c t i o n s r e s p e c t i v e l y , and -»• -*• i and k are the unit vectors i n the x f and z' d i r e c t i o n s r e s p e c t i v e l y . With the further assumption that there are n e g l i g i b l e matric gradients i n the x' d i r e c t i o n , 3i|» /3x'-0 and Q . = k . s i n a, where Q . i s the flow rm x' x' xx' - 67 -Figure 1. Cross-section of s o i l on land with slope angle a, showing two-dimensional coordinate system and flow vectors. - 68 -component i n the x ' d i r e c t i o n and a i s the s lope a n g l e . I f k , i s assumed c o n s t a n t , then 9Q , / 3 x ' = 0; t h a t i s , t he re i s no d ivergence o f f low i n the x ' d i r e c t i o n and the f low o f water through the su r face A i s equa l to t h a t through B i n F i g . 1. From ( 2 ) , the f low o f water through the f o r e s t f l o o r m a t r i x to the m i n e r a l s o i l i s g i v e n by: Q . = -k . 34»/9z' (3) z z where k , and 3<|'/9z' are eva lua t ed f o r the f o r e s t f l o o r m a t r i x adjacent to the i n t e r f a c e between the f o r e s t f l o o r and the m i n e r a l s o i l . The water ba lance f o r a p e r i o d o f t ime o f a volume element o f a s l o p i n g f o r e s t f l o o r c o n t a i n i n g r o o t s and i n which t he r e i s no d ive rgence o f f low i n e i t h e r the y ' o r x ' d i r e c t i o n s i s : P r E + T + A W + R + D + M ( 4 ) where P i s the p r e c i p i t a t i o n ; E i s the e v a p o r a t i o n from the f o r e s t f l o o r : T i s the t r a n s p i r a t i o n (removal o f water by r o o t s ) ; AW i s the change o f s t o r e d water (AW = W - W . where W and W are the i n i t i a l and f i n a l water c o n t e n t s , o ' r e s p e c t i v e l y ) ; R i s the su r face r u n o f f ; D i s the dra inage from the f o r e s t f l o o r m a t r i x normal to the f o r e s t f l o o r su r f ace and i s c a l c u l a t e d from ( 3 ) ; (D = Q , ) ; and M i s "2* the s a t u r a t e d f low through o n l y macropores . (The term macropore i s used here to i n c l u d e a l a r g e p o r e , c a v i t y , passageway, c h a n n e l , t u n n e l , o r v o i d i n the s o i l , th rough - 69 -which water- usually drains by gr a v i t y , Aubertin, 19 71). Since turbulent flow through macropores has been observed (Whipkey, 1969), the Darcy equation cannot be used to c a l c u l a t e the t o t a l flow through the f o r e s t f l o o r ( C h i l d s , 1969). Experimental Site and Methods The experimental s i t e was located at an a l t i t u d e of 460 m i n the Seymour Watershed 32 km north of Vancouver, B.C. within the wetter subzone of the coastal western hemlock biogeoclimatic zone (Krajina, 1965). The over-story vegetation i n the v i c i n i t y of the s i t e was old growth western hemlock (Tsuga hetevophylla (Raf.) Sarg.) and western red cedar (Thuja plioata Conn) 59 meters t a l l . A non-uniform canopy caused large s p a t i a l v a r i a t i o n of p r e c i p i t a t i o n and s o l a r r a d i a t i o n on the f o r e s t f l o o r . The understory was mainly Vaacinium spp. The f o r e s t f l o o r at the s i t e was 17 cm t h i c k , with 1 cm of r e l a t i v e l y undecomposed l i t t e r i n which o r i g i n a l structures were e a s i l y d i s c e r n i b l e (L horizon); 7 cm of p a r t l y decomposed organic matter i n which o r i g i n a l structures were s t i l l d i s c e r n i b l e (F horizon); and 9 cm of highly decomposed organic matter (H horizon). A nearby p r o f i l e and the bulk density of each horizon are shown i n F i g . 2. There were no sharp t r a n s i t i o n s i n - 70 -FOREST FLOOR PROFILE LAYER DEPTH BULK DENSITY F i g u r e 2. T y p i c a l forest f l o o r p r o f i l e i n Seymour Watershed study area showing the bulk d e n s i t i e s of the L, F, and H horizons. - 71 -the degree of decomposition between the three organic horizons. In the. v i c i n i t y of the s i t e , bulk d e n s i t i e s were s i m i l a r among: for-'e^f f l o o r s ranging from 10 to 50 cm i n thickness.- Beneath the for e s t f l o o r was an eluviated mineral;, horizon (Ae). 3 to 5 cm thick containing many d i s c o n t i n u i t i e s - caused by roots, stones , or organic matter. The s o i l : p r o f i l e developed. on compacted g l a c i a l t i l l . Tree roots were prevalent i n the f o r e s t " f l o o r . The water.retention' c h a r a c t e r i s t i c s of the f o r e s t f l o o r were determined '.in- the laboratory. For matric p o t e n t i a l s ranging from 0 to -325 cm of water, a f r i t t e d glass funnel^connected to a hanging water column was used. Standard pressure -membrane apparatus was used to determine volumetric water content at matric p o t e n t i a l s of -1, -4 , and -14 bars. To ensure a good;'rcr>n".tact-between the f o r e s t f l o o r material and the porous plate or membrane, the samples were pressed against a s l u r r y of ground organic matter (Boelter, 1964). The samples were saturated p r i o r to draining. Hydraulic conductivity, f o r matric p o t e n t i a l s ranging from 0 to -100 cm of water was determined by a steady-state method s i m i l a r i n p r i n c i p l e to the one used by Richards (1931). Richards mounted the s o i l sample v e r t i c a l l y between two porous plates. A d i f f e r e n t i a l - 72 -manometer measured the p o t e n t i a l gradient between porous cups positioned i n the sample. A vacuum b o t t l e connected to the top and bottom plates c o n t r o l l e d the water content of the s o i l column. Gravity and the hydrostatic pressure of a water column extending above the upper plate caused water movement through the sample. The inflow and outflov; of water, the matric p o t e n t i a l , and the p o t e n t i a l gradient were measured. S a t i s f a c t o r y contact can be ensured between the highly decomposed H horizon of the f o r e s t f l o o r and a bottom porous plate such as used by Richards, whereas good contact between the F horizon and a top porous plate i s d i f f i c u l t . Thus changes i n Richard's apparatus were necessary. A 10-cm t h i c k , f o r e s t f l o o r sample was supported by a commercial, porous alundum plate fastened to the bottom end of an 11-cm I.D., 30 cm long, p l e x i g l a s c y l i n d e r ; while no plate was used at the top end of the sample (Plamondon, 1972). A chromatography micropump applied preselected, constant water fluxes (of 9 to 110 ml hr-'*') to the top of the column. For flow rates lower than 9 ml hr ^, a cam timer regulated the duty-cycle of the pump. A 10-cm thick layer of coarse sand ( 0 . 2 5 - 0 . 5 mm) added on top of the sample evenly - 7 3 -d i s t r i b u t e d the applied water and also allowed a i r penetration that simulated natural conditions. Water content within the sample was adjusted by hanging a v a r i a b l e water column on the bottom pl a t e . I t was found possible to adjust the length of t h i s column so that the matric p o t e n t i a l gradient was approximately zero and thus the imposed flow l a r g e l y g r a v i t a t i o n a l . Two low impedance porous cups at 2 and 8 cm above the alundum plate and connected to water manometers measured the matric p o t e n t i a l . Evaporation from the system was minimized by i n s e r t i n g a vented rubber stopper i n the top of both the p l e x i g l a s c y l i n d e r and the burette used to c o l l e c t the outflow. The hydraulic conductivity of the Ae horizon was determined by the same technique. Several components of the hydrologic balance a f f e c t i n g the wetting and drying of the f o r e s t f l o o r were measured on the experimental s i t e from September 7 to October 26, 1971. P r e c i p i t a t i o n i n t e n s i t y was recorded under the canopy by a t i p p i n g bucket r a i n gauge. Two standard r a i n gauges were used to obtain a s p a t i a l average of the p r e c i p i t a t i o n . Water flow on the top of the humus layer was measurable during most r a i n f a l l events. A metal sheet folded at a r i g h t angle was i n s t a l l e d at a depth of 2 cm to catch t h i s runoff. One side of the angle was pushed 4 cm into the fo r e s t f l o o r to leave the other side normal to the surface and to channel the water to a b o t t l e . The evaporation was measured by a small, weighing lysimeter containing a fo r e s t f l o o r core. The a c r y l i c c y l i n d e r of the lysimeter was insulated from l a t e r a l heat f l u x by a 2.5-cm thick s h e l l of styrofoam. The core's surface was set f l u s h with the adjacent f o r e s t f l o o r . In the absence of lysimeter data, the evaporation was approximated from energy balance measurements (Plamondon and Black, 1972). In order to c a l c u l a t e the volumetric water content and the drainage from the organic layer, the water p o t e n t i a l at several depths had to be recorded. To ensure minimum disturbance of the natural water flow pat-tern.;, th.e .potential .was measured by a tensiometer system having small, water displacement. A ceramic cup, 2-cm long by 1-cm O.D., having an a i r entry valve of 800 cm of water, was buried at each of the depths of 2, 6, 9, 16, 18 and 20 cm below and normal to the f o r e s t f l o o r surface. The cups at the 18 and 20-cm depths were i n the Ae and the B horizons r e s p e c t i v e l y . The cups were located on a uniform 30° slope about 3 meters downslope - 75 -from a break i n the microtopography. This break did not permit upslope water to flow through the forest f l o o r at the s i t e . The s i x cups were connected to s i x strain-gauge, pressure transducers by brass f i t t i n g s and 0.32-cm I.D. nylon hydraulic l i n e s f i l l e d with d i s t i l l e d water. A d e t a i l e d d e s c r i p t i o n of the pressure-transducer, tensiometer system and i t s c h a r a c t e r i s t i c s has been given by Willington (1971). Wet storage b a t t e r i e s were used to power the system. These were connected to an i n v e r t e r , which powered a D.C. power supply capable of accepting a voltage between 90 and 130 v o l t s A.C. and having a time s t a b i l i t y equal to 0.03% of the output s e t t i n g . The e l e c t r i c a l signals from the pressure transducers were recorded by means of an automatic stepping switch and s t r i p chart recorder. Forest f l o o r drainage was c a l c u l a t e d by equation (3). The volumetric water content at each tensiometer l e v e l was determined from the matric p o t e n t i a l s and the water r e t e n t i o n c h a r a c t e r i s t i c s . T h e t o t a l water content, expressed i n cm of water, was obtained by summing the water content of each depth increment. The volumetric water content of the top 1 c m was r e g u l a r l y measured by gravimetric sampling. This was necessary since the water content of t h i s layer could not be measured with a tensiometer because of poor contact between i t and the highly porous l i t t e r . The volumetric water content of the r e s t of the f o r e s t f l o o r and Ae horizon was sampled g r a v i m e t r i c a l l y at i r r e g u l a r time i n t e r v a l s . Results and Discussion Water Retention Characteristics. The f o r e s t f l o o r p r o f i l e had water retention c h a r a c t e r i s t i c s that varied with depth and the corresponding degree of decomposition of the material ( F i g . 3). The porosity of the l i t t e r was l a r g e l y composed of macropores which drained at a matric p o t e n t i a l greater than -1 cm of water. At matric p o t e n t i a l s less than -9 cm of water, the lower h a l f of the H horizon retained more water than any other l a y e r . This was apparently because of the greater proportion of micropores present. A very small amount of water drained from any depth when the matric p o t e n t i a l was decreased from -1 bar to -15 bars. Within t h i s range of p o t e n t i a l most of the water was probably retained by the fibrous material or i n the highly decomposed bottom l a y e r , by decomposed fibrous substance and i n t e r s t i c e s of the c o l l o i d a l organic matter. Figure 3. Water retention c h a r a c t e r i s t i c s of the forest f l o o r at 1, 2, 6, 10 and 14-cm depths. - 78 -Hydraulic conductivity characteristics. S i n c e t h e w a t e r r e t e n t i o n p r o p e r t i e s w e r e f o u n d t o v a r y w i d e l y v / i t h t h e d e g r e e o f d e c o m p o s i t i o n o f t h e f o r e s t f l o o r , l a r g e d i f f e r e n c e s i n h y d r a u l i c c o n d u c t i v i t y b e t w e e n h o r i z o n s w e r e e x p e c t e d . C o n d u c t i v i t y a s a f u n c t i o n o f m a t r i c p o t e n t i a l w a s d e t e r m i n e d s e p a r a t e l y f o r t h e F (1-8 c m ) a n d H (8-17 c m ) h o r i z o n s ( F i g . 4 ) . A n i s o t r o p y o f t h e F h o r i z o n w a s h y p o t h e s i z e d s o t h e h y d r a u l i c c o n d u c t i v i t y c h a r a c t e r i s t i c s b o t h n o r m a l a n d p a r a l l e l t o t h e s u r f a c e o f t h i s l a y e r w e r e m e a s u r e d . S i n c e t h e H h o r i z o n w a s p r e d o m i n a n t l y m a d e u p o f h i g h l y d e -c o m p o s e d a n d c o l l o i d a l o r g a n i c m a t t e r i t w a s a s s u m e d t o b e i s o t r o p i c . T h e c o n d u c t i v i t y p a r a l l e l t o t h e s u r f a c e i n t h e F l a y e r w a s g r e a t e r t h a n t h a t p e r p e n d i c u l a r t o t h e s u r f a c e i n t h e r a n g e 0 t o -12 c m o f m a t r i c p o t e n t i a l . A t l o w e r m a t r i c p o t e n t i a l s t h e d i f f e r e n c e b e t w e e n t h e t w o c u r v e s w a s p r o b a b l y l e s s t h a n t h e v a r i a b i l i t y b e t w e e n s a m p l e s . A t h i g h m a t r i c p o t e n t i a l s t h e c o n d u c t i v i t y w a s s m a l l e r i n t h e H h o r i z o n t h a n i n t h e F h o r i z o n . I n t h i s r a n g e o f w a t e r c o n t e n t t h e s m a l l e r s i z e o f t h e p o r e s a n d t h e l o w e r p o r o s i t y o f t h e H h o r i z o n r e d u c e d i t s a b i l i t y t o c o n d u c t w a t e r . O n t h e o t h e r h a n d , a t l o w e r m a t r i c p o t e n t i a l s t h e m i c r o p o r e s o f t h e H 79 -Eigure 4. Hydraulic conductivity as a function of the matric p o t e n t i a l for the F (0 to 8-cm depth) and H (8 to 17-cm depth) horizons. The measurement errors i n hydraulic c o n d u c t i v i t i e s of 100, 1, and 0.01 cm day are approximately ± 1.0, ± 0.07, and ± 0.003 cm d a y - 1 r e s p e c t i v e l y . - 80 -h o r i z o n remained r e l a t i v e l y water f i l l e d so t ha t the c o n d u c t i v i t y was g r e a t e r than tha t o f the F h o r i z o n . The most s t r i k i n g f ea tu re o f the f o r e s t f l o o r m a t e r i a l was t h a t a t a m a t r i c p o t e n t i a l o f -3 cm o f water the average h y d r a u l i c c o n d u c t i v i t y o f the whole 2 -1 p r o f i l e was about 10 cm day , w h i l e a t a m a t r i c p o t e n t i a l o f -80 cm i t had decreased by four o rde r s o f magni tude. Very s i m i l a r c h a r a c t e r i s t i c s were r e p o r t e d f o r peat s o i l s by W i l s o n and R icha rds (1938) . They a l s o showed t h a t f o r m a t r i c p o t e n t i a l s between -4 0 and -2 0 0 cm o f water the h y d r a u l i c c o n d u c t i v i t y o f a peat s o i l was lower than t ha t o f a sandy s o i l but h i g h e r than t h a t o f a c l a y . In our s tudy the f o r e s t f l o o r had a lower c o n d u c t i v i t y than t h a t o f the e l u v i a t e d sandy h o r i z o n (Ae) a t m a t r i c p o t e n t i a l s lower than -30 cm o f w a t e r . The h y d r a u l i c c o n d u c t i v i t y o f the Ae was not measured a t h i g h e r m a t r i c p o t e n t i a l s . Water balance of the forest floor during precipitation. I f E and T are n e g l i g i b l e d u r i n g r a i n f a l l , (4) becomes: P = A W + R + D + M (5) S i n c e , P , AW and R are measurable , and D can be c a l c u l a t e d from ( 3 ) , M i s ob ta ined as the r e s i d u a l i n ( 5 ) . The changes o f water p o t e n t i a l w i t h t ime and depth d u r i n g the r a i n s t o r m o f October 12 are p resen ted i n F i g . 5 wh ich shows the depth o f w e t t i n g and the g r a d i e n t s o f - 81 -TOTAL POTENTIAL (cm of water) Figure 5. Changes of t o t a l water po t e n t i a l with time and depth for the forest f l o o r during r a i n f a l l . - 82 -the t o t a l p o t e n t i a l normal to the surface. The volumetric water contents at depths of 2, 6, 9 and 16 cm and the t o t a l water content of the 17-cm thick f o r e s t f l o o r during the above storm as derived from use of Figs. 3 and 5, are shown i n F i g . 6. Half-hourly r a i n f a l l i n t e n s i t i e s i n cm hr-"1' are also shown i n t h i s f i g u r e . Because of the considerable s p a t i a l v a r i a t i o n of r a i n f a l l i n t e n s i t y beneath the canopy, errors i n estimating r a i n f a l l above the tensiometers were expected. Differences between r a i n f a l l measured on both sides of the plot were as large as 50% of the mean. The slow rate of movement of the wetting front through the s o i l matrix i s shown by the time lag between the beginning of the storm and the appearance of the wetting front at any depth. The time lag was a non-linear function of depth. This was quite l i k e l y due to the change i n hydraulic conductivity with depth and to water movement through macropores (Aubertin, 1971). A f t e r reaching a maximum at 2000 hr, the t o t a l water content decreased while the r a i n f a l l continued f o r M hr at an average rate of 0.5 cm hr""1'. An increase of saturated flow through macropores may be responsible f o r t h i s behaviour. The drainage rate c a l c u l a t e d between 2000 and 2400 by (3) was 0.8% of the p r e c i p i t a t i o n normal to the slope during t h i s same period (Table 1). - 83 -Figure 6. Volumetric water content at the 2 , 6 , 9 and 16-cm depths and t o t a l water content of the forest f l o o r during r a i n f a l l . Table 1. Water balance components during r a i n f a l l . The data are f o r periods during which the p r e c i p i t a t i o n i n t e n s i t y , matric p o t e n t i a l and t o t a l p o t e n t i a l gradient were r e l a t i v e l y constant. Date Time 9<J//3z' m (cm) z' (cm/day) P (cm) R1 (cm) M (cm) D (cm) R/P (%) M/P (%) D/P (%) D/M (%) 10/09/71 1700-1900 2.4 70 0.025 1.6 0.4 1.2 0.005 25 75 0.3 0.4 28/09/71 2000-2400 0.4 80 0.018 0.5 0.1 0.4 0.001 20 80 0.3 0.3 i 03/10/71 1400-1700 1.7 55 0.043 1.1 '0.4 0.7 0.009 35 6 5 0.8 CO 1.3 * i 1700-2100 1.5 55 0.043 1.0 0.3 0.7 0.012 30 70 1.2 1.7 2100-2300 1.5 55 0.043 0.8 0.3 0.5 0.006 30 70 0.7 1.2 12/10/71 2000-2400 2.4 61 0.034 1.8 0.6 1.2 0.014 35 65 0.8 1.2 22/10/71 0000-1000 1.6 59 0.036 4.7 1.6 3.1 0.006 35 65 0.1 0.2 25/10/71 1300-1900 1.8 63 0.032 2.6 1.3 1.3 0.001 50 50 0.05 0.1 Runoff ( l a t e r a l flow through the l i t t e r ) was only observed f o r short distances (50 to 100 cm) over the smoothly sloping s i t e . Water running o f f was intercepted by any microtopographic change i n the slope and channelled through the forest f l o o r . - 85 -Table 1 contains the estimates of the water balance components for* 8 periods during which the matric p o t e n t i a l , the t o t a l p o t e n t i a l gradient, and the r a i n f a l l were r e l a t i v e l y constant. Drainage through the forest f l o o r matrix evaluated at the 13 cm depth ranged from 0.1 to 1.2% of the p r e c i p i t a t i o n . , Runoff was estimated to range from 20 to 50% of the p r e c i p i t a t i o n while flov; through macropores from 50 to 80%. Approximately 0.8% of the t o t a l water flow through the f o r e s t f l o o r occurred i n the s o i l matrix. Runoff was estimated with an accuracy of ±25%. That a large quantity of water moved through the forest f l o o r by way of macropores without appreciably wetting the matrix was also observed by others (Whipkey, 1969; Aubertin, 1971). Water balance of the forest floor during drying periods. During drying periods R and M can be neglected and consequently (4) becomes: T + E + AW + D = 0 (6) Since E and AW are measured, and D can be c a l c u l a t e d from (3), then T can be calcu l a t e d as the r e s i d u a l i n (6). The rates of t o t a l water depletion, drainage, evaporation, and t r a n s p i r a t i o n f o r two periods during September and October 19 71 are plotted i n Figs. 7 and 8. The drainage rates were calculated by (3) i n which hydraulic conductivity and p o t e n t i a l gradient were - 86 -T 1 1 1 1 r SEPTEM8ER 1971 Figure 7 . Drainage, evaporation, t r a n s p i r a t i o n , and t o t a l water depletion rates f o r the f o r e s t f l o o r during a drying period i n September. - 87 -Figure Drainage, evaporation t o t a l water depletion f l o o r during a drying , t r a n s p i r a t i o n , and rates f o r the f o r e s t period i n October. - 88 -evaluated at the 13-cm depth. The drainage rate decreased r a p i d l y with time a f t e r the cessation of r a i n f a l l . Since the t r a n s p i r a t i o n rates were cal c u l a t e d as r e s i d u a l s i n (6), t h e i r values contained the errors i n measurement of the other components. The average drainage rate was lower i n September than i n October because of the lower water content of the forest f l o o r . The amount of t r a n s p i r a t i o n was noticeably lower i n October than September. Seasonal distribution of water content in the forest floor. The t o t a l water content and the volumetric water content f o r the 0-8 cm and 8-17 cm depth i n t e r v a l s , as obtained from tensiometer data, shown i n F i g . 9 f o r the period extending from September 7 to October 25. H a l f - d a i l y averages of r a i n f a l l i n t e n s i t i e s i n cm hr~^ and storm t o t a l s are also shown. Volumetrically there was less water i n the upper h a l f (0-8 cm) than i n the lower h a l f (8-17 cm) of the for e s t f l o o r during the measurement period. For drying periods t h i s can be explained by the higher water rete n t i o n capacity of the H horizon. On the other hand, during r a i n f a l l the matric p o t e n t i a l would have to be higher than about -4 cm of water f o r the F horizon to contain more water than the H horizon ( F i g . 3). This l e v e l of matric p o t e n t i a l i s not reached on a slope since the hydraulic conductivity - 89 -Figu re 9. Vo lume t r i c water as a f u n c t i o n o f and r a i n f a l l are content o f the F and H h o r i z o n s t i m e . The t o t a l water content a l s o p l o t t e d . - 90 -of the fo r e s t f l o o r ( F i g . 4) at a matric p o t e n t i a l of -4 cm of water exceeds the recorded maximum r a i n f a l l i n t e n s i t y . The maximum increase of forest f l o o r water content, AW as a r e s u l t of r a i n f a l l was calculated by taking max to the d i f f e r e n c e between the minimum water content before r a i n f a l l , W . and the maximum water content during mm ^ r a i n f a l l , W . Thus, ' max ' AW = W - W . ( 7 ) max max mm The r a t i o s of the maximum increase i n the water content of forest f l o o r to the t o t a l r a i n f a l l (normal to the slope) were computed f o r nine storms during the period of measurement. Eight out of nine r a t i o s ranged from 0.0 3 to 0.44. For the storm on September 23, a l l of the 0.77 cm r a i n f a l l was absorbed by the f o r e s t f l o o r . This i s a t t r i b u t e d to the small s i z e of the storm and to the low i n i t i a l water content of the organic l a y e r . The r e l a t i o n s h i p s between the maximum increase of water content, i n t e n s i t y , slope, and the water reten t i o n and conductivity properties of the fo r e s t f l o o r are complex. I t can be postulated that the p r e c i p i t a t i o n r a t e a f f e c t s the p a r t i t i o n i n g of the flow between R, M and D and that t h i s p a r t i t i o n i n g varies with the slope angle and the fo r e s t f l o o r water content. This - 91 -r e l a t i o n s h i p can be expressed by re w r i t i n g (5) as follows: W = W + P - R (P,o,W) - M (P,a,W) - D (P,a,W) (8) When W = W , then max P = R (P,ct,W ) + M (P,ct,W ) + D (P,ct,W ) (9) ' ' max max ' ' max This simple analysis indicates that the water content of the f o r e s t f l o o r w i l l increase u n t i l the slope and the hydraulic conductivity are such that the rate of water output from the fo r e s t f l o o r (R + M + D) equals the rate of water input (P). In t h i s study the maximum water content of the 17-cm t h i c k , f o r e s t f l o o r was found •to range from 7.4 to 8.1 cm r e s p e c t i v e l y , corresponding to hydraulic c o n d u c t i v i t i e s of 0.06 and 1.4 cm day-"*" i n the F horizon. Since the hydraulic conductivity e x h i b i t s a large increase as a r e s u l t of a small increase of water content, the i n t e n s i t y of r a i n f a l l probably has a n e g l i g i b l e e f f e c t on the maximum water content of the fore s t f l o o r . This may explain why no c l e a r r e l a t i o n s h i p was found between the maximum increase of water content and r a i n f a l l i n t e n s i t y . In addi t i o n , the p a r t i t i o n i n g of the r a i n f a l l between R, M and D i s possibly more complex than (9) suggests since each term may be a function of other f a c t o r s . For example, "shingle a c t i o n " (Whipkey, 1969) of dry l i t t e r can cause more runoff than wet l i t t e r , regardless of the slope angle - 92 -o r the t o t a l f o r e s t f l o o r water content. Since the values of W reached during the period max 5 v o f study can be considered almost constant, there should be a s i m D l e r e l a t i o n s h i p between AW and V/ • . I f the max mm saturation water content was reached during r a i n f a l l , the r e l a t i o n s h i p between AV/ and 17 . would be a s t r a i g h t max mm l i n e ( i n s e r t of F i g . 10). In F i g . 10, the observed values of AW are plotted against W . for nine r a i n -max - J mm storms. The r e s u l t s show that as long as saturation i s not reached, the r e l a t i o n between the two variables may not be l i n e a r . Point (a) i s o f f the l i n e because the t o t a l r a i n f a l l of the September 2 3 storm was only 0 . 7 7 cm. Points (b) and (c) are the maximum increases of water content f o r the October 2 0 and 2 2 storms r e s p e c t i v e l y ( F i g . 9b). Because there was only a short period of time between those storms and that of October 18, only a f r a c t i o n of the retained water from the previous storm drained away. In these two cases t h e r e l a t i o n s h i D between AW and 17 . appears to be max mm * v d i f f e r e n t . On a s i t e with less slope, W would max probably be l a r g e r because of less runoff. Hysteresis, though not considered i n t h i s paper, may also a f f e c t t h e r e l a t i o n s h i p . For p r a c t i c a l purposes a l i n e a r r e l a t i o n s h i p , as i n F i g . 10, can be used to estimate - 93 -Figure 10. Relationship between the minimum water content before r a i n f a l l and the maximum increase of water content during r a i n f a l l for a 17-cm thick forest f l o o r on a 30° slope. The volumetric water content at saturation was 0.8 8 cm3 cm~3. The 1:1 l i n e was f i t t e d by eye to the data. - 94 -the maximum increase of water content from knov/ledge of the minimum water content before the occurrence of a rainstorm. Implications for plant growth. I t i s reasonable to assume that the d i f f e r e n c e between the water content of the f o r e s t f l o o r . a t the time of n e g l i g i b l e drainage and the water content at -15 bars matric p o t e n t i a l i s a v a i l a b l e f o r evapotranspiration. The average matric p o t e n t i a l at the time of n e g l i g i b l e drainage was approximately -9 0 cm of water. This corresponded to a hydraulic conductivity of about 0.015 cm day 1 . The •total water content at the time of n e g l i g i b l e drainage and at -15 bars, and the a v a i l a b l e water fo r evapo-t r a n s p i r a t i o n were 6.9, 4.2 and 2.7 cm r e s p e c t i v e l y . To the l a t t e r amount we can add the water evapotranspired during the d r a i n i n g period (0.4 cm). The f o r e s t f l o o r can, therefore, provide an 8-day water supply f o r evapo-t r a n s p i r a t i o n i f a reasonable summer evapotranspiration rate of 4 mm d a y - 1 (Black and McNaughton, 1972) i s assumed. Implications in watershed hydrology. On sloping land the p o t e n t i a l capacity of the f o r e s t f l o o r to r e t a i n flood-producing runoff and snowmelt i s rather meagre because there i s an upper l i m i t to the amount of water retained by i t . High i n t e n s i t y r a i n f a l l s that often - 95 -r e s u l t i n floods on the west coast of B r i t i s h Columbia occur during the rainy season when the forest f l o o r i s already wet. The maximum amount of water absorbed by the f o r e s t f l o o r during the period of measurement was l . U cm or about 7% of the rainstorm amounts known to have caused flood damage i n the l o c a l area. Furthermore, the average length of time elapsed between the beginning of a rainstorm and the time of the maximum water content of the f o r e s t f l o o r was 12 hours. I f the t o t a l p r e c i p i t a t i o n during these 12 hrs i s s u f f i c i e n t to increase the f o r e s t f l o o r water content to i t s maximum of approximately 8 cm of water, the water ret e n t i v e capacity of the forest f l o o r w i l l have no e f f e c t on peak flows a f t e r t h i s time. By absorbing some water the f o r e s t f l o o r may delay and reduce peak flows caused by storms of le s s than 12-hours duration but apparently w i l l not have any e f f e c t on those caused by storms of longer duration. Forest f l o o r drainage was measurable f o r 3 to 6 days following r a i n f a l l , therefore con t r i b u t i n g to delayed stormflow. A f t e r t h i s period the drainage became very small, i n d i c a t i n g that the f o r e s t f l o o r contributed n e g l i g i b l y to base flow. Forest f l o o r s on h o r i z o n t a l areas and depressions may r e t a i n d i f f e r e n t amounts of water. The senior author has observed water accumulating up to 10 cm deep on top of the f o r e s t f l o o r i n some depressions during high i n t e n s i t y r a i n f a l l (0.5 cm hr-"1' f o r 5 h r s ) . The s o i l had been wetted - 96 -by t o t a l antecedent p r e c i p i t a t i o n of 4 cm. Since the f o r e s t f l o o r on h o r i z o n t a l areas and i n depressions represents a s i g n i f i c a n t f r a c t i o n of the t o t a l watershed area, the e f f e c t s of the f o r e s t f l o o r on peak flow and delayed stormflow may be more important than t h i s study i n d i c a t e s . Conclusion The r o l e of the forest f l o o r i n watershed hydrology i s better understood with knowledge of i t s water retention and conductivity c h a r a c t e r i s t i c s . These c h a r a c t e r i s t i c s were found to be l a r g e l y determined by the degree of decomposition of the organic matter. The hydraulic conductivity of the forest f l o o r changed by about 4 orders of magnitude between matric potentials of -3 and -100 cm of water. A f t e r the f o r e s t f l o o r had reached i t s maximum water content the ca l c u l a t e d matrix drainage rate was about 0.5% of the p r e c i p i t a t i o n rate and about 0.8% of the t o t a l flow through the f o r e s t f l o o r . During drying periods i t was found possible to r e l i a b l y c a l c u l a t e AW and D from matric p o t e n t i a l s measured at several depths. The amount of water absorbed by the f o r e s t f l o o r during r a i n f a l l was l a r g e l y c o n t r o l l e d by the i n i t i a l water content, the angle of the slope and the hydraulic conductivity of the f o r e s t f l o o r . The water re t e n t i v e capacity of the f o r e s t f l o o r can have an e f f e c t on peak flows caused by - 97 -r a i n f a l l of l i m i t e d duration. The f o r e s t f l o o r contributes to delayed stormflow but has a n e g l i g i b l e e f f e c t on base flow. The re t e n t i o n properties of the forest f l o o r may have a s i g n i f i c a n t e f f e c t on plant growth p a r t i c u l a r l y i n south western B r i t i s h Columbia where the summers are dry. The most important contributions of the fo r e s t f l o o r to watershed hydrology are protection of the mineral s o i l against raindrop impact and preservation of the numerous surface depressions which temporarily store water. L i t e r a t u r e Cited AUBERTIN, G.M. 19 71. Nature and extent of macropores i n f o r e s t s o i l s and t h e i r influence on subsurface water movement. U.S.D.A. Forest Serv. Res. Paper NE-192. BLACK, T.A. and K.G. McNAUGHTON. 19 72. Average Bowen-r a t i o methods of c a l c u l a t i n g evapotranspiration applied to a Douglas f i r f o r e s t . Boundary-Layer Meteorol. ( i n press). BOELTER, D.H. 1964. Laboratory techniques f o r measuring water storage properties of organic s o i l s . S o i l S c i . Soc. Amer. Proc. 28: 823-824. CHILDS, E.C. 1969. An introduction to the physical basis of s o i l water phenomena. Wiley-Interscience, John Wiley and Sons Ltd., Toronto. KRAJINA, V.J. 1965. Biogeoclimatic zones and c l a s s i f i c a t i o n of B r i t i s h Columbia. E c o l . of Western N.A. 1: 1-17. LIAKOPOULOS, A.C. 1965. Darcy 1s c o e f f i c i e n t of permeability as symmetric tensor of second rank. Int. Assoc. S c i . Hydrol. X: 41-4 8. LOWDERMILK, W.C. 1930. Influence of f o r e s t l i t t e r on run-off, p e r c o l a t i o n , and s o i l erosion. J . Forestry 28: 474-491. PLAMONDON, P.A. 1972. Hydrologic properties and water balance of the f o r e s t f l o o r of a Canadian West Coast watershed. Unpub. Ph.D. Thesis Univ. o f B r i t . Col. pp PLAMONDON, P.A. and T.A. BLACK. 1972. Energy balance method f o r estimating evaporation from the f o r e s t f l o o r . Can. J . For. Res. (submitted) WHIPXEY, R.Z. 1969. Storm runoff from forested catchments by subsurface routes. In floods and t h e i r computation. Int. Assoc. S c i . Hydrol. Leningrad Symp. Proc. 1967: 773-779. WILLINGTON, R.P. 19 71. Development and a p p l i c a t i o n o f a technique f o r evaluating root zone drainage. Unpub. Ph.D. Thesis, Univ. of B r i t . ' Col. 42 pp. WILSON, B.D. and S.J. RICHARDS. 19 38. C a p i l l a r y c o n d u c t i v i t y of peat s o i l s at d i f f e r e n t c a p i l l a r y tensions. J . Amer. Soc. Agron. 30: 583-588. ZASLAVKSY, D. and A.S. ROGOWSKI. 1969. Hydrologic and morphologic implications of anisotropy and i n f i l t r a t i o n i n s o i l p r o f i l e development. S o i l S c i . -Soc. Amer. Proc. 33: 594-599. - 99 -LABORATORY MEASUREMENT OF HYDRAULIC CONDUCTIVITY CHARACTERISTICS OF THE FOREST FLOOR Abstract. The procedures previously used to measure the hydraulic conductivity c h a r a c t e r i s t i c s of porous material are b r i e f l y reviewed. A simple steady-state method of measuring the hydraulic conductivity of an undisturbed sample of forest f l o o r material i n the laboratory i s described. The main features of the method are that the water i s applied at a constant rate at the top of the sample using a chromatography micropump while the water content within the sample i s co n t r o l l e d by hanging a variable - length water column from a porous plate at the bottom of the forest f l o o r core. An advantage of the method i s that a small matric p o t e n t i a l gradient can be maintained i n the sample by adjusting the length of the hanging water column. Introduction The water retention and conductivity c h a r a c t e r i s t i c s of a s o i l have a considerable e f f e c t on the hydrologic response of a watershed and on plant growth. Because of the d i f f i c u l t y of measurement, there i s a serious look of knowledge of hydraulic conductivity c h a r a c t e r i s t i c s of many s o i l s . The forest organic layer forming the top of forest s o i l i s a highly porous and layered material. The composition of t h i s - 100 -layer (forest f l o o r ) varies- from the r e l a t i v e l y unaltered vegetal debris near the surface to the highly decomposed organic matter at depth. Special care must be taken to preserve the forest f l o o r structure while determining i t s hydraulic conductivity. The objectives of t h i s paper are to b r i e f l y review the procedures previously used to measure the hydraulic conductivity c h a r a c t e r i s t i c s of porous materials and to describe a simple method of measuring the hydraulic conductivity c h a r a c t e r i s t i c s of an undisturbed sample of f o r e s t f l o o r material i n the laboratory. The method discussed here can be used to determine the hydraulic conductivity c h a r a c t e r i s t i c s of the forest f l o o r over the range of water contents between the conditions of saturation and of n e g l i g i b l e drainage. For most forest f l o o r material around Vancouver, B.C., t h i s implies a range of matric potentials between 0 and -100 to -150 cm of water. The hydraulic conductivity, k i s defined by the Darcy equation q = - k 3473Z (1) where q i s the water f l u x density, Bf/aZ i s the t o t a l p o t e n t i a l gradient, and 4* i s the sum of matric, g r a v i t a t i o n a l , and osmotic p o t e n t i a l s . Review of Procedures Used Previously The procedures used to estimate the hydraulic conductivity c h a r a c t e r i s t i c s of porous materials have been received by - 101 -Richards and Moore (1952), E l r i c k (1953), and Klute (1965). The hydraulic conductivity of unsaturated material may be determined e i t h e r by steady-state or non-steady-state techniques. During steady-state conditions the moisture content, matric p o t e n t i a l , p o t e n t i a l gradient and f l u x are constant with time. In the l a t t e r technique these quantities change with time. E l r i c k (196 3) found that the hydraulic conductivity measured by both techniques agreed well at low water content, but at high water content the non-steady-state method was found u n r e l i a b l e . The experimental conditions which f u l f i l l the necessary mathematical assumptions for the non-steady-state case are d i f f i c u l t to a t t a i n (Nielsen and Biggar, 1961). Theoretical methods (Childs and C o l l i s George, 1950; Marshall, 1958) based on s o i l water retention data cannot be used to c a l c u l a t e the hydraulic conductivity of the forest f l o o r since the l a t t e r shrinks and sweels and has a heterogeneous structure. Several s i m i l a r forms of apparatus to determine the conductivity'by the steady-state method have been reported i n the l i t e r a t u r e . Richards (1931) was probably the f i r s t to measure unsaturated hydraulic conductivity by the constant f l u x method. He mounted the sample to be analyzed i n a rectangular frame between two porous plates set about 4 cm apart. Porous cups positioned i n the sample - 102 -and connected to a d i f f e r e n t i a l manometer measured the pot e n t i a l gradient across the sample. A vacuum bo t t l e connected to the top and bottom plates controlled the water content of the s o i l column. The pressure of a hydrostatic column extending above the upper c e l l and the g r a v i t a t i o n a l gradient across the sample caused the water to move through the sample. The inflow and outflow of water, and the pot e n t i a l gradient were measured. A few years l a t e r , Richards and Wilson (19 36) used a s i m i l a r apparatus to determine the unsaturated hydraulic conductivity of peat s o i l s . This time the sample was set ho r i z o n t a l l y between two porous plates to give zero g r a v i t a t i o n a l gradient across the sample. Different tensions were applied at the ends of the s o i l column to cause the water to move through the s o i l . The vacuum bo t t l e used by Richards to control s o i l water content may be replaced by hanging water columns from.both plates, or the sample may be enclosed within a pressure chamber. E l r i c k (1964) set the s o i l core h o r i z o n t a l l y and used low impedance, c e l l u l o s e acetate f i l t e r s to eliminate the need f o r tensiometers. At high water content, flow along the lower side of the sample may occur. It has been found i n t h i s laboratory that clogging of these f i l t e r s - 103 -can lead to erroneous p o t e n t i a l gradient determination, unless correction for membrane impedance i s applied. Richards (1965) found that t h i s impedance, i s d i f f i c u l t to measure and the contact impedance cannot be determined experimentally. Methods i n which one end of the s o i l core i s i n contact with a porous plate, while the other end i s free-l y exposed to evaporation have been used (Gardner and Mi k l i c h , 1962; Nielsen et al. , 1960). The evaporative flux i s maintained by water supplied through the porous plate. Methods requiring porous plates at both ends of the sample must have provision made for a i r to enter or escape as the water content of the sample changes. When using any of these apparatus, the matric p o t e n t i a l gradient should be kept as small as possible i n order to re l a t e the average hydraulic conductivity to a p a r t i c u l a r matric p o t e n t i a l or water content (Childs, 1969). For t h i s reason, the determination of unsaturated hydraulic conduct-i v i t y on horizontal samples cannot be recommended. Zero matric p o t e n t i a l gradient i s also very d i f f i c u l t to obtain i n the evaporative-type of apparatus. Childs and Collis-George (1950) achieved a zero matric p o t e n t i a l gradient by using a long s o i l column with the lower end immersed i n water. The s o i l column was s u f f i c i e n t l y long to generate a zone of uniform water content (the transmission - 104 -zone) i n which the hydraulic conductivity was approximately equal to the c o n t r o l l e d rate of water input at the top. "The moisture content adjusts i t s e l f to provide the necessary permeability to conduct the imposed flow with the g r a v i t a t i o n -a l gradient of p o t e n t i a l " (Childs and Collis-George, 1950). As pointed out by these authors ; t h i s method i s limited to structureless materials such as sands. This technique has been used successfully with P l a i n f i e l d sand (Black et al.3 1969) and with Capilano gravelly sandy loam (Willington, 1971). An a l t e r n a t i v e method i s to measure the flow of i n f i l t r a t i n g water into a s o i l column i n i t i a l l y kept at a uniform low water content. The water i s supplied through a membrane i n order to maintain the surface material at a given suction and at a constant water content less than saturation. "The suction gradient at the surface approaches zero and the moisture p r o f i l e moves downwards at a constant v e l o c i t y with a constant shape a f t e r a long time" (Youngs,1964). In the zone of zero matric p o t e n t i a l gradient the conductivity equals the f l u x . This method i s simple and r e l a t i v e l y short samples can be used. The matric potential, however, at the top of the porous material d i f f e r s from the porous plate's tension since the plate o f f e r s resistance to the flow of i n f i l t r a t i n g water. Thus, a f t e r each conductivity determination a d i f f e r e n t sample - 105 -must be used because the s o i l water content must be measured d e s t r u c t i v e l y . Methods and Results The apparatus described f i r s t by Richards (1931) seemed suited to measurement of hydraulic conductivity character-i s t i c s of an undisturbed forest f l o o r sample i f the need and means of applying a p o s i t i v e head to the sample could be eliminated. With forest f l o o r material, a good contact between the top plate and the r e l a t i v e l y undecomposed F horizon i s very d i f f i c u l t to achieve. On the other hand, a good contact between the bottom plate and the more decomposed H horizon i s e a s i l y achieved. To overcome the d i f f i c u l t y at the upper surface of the sample, the top plate was eliminated and a constant and adjustable water flux was applied at the top of the column by a chromatography micropump. The micropump was adjustable 3 -1 to provide flow rates from 9 to 110 cm hr . For flow 3 -1 rates lower than 9 cm hr , a cam timer was used to regulate the duty cycle of the pump. A 11-cm I.D., 30 cm long, a c r y l i c c y l i n d e r with a commercial porous alundum plate attached to the bottom formed the container f o r undisturbed samples of the forest f l o o r , ( Fig. 1). A 10 cm thick layer of coarse sand (0.2 5-0.5 mm) was put on the sample i n order to evenly d i s t r i b u t e the water over the top of the forest f l o o r . - 106 -W A T E R R E S E R V O I R M I C R O P U M P TIMER—j S T O P P E R S A N O -F O R E S T F L O O R -O U T F L O W B U R E T T E CY::.: c:.v W A T E R M A N O M E T E R S T E N S I O M E T E R C U P  F U N N E L - * 1 A L U M I N U M P O R O U S P L A T E _ T Y G O N . T U B I N G —l 10 • - S T A N D O N L Y T H E S O I L C O L U M N I S D R A W N Figure 1. Diagram of the apparatus used to measure ; - hydraulic conductivity c h a r a c t e r i s t i c s of the f o r e s t f l o o r material i n the laboratory. - 107 -The top p l a t e e l i m i n a t i o n and the pump a p p l i c a t i o n o f water had o the r b e n e f i t s bes ides the one noted above. A i r c o u l d r e a d i l y pene t ra te the top o f the sample to s imula t e n a t u r a l c o n d i t i o n s and, a l s o , the water i npu t r a t e c o u l d be p r e s e l e c t e d . Evapora t i on from the system was minimized by i n s e r t i n g a rubber s topper i n the top o f the a c r y l i c c y l i n d e r . A s topper a l s o prevented evapora t ion from the b u r e t t e used to c o l l e c t the o u t f l o w . The necessary s m a l l g r ad i en t s o f ma t r i c p o t e n t i a l were kept s m a l l by i n c r e a s i n g the t e n s i o n on the bottom p l a t e as the water i npu t r a t e was decreased . I t was t h e o r e t i c a l l y i m p o s s i b l e under cons tant water f l u x c o n d i t i o n s to o b t a i n zero ma t r i c p o t e n t i a l s , s ince the h y d r a u l i c conduct-i v i t y o f f o r e s t f l o o r m a t e r i a l s l o w l y changes w i t h depth and the m a t r i c p o t e n t i a l g rad ien t changes s i m i l a r l y . To min imize the e f f e c t s o f n o n l i n e a r , t o t a l p o t e n t i a l g r ad i en t s and to keep the e r r o r s i n manometer r ead ing below an accep tab le l e v e l , the tens iometers were p o s i t i o n e d v e r t i c a l -l y 6 cm a p a r t . The t h i c k n e s s o f the f o r e s t f l o o r , and thus o f i t s samples , was both troublesome and advantageous to c o n d u c t i v i t y measurements. A disadvantage was tha t a c o n s i d e r a b l e p e r i o d o f t ime was r e q u i r e d to proceed from one s t e a d y - s t a t e to ano ther . For example, w i t h a 10 cm t h i c k sample, 4 days were r e q u i r e d t o reach s t e a d y - s t a t e a t a m a t r i c p o t e n t i a l o f -30 cm o f wa te r . On the o the r hand, s t r u c t u r a l d i s tu rbances caused by c u t t i n g the ends o f the t h i c k samples were r e l a t i v e l y s m a l l . - 108 -The modified Richards 1 method was used to determine the hydraulic conductivity c h a r a c t e r i s t i c s of the F and H horizons of the forest f l o o r of a mountainous watershed near Vancouver, B r i t i s h Columbia. The F and H horizons were each approximately 10-cm thick. Hydraulic conduct-i v i t i e s normal and p a r a l l e l to the forest f l o o r surface were determined f o r the F horizon. The r e s u l t s are shown in F i g . 4 (Chapter 3 ) . Provided that evaporation i s prevented, the method i s r e l i a b l e from saturation to matric potentials of approximately -100 cm of water and appears p r a c t i c a l f o r research i n forest hydrology. L i t e r a t u r e Cited BLACK, T.A., W.R. GARDNER, and G.W. THURTELL. 1969. The pre d i c t i o n of evaporation, drainage, and s o i l water storage for a bare s o i l . S o i l S c i . Soc. Amer. Proc. 33: 655-660. BOELTER, D.H. 1964. Laboratory techniques f o r measuring water storage properties of organic s o i l s . S o i l S c i . Soc. Amer. Proc. 28: 823-824. CHILDS, E.C. 1969. An introduction to the physical basis of s o i l water phenomena. Wiley-Interscience John Wiley g Sons Ltd. Toronto. CHILDS, E.C. and N. COLLIS-GOERGE. 19 50. The permeability of porous materials. Proc. Roy. Soc. A. 201: 392-405. ELRICK, D.E. 1963. Unsaturated flow properties of s o i l s . Aust. J . S o i l . Res. 1: 1-8. ELRICK, D.E., and D.H. BOWMAN. 1964. Note on an improved apparatus f o r s o i l moisture flow measurements. S o i l S c i . Soc. Amer. Proc. 28: 450-453. GARDNER, W.R., and F.J. MIKLICH. 1962. Unsaturated conductivity and d i f f u s i v i t y measurements by a constant f l u x method. S o i l S c i . 93: 271-274. KLUTE, A. 1965. Laboratory measurement of hydraulic conductivity of unsaturated s o i l . In Methods of s o i l analysis Part I, Edited by CA. Black Agronomy 9. 253-272. MARSHALL, T.J. 1958. A r e l a t i o n between permeability and si z e d i s t r i b u t i o n of pores. J. S o i l S c i . 9: 1-8. NIELSEN, D.R., and J.W. BIGGAR. 1961. Measuring c a p i l l a r y conductivity. S o i l S c i . 92: 192-193. NIELSEN, D.R., and D. KIRKHAM, and E.R. PERRIER. 1960. S o i l c a p i l l a r y conductivity: Comparison of measured and calculated values. S o i l S c i . Soc. Amer. Proc. 24: 157-160 RICHARDS, B.G. 1965. Determination of the unsaturated permeability and d i f f u s i v i t y functions from pressure plate outflow data with non-negligible membrane impedance. C.S.I.R.O. S.M.S. Res. Paper No. 57. RICHARDS, L.A. 19 31. C a p i l l a r y conduction of l i q u i d s through porous mediums. Physics 1: 318-333. RICHARDS, L.A., and D.C. MOORE. 1952. Influence of c a p i l l a r y conductivity and depth of wetting on moisture retention i n soil.. Trans. Amer. Geophys. Union 33: 531-5 - 110 -RICHARDS, L.A., and B.D. WILSON. 19 36. C a p i l l a r y conductivity measurements i n peat s o i l s . Jour. Amer. Soc. Agron. 28: 42 7-4 31. RICHARDS, S.J., and L.V. WEEKS. 1953. C a p i l l a r y conductivity values from moisture y i e l d and tension measurements on s o i l columns. S o i l S c i . Soc. Amer. Proc. 17: 206-209. WILLINGTON, R.P. 19 71. Development and app l i c a t i o n of a technique f o r evaluating root zone drainage. Unpub. PhD. Thesis Univ. of B r i t . Col. 42 pp. WILSON, B.D., and S.J. RICHARDS. 1938. C a p i l l a r y conduct-i v i t y of peat s o i l s at d i f f e r e n t c a p i l l a r y tensions. J . Amer. Soc. Agron. 30: 583-5 88. YOUNGS, E.G. 1964. An i n f i l t r a t i o n method of measuring the hydraulic conductivity of unsaturated porous materials. S o i l S c i . 92: 307-311. - I l l -APPENDIX I L i s t of the Plot numbers by area AREA PLOT NUMBER 1 1 to 24 i n c l u s i v e l y 32 to 45 i n c l u s i v e l y 2 25 to 31 i n c l u s i v e l y 3 46 to 53 i n c l u s i v e l y 4 54 to 60 i n c l u s i v e l y - 112 -APPENDIX II Tabulation by plots of the average depths of humus and t o t a l forest f l o o r with t h e i r respective standard deviations, and of the biophysical c h a r a c t e r i s t i c s . Each depth figure i s the average of 40 measurements. Plot Humus No Depth SD (cm) Forest f l o o r Depth SD (cm) Altitude (feet) Slope (degree) Aspect Basal area ( f t 2 ) Radiation Index 1 5.9 4.60 11.1 6.79 730 9 E 200 0.4181 2 2.7 1.89 7.3 6.28 760 18 E 200 0.4185 3 4.3 3.78 7.0 6.18 800 7 E 200 0.4182 4 7.3 8.92 14.7 12.31 850 15 E 220 0.4185 5 6.3 5.56 16.4 16.37 890 18 E 190 0.4185 6 5.5 5.85 15.0 13.76 910 20 E 130 0.4185 7 11.7 11.13 24.5 14.11 950 20 E 40 0 .4185 8 5.6 5 .46 13.8 14 .06 1050 20 E 170 0 .4185 9 6.0 3.68 7.5 5.39 1100 16 E 240 0.4185 10 4.6 5.47 19.2 20.81 1170 21 E 150 0.4185 11 3.2 3.06 5.3 5.03 1230 23 S 220 0.5430 12 5 . 3 4.54 9.0 9.77 1280 26 SE 140 0.5203 13 3.8 4 . 34 3.9 4 . 36 1360 30 SE 310 0.5301 14 11.9 5.51 12.1 5.45 1440 46 E 160 0 .4092 15 9.4 6.59 11.0 8.10 1680 41 E 240 0 .4092 16 3.3 5.52 3.7 6.27 1790 40 E 120 0.4092 17 11.4 8.19 11.4 8.19 2100 46 S 260 0.5912 18 6.2 5.51 6.1 5.56 2430 39 SE 180 0 .5414 19 7.0 3.28 13.2 13.73 720 9 E 160 0 .4181 20 6.6 5.89 11.1 12.00 760 13 E 210 0 .4182 21 5.4 8.40 7.0 11.22 890 27 E 120 0 .4181 22 11.7 8.98 16.2 10.65 920 26 E 110 0.4181 2 3 17.6 13.11 22.3 15.87 1090 22 E 210 0.4181 24 6.1 8.97 15.0 30 .41 1130 30 E 270 0.4172 25 11.5 10 .06 24.1 15.72 910 25 W 250 0.4172 26 9.0 7.33 19.3 17.61 1050 30 W 120 0 .4172 27 13.0 10.47 15.7 14.05 1190 30 W 290 0.4172 28 13.9 11.95 16 .8 12.37 1390 27 W 160 0.4172 29 8.1 9.23 8.9 9.42 1850 36 W 210 0.4172 30 10.7 10.24 13.0 10.90 2080 45 W 170 0.4092 i i (continued) Plot Humus Forest f l o o r Altitude Slope Aspect Basal Radiation No Depth SD Depth SD area Index (cm) (cm) (feet) (degree) ( f t 2 ) 31 15.1 10.15 16.0 9.95 2430 33 W 160 0.4165 32 4.1 2.81 6.9 6.08 740 9 E 240 0.4181 33 5.2 3.31 11.3 11.14 790 10 E 240 0.4182 34 7.7 5.48 24.1 16.54 810 15 E 200 0.4182 35 4.6 5.30 10.4 11.58 880 18 E 100 0.4185 36 4.0 3.27 9.5 11.07 .950 20 E 40 0.4185 37 7.0 5.47 18.0 14 .04 1060 18 E 160 0.4185 38 8.0 9.04 13.5 13.34 1080 15 E 120 0.4185 39 9.9 7.61 18.0 12.88 720 5 E 440 0.4179 40 5.5 4.47 7.2 6.89 740 8 E 160 0.4179 41 5.7 4.24 15.4 10.68 760 7 E 160 0.4179 42 6.3 4.77 11.6 11.12 830 10 E 160 0.4182 43 4.7 5.18 5.0 5.33 870 9 E 160 0.4182 44 3.0 2.70 8.7 11.31 910 10 E 160 0.4182 45 8.4 8.86 10.4 8.87 960 15 E 280 0.4185 46 2.9 1.65 3.0 1.72 880 10 SW 280 0.4690 47 8.1 7 .17 10.4 8 .32 1100 34 SW 480 0.5370 48 7.7 5.92 9.9 6.68 1300 42 SW 400 0.5447 49 8.9 5.21 16.8 10.10 1400 13 W 320 0.5414 50 12.8 6.19 17.1 9.47 1800 38 S 360 0.5860 51 8.7 5.43 15.4 9.14 2100 40 s 440 0.5860 52 11.9 9.33 16.6 10.87 2500 44 s 440 0.5860 53 5.2 6.72 12 .2 19.78 880 1 s 360 0.4178 54 12.2 10.96 23.4 12 .88 1030 9 NE 440 0.3713 55 . 13.8 10.74 27.3 19.85 1250 2.8 NE 400 0.2800 56 8.2 8.33 13.2 10.71 1400 25 NE. 280 0.2893 57 22.0 10.65 26.1 11.34 1830 28 NE 320 0.2800 58 34.5 27.82 45.3 29 .01 2180 33 N 360 0.1862 59 21.8 20.73 28.6 28.67 2430 36 N 240 0.1862 60 12.1 11.66 14.7 13.44 1950 36 NE 400 0.2561 - 115 -APPENDIX H I LISTING OF SAMPLE CHARACTER!STIIS FOUR SAMPLES WERE CCLLECTED IN EACH PLOT PLOT ND DEPTH WEIGHT B . DENS SAT CPTY F.M.C SAT CPTY F . M.C (CM) (G/M2) (O/CMi) U OF WEIGHT) (CM OF WATER) 1 8.4 1 7 . 6 1 9.4 1 5. 1 2 14.0 2 3.8 2 1.8 2 10. 2 3 3.6 3 4.3 3 2.8 3 3.8 4 9.7 4 2.5 4 5.6 4 4.3 3 5.1 5 7. 6 5 5.3 5 5.6 6 5. 1 6 9.7 6 5.6 6 10.2 7 3.3 7 14. 2 7 4.8 7 5 . 1 8 12.4 8 2.3 8 20.1 8 1.3 9 2.3 9 4.3 9 2 .3 9 4.3 10 8.4 10 7.6 10 2.8 10 4.3 11 1.0 11 1.8 11 4. 1 11 2.5 12 3.6 12 2.5 12 2.3 12 2.0 0.951 0.110 0.600 0.076 1.426 0.147 0.758 0.145 1.692 0. 117 0.617 0.157 0. 379 0.207 1. 839 0. 175 0.538 0.146 0.538 0.121 0.379 0.131 0.600 0. 153 1.109 0.111 0.509 0.194 0.826 0.143 0.442 0.099 0.600 0.114 0. 758 0.C96 0.668 0.121 0.696 0.115 0.668 0. 127 1.075 0.100 0. 730 0. 127 1.172 0.112 0.539 0.149 1.681 0.114 0.600 0.120 0.758 0.145 1.109 0.086 0.317 0.134 3.865 0.187 0.193 0.147 0. 442 0. 187 0.600 0.135 0.351 0.149 0.475 0.107 1.392 0. 161 0.888 0.113 0.696 0.241 0.572 0.128 0.379 0.362 0.475 0.259 0.600 0. 143 0.351 0.134 0.413 0.113 0. 379 0. 145 0.634 0.269 0.351 0.167 445. 230. 457. 249. 378. 243. 4 37. 262. 282. 189. 40 9. 194. 467. 206. 305 . 154. 39 5. 184. 289. 153. 564. 205. 424. 2 07. 441. 229. 43 3 . 194. 386. 225. 464. 240. 466. 216. 553 . 243. 459. 235. 498. 2H2. 455 . 214*. 4 50. 224. 443 . 24 9 . 475. . 207. 400 . 194. 464 . 301. 513. 282. 381 . 240. 551 . 300. 463 . 195. 224. 114. 576. 179. 368. 137. 475. 207. 513. 198. 471 . 227. 335. 203. 400. 222. 441 . 201. 450. 232. 407. 115. 33 5. 150. 518. 295 . 755. 327. 599. 236. 482 . 169. 320. 101. 594. 134. 4.?3 2. 19 2 .74 1. 49 5.39 3.47 3.31 1.99 4.77 3.23 2.52 1.23 1. 77 0. 78 5.61 2.83 2.12 0.99 1.55 0. 8? 2. 14 0.78 2 .54 1.24 4.89 2. 54 2.21 0.9 9 3.19 1.86 2. 05 1.0 6 2.80 1. 30 4.19 1.84 3. 06 1 . 57 3. 4 7 1.96 3.04 1. 43 4. 84 2. 41 3.23 1.82 5. 57 2.43 2. 04 0. 99 7.80 5.06 3. 08 1 . 69 2. £9 1.8 2 6.11 3. 33 1 .47 0.62 8. 66 4. 41 I. 1 I 0. 34 1 .62 0.63 2. t)5 1.24 1. BO 0. 69 2.24 1.38 4.66 2. 83 3.55 1.97 3 .07 1. 43 2.57 1.33 1. 54 0. 44 1.59 0. 71 3.11 1.78 2. 65 1.15 2.47 0. 97 1.83 0.64 2. 03 0. 64 2.08 0.47 - 116 -APPENDIX III LISTING OF SAMPLE CHARACTERISTICS FOUR SAMPLES WERE COLLECTED IN EACH PLOT IT NO DEPTH WEIGHT B . DENS SAT CPTY F.M.C SAT CPTY F . M . C (CM ) (G/M2) (G/CM3) {% OF WE I GHT) (CM OF WATER) 13 4.1 0.475 0.113 519. 163. 2.47 0.30 13 6. 1 0. 600 0. 095 560. 263. 3.36 1 .61 13 4.6 0.730 0. 155 396. 175. 2.89 1.28 13 4.1 0.379 0.090 564. 213. 2. 14 0.81 14 6. 1 0. 679 0. 108 423 . 102. 2 .87 0.69 14 3.8 0. 300 0. 076 413. 158. 1.24 0.47 14 8.9 1.743 0. 190 233. 84. 4.06 1.46 14 9.4 0.985 0.10 1 50 5. 189. 4.97 1.86 15 12.4 2.111 0. 164 355. 187. 7.49 3.9 5 15 6.6 1.953 0. 286 278. 80. 5.43 1. 56 15 8.6 0.940 0. 105 328 . 165. 3.08 1. 55 15 5.3 0. 849 0. 154 311 . 61. 2.64 0. 52 16 3.8 0.990 0.252 280. 160. 2. 77 1 . 58 16 6.3 0.934 0.142 427. 215. 3. 99 2. 01 16 6. 1 0. 691 0.110 53 8. 111. 3.72 0.77 16 3.0 0.434 0. 131 482. 167. 2.09 0.72 17 14.5 2.224 0. 149 398. 140. 8. 85 3. 11 17 4. 1 0. 504 0. 120 516. 221. 2.60 1.11 17 10.4 1.228 0. 114 532. 235. 6.53 2.89 17 9.4 1.290 0. 133 427. 198. 5.51 2. 56 18 3.0 0. 538 0.171 50 7. 218. 2. 73 1.17 18 1.0 0. 164 0. 157 54 5. 252. 0.89 0.41 18 2.5 0. 328 0.125 569. 233. 1. 87 0. 77 18 7.4 0.996 0.131 50 7. 220. 5. 05 2. 19 19 6.9 0. 758 0. 107 508. 243. 3.85 1.84 19 9.7 1. 109 0.111 439. 242. 5.42 2. 68 19 2.0 0.7 30 0. 348 210. 63. 1.53 0. 46 19 9.9 1.805 0. 177 309. 181. 5.58 3. 27 20 12.7 2.77 3 0. 212 255. 117. 7.07 3.24 20 5.8 0.481 0.080 635. 282. 3.05 •1.36 20 8.4 1 .868 0.21S 271. 271. 5. 06 5.06 20 5.3 0. 566 0. 103 465. 233. 2 .75 1. 3D 21 5.6 0. 594 0. 103 619. 267. 3.68 1. 59 21 6.9 0.566 0 .080 60 5. 295. 3.42 1.67 21 2.5 0. 226 0. 086 613 . 225. 1.39 0. 51 21 3.0 0.368 0. 117 608. 369. 2.24 1.36 22 3.3 0.396 0.1 16 564. 250. 2.23 0.99 22 5.3 0.764 0.139 400 . 207. 3 .06 1. 58 22 3.0 0.368 0. 1 17 546. 233. 2.01 0.88 22 3.8 0.821 0. 209 307. 143. 2.52 1.21 23 30.5 4.075 0. 129 39 4. 247. 16.05 10.06 23 8. 9 0. 905 0. 099 449. 213. 4 .07 1.93 23 7.1 1.070 0. 146 348. 102. 3.72 1.09 23 10.9 2.0 49 0.182 300. 150. 6. 15 3. 07 24 6. 9 0. 888 0. 125 52 5. 217. 4.66 1.93 24 9.7 0.747 0. 075 52 7. 186. 3.94 1. 39 24 12.7 1.862 0. 142 308. 145. 5.73 2.70 24 13.0 1.070 0.080 511. 229. 5.47 2.45 - 117 -A P P E N D I X I I I L I S T I N G OF SAMPLE C H A R A C T E R I S T I C S FOUR SAMPLES WERE COLLECTED I N EACH PLOT >r NO DEPTH WEIGHT B. DENS SAT CPTY F.M.C SAT CPTY F.M.C (CM) (G/M2) (0/CM 3 ) {% UF WEIGHT) (CM OF WATER) 25 9.4 1. 143 0. 118 41 9. 211. 4.79 2.41 25 4.6 0.651 0. 138 478. 222. 3. 11 1. 44 25 10.4 1.019 0.095 574. 254. 5. 85 2. 59 25 14.0 2. 643 0.183 245 . 123. 6.48 3.25 26 8.6 0.990 0. I l l 469. 223. 4. 64 2.21 26 9.1 1.273 0. 135 387. 222. 4.93 2.83 26 4.8 0.481 0. 097 600 . 288. 2.89 1. 39 26 17.0 2.479 0. 14 1 340. 216. 8.43 5.35 27 2.3 0.340 0. 144 550. 267. 1. 87 0.91 27 6. 1 1.613 0.256 277. 184. 4.4 7 2.97 27 10. 2 2. 63 3 0. 256 22 7. 154. 6.09 4.13 27 2.8 0.311 0. 108 707. 255. 2.20 0.7 9 28 14.2 2.039 0. 137 343. 161. 6. 89 3. 23 28 5. 6 0. 707 0. 123 476. 243. 3.3 7 1.70 28 4.8 0.679 0. 136 467. 242. 3.17 1. 64 28 20.1 2.156 0. 104 490 . 268. 10.57 5. 78 29 3.8 0. 538 0. 137 404. 73. 2.17 0. 39 29 4.1 0.894 0.2 13 359. 79. 3.21 0.71 29 4.1 0.787 0.187 455. 150. 3. 58 1.13 29 4. 1 0. 985 0.235 249. 71. 2.45 0.73 30 6.9 0.753 0. 106 484. 133. 3 .64 1.04 30 2.8 0.335 0. 106 654 . 117. 2.00 0. 36 30 11.2 1.154 0. 100 40 5. 230. 4.68 2.66 30 2.5 0.243 0. 093 858. 300. 2.09 0.73 3i 12.7 1.822 0. 139 510. 347. 9. 29 6.32 31 21.8 3.181 0. 141 411 . 303. 13.07 9. 64 31 6. 9 1. 862 0. 26 3 2 63 . 102. 4.90 1 .93 31 6.9 2.411 0.341 181 . 96. 4.36 2. 31 32 4.6 0.539 0. 108 617 . 317. 3. 14 1.61 32 2.3 0. 198 0. 084 757. 242. 1.50 0. 48 32 3.3 0.453 0. 133 53 8. 136. 2.44 0.62 32 2 .3 0.990 0.378 143. 80. l.<t2 0. 79 33 4.1 0. 424 0. 101 633 . 240. 2.69 1.0 2 33 1.5 0.283 0. 180 580. 230. 1.64 0.65 33 4.6 0.707 0.150 456. 224. 3. 23 1. 58 33 3.6 0.566 0. 154 510 . 260. 2. 89 1. 47 34 3.6 0. 368 0. C99 73 3. 263. 2.71 0.97 34 7.6 1. 370 0. 174 336. 183. 4.60 2. 51 34 4.1 0.594 0.142 543. 462. 3.23 2. 75 34 5.6 0. 623 0. 108 53 6. 277. 3.34 1.72 35 2.5 0. 283 0.108 , 630. 240. - 1.78 0. 68 35 3 .3 0.226 0.066 913. 275. 2.07 0.62 35 5. 1 0.877 0.167 374. 232. 3.28 2.3 4 35 2.8 0.340 0. 118 600. 225. 2.04 0. 76 36 7.9 1.426 0. 175 362. 226. 5. 16 3.22 36 4.3 0.464 0.104 571 . 262. 2.65 1.22 36 4. 1 0. 470 0. 112 599. 329. 2.81 1. 55 36 5.1 0. 566 0. 108 543. 280. 3. 07 1.58 - 1 1 8 -A P P E N D I X I I I L I S T I N 3 OF S A M P L E C H A R A C T E R I S T I C S F O U R S A M P L E S WERE C O L L E C T E D I N E A C H P L O T P L O T NO D E P T H ( C M ) 3 7 2 . 8 3 7 5 . 1 3 7 1 7 . 0 3 7 5 . 1 38 1 5 . 7 3 8 1 4 . 2 38 6 . 1 3 8 1 1 . 9 3 9 7 . 9 3 9 6 . 6 3 9 3 . 8 3 9 3 . 3 AO 6 . 6 4 0 3 . 6 4 0 6 . 1 4 0 8 . 6 4 1 3 . 0 4 1 7 . 1 4 1 3 . 0 4 1 7 . 1 4 2 8 . 6 4 2 6 . 1 4 2 4 . 6 4 2 6 . 1 4 3 4 . 1 4 3 3 . 0 4 3 3 . 0 4 3 3 . 8 4 4 2 . 0 4 4 2 . 0 4 4 1 . 0 4 4 2 . 8 4 5 3 . 0 4 5 3 . 8 4 5 1 . 3 4 5 6 . 6 4 6 2 . 0 4 6 5 . 1 4 6 3 . 6 4 6 1 . 8 4 7 4 . 6 4 7 2 . 8 4 7 5 . 1 4 7 3 . 8 4 8 1 2 . 4 4 8 5 . 1 4 8 4 . 1 4 8 4 . 1 W E I G H T 6 . D E N S ( G / M 2 ) ( G / C M 3 ) 0 . 3 1 1 0 . 1 0 8 0 . 5 3 8 0 . 1 0 3 3 . 3 0 5 0 . 1 8 8 0 . 5 2 6 0 . 1 0 0 2 . 5 8 6 0 . 1 5 9 3 . 6 1 6 0 . 2 4 6 0 . 7 3 0 0 . 1 1 6 2 . 8 52 0 . 2 3 1 1 . 1 3 7 0 . 1 4 0 1 . 2 0 5 0 . 1 7 7 0 . 5 6 0 0 . 1 4 2 0 . 6 3 9 0 . 1 8 3 1 . 6 8 1 0 . 2 4 7 0 . 5 0 4 0 . 1 3 7 0 . 5 6 3 0 . 0 9 3 1 . 7 3 4 0 . 1 9 1 0 . 5 1 5 0 . 1 6 4 1 . 1 6 0 0 . 1 5 8 0 . 6 6 8 0 . 2 1 2 1 . 0 5 8 0 . 1 4 4 0 . 8 7 2 0 . 0 9 8 0 . 5 8 9 0 . 0 9 4 0 . 4 5 3 0 . 0 9 6 0 . 5 0 4 0 . 0 8 0 0 . 3 9 0 0 . 0 9 3 0 . 4 0 2 0 . 1 2 8 0 . 5 8 3 0 . 1 8 5 0 . 5 2 6 0 . 1 3 5 0 . 2 2 6 0 . 1 0 8 0 . 3 3 4 0 . 1 5 9 0 . 1 5 3 0 . 1 4 6 0 . 4 5 8 0 . 1 5 9 0 . 4 3 6 0 . 1 3 8 0 . 5 2 6 0 . 1 3 4 0 . 2 3 2 0 . 1 7 7 0 . 8 4 9 0 . 1 2 5 0 . 2 3 8 0 . 1 1 3 0 . 2 7 7 0 . 0 5 3 0 . 4 6 4 0 . 1 2 6 0 . 2 2 6 0 . 1 2 3 0 . 5 2 1 0 . 1 1 0 0 . 3 0 5 0 . 1 0 6 0 . 7 0 7 0 . 1 3 5 0 . 6 1 1 0 . 1 5 5 1 . 7 7 1 0 . 1 3 6 0 . 6 7 9 0 . 1 2 9 0 . 7 5 3 0 . 1 7 9 0 . 7 5 8 0 . 1 8 1 S A T ( C P T Y F . M . C Z OF W E I G H T ) 7 2 4 . 2 9 1 . 4 8 5 . 3 0 4 . 3 0 4 . 2 4 9 . 5 0 4 . 3 2 9 . 3 5 9 . 2 1 6 . 2 1 5 . 1 0 3 . 4 2 7 . 2 2 5 . 2 2 1 . 1 1 5 . 4 5 8 . 2 3 4 . 3 1 8 . 1 9 4 . 5 0 8 . 3 0 1 . 3 5 4 . 1 4 5 . 2 4 4 . 1 5 2 . 5 2 0 . 2 5 5 . 6 0 0 . 2 3 9 . 2 7 6 . 1 5 5 . 4 6 6 . 2 6 7 . 3 3 5 . 1 7 6 . 3 4 5 . 2 1 3 . 4 2 1 . 2 9 1 . 5 2 1 . 2 5 1 . 5 5 6 . 2 2 7 . 6 1 4 . 2 1 5 . 4 9 4 . 2 0 9 . 5 3 3 . 2 9 1 . 62 6 . 3 0 0 . 3 2 9 . 2 0 0 . 5 0 8 . 2 4 5 . 6 3 9 . 3 1 3 . 5 3 1 . 18 1 . 41 8 . 2 9 3 . 5 2 2 . 2 9 3 . 5 1 0 . 1 5 3 . 5 5 8 . 2 2 5 . 6 1 7 . 1 9 8 . 5 1 3 . 2 3 9 . 7 3 3 . 3 3 8 . 7 5 7 . 2 5 1 . 5 1 8 . 2 0 9 . 9 7 0 . 3 2 3 . 5 4 9 . 3 2 4 . 6 3 5 . 2 3 9 . 4 6 3 . 2 2 6 . 4 0 9 . 2 0 0 . 3 8 0 . 2 5 5 . 5 0 3 . 2 7 3 . 3 4 6 . 1 8 9 . 3 4 3 . 1 8 1 . S A T C P T Y F . M . C ( C M OF W A T E R ) 2 . 2 5 0 . 9 1 2 . 6 1 1 . 6 3 1 0 . 0 5 8 . 2 3 2 . 6 5 1 . 7 3 9 . 2 8 5 . 5 9 7 . 7 8 3 . 9 1 3 . 1 2 1 . 6 4 6 . 3 0 3 . 2 8 5 . 2 1 2 . 6 6 3 . 8 3 2 . 3 4 2 . 8 5 1 . 6 9 2 . 2 6 0 . 9 3 4 . 1 0 2 . 5 5 2 . 6 2 1 . 2 8 3 . 5 0 1 . 3 9 4 . 7 0 2 . 6 4 2 . 4 0 1 . 3 7 3 . 8 9 2 . 0 4 2 . 3 0 1 . 4 6 4 . 4 6 3 . 0 8 4 . 5 4 2 . 1 9 3 . 2 7 1 . 3 4 2 . 7 8 0 . 9 7 2 . 4 9 1 . 0 5 2 . 0 3 1 . 1 4 2 . 5 1 1 . 2 1 1 . 9 2 1 . 1 7 2 . 6 7 1 . 2 9 1 . 4 5 0 . 7 0 1 . 7 7 0 . 6 0 0 . 6 4 0 . 4 5 2 . 3 9 1 . 3 4 2 . 2 2 0 . 6 7 2 . 9 4 1 . 1 8 1 . 4 3 0 . 4 6 4 . 3 5 2 . 0 3 I . 74 0 . 8 0 2 . 1 0 0 . 7 0 2 . 4 0 0 . 9 7 2 . 2 0 0 . 7 3 2 . 8 6 1 . 6 9 2 . 0 9 0 . 7 3 3 . 2 8 1 . 6 0 2 . 5 0 1 . 2 2 6 . 7 3 4 . 52 3 . 4 2 1 . 8 5 2 . 6 0 1 . 42 2 . 6 0 1 . 3 7 - 1 1 9 -A P P E N D I X I I I L I S T I N G O F S A M P L E C H A R A C T E R I S T I C S F O U R S A M P L E S W E R E C O L L E C T E D I N E A C H P L O T )T N O D E P T H W E I G H T B . D E N S S A T C P T Y F . M . C S A T C P T Y F . M . C ( C M ) ( G / M 2 ) ( G / C M 3 ) U O F W E I G H T ) ( C M O F W A T E R ) 4 9 1 4 . 7 3 . 4 0 9 0 . 2 2 3 2 4 1 . 1 4 4 . 8 . 2 2 4 . 9 1 4 9 9 . 1 1 . 5 5 6 0 . 1 6 5 3 3 9 . 1 7 9 . 5 . 2 8 2 . 7 9 4 9 1 2 . 4 1 . 5 2 8 0 . 1 1 9 3 6 4 . 2 1 4 . 5 . 5 6 3 . 2 7 4 9 6 . 6 1 . 0 9 8 0 . 1 6 1 3 5 6 . 2 0 6 . 3 . 9 1 2 . 2 6 5 0 1 7 . 8 1 . 7 0 4 0 . 0 9 3 5 2 3 . 3 7 9 . 8 . 9 1 6 . 4 6 5 0 1 6 . 8 1 . 5 1 1 0 . 0 8 7 5 6 4 . 3 1 6 . 8 . 5 2 4 . 7 7 5 0 1 1 . 2 1 . 2 6 2 0 . 1 0 9 4 4 2 . 2 1 3 . 5 . 5 8 2 . 6 9 5 0 6 . 6 0 . 6 9 1 0 . 1 0 1 5 7 5 . 2 3 6 . 3 . 9 7 1 . 6 3 5 1 5 . 3 0 . 7 5 3 0 . 1 3 7 4 8 1 . 2 2 4 . 3 . 6 2 1 . 6 9 5 1 5 . 6 0 . 3 4 0 0 . 0 5 9 6 5 7 . 2 3 8 . 2 . 2 3 0 . 8 1 5 1 6 . 1 0 . 8 6 6 0 . 1 3 8 3 8 7 . 1 9 3 . 3 . 3 5 1 . 6 7 5 1 6 . 3 1 . 1 5 4 0 . 1 7 6 3 6 0 . 1 5 0 . 4 . 1 6 1 . 7 3 5 2 5 . 6 0 . 8 9 4 0 . 1 5 5 4 0 3 . 1 8 5 . 3 . 6 0 1 . 6 5 5 2 9 . 9 1 . 2 5 6 0 . 1 2 3 3 6 4 . 1 5 1 . 4 . 5 7 1 . 9 0 5 2 6 . 6 0 . 9 3 4 0 . 1 3 7 4 7 8 . 2 5 4 . 4 . 4 6 2 . 3 7 5 2 1 2 . 4 2 . 1 1 1 0 . 1 6 4 3 8 6 . 1 4 3 . 8 . 1 5 3 . 0 2 5 3 2 . 5 0 . 9 1 1 0 . 3 4 7 2 1 9 . 1 1 4 . 2 . 0 0 1 . 0 4 5 3 1 . 3 0 . 4 3 0 0 . 3 2 8 2 8 8 . 1 2 6 . I . 2 4 0 . 5 4 5 3 2 . 5 0 . 2 8 9 0 . 1 1 0 5 2 4 . 1 8 0 . 1 . 5 1 0 . 5 2 5 3 1 . 5 0 . 3 0 5 0 . 1 9 4 5 0 6 . 1 3 7 . 1 . 5 5 0 . 4 2 5 4 5 . 1 0 . 5 6 0 0 . 1 0 7 5 6 5 . 2 5 3 . 3 . 1 7 1 . 4 5 5 4 7 . 1 0 . 8 3 8 0 . 1 1 4 4 9 9 . 1 7 8 . 4 . 1 8 1 . 4 9 5 4 8 . 4 0 . 7 1 3 0 . 0 8 3 6 6 5 . 2 5 4 . 4 . 7 4 1 . 8 1 5 4 8 . 4 1 . 0 4 7 0 . 1 2 1 5 1 0 . 2 6 3 . 5 . 3 4 2 . 7 5 5 5 3 . 8 0 . 6 5 1 0 . 1 6 5 4 2 3 . 2 7 5 . 2 . 7 5 1 . 7 9 5 5 1 3 . 2 3 . 3 4 5 0 . 2 4 5 2 0 1 . 9 1 . 6 . 7 2 3 . 0 4 5 5 5 . 6 0 . 5 8 9 0 . 1 0 2 1 8 6 . 9 7 . 1 . 0 9 0 . 5 7 5 5 3 . 0 0 . 6 0 0 0 . 1 9 1 3 8 2 . 1 9 9 . 2 . 2 9 1 . 1 9 5 6 1 . 5 0 . 2 4 9 0 . 1 5 8 5 9 8 . 2 1 1 . 1 . 4 9 0 . 5 3 5 6 9 . 1 1 . 7 0 9 0 . 1 6 1 3 7 0 . 1 4 6 . 6 . 3 2 2 . 5 0 5 6 1 4 . 2 1 . 6 8 7 0 . 1 1 5 4 4 1 . 3 6 7 . 7 . 4 4 6 . 1 9 5 6 4 . 1 0 . 5 4 3 0 . 1 2 9 5 2 4 . 2 4 1 . 2 . 8 5 1 . 3 1 5 7 1 1 . 2 1 . 4 8 8 0 . 1 2 9 4 2 1 . 2 7 0 . 6 . 2 7 4 . 0 2 5 7 8 . 9 1 . 5 6 8 0 . 1 7 1 3 2 6 . 1 9 7 . 5 . 1 1 3 . 0 9 5 7 2 6 . 2 2 . 5 1 3 0 . 0 9 3 4 7 1 . 3 2 7 . 1 1 . 8 4 8 . 2 2 5 7 1 4 . 5 2 . 3 0 3 0 . 1 5 4 3 3 5 . 1 5 2 . 7 . 7 2 3 . 5 0 5 8 7 . 4 1 . 2 2 2 0 . 1 6 1 3 7 3 . 1 8 0 . 4 . 5 6 2 . 2 0 5 8 1 6 . 8 2 . 2 2 4 0 . 1 2 9 4 1 2 . 2 7 2 . 9 . 1 6 6 . 0 5 5 8 1 6 . 8 2 . 1 9 0 0 . 1 2 7 4 3 7 . 3 1 1 . 9 . 5 7 6 . 8 1 5 8 2 4 . 1 3 . 4 1 3 0 . 1 3 7 4 4 4 . 3 0 3 . 1 5 . 1 5 1 0 . 3 4 5 9 1 0 . 2 2 . 6 0 9 0 . 2 4 9 2 4 5 . 1 3 7 . 6 . 3 9 3 . 5 7 5 9 5 . 1 0 . 9 9 6 0 . 1 9 0 3 3 8 . 2 0 5 . 3 . 3 7 2 . 0 4 5 9 1 5 . 0 2 . 9 4 3 0 . 1 9 0 3 0 1 . 1 7 5 . 8 . 8 6 5 . 1 5 5 9 9 . 9 1 . 6 9 2 0 . 1 6 5 3 0 4 . 1 9 9 . 5 . 1 4 3 . 3 7 6 0 7 . 9 1 . 6 0 2 0 . 1 9 7 3 7 6 . 2 2 8 . 6 . 0 2 3 . 6 5 6 0 8 . 9 1 . 4 9 4 0 . 1 6 3 4 1 3 . 2 9 2 . 6 . 1 7 4 . 3 6 6 0 1 4 . 5 3 . 0 1 7 0 . 2 0 2 2 7 8 . 1 3 8 . 8 . 3 9 4 . 1 6 6 0 6 . 9 1 . 5 5 6 0 . 2 2 0 1 9 1 . 1 1 1 . 2 . 9 7 1 . 7 3 - 120 -APPENDIX IV Time t rends o f t o t a l water p o t e n t i a l p r o f i l e s f o r th f o r e s t f l o o r d u r i n g th ree d r y i n g p e r i o d s . The g r a v i t a t i o n a l p o t e n t i a l i s zero a t the f o r e s t f l o o r su r fac These data were used to c a l c u l a t e the water balances presented i n F igu res 7 and 8 i n Chapter I I I and i n Appendix V . - 121 -T 1 i 1 1 r— SEYMOUR WATERSHED TOTAL POTENTIAL (cm ©< »ol«r) - 122 -SEYMOUR WATERSHED TIME 0800 I2O0I8O0, 0200 o O FOREST FLOOR Ae HORIZON -220 -180 -140 -too -60 -20 TOTAL POTENTIAL (cm of water) - 123 -SEYMOUR WATERSHED TIME 0600 1200 P " 1200/0800 '1800 0200 '/ ' I / " DATE 18 '17 16'15 14 13 13 o oo FOREST FLOOR Ae HORIZON i i -100 o o o o < < or u. o o z LU UJ m O r-O o - 6 0 -20 TOTAL POTENTIAL (cm of woter) - 124 _ APPENDIX V Drainage, evaporation, t r a n s p i r a t i o n , and t o t a l water depletion rates f o r the forest f l o o r during a drying period i n October. This i s a further example of a water balance during a drying period discussed i n Chapter I I I . - 125 -T 1 1 1 1 1 1 r - 126 APPENDIX VI Table of measured volumetric water contents at the time of n e g l i g i b l e drainage and at a matric p o t e n t i a l of -15 bars f o r several drying periods (Seymour Watershed). Drying period Volumetric water content at time 1971 of n e g l i g i b l e , 3 -3 N (cm cm ). drainage f o r 4 depth: 2 cm 6 cm 9 cm 16 cm 1 1 - 2 3 Sept. 0 . 30 0. 39 0.43 0 .49 4 - 1 2 Oct. 0 .28 0 . 39 0.42 0 .49 13 - 18 Oct. 0 .30 0.40 0.43 0 .49 Average water content 0 .29 0.39 0.43 0 .49 Average matric p o t e n t i a l -84 -92 -105 -90 Total water content at time of n e g l i g i b l e drainage 6 . 9 cm Total water content at -15 bars 4 . 2 cm Available water f o r evapotranspiration 2.7 cm 

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