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Terrain mapping and regional slope stability evaluation in the Fraser Canyon, British Columbia Bell, Alison 1980

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TERRAIN MAPPING AND REGIONAL SLOPE STABILITY EVALUATION IN THE FRASER CANYON, BRITISH COLUMBIA by ALISON BELL B.Sc, McGill University, 1977 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES :. \ Department of Geography '% We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF July, (£) Alison BRITISH COLUMBIA 1980 B e l l , 1980 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of Brit ish Columbia, I agree that the Library shall make i t freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department nf Geography  The University of Brit ish Columbia 2075 wesbrook Place Vancouver, Canada V6T 1W5 n.tp J u l y 17 . 1 9 8 0 . A B S T R A C T T e r r a i n a n a l y s i s of the 22-mile (32.5 km) F r a s e r Canyon between China Bar and Y a l e , B r i t i s h Columbia, i s the theme of t h i s r e s e a r c h . M i c r o - , meso-, and macro-scale v a r i a b l e s are d i f f e r e n t i a t e d as a b a s i s f o r slope s t a b i l i t y e v a l u a t i o n . R e l a t i o n s h i p s between slope f a i l u r e and meso-s c a l e slope a t t r i b u t e s o n l y are examined i n d e t a i l . S u r f i c i a l m a t e r i a l s are c l a s s i f i e d a c c o r d i n g t o the ELUC t e r r a i n c l a s s i f i c a t i o n system i n terms of t e x t u r e , g e n e s i s , form, and s u r f a c e - m o d i f y i n g p r o c e s s e s . The m a t e r i a l s are mapped to an e l e v a t i o n of 1500 f e e t (6 40 m) as t e r r a i n u n i t s on an a i r photo mosaic a t the approximate s c a l e of 1:25,000. The t e r r a i n map i s the f i r s t example of the a p p l i c a t i o n o f the ELUC c l a s s i f i c a t i o n scheme i n the F r a s e r Canyon. Twelve meso-scale slope a t t r i b u t e s d e s c r i b i n g s u r f i c i a l and bedrock geology, slope geometry, and anthropogenic e f f e c t s are e v a l u a t e d a t s i t e s a t 0.1 m i l e (0.16 km) i n t e r v a l s along r a i l w a y l i n e s on both s i d e s of the canyon. A 20-year r a i l w a y maintenance r e c o r d along the e a s t e r n canyon s i d e i s the source of s l o p e f a i l u r e d a ta. An Automatic I n t e r a c t i o n - D e t e c t o r (AID3) program i s used to determine which a t t r i b u t e s c o n t r i b u t e most to the e x p l a n a t i o n o f v a r i a t i o n i n slope f a i l u r e i n c i d e n c e along the e a s t e r n s l o p e s . S i x a t t r i b u t e s are the most important c o n t r i b u t o r s : s u r f i c i a l m a t e r i a l ( s ) , s u r f a c e -modifying process.(es) , slope h e i g h t above and d i s t a n c e away from the railway tracks, angle, and the presence or absence of excavation. Together the variables explain 41.4% of the t o t a l v a r i a t i o n of f a i l u r e incidence. The most s i g n i f i c a n t variable i s s u r f i c i a l material. Colluvium i s the most common s u r f i c i a l material, comprising 60.5% of a l l slope s i t e s . Bedrock units along the eastern slopes exhibit the highest mean incidence of f a i l u r e with 3.0 3 events per s i t e over the 20-year period, followed by c o l l u v i a l units at 1.95 events per s i t e . F l u v i a l and f l u v i o - g l a c i a l s i t e s show the lowest mean incidence of f a i l u r e , with 0.24 and 0.4 8 events per s i t e , respectively. Sites where the slope has been excavated during railway construction (80% of the t o t a l number) experience above-average f a i l u r e incidence, where the average for a l l s i t e s i s 1.84 events per s i t e . Where the trackside slope angle i s greater than 41° i n unconsolidated material, and greater than 70° i n bedrock, above-average f a i l u r e incidence occurs (3.03 and 2.15 events per s i t e , r e s p e c t i v e l y ) . Guttmannv- Lingoes multi-dimensional scalogram analysis (MSA-T)and a clustering program (HCLUS) are used to group the s i t e s on the basis of the six most i n f l u e n t i a l slope a t t r i b u t e s . The resultant categories do not display s i g n i f -i c a n t l y d i f f e r e n t f a i l u r e means. C l a s s i f i c a t i o n of s i t e s on the basis of s u r f i c i a l material only yields broad hazard categories, i n which bedrock and c o l l u v i a l s i t e s f a l l ' i n t o high and intermediate classes, respectively. i v The value of th i s research i s that i t provides a method for regional slope s t a b i l i t y evaluation at the reconnaissance stage of a development proposal. V CONTENTS Page ABSTRACT . i i ACKNOWLEDGEMENTS . . x i CHAPTER 1 - INTRODUCTION 1 Introduction 1 Objectives 6 CHAPTER 2 - THE FRASER CANYON STUDY AREA 9 Introduction 9 Physiographic Description 9 Drainage 18 Geology 20 Hozameen Group 2 3 Custer Gneiss 24 Spuzzum Intrusives 25 Yale Intrusives 26 Scuzzy Pluton 26 Regional Faulting 27 Ouarternary History 29 S u r f i c i a l Materials 33 Climate 34 Vegetation and S o i l s 35 History and Economic Development 36 CHAPTER 3 - TERRAIN CLASSIFICATION AND SLOPE STABILITY . 41 Introduction 41 Terrain C l a s s i f i c a t i o n 41 Slope S t a b i l i t y 48 Micro-Scale Concepts 48 Surrogate Variables at Meso- and Micro-Scales 51 Case Studies 57 CHAPTER 4 - METHODS 6 8 Introduction 6 8 Mapping of the Terrain 6 8 The ELUC Terrain C l a s s i f i c a t i o n 69 F i e l d V e r i f i c a t i o n and Site Investigation . 72 Fieldwork 72 Slope Attributes as Surrogate Variables . 72 Analysis 80 Objectives 80 H i s t o r i c a l Slope F a i l u r e Records . . . . 81 Descriptive S t a t i s t i c s . . . 85 Numerical Site C l a s s i f i c a t i o n 86 v i Page CHAPTER 5 - RESULTS . , 8 9 Introduction 8 9 Terrain C l a s s i f i c a t i o n Mapping and Fieldwork 8 9 Topographic P r o f i l e s 8 9 S u r f i c i a l Materials 9 ^ Mass Movement 10 2 Analysis l y 5 Frequency Distributions of the Slope Attributes 1 0 6 Slope Attributes and Associated Failure . I l l -Relative Importance of the Slope Attributes 1 1 5 S t a b i l i t y C l a s s i f i c a t i o n of Sites . . . . 120 Alternate Means of Site C l a s s i f i c a t i o n . . I 2 3 CHAPTER 6 - CONCLUSIONS 1 2 8 Overview I 2 8 Implications of the Results 1 3 0 REFERENCES . . . . . . . 1 3 4 APPENDIX I. Climatic Data for Lytton, Hell's Gate, and Hope 140 I I . The ELUC Terrain C l a s s i f i c a t i o n 142 I I I . Methods of Analysis 146 IV. Types of Slope Failu r e 15 8 V. Frequency Distributions of the Slope Attributes I 6 2 VI. Mean Slope Failure Incidence 170 VII. AID3 Tree Diagram 1 7 2 VIII. MSA-I Scalograms 1 7 4 v i i LIST OF TABLES Table Page 2.1 Monthly discharge (1912-1976) and suspended sediment load (1965-1976) for the Fraser River measured at Hope 19 2.2. G l a c i a l episodes i n southwestern B r i t i s h Columbia 30 2.3 Stages of g l a c i a l development and the associated landforms 31 3.1 The hierarchy of t e r r a i n information 43 '3.2 System of slope p r i o r i t y ratings employed along the Canadian P a c i f i c Railway l i n e 6 4 4.1 A e r i a l photography used i n the study 69 4.2 Slope attributes considered i n the study 74 4.3 Relevance of slope attribues measured 75 5.1 Modes of f a i l u r e encountered on the Fraser Canyon slopes 10 4 5.2 Mean f a i l u r e incidence on slopes of the p r i n c i p a l s u r f i c i a l materials 106 5.3 Summary of the frequency of occurrence of p r i n c i p a l s u r f i c i a l materials. 10 8 5.4 Failur e incidence of the p r i n c i p a l s u r f i c i a l materials 112 5.5 S u r f i c i a l material types showing the highest and lowest mean incidence of f a i l u r e s 112 5.6 Association between cutslope and f a i l u r e incidence 114 5.7 Association between slope height and distance from the track with f a i l u r e incidence 114 5.8 Association of trackside slope angle with f a i l u r e incidence 116 5.9 S u r f i c i a l materials, slope angles, and f a i l u r e incidence 116 v i i i Table Page 5.10 ETA values of the twelve independent slope attributes H8 .5.11 Results of the c l a s s i f i c a t i o n methods . . . . . . . I 2 2 5.12 C l a s s i f i c a t i o n of s i t e s along the eastern slopes I 2 4 5.13 C l a s s i f i c a t i o n of s i t e s along the eastern and western slopes I 2 4 5.14 General slope f a i l u r e hazard categories l 2 ^ 5.15 Slope f a i l u r e hazard categories based on the s u r f i c i a l material variable at the th r e e - d i g i t l e v e l i 2 6 ix LIST OF FIGURES Figure Page 1.1 Location of the study area 3 1.2 Organization of the research 7 2.1 Map of the study area 10 2.2 Aspects of p o s t - g l a c i a l landslides 15 2.3 Geology of the Fraser Canyon area 22 ;3.1 Examples of the morphological mapping technique 47 3.2 Mean monthly temperature and p r e c i p i t a t i o n and t o t a l monthly incidence of r o c k f a l l s (1933-1970) 5 5 3.3 Seasonality of movement on rock slopes at Ferabee B l u f f s (near Hell's Gate) 56 3.4 Int e r - r e l a t i o n of micro-, meso-, and macro-scale slope s t a b i l i t y .-variables 5 8 3.5 Selection of slope treatment at a s i t e 67 4.1 Slope attributes considered i n the study 76 4.2 Typical trackside slope conditions encountered in the Fraser Canyon 8^ .4.3 Number of slope f a i l u r e s per 0.1 mile (0.16 km) of track as recorded by the Canadian National Railway from 1948 to 196 8 8 2 4.4 Number of slope f a i l u r e s per 0.1 mile (0.16 km) of track as recorded by the Canadian P a c i f i c Railway from 19.74 to 1978 . . - 8 4 5.1 Four topographic p r o f i l e s encountered i n the Fraser Canyon 90 Accomp&v^uA ta«.| X ^£o~Xi^. _ - - - . - - - . . . . m S p e c i a , ! X LIST OF PHOTOGRAPHS Photo Page 2.1 Extensive c o l l u v i a l slope I 4 2.2 F l u v i a l Terrace: on. both sides of the canyon I 7 2.3 The Cariboo Wagon Road near Black Canyon 3 8 5.1 Blocky c o l l u v i a l material i n a fine matrix . . . . 9 3 5.2 Retaining wall to prevent dry r a v e l l i n g material from reaching the track 9-> 5.3 E l e c t r i c warning fence beneath a steep rock slope 9f> 5.4 Loosened joint-blocks beside the tracks 9 ^ 5.5 F l u v i o - g l a c i a l terrace near the Alexandra Bridge 9 8 5.6 Dipping and contorted strata i n f l u v i o - g l a c i a l material 9 9 5.7 Blocky f a i l u r e i n cemented f l u v i o - g l a c i a l material 9 9 5.8 View of a f l u v i o - g l a c i a l exposure along the eastern slope 100 5.9 Poorly sorted f l u v i o - g l a c i a l material 100 5.10 Steeply dipping gravel-and-fines strata . . ... . 101 5.11 Unsorted f l u v i o - g l a c i a l material along the eastern slope 101 5.12 F l u v i a l terrace at Stout 10 3 5.13 Trackside slope cut into f l u v i a l material of the Spuzzum a l l u v i a l fan 10 3 x i A C K N O W L E D G E M E N T S I am indebted to a number of people f o r t h e i r h e l p at a l l stages of t h i s r e s e a r c h . D i s c u s s i o n and i n f o r m a t i o n of t e r r a i n c o n d i t i o n s i n the F r a s e r Canyon area were p r o v i d e d i n the e a r l y stages of t h i s r e s e a r c h by D. W y l l i e , C O . Brawner, and D.R. P i t e a u . My f a m i l i a r i t y w i t h the t e r r a i n c l a s s i f i c a t i o n system r e s u l t e d from s e v e r a l days spent working with Dr. June Ryder and the s t a f f of the mapping d i v i s i o n of the Resource A n a l y s i s Branch i n V i c t o r i a . Mr. N.H. P r i c e and Mr. E.N.A. (Ted) Sewell of the en g i n e e r i n g department at the Vancouver o f f i c e o f Canadian P a c i f i c Railway were very c o - o p e r a t i v e w i t h the r e s e a r c h and granted access to the r a i l w a y right-of-way. I n t e r e s t i n t h i s r e s e a r c h was shown by Mr. W.E. Jubien and Mr. W.A. Abrahamson a t Canadian N a t i o n a l Railway. Transport along the r a i l w a y l i n e s to l e s s a c c e s s i b l e p a r t s o f the canyon was arranged by Mr. J.M. McAree, the C.P.R. roadmaster a t North Bend, and Mr. A. Van Dyke, the C.N.R. weekend roadmaster at Hope. A s s i s t a n c e with methods of a n a l y s i s was given by Mr. F. Fly n n and Mrs. V. Green a t the F a c u l t y o f A r t s c e n t e r f o r computing and d a t a . a n a l y s i s . Mr. P. Wong gave advice and i n s t r u c t i o n of assembly of the f i n a l a i r photo mosaic. The t e r r a i n c l a s s i f i c a t i o n map was reproduced at Burnett Resource Surveys L i m i t e d , i n x i i Burnaby, B.C. Comments on the manuscript made by Dr. M.J. Bovis were greatly appreciated. The thesis was typed by C. Mackenzie. Financing for t h i s research was provided by the National Research Council, operating grant number 67-7073, and by a summer grant from the Youth Employment Program of the B r i t i s h Columbia P r o v i n c i a l Government. I am e s p e c i a l l y g r a t e f u l to my supervisor, Dr. H. Olav Slaymaker, for his encouragement and support throughout the project. 1 CHAPTER 1 I N T R O D U C T I O N Introduction The i d e n t i f i c a t i o n of landforms and of t h e i r r e l a t i v e size and d i s t r i b u t i o n plays an important role i n the geomorphologic description of t e r r a i n . Landform morphology i s dependent upon s p a t i a l and temporal v a r i a b i l i t y i n geologic, c l i m a t i c , physiographic, and hydrologic conditions, as well as human a c t i v i t y . Variation i n a l l of these factors and t h e i r complex interdependence leads to a wide range of landforms, each of which can be the topic of separate research. Terrain may be described according to constituent materials, form, and/or dominant geomorphologic processes. The organization of t h i s information constitutes geomorpho-lo g i c t e r r a i n c l a s s i f i c a t i o n . Information within the c l a s s i f i c a t i o n system can be retrieved by geomorphologists, engineers, or environmental planners, and applied i n t e r r a i n analysis. The purpose of t h i s study i s to c l a s s i f y and to map the te r r a i n of a steep-sided canyon i n order to provide a detailed discussion of s u r f i c i a l material i n terms of texture, form, genesis,;, and surface-modifying processes. Several measured attributes are used to characterize the canyon slopes i n addition to geomorphologic attributes derived from the t e r r a i n c l a s s i f i c a t i o n . A portion of the Fraser River Valley i n southwestern 2 B r i t i s h Columbia has been chosen for t h i s t e r r a i n c l a s s i f i c a t i o n study (Fig. 1.1). The well-defined valley i s p a r t i c u l a r l y steep-sided i n the section between Yale and Petch Creek, a 22-mile (35 km) stretch which trends d i r e c t l y north-to-south. This area i s here c a l l e d the Fraser Canyon, a r e s t r i c t e d part of the commonly defined canyon between Lytton and Yale. In this area, the upper slopes exhibit much steep, bare bedrock with some coarse c o l l u v i a l material. With increased proximity to the r i v e r , the proportion of colluvium increases, and at the base of the canyon slopes are some f l u v i a l and f l u v i o - g l a c i a l deposits. As i t i s the p r i n c i p a l passageway through the Coast Mountains to the Interior Plateau, the canyon houses both the Canadian National Railway and the Canadian P a c i f i c Railway, as well as the Trans Canada Highway. Slope i n s t a b i l i t y i s a constant concern to engineers responsible for the maintenance of slopes along these routes. The slope attributes derived from a i r photo and f i e l d reconnaissance of the Fraser Canyon are mapped, and then used i n an investigation of slope f a i l u r e i n the region. This i s an example of application of information stored i n a t e r r a i n c l a s s i f i c a t i o n to a geomorphologic analysis or slope f a i l u r e . The hypothesis to be considered i s that the l o c a l i z a t i o n of slope f a i l u r e s along the railway tracks can be related.to upslope s u r f i c i a l geology and to t e r r a i n attributes of slopes adjacent to the tracks. While slope s t a b i l i t y t r a d i t i o n a l l y i s estimated a f t e r intensive research a t - a - s i t e , i t i s impractical to extrapolate 3 4 results of such an investigation to the regional scale of the Fraser Canyon. Thus, to i s o l a t e several geomorphologic slope attributes and to evaluate t h e i r association with slope f a i l -ure i s a more manageable means of assessment. A study of t h i s kind l o g i c a l l y precedes s i t e - s p e c i f i c geotechnical work performed by consulting engineers for the railway and highway companies. I t i s a regional-scale geomorphic inventory of slope character and s t a b i l i t y along the canyon sides. Inquiry at t h i s scale i s of use i n preliminary stages of geotechnical or environmental projects. The reasons for choosing t h i s study area are several. F i r s t , i t i s the most constricted part of the r i v e r v a i l e y . I t exhibits both active and r e l i c t features of i n s t a b i l i t y . Secondly, though the canyon has been of major use as a trans-port corridor for over a century, no t e r r a i n analysis or hazard c l a s s i f i c a t i o n has been made. Since both railway companies are considering increased t r a f f i c load and upgraded track f a c i l i t i e s through the canyon area, i t i s of i n t e r e s t to i d e n t i f y s p e c i f i c t e r r a i n conditions associated with high f a i l u r e incidence. F i n a l l y , the presence of the railway companies, t h e i r potential co-operation with t h i s project, and t h e i r source of f a i l u r e incidence data provided early incentive to work i n .this region. Information gathered i n this study i s from three sources and i s used i n combination to achieve the objectives outlined. A i r photo interpretation and subsequent c l a s s i f i c a t i o n and mapping of the canyon slopes into t e r r a i n units i s the f i r s t 5 data source. Second i s slope attributes co l l e c t e d during the f i e l d season. The incidence of slope f a i l u r e , derived from maintenance records, comprises the t h i r d data source. In generating a t e r r a i n c l a s s i f i c a t i o n map for the Fraser Canyon, a d i s t i n c t i o n must be made between t e r r a i n units and s u r f i c i a l geology. The l a t t e r term refers to materials exposed at the surface of a land area; t h i s may be bedrock or a deposit of unconsolidated material, and i s largely responsible for features of m i c r o - r e l i e f . Methods of description of s u r f i c i a l geology usually include genesis and s p e c i f i c l i t h o l o g i c content of the material. Terrain units define areas within which the s u r f i c i a l geology, geomorphic form, and genesis are homogeneous. The slope attributes describe the geometry and constituent materials of the canyon slopes. Other factors which a f f e c t slope s t a b i l i t y are climate, hydrology, seismicity, and anthropogenic a c t i v i t y . While these aspects are not considered i n d e t a i l i n this project, they present alternate avenues for slope s t a b i l i t y research. For example, the increased incidence of r o c k f a l l s along the west side of the canyon (Canadian P a c i f i c Railway line) since 19 74 has been linked to the introduction of the unit t r a i n concept at that time. These tra i n s consist of more than one hundred uniformly loaded boxcars and are responsible for i n i t i a t i n g strong resonance i n adjacent bedrock. The p r a c t i c a l implications of t h i s i n f o r -mation relate to remedial slope work and to the evaluation of the appropriateness of concrete railway t i e s currently being used to replace old wooden ones i n the area (CO. Brawner, 6 pers. comm.). Better understanding of a l l factors a f f e c t i n g slope s t a b i l i t y i s demanded. The present study has evolved i n stages presented i n a flowchart i n Figure 1.2. I d e n t i f i c a t i o n of the study theme was followed by investigation of t e r r a i n c l a s s i f i c a t i o n techniques and an eventual selection of one scheme. Fieldwork was effected to v e r i f y c l a s s i f i c a t i o n on a e r i a l photography and to evaluate slope attributes along the railway l i n e s . Using f a i l u r e incidence data for the east side of the canyon, s t a t i s t i c a l analysis was performed, exposing relationships between f a i l u r e and slope a t t r i b u t e s . Lastly, methods of r e c l a s s i f i c a t i o n of the slopes into groups of similar t e r r a i n attributes were employed and evaluated. O B J E C T I V E S The primary objectives of t h i s project are: i) to generate a t e r r a i n c l a s s i f i c a t i o n map at an approximate scale of 1:25,000, i i ) to investigate the incidence of slope f a i l u r e , and, i i i ) to i d e n t i f y the slope attributes which contribute most to the explanation of v a r i a t i o n i n the incidence of slope f a i l u r e . The secondary objectives include: i) to i d e n t i f y general i n t e r - r e l a t i o n s h i p s between slope a t t r i b u t e s , i i ) to catalogue types of f a i l u r e occurring i n the area, and i i i ) to evaluate the methodology. Also, methods of generating a c l a s s i f i c a t i o n of slope s i t e s 7 a i r photo i n t e r p r e t a t i o n and t e r r a i n mapping. d e s c r i p t i v e s t a t i s t i c s and frequency d i s t r i b u t i o n s f o r slope a t t r i b u t e s I r e l a t i o n s h i p s between slope a t t r i b u t e s conclusions i d e n t i f i c a t i o n of the study theme fie l d w o r k a n a l y s i s e v a l u a t i o n of methodology and r e s u l t s ~1 slope f a i l u r e data i d e n t i f i c a t i o n of the most s i g n i f i c a n t a t t r i b u t e s c l a s s i f i c a t i o n of s i t e s with respect to slope a t t r i b u t e s and f a i l u r e tendency recommendations f o r f u r t h e r study F i g . 1.2 Organization of the research. 8 adjacent to the two railway l i n e s are evaluated. The success of such a c l a s s i f i c a t i o n i s measured by how well the categories r e f l e c t slope f a i l u r e . The s i t e categories then indicate zones of si m i l a r f a i l u r e tendency assuming that the slope attributes are responsible for, or are reasonable indices of, slope f a i l u r e . 9 CHAPTER 2 T H E F R A S E R C A N Y O N S T U D Y A R E A INTRODUCTION T e r r a i n a n a l y s i s i n v o l v e s the i n t e r a c t i o n of p h y s i c a l c h a r a c t e r i s t i c s of t e r r a i n w i t h environmental v a r i a b l e s o p e r a t i n g i n the study area. An understanding o f the v a r i a -b l e s i s necessary before a l i n k can be made between i n f o r m a t i o n from the t e r r a i n c l a s s i f i c a t i o n and mass movement on s l o p e s . In t h i s chapter, the physiography of the study area i s d e s c r i b e d , and h i s t o r i c a l and environmental i n f o r m a t i o n which i s d i r e c t l y r e l a t e d to e v o l u t i o n of the t e r r a i n i s presented. PHYSIOGRAPHIC DESCRIPTION The F r a s e r R i v e r f o l l o w s a s t r a i g h t , n o r t h - t r e n d i n g v a l l e y between Hope and L y t t o n , B r i t i s h Columbia. From Hope to Yal e , and from Petch Creek t o L y t t o n , the v a l l e y i s r e l a t i v e l y wide and the r i v e r ' s grade moderate. The area chosen f o r study extends from Yale (121026'W; 49°34'N) t o Petch Creek (121°26'W; 49°49'N) and i s c a l l e d the F r a s e r Canyon ( F i g . 2.1). I t i s a s t e e p - s i d e d , f a u l t - d e f i n e d v a l l e y w i t h no major t r i b u t a r i e s and l i e s between the Cascade Mountain complex t o the south and e a s t and the Coast Mountain complex t o the west. G e n e r a l l y the v a l l e y - s i d e s are c h a r a c t e r i z e d by steep rock faces on the upper slo p e s w i t h l a r g e accumulation o f t a l u s a t the base, o c c a s i o n a l f l u v i a l and f l u v i o - g l a c i a l d e p o s i t s , l a r g e 1 0 11 pr e - h i s t o r i c landslide basins, and steep-sided t r i b u t a r y notches. The canyon slopes r i s e 3000 to 4000 feet (1000 to 1200 m) though to the west mountain peaks reach a height of 7000 feet (2100 m). Within the canyon the Fraser River i s bedrock controlled, and i n some places, has incised a notch into the base of the glacially-rounded v a l l e y (Camsell, 1911, p. 108). I t i s not improbable that the actual v a l l e y of the Fraser be due c h i e f l y to i t s own action of 'corrasion' while the predisposing hollow depends on the o r i g i n a l flexures of the rocks . . . (Dawson, 1879, p. 9 8). Currently i t i s thought that i n the Ter t i a r y period, the r i v e r occupied a wide v a l l e y well above i t s present l e v e l , and that i n response to major u p l i f t in the Pliocene epoch, the r i v e r has cut the present canyon. The l a t t e r has since been smoothed during Pleistocene g l a c i a t i o n , and subsequently notched i n the Recent epoch (Holland, 19 76). Davis and Mathews C1944) a t t r i b u t e t h i s type of v a l l e y cross-section to multiple g l a c i a t i o n s , thereby dating the form as Pleistocene. This seems unlikel y at the scale of the Fraser Canyon. The natural steepness of the canyon sides has been l o c a l l y modified by construction of the two railways and the highway. Early descriptions of the unaltered v a l l e y r e f l e c t great d i f f i c u l t y i n i t s penetration: The view Csouth of Boston Bar) changes from the grand to the t e r r i b l e . Through t h i s gorge, so deep and narrow i n many places that the rays of the sun hardly enter i t , the black and ferocious waters of the great r i v e r force t h e i r way (Canadian P a c i f i c Railway Company, 1893). 12 Early t r a v e l l e r s were forced to use t r a i l s and a small road along the v a l l e y slope as the r i v e r i s impassable for any form of vessel. North of Petch Creek the v a l l e y i s r e l a t i v e l y wide, the r i v e r channel i s smooth-sided and the gradient i s 4 feet per mile (0.75m/km) (Piteau, 1977, p. 86). F l u v i a l and f l u v i o -g l a c i a l deposits are continuous along the r i v e r as terraces or a l l u v i a l fans, and l o c a l l y form a narrow zone of gently sloping t e r r a i n along which the road and railway run. At Petch Creek, the r i v e r becomes constricted between steep rock walls, i t s channel i r r e g u l a r i n width and rough-sided. This difference i s attributed to a s i g n i f i c a n t change i n l i t h o l o g y at t h i s point, between soft Paleozoic sediments to the north and younger c r y s t a l l i n e rocks to the south. Between here and Yale, a l l u v i a l fans and f l u v i o - g l a c i a l deposits are infrequent and often dissected, and only near Spuzzum Creek i s there any extensive f l a t land. Scuzzy Creek joins the Fraser River through a narrow gorge and at i t s mouth i s evidence of the major Hope and Yale f a u l t l i n e trending d i r e c t l y north. Opposite Scuzzy Creek is.<: an old landslide scar whose base seems to l i e well above the current r i v e r l e v e l . Though th i s and other landslide scars are commonly attributed to p o s t - g l a c i a l (Recent) adjustment of the slopes (Read, 1960; Piteau, 19 77), the writer believes that some such scars may be related to e a r l i e r landslide a c t i v i t y i n response to late T ertiary f l u v i a l i n c i s i o n . South to Chapmans, the canyon walls are r e l a t i v e l y uniform, 13 comprising steep rock and colluvium extending to the r i v e r (Photo 2.1). Hell's Gate i s the narrowest point i n the canyon, o r i g i n a l l y less than 100 feet (30m) i n width from bank to bank. Since construction of the two railways, many modifications to the natural c o n s t r i c t i o n have been made, including accidental narrowing of the r i v e r immediately upstream from the gate by a large anthropogenic landslide i n 1913, and subsequent building of salmon ladders i n the channel. Black Canyon i s a straight section of the r i v e r where the Recent rock-faced notch i s evident. From Black Canyon south to the Alexandra Bridge, both sides of the canyon are characterized by rockslide scars. A p r e - h i s t o r i c scar on the western side, the Teequaloose landslide, i s greater than one mile (.2 km) i n width. This bowl-shaped scar exhibits steep headwalls, a c t i v e l y f a i l i n g i n some places, a more gently sloping and dissected base, and prominent bedrock mounds of 30Q feet C100 m) i n height at the r i v e r ' s edge.(Fig. 2.2 a). The same configuration i s seen at the larger Kuthlath landslide opposite Yale, where some f l u v i a l gravels are c l e a r l y exposed adjacent to the rock mounds. This evidence suggests that the present landform derives from a landslide whose base was cut away and/or reworked by f l u v i a l processes. It seems that the r i v e r flowed i n the bowl of the s l i d e at one time, but has since cut a more d i r e c t route across the mouth of the bowl (Fig. 2.2 b,c). On the basis of subsequent Fraser River i n c i s i o n , these landslide events may have been pre-Pleistocene. From the Alexandra Bridge south to Stout the canyon i s Photo 2.1 Extensive c o l l u v i a l slope above mile 11.6 (18.6 km) on the western side of the canyon. Note also the steep trackside slope of bedrock i n the foreground. 15 x headscarp ,,^,~7 r o ck fluvial  L A N D S L I D E S C A R I I R O C K M O U N D © © © F i g 2.2 Aspects of p o s t - g l a c i a l l a n d s l i d e s . a) C r o s s - s e c t i o n b) P l a n view o f the hypothesized channel c o n f i g u r a t i o n i n the l a n d s l i d e bowl s h o r t l y a f t e r the f a i l u r e event c) P l a n view o f the present channel c o n f i g u r a t i o n 16 marked by occasional benches of f l u v i a l and f l u v i o - g l a c i a l material on both sides up to the 1000 foot (300 m) l e v e l (Photo 2.2). The r i v e r channel here i s smooth-sided and wider than to the north or south. At Stout, the large f l u v i o - g l a c i a l l e v e l ends and the canyon becomes constricted again. On the western slope the a l l u v i a l fan of Spuzzum Creek has been deeply dissected by the creek and truncated by the Fraser River, and i s graded to the terminal surface of the f l u v i o -g l a c i a l l e v e l s . Signs of aeolian deposition occur throughout the study area and the most extensive capping of windblown sand and s i l t occurs on the south side of the Spuzzum Creek fan. The area south of Stout i s the most precipitous of the entire canyon, having steep rock faces up to 1500 feet (460 m) i n elevation, and r e l a t i v e l y l i t t l e gently sloping land or area of talus accumulation. The r i v e r i s of variable width and has an i r r e g u l a r channel boundary. Some prominent rock islands and rapids occur i n t h i s stretch, ending with the l a s t bedrock c o n s t r i c t i o n i n the r i v e r near Yale. The grade of the Fraser River over the entire canyon section i s 8 feet per mile (1.5 m/km) (Camsell, 1911, p. 108; Piteau, 1977, p. 86). The Kuthlath landslide bowl, on the eastern side of the canyon just upstream from Yale, i s roughly 115 miles (3 km) i n diameter and i s si m i l a r to the Teequaloose bowl mentioned previously. South of Yale, the valley widens, steep rock faces are less prevalent and set back from the r i v e r , and terraces of Photo 2.2 F l u v i a l terraces at mile 18.0 (29.0 km) of the eastern side and mile 20.0 (32.2 km) of the western side of the canyon. Photo looks southeast. 18 f l u v i a l and f l u v i o - g l a c i a l material are common along i t s length. The gradient of the r i v e r i n th i s section i s 3.5 feet per mile (0.65 m/km) (Piteau, 1977, p. 86). DRAINAGE While no major t r i b u t a r i e s j o i n the Fraser River within the study area, several streams enter from the western slopes: Scuzzy, Spuzzum and Sawmill creeks [Fig. 2.1). Only one of equivalent size to these, Siwash Creek, enters from the east. Tributary creeks enter the Fraser River v i a steep bedrock notches, and flow through rounded valleys hanging well above the present r i v e r l e v e l . Spuzzum Creek alone flows conformably into the Fraser River through i t s a l l u v i a l fan deposits. The Fraser River drains an area of 83,500 square miles 2 (.216,300 km ) upstream from Hope. Average monthly discharge and suspended sediment load measured at the Hope sta t i o n are shown i n Table 2.1. Because t h i s portion of the r i v e r i s bedrock-controlled, changes i n i t s channel morphology are slow, and only i n several places can any a l t e r a t i o n i n the r i v e r ' s course be detected. Rather, the r i v e r has degraded i t s channel i n Recent time, and t h i s process i s ongoing. Piteau (1977) claims that l a t e r a l erosion i s as important as v e r t i c a l i n c i s i o n , but t h i s i s not evidenced i n the canyon region. The long p r o f i l e of the r i v e r i s r e l a t i v e l y straight, with step-like breaks occurring near Scuzzy Creek, Hell's Gate, and i n several locations upstream from Yale. The seasonal nature of discharge and sediment load i s also 19 Period Discharge (1912-76) f f v s e c nr/sec Suspended Sediment Load (1965-76) tons/day January 32600 923 3370 February 30400 861 3110 March 28700 813 7050 A p r i l 58500 1656 55700 May 171000 1927 240000 June 252000 7136 221000 July 200000 5663 94000 August 128000 3625 43800 September 86000 2135 18200 October 70500 1996 16500 November 56200 1487 9720 December 40400 1144 3320 Annual 96900 2744 59400 Table 2.1 Mean monthly discharge and suspended sediment load for the Fraser River, measured at Hope, B.C. (Water Survey of Canada, Historical Streamflow Summary, 1977, and His t o r i c a l Sediment Data Summary, 1978). 20 noted i n Table 2.1. May, June and July t y p i c a l l y experience the highest discharges, and the annual discharge maximum occurs most frequently i n the second week of June. This peak averages 250,000 to 350,000 cubic feet per second (7079 to 9911 m3/s) l(.Muir, 1969, p. 9). The freshet i s caused by snowmelt runoff, the contribution by r a i n f a l l at that time being small. For peak flood conditions to develop, there must be cool weather and at le a s t average snowfall, followed by a sudden and continued temperature r i s e (Quick, 1965, p. 62). Such a flood occurred i n 189 4 when the Fraser River rose more than 70 feet (20 m) and washed out the f i r s t Alexandra Suspension Bridge north of Spuzzum. The discharge has been estimated at 620,000 3 cubic feet per second (.17,556 m /s) compared to that of 3 520,000 cubic feet per second (.14,725 m /s) during another major flood i n 1948 (Muir, 1969, p.6). At Hell's Gate during high water, the l e v e l may r i s e to a t o t a l depth of 200 feet C.60 m) or more. GEOLOGY Interest on the part of Canadian P a c i f i c Railway i n a r a i l passage through the C o r d i l l e r a sparked many studies of the t e r r a i n and geology of major r i v e r valleys through the mountains. The f i r s t report on the geology of the Fraser River Valley was made to the Geological Survey of Canada by A.R.C. Selwyn i n 1872 CSelwyn, 1872). The most complete report was made by George Dawson, who detailed aspects of physiography and geology i n southwestern B r i t i s h Columbia (Dawson, 1879). Reginald 21 Daly (1912) was the f i r s t to report f u l l y , and name, rock units i n the v i c i n i t y of the Fraser Canyon. Since the 19 40's, further work i n southwestern B r i t i s h Columbia and northwestern Washington State comprises geologic mapping including the Fraser Canyon area (Cairnes, 1944; McTaggart and Thompson, 1967; Monger, 1970) and studies of the s t r u c t u r a l relationships between rock units (Morris, 1955; Read, 1960; McTaggart and Thompson, 1967; Roddick and Hutchinson, 1969; Monger, 1970; Wheeler, 1970). For more complete l i s t i n g s of work i n surrounding areas, see Read (1960), Misch (.1966) , and Monger (.1970) . Of the various geologic maps mentioned previously, that by Monger (19 70) has been adopted for use i n this study since i t i s the most recent version covering the whole study area at a scale of 1:250,000. Five rock units are found exposed i n the valley walls of the Fraser Canyon between Yale and China Bar (Monger, 19 70, Hope map sheet, west h a l f ) . These are the i) Scuzzy Pluton (Late Eocene to Miocene) i i ) Yale Intrusives (Late Cretaceous or Early Tertiary) i i i ) Spuzzum Intrusives (Late Cretaceous or older) iv) Custer Gneiss (Late Permian or older) v) Hozameen Group (Devonian? Carboniferous? and Permian?) They w i l l be described i n chronological sequence (Fig. 2.3). 22 23 Hozameen Group The Hozameen Group r e p r e s e n t s the o l d e s t and l a r g e s t s t r a t i f i e d bedrock type exposed i n the F r a s e r Canyon. I t i s represented by f o u r u n i t s o f Late P a l e o z o i c (?) sedimentary and v o l c a n i c rocks of gr e a t magnitude, a s i n g l e u n i t a c h i e v i n g as much as 10,000 f e e t (3000 m) i n depth (McTaggart and Thompson, 1967, p. 1201). Most l i k e l y i t i s the uppermost of these u n i t s , approximately 7000 f e e t (2100 m) i n t h i c k n e s s , t h a t i s exposed along the e a s t bank of the F r a s e r R i v e r , extending 2.5 m i l e s (4 km) nor t h and 3.7 m i l e s (.6 km) south of Stout (McTaggart and Thompson, 1967, p. 1201) . The Hozameen Group comprises greenstone, c h e r t , p e l i t e , and some limestone, the greenstone being i n t r u d e d near Stout by younger g r a n i t e s and g r a n o d i o r i t e s (Monger, 19 7 0, p. 3). Greenstone r e f e r s t o somewhat a l t e r e d b a s i c v o l c a n i c s , i n t h i s case, a n d e s i t i c b a s a l t and s p i l i t e (Monger, 19 70, p. 4). The o r i g i n a l composition and t e x t u r e has been o b l i t e r a t e d by subsequent s h e a r i n g (McTaggart and Thompson, 1967, p. 12Q2). Chert i s the most common sediment represented i n the Hozameen Group, as limestone i s i n f r e q u e n t and occurs w i t h i n the v o l c a n i c sequences (Monger, 1970, p. 4). L i n e a t i o n s , f o l d s , and j o i n t s occur i n the Hozameen rocks, and i n the greenstones i n p a r t i c u l a r , minor s t r u c t u r e takes the form of c l o s e j o i n t s and f a u l t s (McTaggart and Thompson, 196 7, p. 120 3). They u s u a l l y are o r i e n t e d northwest t o southeast. G e n e r a l l y the greenstones are h i g h l y competent while the ch e r t i s weak. 24 To the south of the p r e s e n t study area, the Hozameen Group i s c l e a r l y i n f a u l t c o n t a c t w i t h the younger Custer Gneiss to the west, whereas near Stout t h i s r e l a t i o n i s g r a d a t i o n a l Near the g n e i s s the raetamorphic grade i s r e l a t i v e l y h i g h , and the g r a i n s i z e o f c o n s t i t u e n t m i n e r a l s c o r r e s p o n d i n g l y l a r g e r (McTaggart and Thompson, 196 7, p. 12 03). The Hozameen F a u l t separates the Hozameen Group from the J u r a s s i c rocks to the e a s t . The f a u l t t r a c e can be f o l l o w e d n o r t h from the i n t e r n a t i o n a l border to L y t t o n , where i t merges with other major f a u l t s . C u s t e r Gne1ss The Custer Gneiss named by Daly (1912) l i e s t o the west of the Hozameen Group and has s p o r a d i c occurrence along the western s i d e of the F r a s e r Canyon ( F i g . 2.3). Formation was thought to have occ u r r e d v i a metamorphic a l t e r a t i o n of a g r a n o d i o r i t e b a t h o l i t h d u r i n g f a u l t i n g and s h e a r i n g . McTaggart and Thompson p o s t u l a t e d t h a t the gneiss was formed by metamorphism and migmatization of the o l d e r Hozameen Group (McTaggart and Thompson, 1967, p. 1208, a f t e r M i s c h ) . The gneiss i s a c o n t i n u a t i o n of the S k a g i t metamorphic b e l t (McTaggart, 1970, p. 138 a f t e r Misch, 1968) . The gneiss comprises " l i g h t l a y e r s r i c h i n p l a g i o c l a s e . . . a l t e r n a t i n g w i t h dark l a y e r s r i c h i n b i o t i t e and/or hornblende" (Monger, 1970, p. 35). Toward Yale and northwards to Stout the u n i t appears p a l e i n c o l o r , f r i a b l e , s h a t t e r e d and j o i n t e d , and i n d i v i d u a l m i n e r a l c r y s t a l s are sheared, or m y l o n i t i z e d . 25 T h i s l i g h t e n e d c o l o r r e s u l t s from a l t e r a t i o n and b l e a c h i n g o f the mafic m i n e r a l s and to accumulation of a l t e r a t i o n products on the many s m a l l j o i n t and f r a c t u r e s u r f a c e s (McTaggart and Thompson, 1967, p. 1206) . Minor s t r u c t u r e s i n the Custer Gneiss are s i m i l a r t o those e x h i b i t e d by the Hozameen Group, i n c l u d i n g i n t e n s e s h e a r i n g and m y l o n i t i z a t i o n near t h e i r j u n c t i o n (McTaggart and Thompson, 1967, p. 1205). O r i e n t a t i o n of l i n e a t i o n s and s m a l l f o l d s i s toward the northwest. In the F r a s e r Canyon area, the Custer Gneiss l i e s i n f a u l t -c o n t a c t w i t h s c h i s t s t o the west (Monger, 1970, p. 36) and i t i s p o s s i b l e t h a t the a l t e r a t i o n and d i s i n t e g r a t i o n of the a d j o i n i n g g n e i s s r e s u l t e d from f o l d i n g and s h e a r i n g of these s c h i s t s (McTaggart and Thompson, 1967, p. 1210). In the v i c i n i t y o f Y ale, the Custer Gneiss grades through younger Ya l e I n t r u s i v e s i n t o the Hozameen u n i t to the e a s t ; however, at Saddle Rock the gneiss grades d i r e c t l y i n Hozameen r o c k s . Spuzzum I n t r u s i v e s The Spuzzum I n t r u s i v e rock extends from Saddle Rock to the Alexandra Bridge on the west bank, with another s m a l l occurrence on the same s i d e of the r i v e r a t China Bar. On the e a s t s i d e o f the r i v e r i t extends from o p p o s i t e Spuzzum Creek to China Bar, w i t h a gap a t the H e l l ' s Gate a r e a . The predominant rock type i s quartz d i o r i t e , or t o n a l i t e , which appears b l a c k and white and i s darkened more by hornblende than by b i o t i t e (Monger, 1970, p. 40). The t o n a l i t e i s g n e i s s o i d i n the F r a s e r Canyon, and toward China Bar i s very c o a r s e - g r a i n e d . 26 Folding and high-grade metamorphism along a northwest axis passing through Spuzzum i s associated with the emplacement of t h i s intrusive rock (McTaggart, 1970, p. 146). Yale Intrusives The Yale intrusives occur as s i l l s , dykes, and small masses on the western edge of the Hozameen Group. They are more or less continuous from 8 miles (12.9 km) south of Hope northwards to Saddle Rock and occur mostly on the east side of the Fraser River. These intrusions comprise granodiorite with minor a p l i t e and quartz d i o r i t e . The rocks exhibit graded junctions with the Spuzzum to n a l i t e and the Custer gneiss, and may contain inclusions of the l a t t e r rocktype (McTaggart and Thompson, 1967, p. 1215; Monger, 1970, p. 41). The Yale Intrusions are strongly sheared and f o l i a t e d , and of i n t e r -mediate competence. The Hozameen and Custer units are cut by dykes and s i l l s of Yale Intrusive material which has taken on the mirror structure of the host rock. Scuzzy Pluton Extensive g r a n i t i c rocks i n the:..northern end of the study area are attributed to mid-Tertiary intrusion by the Scuzzy Pluton. This l a t t e r was one of three major batholiths appearing i n that period; the Needle Peak and Chilliwack plutons occur further south. The rock unit appears on the east bank i n the v i c i n i t y of Hell's Gate, and on the west bank from Tsileuh Creek northward past China Bar. At Hell's Gate the granodiorite 27 i s considerably finer-grained, less obviously f o l i a t e d , and more massive than toward Scuzzy Mountain but i s considered part of the same intru s i v e event (Monger, 1970, p. 42). The rock comprises fine-grained b i o t i t e and coarser quartz and feldspar, and i s of considerably lower mafic mineral content than the main body of Scuzzy Pluton. Jointing and fracture i s r e l a t i v e l y i s o t r o p i c and coarse, giving the granodiorite much higher competence than other granites i n the region. REGIONAL FAULTING At the regional scale, f a u l t s run predominantly north-south, with smaller s p l i n t e r - f a u l t s as the signature of l o c a l stress release CFig. 2.3). Faults are important i n terms, of s t r u c t u r a l history and resultant physiography of the area, and influence rockslope s t a b i l i t y along the canyon. McTaggart and Thompson (1967, p. 1223) recognize three main f a u l t contacts i n the Fraser Canyon area. These are: i) between the Custer gneiss and the Hozameen unit, i i ) the Hozameen Fault, between Hozameen rock and Jurassic-Cretaceous units to the east i i i ) within the Custer gneiss, Hozameen Group and Spuzzum Intrusions, forming the south east end of the Fraser River Fault Zone. In the Fraser Canyon, the boundary between the gneiss and the Hozameen rock i s a gradational, metamorphosed band and probably i s not fault-contact. Two major f a u l t l i n e s c a l l e d the Hope and Yale fau l t s together define the Fraser River Fault Zone (Duffel 1 and McTaggart, 1952; McTaggart, 1970, p. 146). 28 T h i s f a u l t zone i s thought to s t a r t a t the S t r a i g h t Creek f a u l t , a p o s s i b l e e x t e n s i o n of the Yale f a u l t , and be t r a c e d northwards f o r more than 200 m i l e s (3 20 km) beyond the i n t e r n a t i o n a l border (Misch, 1966, p. 108; McTaggart and Thompson, 1967, p. 1224). The Hozameen f a u l t i s the e a s t e r n -most one, and e x h i b i t s a narrow band of s e r p e n t i n i z e d rock along most of i t s l e n g t h . The f a u l t zone i s a- s e r i e s of p a r a l l e l f a u l t s , r a t h e r than a s i n g l e plane of r u p t u r e , and i t s t r a c e o f t e n u n c l e a r (McTaggart and Thompson, 1967, p. 1224) The Hope f a u l t runs d i r e c t l y north from Hope along the west s i d e of the F r a s e r R i v e r , and d i p s s t e e p l y to the e a s t . North of Hope, the Yale f a u l t trends s l i g h t l y west of n o r t h and c r o s s e s the F r a s e r R i v e r from eas t to west bank at Y a l e . I t p a r a l l e l s the Hope f a u l t n o r t h t o the Alexandra B r i d g e , where i t c r o s s e s the r i v e r again ( F i g . 2.3). At t h i s p o i n t i t may merge wit h the n o r t h e a s t t r e n d i n g Hozameen f a u l t t o the e a s t (McTaggart and Thompson, 1967, p. 1225), though i s mapped s e p a r a t e l y from the Hozameen f a u l t by P i t e a u (1977, p. 87). C e r t a i n l y the two f a u l t s seem to have c o a l e s c e d near North Bend. The northward t r e n d of the f a u l t s cuts across the northwest s t r u c t u r a l t r e n d of the l i t h o l o g y . The l a s t major movement along the Hope and Yale f a u l t s probably o c c u r r e d i n Eocene epoch though movement may have continued i n t o l a t e T e r t i a r y time i n response to nearby batho-l i t h i c emplacement. North o f the F r a s e r Canyon, however, there i s evidence f o r p e r i o d i c movement along the f a u l t s from C r e t a -ceous through to Recent times ( D u f f e l l and McTaggart, 1952, p. 29 Q U A T E R N A R Y H I S T O R Y I n s o u t h w e s t B r i t i s h C o l u m b i a a n d n o r t h w e s t W a s h i n g t o n S t a t e , f o u r m a j o r P l e i s t o c e n e g l a c i a t i o n s h a v e b e e n d o c u m e n t e d ( A r m s t r o n g e t a l . 1965, p .323, a f t e r C r a n d e l l ; R y d e r , 1969, p . 1 4 ) ( T a b l e 2.2) M o s t r e c e n t o f t h e s e w a s t h e F r a s e r G l a c i a -t i o n w h i c h f o l l o w e d t h e O l y m p i a I n t e r g l a c i a t i o n a n d h a s b e e n c o r r e l a t e d w i t h " t h e c l a s s i c a l W i s c o n s i n g l a c i a t i o n o f t h e m i d - w e s t e r n U n i t e d S t a t e s " ( A r m s t r o n g e t a l . 1965, p .326, a f t e r F l i n t ) . I n t h e l o w e r F r a s e r V a l l e y , s t r a t i g r a p h i c e v i d e n c e f o r s t a d e s i s i n t h e f o r m o f d r i f t , g l a c i o - m a r i n e a n d f l u v i a l s e d i m e n t s . I c e s p r e a d s o u t h a n d e a s t f r o m c e n t e r s i n t h e C o a s t M o u n t a i n R a n g e . N o r t h o f L y t t o n , i c e m o v e m e n t w a s f r o m t h e w e s t a n d c r o s s e d t h e F r a s e r R i v e r v a l l e y a x i s ( R y d e r , 1969, p . 25) . I n t h e F r a s e r C a n y o n a r e a , e v i d e n c e o f m o v e m e n t i s s p a r s e , y e t i c e i s t h o u g h t t o h a v e m o v e d f r o m t h e n o r t h d o w n t h e v a l l e y ( P r e s t , 1970, m a p 1253 A ) . B e c a u s e o f i t s c o n s t r i c t e d n a t u r e , t h e F r a s e r C a n y o n c o n t a i n s l i t t l e g l a c i a l m a t e r i a l . D e v e l o p m e n t o f t h e g l a c i e r s i n s o u t h w e s t e r n B r i t i s h C o l u m b i a o c c u r r e d i n f o u r s t a g e s , i n w h i c h t h e u n d e r l y i n g t o p o g r a p h y h a d v a r y i n g i m p o r t a n c e i n d e t e r m i n i n g i c e m o v e m e n t a n d c o n s e q u e n t g l a c i a l e r o s i o n a n d d e p o s i t i o n ( D a v i s a n d M a t h e w s , 1944, p . 404) ( T a b l e 2.3) I t s e e m s t h a t t h e F r a s e r C a n y o n a r e a m a y o n l y h a v e e x p e r i e n c e d t h e s e c o n d s t a g e o f g l a c i a t i o n , a s e v i d e n c e d b y s h a r p - f a c e d n u n a t a k p e a k s n e a r b y , r o u n d e d h i l l t o p s , t h e s t e e p 30 GLACIAL EPISODE SUBSTAGE TIME lOOO's years B.P. STRATIGRAPHIC EVIDENCE IN THE FRASER LOWLAND NATURE OF THE ICE IN THE COAST MOUNTAINS IV III II I FRASER GLACIATION Sumas Stade Sumas Drift extension of Cordilleran ice to the eastern Fraser Lowland Everson Inter-stade J. X Capilano Sediments uncertain effect of the interstade on the extent of ice in the mountains Vashon Stade ± j — ±H 1 in. Surrey Drift continental ice sheet up to 7500 feet (2300 m) thick Evans Creek Stade large alpine glaciers; i n i t i a l development of the Cordilleran ice sheet OLYMPIA INTERGLACIATION - o — o ~ Quadra Sediments SALMON SPRINGS GLACIATION 3b? Semiamu Drif t PUYALLUP INTERGLACIATION non-glacial •sediments STUCK GLACIATION unnamed d r i f t ALDERTON INTERGLACIATION ? ORTING GLACIATION unnamed d r i f t Table 2.2 Glacial episodes i n southwestern B r i t i s h Columbia (after Armstrong et a l . , 1965; Ryder. 1969). 31 STAGE PHYSIOGRAPHIC CHARACTER GLACIAL CHARACTER CONTROL ON GLACIAL MOVEMENT ASSOCIATED LANDFORMS GLACIAL EROSIVITY 1 r e l i e f much greater than ice thickness alpine glaciers tOpO- ; graphic cirques, horns, U-shaped valleys, hanging tributary valleys, over-deepened gl a c i a l channels ( a l l of southwestern B.C.) strong 2 r e l i e f just exceeds Ice thickness branching glacier systems, extensive Ice fields topo-graphic heavily glaciated trunk valleys, zones of late r a l flow of ice between major valleys ( a l l of southwestern B.C.) moderate 3 ice thickness just exceeds the r e l i e f continuous ice sheet, sometimes _ thin topo-graphic and climatic glaciated valley floors, domed summits, rounded ridges (western Coast Mountains and Georgia Stralt-Puget Sound depression only) limited except at ridge tops and peaks 4 ice thickness much greater than r e l i e f continuous ice sheet of great thickness climatic small, undrained depressions, rounded h i l l s and valleys (Georgia Strait-Puget Sound depression only) negligible Table 2.3 Stages of gla c i a l development and the associated landforms (after Davis and Mathews, 1944). 32 U-shaped F r a s e r R i v e r v a l l e y , and hanging t r i b u t a r y channels. Since the r e t r e a t of the P l e i s t o c e n e g l a c i e r s the area has been a f f e c t e d by s e v e r a l n o t a b l e p r o c e s s e s . These are: i ) The formation of p a r a - g l a c i a l a l l u v i a l fans, p r i m a r i l y at the confluences of Spuzzum and Yale creeks w i t h the F r a s e r R i v e r . The c h a r a c t e r o f s i m i l a r fans i s w e l l documented, p a r t i c u l a r l y i n the upper F r a s e r R i v e r V a l l e y and i n other l o c a t i o n s i n B r i t i s h Columbia by Ryder (1969). They are formed along major r i v e r v a l l e y s i n response to r a p i d t r a n s p o r t and d e p o s i t i o n of g l a c i a l m a t e r i a l s by t r i b u t a r y streams. In the F r a s e r Canyon, there was l i m i t e d space f o r the development of fans with the r e s u l t t h a t m a t e r i a l from t r i b u t a r y streams has been t r a n s p o r t e d by the F r a s e r R i v e r to the F r a s e r Lowland and d e p o s i t e d t h e r e . i i ) The occurrence of e x t e n s i v e p o s t - g l a c i a l l a n d s l i d i n g along the F r a s e r R i v e r i n response to unloading of the s l o p e s and down-cutting by the main r i v e r . Some of these appear to have been r e l a t i v e l y shallow f a i l u r e s , as i n the v i c i n i t y of H e l l ' s Gate. C l o s e r examination of s e v e r a l of the s l i d e s c a r s suggests t h a t they may be o l d e r , perhaps P l i o c e n e or i n t e r -g l a c i a l . i i i ) Continued i n c i s i o n by the F r a s e r R i v e r i n response to P l i o c e n e - P l e i s t o c e n e u p l i f t , r e s u l t i n g i n d i s s e c t i o n of g l a c i a l l y d e r i v e d m a t e r i a l and bedrock. iv) I n c i s i o n by the t r i b u t a r y streams, i n response t o downcutting by the trunk stream. v) J o i n t i n g and s p a l l i n g of bedrock exposed i n near-v e r t i c a l f a c e s along the canyon i n response t o the r e l e a s e of v e r t i c a l and l a t e r a l p r e s s u r e , and to mechanical s t r e s s imposed by seasonal i c e , producing l o c a l i z e d t a l u s accumulations. The r e s u l t i s t h a t the g l a c i a l h i s t o r y i s d i f f i c u l t t o a s c e r t a i n , although i t i s l i k e l y t h a t most of the g l a c i a l m a t e r i a l found i n the canyon d e r i v e s from the l a t e s t phase of the F r a s e r G l a c i a t i o n . 33 SURFICIAL MATERIALS Coll u v i u m i s the predominant s u r f i c i a l m a t e r i a l on s l o p e s o f the F r a s e r Canyon. The c o l l u v i a l s l o p e s are e x t e n s i v e , sometimes i n the form o f c o a l e s c i n g fans or aprons ( F i g . 2.1). On bare and/or a c t i v e s l o p e s the m a t e r i a l tends to comprise very coarse, angular fragments. The depth o f . c o l l u v i u m ranges from s e v e r a l f e e t ( l e s s than one metre) to tens• of f e e t ( s e v e r a l metres), and o f t e n the m a t e r i a l at depth i s f i n e r than .that a t the s u r f a c e . Some d e p o s i t s may be q u i t e deep, p a r t i c u l a r l y i n the bowls of l a r g e p o s t - g l a c i a l l a n d s l i d e s , but t h i s was not measured. F l u v i a l and f l u v i o - g l a c i a l m a t e r i a l s are found o c c a s i o n a l l y along the lower s l o p e s o f the canyon t o an a l t i t u d e o f approximately 1000 f e e t (300 m). E x c e p t i o n s occur i n wider l o c a t i o n s i n the canyon where these m a t e r i a l s have had an o p p o r t u n i t y to accumulate and have escaped subsequent e r o s i o n . Most of t h i s m a t e r i a l was d e p o s i t e d as the Coast Mountain g l a c i e r s were waning at the end of the P l e i s t o c e n e epoch. At t h a t time l a r g e volumes of meltwater were r e l e a s e d and e f f e c t e d t r a n s p o r t and d e p o s i t i o n of g l a c i a l d e b r i s i n the r i v e r v a l l e y s . The d e p o s i t s are found hanging above the Recent bedrock notch i n c i s e d by the F r a s e r River and have the form of l o c a l i z e d patches or t r u n c a t e d l e v e l s . F l u v i o - g l a c i a l m a t e r i a l c h a r a c t e r i s t i c a l l y comprises rounded p a r t i c l e s r anging i n s i z e from g r a v e l s t o b o u l d e r s , i n t e r s p e r s e d w i t h accumulations of s t r a t i f i e d sand and s i l t . I t o c c a s i o n a l l y e x h i b i t s s t e e p l y d i p p i n g and c o n t o r t e d s t r a t a . 34 The fab r i c of f l u v i a l materials i s similar, although the grainsize d i s t r i b u t i o n i s smaller. Well-sorted beds of sand and rounded gravel characterize f l u v i a l deposits. Aeolian sand and s i l t forms a veneer over f l u v i a l and f l u v i o - g l a c i a l deposits i n several spot locations i n the canyon. CLIMATE Between Hope and Lytton there i s a strong c l i m a t i c gradient from marine west coast to sub-humid continental conditions (Appendix I ) . The Fraser Canyon i s seen to e x h i b i t a c l i m a t i c character intermediate between that of Hope and Lytton. This i s most evident i n p r e c i p i t a t i o n trends. There i s considerably less p r e c i p i t a t i o n at Boston Bar than at Yale, and t h i s i s r e f l e c t e d by the sparse forest cover there. At Hell's Gate, 75% of the annual p r e c i p i t a t i o n occurs in the winter months (October to March) of which roughly 16% f a l l s as snow. Large d a i l y temperature ranges, p a r t i c u l a r l y i n the winter months r e s u l t i n up to f i f t e e n freeze-thaw cycles i n each of December, January and February (Piteau, 1973, p. 26). Because of the large portion of steep rock faces i n the Fraser Canyon, much of the bedrock surface i s d i r e c t l y exposed, from lack of snowcover, to frequent wintertime freeze-thaw cycles. These contribute to rock fracture and progressive loss of strength. Piteau (.1973) found that 86% of slope f a i l u r e s recorded by Canadian National Railway (including snow-slides) occurred i n the winter months. 35 VEGETATION AND SOILS The slopes of the F r a s e r Canyon o f f i c i a l l y f a l l i n t o the I n t e r i o r Douglas F i r b i o g e o c l i m a t i c zone, but show c h a r a c t e r i s t i c s of the nearby Mountain Hemlock and C o a s t a l Western Hemlock zones as w e l l . The canyon's f o r e s t s are r e l a t i v e l y sparse and comprise immature or non-productive timber stands ( B r i t i s h Columbia F o r e s t S e r v i c e Inventory Map, 1954). In s e v e r a l l o c a t i o n s where the timber i s a c c e s s i b l e v i a h a s t i l y c o n s t r u c t e d roads, commercial l o g g i n g has o c c u r r e d , e s p e c i a l l y near Spuzzum Creek. Many of the lower s l o p e s were burned d u r i n g the c o n s t r u c t i o n of the two r a i l w a y l i n e s , and the f o r e s t regrowth has not y e t reached m a t u r i t y (Duncan W y l l i e , p e r s . comm.). The f o r e s t s comprise Douglas f i r , mountain hemlock and western hemlock predominantly, w i t h secondary western l a r c h , white spruce, and some Ponderosa pine towards the northern end of the canyon. The f o r e s t undergrowth i s g e n e r a l l y sparse owing to deep shade, mostly comprising f e r n , l i c h e n and moss (Jones and Annas, 19 7 8) . C l e a r e d areas are grassy with few shrubs and b e r r y bushes. Toward the n o r t h e r n end of the canyon, o c c a s i o n a l cactus s p e c i e s i n h a b i t the dry s l o p e s . Most p l a n t forms found i n the canyon have shallow r o o t systems, a l l o w i n g them to s u r v i v e i n l o c a t i o n s where s o i l i s s p a r s e . F r a s e r Canyon s o i l s are b r o a d l y c l a s s i f i e d as humo-ferric p o d z o l s . However, on most of the steeper p o r t i o n s of the s l o p e s , the s o i l i s t h i n and p o o r l y developed comprising a t h i c k o r g a n i c l i t t e r and t h i n m i n e r a l h o r i z o n s and i s more c o r r e c t l y 36 c l a s s i f i e d as a regosol. Where the podzols have developed more f u l l y , the s o i l section i s made up of l i t t e r , f e r r i c and humic organic layers, a l i g h t - c o l o r e d e l u v i a l horizon, and a moderately to heavily cemented mineral horizon. Where the parent material i s colluvium, the s o i l s are usually well-drained. F l u v i a l and f l u v i o - g l a c i a l parent materials can give r i s e to poorly-drained s o i l p r o f i l e s . The s o i l i s often red-brown i n color, coarse-grained, and a c i d i c (Jungen and Lewis, 19 7 8) . HISTORY- AND ECONOMIC DEVELOPMENT Simon Fraser was the f i r s t white man to penetrate the Fraser Canyon area, i n 1808. Having approached by canoe from the north, he was forced to abandon use: of his vessels i n the canyon, and to t r a v e l overland (Downs, 1960, p. 9). The area remained largely unexplored u n t i l a trading post, Fort Yale, was established by the Hudson's Bay Company at the uppermost l i m i t of navigable water on the Fraser River. By 1858, a t r a i l had been cut extending northwards from Yale to Spuzzum along the f a u l t l i n e above and to the west of the r i v e r , across the r i v e r and along the east bank to Chapman's Bar, whence i t l e f t the canyon and followed an overland route to the Anderson River Valley (Lindsay, 1958, p. 13; Howay, 1910, p. 7). This was the route by which supplies were packed, at great expense, to Kamloops, and to miners opening up the Cariboo country. In the 1850's, placer gold was discovered i n Pleistocene deposits along the Fraser River (Monger, 1970, p. 28). Later, i n 1859 and 1860, the Quesnel River and Antler Creek gold s t r i k e s 37 sparked northward movement of miners and goods, usually bypassing the Fraser Canyon by the Harrison Lake-Lillooet or Coquihalla River t r a i l s . Also i n 1859, the town of Yale was surveyed by the Royal Engineers, and i n 1860 a t r a i l was b u i l t by them from Yale to Spuzzum along the Fraser Canyon. In 1861, the Royal Engineers was commissioned to survey for the construction of a wagon road from Yale northward to Clinton, to serve the developing mining community, and by 1862, work was begun on the road (Howay, 1910, p. 8) . The f i r s t six miles northward from Fort Yale had to be blasted from the face of the c l i f f s and some sections were even b u i l t r i g h t over the r i v e r on s t i l t s and cribbing (Downs, I960, p. 2 4). By 1863, the road had been b u i l t through the Fraser Canyon, and the Alexandra Suspension Bridge spanned the r i v e r a mile north of Spuzzum. When completed the road was 18 feet (5 m) i n width and 390 miles (6 30 km) long, and was referred to as the eighth wonder of the world, B r i t i s h Columbia's Appian Way (Laut, 1916, p. 101) (Photo 2.3). In 1872, investigation by the Geological Survey of Canada began i n connection with routing the Canadian P a c i f i c Railway through the mountains (Cairnes, 19 25, p. 5). While several routes were proposed, that along the west side of the Fraser Canyon was recognized as best o v e r a l l for i t s grade, though much rock bl a s t i n g was required along i t s length (Fleming, 1874; Smith, 1878, p. 44). The work was completed i n 1886. The railway was b u i l t quickly and with l i t t l e consideration of the extensive rock shattering e f f e c t of the black powder bl a s t i n g Photo 2 . 3 The Cariboo Wagon Road near B l a c k Canyon ( c o u r t e s y of Vancouver C i t y A r c h i v e s ) 39 e m p l o y e d ( J . M c A r e e , p e r s . c o m m . ) . I n 1 9 1 5 , t h e C a n a d i a n N a t i o n a l R a i l w a y w a s c o m p l e t e d , o c c u p y i n g t h e e a s t e r n s l o p e o f t h e F r a s e r C a n y o n ( T h o m p s o n a n d E d g a r , 1 9 3 3 , p . 2 2 5 ) . R o c k b l a s t i n g i m m e d i a t e l y u p s t r e a m f r o m H e l l ' s G a t e r e s u l t e d i n a m a j o r l a n d s l i d e i n 1 9 1 3 . A l o n g t h i s p o r t i o n o f t h e l i n e , c o n t i n u a l r o c k w o r k i s r e q u i r e d t o r e m o v e l o o s e n e d b l o c k s a n d t o m a i n t a i n t h e t r a c k . T h e T r a n s C a n a d a H i g h w a y w a s b u i l t a l o n g t h e c a n y o n i n . t h e l a t e 19 5 0 ' s , a t w h i c h t i m e t h e C a r i b o o R o a d w a s p u t o u t o f u s e . T h e h i g h w a y f o l l o w s t h e w e s t b a n k f r o m Y a l e n o r t h w a r d t o S p u z z u m , w h e r e i t c r o s s e s t o t h e e a s t b a n k a n d c o n t i n u e s t o L y t t o n . T h e h i g h w a y i s u p s l o p e f r o m t h e r a i l l i n e s a t a l l l o c a t i o n s . A t t h e e n d o f t h e C a r i b o o g o l d r u s h t h e c a n y o n a r e a e x p e r i e n c e d d e p o p u l a t i o n a n d e c o n o m i c d e p r e s s i o n u n t i l i t s r e a l i z a t i o n a s a s c e n i c a r e a . L a n d a d j a c e n t t o t h e r i v e r i s o f m o d e r a t e r e c r e a t i o n c a p a b i l i t y , w h i l e t h e u p p e r c a n y o n s l o p e s h a v e l o w r e c r e a t i o n a l c a p a b i l i t y ( C a n a d a L a n d I n v e n t o r y , 1 9 7 1 ) . T h e c a n y o n s l o p e s a r e t o o p r e c i p i t o u s t o a l l o w c o m m e r c i a l o r a g r i c u l t u r a l d e v e l o p m e n t . T h e e f f e c t o f c o n s t r u c t i o n o f t h e t h r e e m a i n t r a n s p o r t r o u t e s i s m a j o r a l t e r a t i o n a n d o v e r -s t e e p e n i n g o f t h e c a n y o n w a l l s . A l s o , t h e n a t u r a l s t a t e o f s l o p e s h a s b e e n c h a n g e d l o c a l l y b y p o o r l y p l a n n e d c o n s t r u c t i o n o f p r i v a t e l o g g i n g r o a d s . S l o p e o v e r s t e e p e n i n g t h r o u g h h u m a n a c t i v i t y c a n n o t b e b a l a n c e d a d e q u a t e l y b y r e m e d i a l s t a b i l i z a t i o n m e a s u r e s a l o n g t h e e n t i r e c a n y o n . R a t h e r , o n l y t h o s e l o c a t i o n s 40 are treated where slope f a i l u r e occurs most frequently and i s hazardous to the road and railways. 41 CHAPTER 3 T E R R A I N C L A S S I F I C A T I O N A N D S L O P E S T A B I L I T Y INTRODUCTION While the bedrock geology has been mapped i n the Fraser Canyon, the d i s t r i b u t i o n and form of s u r f i c i a l materials have not been investigated. Terrain c l a s s i f i c a t i o n i s a means of organizing and storing geomorphic attributes of the Fraser Canyon. The attributes are subsequently retrieved and analyzed with respect to slope s t a b i l i t y . This chapter comprises an overview of t e r r a i n c l a s s i f i c a t i o n methods followed by a discussion of th e o r e t i c a l slope s t a b i l i t y concepts. The scale dependence of variables i n slope s t a b i l i t y analysis i s discussed, and several case studies i n which t e r r a i n attributes have been related to active geomorphic processes are reviewed. TERRAIN CLASSIFICATION Terrain units are i d e n t i f i e d by "the ch a r a c t e r i s t i c s of the observed landform elements i n the area studied, by the use of a p a r t i c u l a r array of attributes and a p a r t i c u l a r c l a s s i f i c a t i o n procedure" (Speight, 1976, p. 155). Attributes, or t e r r a i n factors, are c r i t i c a l landform descriptors such as form, geometry, s u r f i c i a l material, etc., of which the evaluation determines the qual i t y and boundaries of t e r r a i n units. Terrain factors may be q u a l i t a t i v e or quantitative. 42 The study o f t e r r a i n i n v o l v e s f i v e stages which are c l o s e l y i n t e r - r e l a t e d . These are the d e t e c t i o n , i d e n t i f i c a t i o n , a n a l y s i s , c l a s s i f i c a t i o n and e v a l u a t i o n o f t e r r a i n components (Verstappen, 1977, p. 28; Speight, 1976, p. 162). The i n i t i a l task i s determining which f a c t o r s and landforms are to be co n s i d e r e d i n the c l a s s i f i c a t i o n . A t t r i b u t e s chosen t o c h a r a c t e r i z e the t e r r a i n should a l l be e v a l u a t e d f o r each u n i t o f the study area and l i m i t e d i n number f o r ease i n subsequent a n a l y s i s and i n t e r p r e t a t i o n . A l a r g e number of a t t r i b u t e s s t o r e d w i t h i n a c l a s s i f i c a t i o n system reduces the p r a c t i c a l use of the system. A t t r i b u t e s should be fundamental to the d e s c r i p t i o n of the t e r r a i n u n i t . The nature o f c l a s s i f i c a t i o n of these t e r r a i n u n i t s i s dependent on the envisaged use of the i n f o r m a t i o n . C l a s s i f i c a t i o n s have been made f o r storage o f t e r r a i n i n f o r m a t i o n f o r m i l i t a r y , e n g i n e e r i n g and geographic purposes each w i t h emphasis on d i f f e r e n t s e t s o f t e r r a i n a t t r i b u t e s . The use of t e r r a i n c l a s s i f i c a t i o n and a n a l y s i s as a forerunner t o d e t a i l e d e n g i n e e r i n g s t u d i e s i s becoming more p r e v a l e n t . Such work r e c e n t l y has been u s e f u l i n the proposed r o u t i n g of the A l a s k a o i l p i p e l i n e , and i n highway design i n nor t h e r n B r i t i s h Columbia. A summary of the importance t o g e o t e c h n i c a l e n g i n e e r i n g of t e r r a i n a n a l y s i s i n understanding mass movement and i n e v a l u a t i n g slope s t a b i l i t y i s given by Patton and Hendron (19 74) A h i e r a r c h y o f i n f o r m a t i o n which i s l i n k e d t o t e r r a i n a n a l y s i s i s shown i n Table 3.1. A t t r i b u t e s are used to i d e n t i f y 43 ORDER HIERARCHICAL COMPONENTS EXAMPLES IN THE TERRAIN 1 high generalization and internal v a r i a b i l i t y low RECURRENT LANDSCAPE PATTERN or TOPOSEQUENCE TERRAIN UNIT ATTRIBUTE or TERRAIN FACTOR 1. rock scarp: c o l l u v i a l apron: f l u v i a l terrace 2. gully: a l l u v i a l fan: f l u v i a l terrace: f l u v i a l plain 1. co l l u v i a l apron 2. f l u v i a l terrace 3. a l l u v i a l fan 1. slope angle 2. material texture 3. material genesis Table 3.1 The hierarchy of terrain Information. 44 and define the t e r r a i n units, which commonly occur i n c h a r a c t e r i s t i c associations. These may be l i n e a r or areal relations and are c a l l e d toposequences, or recurrent landscape patterns (Speight, 1968, 1976; Beckett and Webster, 1965) . At best, those attributes chosen to define t e r r a i n units can only be a subset of the t o t a l number of factors determining landform configuration. D i f f i c u l t y arises i n selecting the attributes which contribute most s i g n i f i c a n t l y to the d e f i n i t i o n of the t e r r a i n unit. The development of t e r r a i n c l a s s i f i c a t i o n systems for uses other than geographic information storage derives from two major sources: - the problem of choosing attributes which adequately define t e r r a i n character and give s p e c i f i c information to the user, simultaneously, and - the i n a b i l i t y of the c l a s s i f i c a t i o n designer to specify and i s o l a t e the c r i t i c a l requirements of the user. In a geographic sense, t e r r a i n c l a s s i f i c a t i o n has been developed and used to store s p a t i a l r e l ations of units, primarily categorized by morphometric, genetic, l i t h o l o g i c , and hydrologic variables. Where the user's requirements are straightforward t e r r a i n c l a s s i f i c a t i o n i s most suitable. Desert t e r r a i n has been evaluated for m i l i t a r y vehicle t r a f f i c a b i l i t y , using slope angle as the major c r i t e r i o n (Beckett and Webster, 1965). In engineering practice, however, the demand for detailed i n f o r -mation has often demonstrated the inadequacies of t e r r a i n c l a s s i f i c a t i o n . This p a r t l y stems from the i n a b i l i t y of the engineer to define his requirements i n quantitative form within 45 a c l a s s i f i c a t i o n framework. Also.,- " i t must not be assumed that, because a t e r r a i n c l a s s i f i c a t i o n exists as an apparently l o g i c a l subdivision in nature, i t necessarily have any : significance to an engineer" (Aitchison and Grant, 1968, p. 40). The storage of t e r r a i n information v i a a c l a s s i f i c a t i o n system i s most functional when the number of classes i s reasonable for data processing and subsequent assessment, and when, for each category, a wide range of generalizations can be made (Speight, 1968, p. 162; M i t c h e l l , 1973, p. 27). The number of classes i s determined by the complexity of the t e r r a i n and by the attributes chosen to characterize i t . The i d e a l r e s u l t i s a small number of classes with i n t e r n a l homo-geneity and minimal overlap (Speight, 1976, p. 162) . This perhaps shows the l i m i t a t i o n s of t e r r a i n c l a s s i f i c a t i o n s for engineering use: that generalized t e r r a i n classes do not necessarily i s o l a t e s p e c i f i c variables necessary for an assessment of s u i t a b i l i t y for a p a r t i c u l a r land use. Rather, thi s generalized subdivision of t e r r a i n should be viewed as an important f i r s t step i n engineering (and other) studies, f a c i l i t a t i n g precise focussing of subsequent geotechnical studies. For example, The budget for building or maintaining (a transportation route) must be spread t h i n l y . It w i l l be quite unusual for a p a r t i c u l a r location to be the subject of...a thorough study...Under these circumstances dealing with rock slopes on transportation routes i s as- much an art as a science...geotechnical competence tempered with common sense and experience must be combined with a r e a l i s t i c appraisal of economics to provide an acceptable l e v e l of safety to the user... (Peckover and Kerr, 1977, p. 488) . 46 Several approaches to t e r r a i n c l a s s i f i c a t i o n have emerged with changes i n technology and s p e c i f i c a t i o n s of usage. Terrain units usually r e f l e c t naturally occurring elements defined by th e i r geomorphic character. A l t e r n a t i v e l y , unit may be superimposed onto the t e r r a i n within which a p a r t i c u l a r a t t r i b u t e , or s u i t a b i l i t y for a s p e c i f i c land use, i s defined. In the so-called landscape approach, the t e r r a i n unit, i d e n t i f i e d v i s u a l l y as being separate from i t s neighboring units, i s the basis of the c l a s s i f i c a t i o n system (Mabbutt, 196 8). The unit i s i d e n t i f i e d on the basis of form and material attributes, and within i t the v a r i a t i o n i n these attributes i s small. These are then c l a s s i f i e d into a combinatorial hierarchy of groups with increasing generalization and i n t e r n a l v a r i a b i l i t y . This approach has come about as a r e s u l t of inter e s t i n t e r r a i n at regional and l o c a l scales, not continental and global ones, and of improved methodology with respect to measuring landform character. In p a r t i c u l a r , the use of a i r photographs and t h e i r interpretation i n giving an overview of the area of in t e r e s t , and from which s p e c i f i c s p a t i a l and morphometric information may be e a s i l y acquired, has served to popularize this approach. The p r a c t i c a l outcome has been maps of the morphologic character of t e r r a i n at the l o c a l and regional scales, the c l a s s i f i c a t i o n t y p i c a l l y based on the process of landform development attributes (Fig. 3.1 a,b). The parametric approach to c l a s s i f i c a t i o n has been promoted by engineers whose demand i s for s i t e - s p e c i f i c , rather than 47 M O R P H O L O G I C A L M A P P I N G S Y M B O L S ( a ) "V V V~ Angular convex break of slope v v v Angular concave break of Mope ~V V V~ Smoothly convex change of slope V V v _ Smoothly concave change of slope 6 Angle of slope (degrees) Cliffs (bedrock, 40* or more) TTl l l II IT 11 M Breaks of slope TT I T T~ Changes of slope ^ » . Convex slope unit | «*• Concave slope unit Convex and concave too close together to allow the use of separate symbols (b) M O R P H O L O G Y Steepness of slope (degrees) B R E A K S O F S L O P E -tj ^ ^- Convex Concave C H A N G E S O F S L O P E -V---V--V- Convex Smal l scarp w-w- Free face Incised gulley dkm F i g . 3.1 (a) I l l u s t r a t i o n of symbols used i n morphological mapping (from Cooke and Doornkamp, 197^, p.3 5 8 ) . (b) Morphological map of an area near Johannesburg (from Cooke and Doornkamp, 197^, p.3 5 9 ) . 4 8 general, t e r r a i n information. Accordingly, the c l a s s i f i c a t i o n often depends on a narrow range of chosen factors, such ; as s o i l clay content, slope angle, or surface material p a r t i c l e s i z e . While th i s approach i s suitable for some situations i t s p r a c t i c a l use i s narrower and less f l e x i b l e than other methods of c l a s s i f i c a t i o n . The landscape approach to t e r r a i n c l a s s i f i c a t i o n permits storage of a wide range of geomorphic variables. L i t t l e attempt has been made, however, to examine the relationship of geomorphic t e r r a i n attributes to slope f a i l u r e incidence. Theoretical slope s t a b i l i t y concepts address the l i k e l i h o o d of f a i l u r e i n small laboratory samples of material, or at pa r t i c u l a r locations. Parameters determining the material strength at t h i s small scale (or micro-scale) are well under-stood. At the regional scale, surrogates for the micro-scale parameters are necessary. SLOPE STABILITY Micro-Scale Concepts The e a r l i e s t equation describing the strength of dry material was presented by Coulomb i n 1776, and had the form, s = c + CT tan 0 , where s i s the material shear strength, c i s the cohesion,& i s the normal stress component of weight, W of the material overlying the f a i l u r e plane, and 0 i s the angle of shearing resistance 49 (Coulomb, 17 76). When groundwater i s present i n fissures or pores i n the material, an omnidirectional hydrostatic pressure, jU., i s exerted on the s o l i d components (rock faces or p a r t i c l e surfaces), which serves to reduce the shear strength. The new form of the equation i s s = c 1 + (CT -JUL) tan 0 1 = c 1 + CV tan 0 1 , where LCf-JLL) = 0" i s the e f f e c t i v e normal stress (Terzaghi, 1943), and c' and tan 0 1 are the e f f e c t i v e cohesion and e f f e c t i v e angle of i n t e r n a l f r i c t i o n , of which the values have changed from the dry condition due to the e f f e c t of water. The preceding equations were developed for s o i l and rock of which the strength has been tested by a r t i f i c i a l shearing imposed along a horizontal f a i l u r e surface. In sloping situations, the normal stess component, (X , i s not equivalent to the weight of the overlying material as discussed previously, but i s reduced by a factor determined by the slope angle i t s e l f : CT = W cos oc where oc i s the angular deviation of the f a i l u r e plane from the h o r i z o n t a l . The o v e r a l l shear strength equation becomes, s = c' + (W cos oc -JUL) tan ^ 1 50 i n moist conditions, whereby (W cos oc -JUL) = CS ' i s the e f f e c t i v e normal stress. The strength of material i s interpreted as the upslope force counterbalancing downslope disturbing forces. This l a t t e r i s termed the shear stress, T , and i s proportional to the weight, W, of the underlying material, and to the i n c l i n a t i o n of the f a i l u r e plane: X = W s i n oc The material remains stable when the shear strength, s, exceeds the shear stress, *"C / and becomes less stable as strength decreases and X—• s. Parameters i n the t h e o r e t i c a l strength equation vary widely i n nature, and are measured i n laboratory or f i e l d tests on very small samples. Here, they are considered to be micro-scale variables. The cohesion term, c, i s a measure of material strength due to a t t r a c t i v e forces or chemical bonding. In unconsolidated materials containing clay-sized p a r t i c l e s , t h i s component of shear strength i s seen to increase with porewater content to a s p e c i f i c maximum point, and then decrease d r a s t i c a l l y as i n t r a - p a r t i c u l a r electrochemical bonds are broken. The value of the cohesion component i n coarser-grained materials i s re l a t i v e l y small, regardless of water content. I t inta c t bedrock, cohesiveness results from chemical bonding and cementation, and i s very high. 5 1 Both rock and unconsolidated materials are seen to have c h a r a c t e r i s t i c f r i c t i o n components dictated by t h e i r c r y s t a l l i n e nature, or by size and gradation of p a r t i c l e s , respectively. For shear f a i l u r e to occur, cr y s t a l s i n rock and grains i n s o i l must move past one another. Two aspects of f r i c t i o n are immediately recognized; the i n t e r - c r y s t a l l i n e or inter-granular f r i c t i o n , and the " f r i c t i o n " of volume increase necessary to e f f e c t shear. Together these factors determine the angle of shearing resistance, $ , which i s dependent on p a r t i c l e shape, sorting, packing, density, water content, and normal stress i n unconsolidated material, and on c r y s t a l structure, j o i n t i n g , and cementation i n bedrock. Further discussion of strength of rock slopes i s found i n Hoek and Bray (1974), and of s o i l strength i n Terzaghi and Peck (1967). Surrogate Variables at Meso- and Micro-Scales Of the many factors known to a f f e c t slope s t a b i l i t y , some may be measured reasonably well at a s i t e while others may not. Problems arise at a given sampling location when, i) data must be extrapolated from that point to represent a larger area, i i ) attributes vary considerably over time (diurnal, seasonal, h i s t o r i c , geologic), i i i ) relevant attributes are i n c o r r e c t l y measured or are overlooked. Although the geomorphologic and engineering emphasis has been on quantitative measurements and calculations, Terzaghi notes that, 52 If a s t a b i l i t y computation i s required under these conditions, i t i s necessarily based on assumptions which have l i t t l e i n common with r e a l i t y . Such computations do more harm than good because they divert the designer's attention from the inevitable but important gaps i n his knowledge of the factors which determine the s t a b i l i t y of slopes. (Terzaghi, 1962, p. 252) The forementioned factors of normal stress, porewater pressure, angle of shearing resistance, and cohesion, are the basic micro-scale components of strength of material against shearing. I t i s costly and time-consuming to evaluate these parameters throughout large areas. Some of the many q u a l i t a t i v e aspects of t e r r a i n which influence the shear strength and can be used i n s t a b i l i t y analysis of material i n slopes at the regional or me_so-scale are b r i e f l y reviewed below. 1. Bedrock geology, structure and metamorphic  history; the mineralogic components of rock, i t s dip and s t r i k e , l o c a l folding, i n t r a - and i n t e r - c r y s t a l l i n e shearing, displacement along strat a , degree of metamorphic a l t e r a t i o n and weakening, nature of weathering products 2. Faulting and jo i n t i n g ; degree of displacement along f a u l t s , nature of the faultzone, density of p r i n c i p a l and " s p l i n t e r " f a u l t s , closeness of j o i n t i n g , attitude of p r i n c i p a l and secondary j o i n t sets, interlocking of j o i n t blocks, degree of i n - f i l l i n g of j o i n t s by debris, action of groundwater i n j o i n t s i n increasing j o i n t spacing, fi s s u r e s , tension cracks 3. Texture of s u r f i c i a l geology; p a r t i c l e s i z e , gradation, angularity, mode of deposition, degree of s t r a t i f i c a t i o n , cementation, porosity, permeability, i n f i l t r a t i o n rate, s u s c e p t a b i l i t y to expansion by water or ice 4. Slope geometry; o v e r a l l angle and aspect of the slope, variations i n angle over the slope, 53 breaks of slope, convexity-concavity, undercutting of the slope base by f l u v i a l or anthropogenic forces 5. Drainage character; pattern and density of stream channels, presence of i n f i l t r a t i o n zones on upper slopes, poorly drained areas 6. Anthropogenic influence; changes i n many of the forementioned factors as a r e s u l t of Man's a c t i v i t i e s The status of slopes i s attributed to a del i c a t e balance struck amongst the factors already mentioned. Some fluc t u a t i o n i n micro- and meso-scale factors frequently occurs within a slope with no outward change i n i t s form. A l t e r n a t i v e l y , a very small change i n one (or more) of these a t t r i b u t e s might suddenly e f f e c t slope f a i l u r e , i n dicating that a geomorphic  threshold i n the balance of slope-determining factors had been attained. This type of threshold may be crossed whether or not factors external to the slope ( i . e . macro-scale variables) are f l u c t u a t i n g . When f a i l u r e occurs due to stimulus by a macro-scale variable, an e x t r i n s i c threshold has been exceeded. ...the threshold exists within the system but w i l l not be crossed and change w i l l not occur without the influence of an external variable (Schumm, 19 73). Superimposed on the meso- and micro-scale factors are continually varying macro-scale variables; climate and seismic a c t i v i t y . The long-term c r e d i b i l i t y of q u a l i t a t i v e and quanti-ta t i v e s t a b i l i t y assessments, based so l e l y on i s o l a t e d measurements of slope strength attributes, must therefore be questioned. 54 The e f f e c t of climate i s exerted v i a temperature and p r e c i p i t a t i o n . The l a t t e r controls the amount of groundwater available for i n f i l t r a t i o n into s o i l or bedrock slopes. Failures occur most frequently during periods of high ground-water recharge, e s p e c i a l l y following snowmelt i n spring and heavy rains i n autumn (Dunne and Leopold, 1978, p. 566; Luckman, 1976, p. 290; Bjerrum and Jorstad, 1968, p. 2). In temperate zones, these periods are associated with frequent f l u c t u a t i o n i n temperature about the freezing point (Piteau, 1977, p. 103; Bjerrum and Jorstad, 1968, p. 2). These cycles cause the buildup of i n t e r s t i t i a l ice which i s thought to weaken unconsolidated material by i t s expansion, and rock faces by increasing outward pressure along j o i n t s and f i s s u r e s (Carson and Kirkby, 1972; Bjerrum and Jorstad, 1968, p. 2). Figure 3.2 shows the average monthly temperature and p r e c i p i t a t i o n curves for the Fraser Canyon, as well as the monthly t o t a l number of r o c k f a l l s recorded along the Canadian National Railway. Figure 3.3 depicts the seasonality of f a i l u r e events at Ferrabee B l u f f s between Black Canyon and Hell's Gate i n the Fraser Canyon. The incidence of events i s seen to be highest when mean temperature i s roughly at the freezing l e v e l , and p r e c i p i t a t i o n i s high. This i s due to the buildup of i n t e r s t i t i a l i c e i n rock joi n t s during freeze-thaw cycles leading to a high t o t a l water content, and to the continuing supply of water v i a p r e c i p i t a t i o n to feed the process. Similar d i s t r i -bution and explanation appears i n a study by Rapp (19 61) i n northern Scandinavia. 55 80 r X •70 (T60 UJ 0_ CO 50 ^ 3 0 20r-o z 10 2 p 10 II 12 P i g . 3.2 Mean monthly temperature and p r e c i p i t a t i o n , and t o t a l monthly incidence of r o c k f a l l s , between 1933 and 1970 (from Peckover and Kerr, 1977 , p.4 9 0 ) . 56 1 9 6 6 1967 1968 1969 1970 F i g . 3.3 Seasonality of movement on rock slopes at Ferabee B l u f f s , near Hell's Gate, between 1966 and 1971 (from Peckover and Kerr, 1977 , P. 4 9 0 ) . 57 The role of seismic shock i n triggering slope f a i l u r e has been documented extensively. In North America, where seismic a c t i v i t y i s r e l a t i v e l y low, the e f f e c t has been noted in a landslide i n 1959 at Madison Canyon, Montana, i n the 196 5 Hope landslide, B r i t i s h Columbia, and i n multiple smaller landslides on Vancouver Island following an earthquake i n 1946 (Hadley, 1978; Skermer, 1976; Mathews and McTaggart, 1969, 1978; Mathews, 1979). Coastal B r i t i s h Columbia experiences moderate seismic a c t i v i t y . Several major quakes have occurred i n the Queen Charlotte Islands to Puget Sound trough (Skermer, 19 76, p. 6, after Gutenberg and Richter). Zones east of the Coast Mountains are found to be of minor seismicity. Thus; the Fraser Canyon, l y i n g at the junction of these two regions, i s thought to experience r e l a t i v e l y l i t t l e s i g n i f i c a n t a c t i v i t y . While the canyon i s located along a major f a u l t system, i t l i k e l y has not been subjected to major movement since the late Eocene epoch (Monger, 1970, p. 54), though may have been active more recently ( D u f f e l l and McTaggart, 1952, p. 89). In Scandinavia where seismic a c t i v i t y i s low also, the e f f e c t of cli m a t i c variables i s assumed to be of much greater importance (Rapp, 1961, p. 109). The i n t e r - r e l a t i o n of micro-, meso- and macro-scale variables as reviewed previously i s shown i n Figure 3.4. CASE STUDIES The micro-, meso-, and macro-scale attributes previously 58 Lithology^ SEISMICITY] Slope Geometry Jointing, Faulting Texture of Unconsolidated Material shear stress Jj effective * cohesion effective normal stress hydrostatic pressure Anthropogenic Influence I angle of shearing resistance K pi£. 3 . H| Inter-relation of_ micro-,'meso-, and macro-scale slope s t a b i l i t y variables . 59 described have been used i n many studies of geographical, geological, and geotechnical nature, some of which are reviewed here. In p a r t i c u l a r cases, h i s t o r i c records have been used to extend the data base. For example, information on g l a c i a l advance and retreat i n the Mont Blanc area has been gathered from h i s t o r i c a l t i t h e records maintained since the sixteenth century (Grove, 1966, p. 129). While i t i s rare to discover so long a record, i t i s not unusual to f i n d obscure but sound documentation of cl i m a t i c or geomorphic phenomena from which an idea of the dynamics of the system may be gleaned. For nearly t h i r t y years, Anders Rapp has been investigating geomorphic processes on slopes i n Scandinavia using a wide range of methods. The objective i n recording type, location, and frequency of slope f a i l u r e i s the quantitative understanding of mass movement i n mountainous t e r r a i n . This i s approached by the detailed q u a l i t a t i v e and quantitative description of r o c k f a l l s , landslides and debris movement. After careful t e r r a i n mapping and inventory of f a i l u r e events, Rapp (1961) investigated, i) the role of temperature fluctuations on material strength, i i ) the rate of retreat of rock walls, i i i ) the geomorphic e f f e c t of slush and snow avalanches iv) debris movement, and v) slow downslope movement of talus and s o i l . In order to extend the f a i l u r e frequency record beyond the scope of his own investigations, Rapp used maintenance records 60 from several nearby railway l i n e s which add as much as t h i r t y years to his own observational data. From these he noted the s p a t i a l d i s t r i b u t i o n of slopes with frequent i n s t a b i l i t y events, as well as the temporal r e l a t i o n of f a i l u r e s to cl i m a t i c factors (Rapp, 1961, p. 104-106) . The d i s t r i b u t i o n of r o c k f a l l s i n Norway has been mapped and related to bedrock and p o s t - g l a c i a l unloading e f f e c t s ; i t i s found that valleys i n metamorphic rock have experienced oversteepening during g l a c i a l periods and currently exhibit the highest r o c k f a l l frequency (Bjerrum and Jorstad, 19 68, p. 1). Although the bedrock i s generally competent i t exper-iences j o i n t i n g and s p a l l i n g where i t i s exposed along the steep valley walls, as well as occasional deepseated landslides of large extent. Thus the reg i o n a l i z a t i o n of f a i l u r e events i s related to geology, slope morphology and g l a c i a l history. In North America, most work on rock slope s t a b i l i z a t i o n has been connected with a r t i f i c i a l l y cut slopes i n open-pit mines. Steep mountain t e r r a i n i n Canada i s sparsely populated and has not commanded the concentrated i n t e r e s t that i t has i n Norway. However, studies have been made of s p e c i f i c locations, generally associated with transport routes, of which several have been carried out i n the Fraser Canyon. The track of the Canadian National Railway follows the east bank of the Fraser River Canyon. Because i t was the second railway constructed along t h i s route, i t occupies the more d i f f i c u l t and precipitous side of the canyon. Relatively sound records have been maintained of the location and frequency 61 of slope f a i l u r e s which i n some way have affected the company's right-of-way. In 1972, a consulting engineer was retained "to determine the c o n t r o l l i n g factors which lead to i n s t a b i l i t y of the slopes along the C.N.R. and to evaluate the quantitative as well as q u a l i t a t i v e significance of these factors i n terms of p o t e n t i a l i t y of future s t a b i l i t y problems" (Piteau, 1973, p. 1) . Ensuing work between Hope and Lytton, B r i t i s h Columbia;, included locating and mapping landforms and slope conditions that could be linked i n a slope s t a b i l i t y assesment. Piteau investigated: i) aspects of slope morphology; mean slope of the canyon walls, i n d i c a t i o n of mass movement i n the form of landslide scars, debris s l i d e s , avalanche tracks, a l l u v i a l fans, abandoned r i v e r channels i i ) Fraser River channel geometry and form; large scale bends, anomalous bulges i n the plan-form of the channel i i i ) slope and f l u v i a l process indicators; l a t e r a l and v e r t i c a l erosion, degradation, aggradation iv) empirical slope f a i l u r e information; date and location of events Other aspects which were considered but not used i n the f i n a l s t a t i s t i c a l analysis were regional f a u l t i n g , s t r u c t u r a l geology, li t h o l o g y and s u r f i c i a l material, g l a c i a l e f f e c t s , c l i m a t i c variables, groundwater ef f e c t s and anthropomorphic changes. Using the information mentioned above, Piteau determined that slope f a i l u r e occurrence was c l o s e l y related to dynamic aspects of r i v e r channel configuration. Where the channel had been constricted by a p o s t - g l a c i a l landslide or forced against the opposite bank by impingement of a tributary a l l u v i a l fan, 62 t h e i n c i d e n c e o f s l o p e f a i l u r e s a l o n g t h e r a i l w a y was h i g h . T h i s was a t t r i b u t e d t o u n d e r c u t t i n g a n d o v e r s t e e p e n i n g o f t h e s e s l o p e s b y t h e F r a s e r R i v e r a s t h e l a t e r a l p o s i t i o n o f i t s c h a n n e l c h a n g e d . S i m i l a r u n d e r c u t t i n g o n s l o p e s a b o v e t h e o u t s i d e b a n k o f t h e r i v e r b e n d s was s u g g e s t e d . T h e r e s u l t s o f a s t a t i s t i c a l a n a l y s i s o f f a i l u r e f r e q u e n c y d a t a w e r e , i ) t h a t b e t w e e n L y t t o n a n d H o p e , 6 6 % o f a l l t h e f a i l u r e i n c i d e n t s o c c u r r e d a l o n g 3 1 % o f t h e v a l l e y l e n g t h , s p e c i f i c a l l y i n t h o s e a r e a s o p p o s i t e a l l u v i a l f a n s a n d o u t s i d e r i v e r b e n d s , i i ) t h a t b e t w e e n B o s t o n B a r a n d Y a l e ( r o u g h l y ) e q u i v a l e n t t o t h e c u r r e n t s t u d y a r e a ) , 6 4% o f a l l e v e n t s o c c u r r e d a l o n g t h e 3 8% o f t h e c a n y o n l e n g t h o p p o s i t e a l l u v i a l f a n s a n d r i v e r b e n d s , i i i ) t h a t 86% o f t h e t o t a l n u m b e r o f s l o p e f a i l u r e s r e c o r d e d ( t h e s e i n c l u d e d s n o w s l i d e s ) o c c u r r e d i n t h e w i n t e r m o n t h s , a n d i v ) t h a t t h e e f f e c t o f a l l u v i a l f a n a n d r i v e r b e n d l o c a t i o n o n t h e f r e q u e n c y o f s l o p e f a i l u r e s was c o n s i d e r a b l y l e s s i n t h e r e a c h b e t w e e n B o s t o n B a r a n d Y a l e t h a n t o t h e n o r t h o r s o u t h . No e x p l a n a t i o n was made o f e v e n t s o c c u r r i n g o n s l o p e s n o t a s s o c i a t e d w i t h a l l u v i a l f a n s o r r i v e r b e n d s ( P i t e a u , 1 9 7 7 ) . I n t h e c a n y o n b e t w e e n B o s t o n B a r a n d Y a l e , P i t e a u ' s e x -p l a n a t i o n i s u n s a t i s f a c t o r y a s t h e r i v e r c h a n n e l i s b e d r o c k -c o n t r o l l e d . D e s p i t e l a r g e s e d i m e n t l o a d a n d h i g h e r o s i o n c a p a -b i l i t y , t h e r i v e r d o e s n o t e x h i b i t p r o m i n e n t l a t e r a l e r o s i o n i n t h e c a n y o n , t h o u g h v e r t i c a l s c o u r i n g h a s o c c u r r e d t o a d e p t h o f 100 f e e t (30 m) i n p o s t - g l a c i a l t i m e . A l s o , t h e n u m b e r , e x t e n t a n d a c t i v i t y o f a l l u v i a l f a n s i n t h e c a n y o n a r e s m a l l , " a n d i n t h e 63 ease of the two largest (at Spuzzum and Yale), the r i v e r channel shows l i t t l e sign of constriction., or d e f l e c t i o n . The influence of channel configuration on s t a b i l i t y of these slopes, even considering the lag-time for slope response, seems to have been over-emphasized. Due to a l t e r a t i o n of the slopes during railway construction the f a i l u r e frequencies may not be in d i c a t i v e of natural f a i l u r e , but rather of that induced by a r t i f i c i a l l y cutting, rock slopes or oversteepening c o l l u v i a l slopes. The r e l a t i o n of these incidents to f l u v i a l controls at the base of the slope i s not d i r e c t , e s p e c i a l l y over the f i f t y - y e a r time span considered. Also, the f a i l u r e records comprise only those events which have d i r e c t l y affected the railway right-of-way, and thus i s incomplete. These aspects must be taken into account both i n the Piteau study and i n thi s project. HAZARD CLASSIFICATION In 19 76 a report was made by Colder Associates to Canadian P a c i f i c Railway i n which trackside slopes were cl a s s -i f i e d according to th e i r hazard to safe passage of t r a i n s . Recommendations as to the type and amount of remedial work were included, based on geology, s u r f i c i a l material and past i n s t a -b i l i t y . The report was not made available to the writer but a similar study performed between North Bend and Savona was released. The c l a s s i f i c a t i o n scheme consisted of a series of p r i o r i t y ratings for preventive or f a i l u r e warning systems (Table 3.2 a,b); Slopes o r i g i n a l l y c l a s s i f i e d into the most 64 a. PRIORITY RATINGS A Moderate probability of failure of sufficient volume in the near future to result i n derailment i f failure undetected. B Some probability of failure i n sufficient volume in the near future to result i n derailment i f failure undetected. C Moderate probability of failure of small volumes which might reach the track. D Moderate probability of localized rocks or rockfalls occurring from extreme climatic conditions - very heavy r a i n f a l l or run-off, extreme freeze-thaw cycles. E Slight p o s s i b i l i t y of localized failures under extreme climatic conditions. Note: Locations with warning fences have been rated 'B'. b. EXAMPLES Mile* Rating Potential Problem Stabilization 99.7 E Local boulder f a l l -Maintain deep ditch 99.9 B Numerous rockfalls -Scale, shotcrete 100.1 A Large wedge failure -Scale, deepen ditch, remove wedge 100.9 D Boulder f a l l -Scale boulders, deepen ditches 101.1 C Local f a l l . One large -Dowels, scale block Table 3.2 a) Priority ratings employed by Golder Associates for trackside slopes i n the Thompson subdivision of the Canadian Pacific Railway (Golder Associates, 1976, p.8) b) Priority c l a s s i f i c a t i o n applied to slopes, with corresponding remedial stabilization recommendations. •Mileages are measured westward from Savona, B.C. (Golder Associates, 1976, p.3 of Table 2). 65 hazardous category 'A' are r e c l a s s i f i e d into a moderately lower hazard category 'B' as soon as any remedial work i s performed. The success of thi s c l a s s i f i c a t i o n system, which stems from a subjective assessment of slopes by experienced rock engineers, was demonstrated the following year. Of twelve f a i l u r e s along rock slopes, f i v e occurred on slopes i n category 'A', six i n 'B1, and one i n 'C. Ten f a i l u r e s on unconsolidated slopes were not reviewed (Colder Associates, 1976, p. 6). A study of rock slopes along transportation l i n e s i n B r i t i s h Columbia was made by Peckover and Kerr (1977). They evaluated rock slope s t a b i l i t y and remedial programs and included a cost-benefit analysis of safety measures. Hydro-s t a t i c pressure i n rock j o i n t s and f r o s t shattering are presented as the two most s i g n i f i c a n t factors leading to rock-slope i n s t a b i l i t y . The paper refers to slopes along the Canadian National Railway as well as those adjacent to highways. Similar reports have been made incorporating the Canadian P a c i f i c Railway slopes, by Brawner and Wyllie (1976), and Brawner (.197 8) . Remedial s t a b i l i z a t i o n measures for various types of slope problem are reviewed. Suggested forms of remedial work are of three types: - those which would increase the s t a b i l i t y of the slope - those designed to protect the right-of-way against obstruction or damage by f a l l i n g material, and, - those designed to give early warning to vehicles approaching an obstruction caused by a slope f a i l u r e . 6 6 The former two are a c t i v e measures while warning systems are termed p a s s i v e (Peckover and K e r r , 1977, p. 493). The e f f e c t i v e n e s s of p r e v e n t i v e slope work i s dependent on economic and s a f e t y p o l i c y , p l a n n i n g , and continuous maintenance of s l o p e s by the r e s p o n s i b l e agents, r e c o g n i z i n g t h a t "the s i z e of an unstable slope i s not a good c r i t e r i o n o f its' danger as a s i n g l e rock can cause an a c c i d e n t " , and " t h a t r o c k f a l l s w i l l not n e c e s s a r i l y occur a t expected l o c a t i o n s (Peckover and Kerr, 1977, p. 504). The i n t e r a c t i o n of slope a t t r i b u t e e v a l u a t i o n and expert judgement i n d e c i d i n g on remedial s t a b i l i z a t i o n measures i s d e p i c t e d i n F i g u r e 3.5. P l a n n i n g the maintenance of rock slopes along t r a n s p o r t routes i n v o l v e s s e v e r a l processes o f i n f o r m a t i o n a c q u i s i t i o n . As o u t l i n e d by Peckover and Kerr (1977), these are: I) study of maintenance records i i ) a p p r a i s a l of i n a c c e s s b i l e upper p r o t i o n s of s l o p e s , i i i ) d e t a i l e d study of s l o p e s adjacent to the r o u t e , iv) i n v e s t i g a t i o n of c o n d i t i o n s a t s p e c i f i c s i t e s , v) formation o f suggestions f o r slope treatment. T h i s study addresses the f i r s t t h r e e stages of the p l a n n i n g p r o c e s s a t the r e g i o n a l , or meso-scale, l e v e l . 67 Site conditions Angle, height, and condition of slopes Size, shape, and soundness of rock Path of rock fall to track Maintenance required Engineering judgement and economics Stabilization methods • r Scaling, trimming Slope modification Drainage Shotcrete Buttress Rock bolts or dowels Anchored cables or nets Anchored mesh Protection methods • Roadway relocation Wire mesh blanket Shaped ditch Catchment area Catch net or fence Catch wall Rock shed or tunnel Warning methods Electric fence Electric wire Combination with protection F i g . 3 . 5 Selection of slope treatment at a s i t e (from Peckover and Kerr, 1977, p.5 0 5 ) . 68 CHAPTER 4 M E T H O D S INTRODUCTION The t e r r a i n c l a s s i f i c a t i o n o f slopes i n the F r a s e r Canyon i n v o l v e d three stages: i ) mapping of the t e r r a i n , i i ) f i e l d v e r i f i c a t i o n and s i t e i n v e s t i g a t i o n , and i i i ) a n a l y s i s The methods used i n a l l three stages are d i s c u s s e d i n t h i s chapter. MAPPING OF THE TERRAIN A i r photography coverage of t h e ! F r a s e r Canyon between Yale and North Bend was a v a i l a b l e a t two s c a l e s , 1:20,000 and 1:40,000. The 1:20,000 photos were most e x t e n s i v e l y used f o r the t e r r a i n c l a s s i f i c a t i o n ; the 1:40,000 frames were used to d e l i n e a t e l a r g e landforms whose boundaries otherwise would not be c l e a r . Because of the g r e a t r e l i e f e x h i b i t e d i n the canyon, the two s e t s were found to have c o r r e c t e d s c a l e s o f 1:19,000 and 1:36,000, measured a t a mean e l e v a t i o n o f 1000 f e e t (300 m) above sea l e v e l . Catalogue numbers of photos used i n t h i s p r o j e c t are l i s t e d i n Table 4.1. The i n t e r p r e t a t i o n was done wi t h the a i d of a Wild Heerbrugg desk-top m i r r o r stereoscope and an Abrams CB-1 pocket ste r e o s c o p e . The l a t t e r o f f e r s both two- and four-power 69 scale f l i g h t frame date number numbers 1:20,000 BC7468 36-38 July 1973 BC7470 16-18; 123-126; 164-167; 228-291 " BC7471 14-17; 141-144 " BC7474 142-144; 264-266 " " BC7475 26-28; 147-149; 200-202 " BC7476 270-272 " " BC7477 104-107; 139-142; 252-255 " " .1:20,000 BC5169 188-194 Sept. 1964 B C 5 2 1 2 148-154 II II Table 4.1 A e r i a l photography used i n the study. magnification and was used i n labwork and i n fieldwork when increased d e t a i l i n c l a s s i f y i n g or delineating s u r f i c i a l material was necessary. After i n i t i a l inspection of the a e r i a l photography, the f i n a l boundaries of the study area were set, extending from the town of Yale to the mouth of Petch Creek, a distance of 22 miles (35 km). An ar b i t r a r y a l t i t u d i n a l l i m i t of 1500 feet a . s . l . (46 0 m) was adopted for the t e r r a i n mapping. Except from very low-frequency, high magnitude events, i t i s unlikely that material would be contributed to the track area from above t h i s l e v e l . The ELUC Terrain C l a s s i f i c a t i o n A new system of t e r r a i n c l a s s i f i c a t i o n has recently been devised for B r i t i s h Columbia. The system, developed i n 1976 by the Environment and Land Use Committee (ELUC) i n V i c t o r i a , 70 was proposed to incorporate t e r r a i n types encountered i n mountainous and plateau regions of the province. I t was designed for use i n a i r photo interpretation at a scale of 1:50,000 and by i t s nature can e a s i l y be extended to other t e r r a i n types as w e l l . Its intended use i s as "a data base suitable to land-use planning and management" (ELUC, 1976, i n t r o . ) . Due to i t s recent introduction the ELUC c l a s s i f i c a t i o n has been applied to a r e l a t i v e l y small proportion of B r i t i s h Columbia to date. The use of the ELUC c l a s s i f i c a t i o n ranges from c o l l e c t i n g and storing data for interpretation of i t s s p a t i a l d i s t r i b u t i o n , to assessing the t e r r a i n with respect to a s p e c i f i c environmental c h a r a c t e r i s t i c or to a p a r t i c u l a r land use (Appendix I I ) . An advantage of the system i s that i t includes both morphologic and genetic information, and allows for ind i c a t i o n of on-going slope and f l u v i a l processes within each mapping unit. These aspects together "generate an empirically-supported q u a l i t a t i v e geological data base for both geological and multiple resource interpretations" (ELUC, 19 76, i n t r o . ) . The ELUC system of t e r r a i n c l a s s i f i c a t i o n was chosen for use i n this study of the Fraser Canyon for several reasons. F a m i l i a r i t y with the c l a s s i f i c a t i o n system and with the t e r r a i n i t s e l f maximizes e f f i c i e n c y i n a i r photo interpretation and minimizes the need for f i e l d v e r i f i c a t i o n . While o r i g i n a l l y designed for use at a scale of 1:50,000, the system has been found useful, at the scale of 1:20,000 chosen for the Fraser 71 Canyon study. The system i s f l e x i b l e i n the amount o f d e t a i l with which t e r r a i n i s d e s c r i b e d . R e s o l u t i o n o f a l l of the t e r r a i n p r o p e r t i e s d e s c r i b e d p r e v i o u s l y w i t h i n the c l a s s i f i -c a t i o n system i s enhanced a t the l a r g e r s c a l e . Two a d d i t i o n s were made to the c l a s s i f i c a t i o n t o expand i t s u s e f u l n e s s w i t h i n the F r a s e r Canyon study area, both o c c u r r i n g w i t h i n the d e s c r i p t i v e terminology f o r slope modifying processes,(Appendix II) . The f i r s t o f these (-X) s i g n i f i e s t e r r a i n u n i t s which are t r a v e r s e d by r a i l or road r o u t e s , and of which the o r i g i n a l form and nature have been a l t e r e d . The c o n s t r u c t i o n o f these ri g h t s - o f - w a y has one of three e f f e c t s on s l o p e s : i ) o versteepening of the rock and/or c o l l u v i a l s l ope by i t s e x c a v a t i o n , i i ) augmentation o f the n a t u r a l slope by a r t i f i c i a l f i l l , or i i i ) combination o f (i) and ( i i ) above. Augmentation of the slop e s f o r the purpose of r a i l w a y t r a c k support i s the l e a s t common of these e f f e c t s o f c o n s t r u c t i o n i n the F r a s e r Canyon because of the steep t e r r a i n encountered t h e r e . Secondly, t e r r a i n u n i t s which have been a r t i f i c i a l l y d e f o r e s t e d f o r c o n s t r u c t i o n or lumbering purposes are marked (-Y). Th i s i s c o n s i d e r e d important, e s p e c i a l l y where these slopes are a l s o t r a v e r s e d by roads (-X) s i n c e the e f f e c t of d e f o r e s t a t i o n i s t o reduce the s t r e n g t h of s u r f a c e m a t e r i a l s , and i n c r e a s e l i k e l i h o o d of f a i l u r e (0'Loughlin, 19 72). Because of the steepness and v e h i c u l a r i n a c c e s s a b i l i t y of many of the canyon 7 2 slopes, r e l a t i v e l y few t e r r a i n units bear th i s symbol. FIELD VERIFICATION AND SITE INVESTIGATION  Fieldwork With the photo interpretation and t e r r a i n c l a s s i f i c a t i o n complete, additional information was needed for a f u l l discussion of slopes i n the study area. A f i e l d program was designed i n which semi-quantitative t e r r a i n attributes were gathered from trackside s i t e s at 0.1 mile (0.16 km) interv a l s along both the Canadian National Railway and the Canadian P a c i f i c Railway l i n e s . The spacing of the sampling points i s consistent with that used i n track maintenance records kept by both railway companies. V e r i f i c a t i o n of the boundaries of t e r r a i n units and st r a t i g r a p h i c d e t a i l was achieved at that time. Slope Attributes as Surrogate Variables The slope attributes were chosen for two purposes. F i r s t , a systematic investigation of slope properties i n the f i e l d y i e l d s r e l i a b l e data on the detailed nature of the slopes. For example, the j o i n t i n g of bedrock or the e f f e c t of excavation of a slope i s not clear from a i r photos. The frequency of occurrence and the di s t r i b u t i o n " of slope attributes augment information stored i n the t e r r a i n c l a s s i f i c a t i o n . Second, since the precise evaluation of micro-scale parameters contributing to slope form and s t a b i l i t y could not be measured within the scope of this project, some v i s i b l y 73 accessible surrogate attributes were selected. The attributes were chosen because they are i n d i c a t i v e of slope s t a b i l i t y , and could be evaluated e a s i l y over the region of t h i s study. Their value as s t a b i l i t y variables at the meso-scale was investigated. The complete l i s t of t e r r a i n attributes, the slope to which they pertain, and t h e i r data sources appear i n Table 4.2. Some attributes are retrieved from the t e r r a i n c l a s s i f i c a t i o n , and one, bedrock geology, has a..source''outside of this study. The attributes acquired i n the f i e l d were subdivided into various value ranges, some dichotomous, others with multiple options, or l e v e l s . For example, f i v e categories of slope angle were used (Table 4.3). A generalized picture of the s p a t i a l r e l a t i o n of the slope attributes appears i n Figure 4.1. The attribute "cutslope" was determined by examination of the slope adjacent to the track for signs of basal over-steepening by b l a s t i n g , bulldozing, or excavation. Whether or not the slope was cut, the material exposed along the upslope and downslope side of the track was recorded as the variable "material". A wide range of maximum stable slope angles has been published for slopes i n bedrock and unconsolidated material. Slopes i n randomly jointed c r y s t a l l i n e rock are unstable at angles greater than 70° (Terzaghi, 196 2), though t h i s value may decrease s i g n i f i c a n t l y where j o i n t i n g i s more regular and roughly p a r a l l e l to the slope face. The bedrock of the Fraser Canyon i s s i m i l a r to that described by Terzaghi, and the value 74 Slope Attribute Relevant Slope Data Source 1. failure incidence trackside and terrain unit h i s t o r i c a l records 2. material genesis terrain unit a i r photos 3. modifying processes terrain unit a i r photos k. bedrock geology terrain unit map (Monger, 1970) 5. cutslope trackside f i e l d observation 6. material of the cutslope trackside f i e l d observation 7. angle trackside f i e l d observation S. height of the slope trackside f i e l d observation 9. distance from the track trackside f i e l d observation 10. jointing trackside f i e l d observation 11. fines trackside f i e l d observation 12. seepage trackside f i e l d observation 13. remedial measures trackside or terrain unit f i e l d observation Table .4.2 Slope attributes considered in the study. 75 Slope Attribute Level Relevance to this study CUTSLOPE MATERIAL ANGLE HEIGHT-DISTANCE" JOINTING FINES-SEEPAGE-REMEDIAL MEASURES -rock • unconsolidated •rock plus unconsolidated • c r i t i c a l -non-critical • c r i t i c a l non-critical coarse intermediate fine intact not applicable -present •absent not applicable -present •absent present absent whether the terrain unit had been cut into for the purpose of construction and thus oversteepened material exposed alongside the track corresponding to the terrain unit c l a s s i f i c a t i o n and (or) the effect of CUTSLOPE angle of the slope adjacent to the track. In rock cuts, 70 i s the angle above which slopes are unstable (Terzaghi, 1962) . In unconsolidated slopes, 410 i s the maximum slope angle for loose material (Evans, 1972) . whether material from the upper parts of the slope might be contributed to the track by mass movement whether the trackside slope i s close enough at i t s base to contribute material to the track by mass movement degree of fracturing in the rock faces: "coarse" denotes joint spacing of roughly 20 feet (6 m) , while "fine" denotes small blocks and shards (not applicable to unconsolidated slopes) whether fine ( s i l t - c l a y ) material was present (not applicable to rock slopes) whether groundwater seepage was seen on the slope above the track whether action had been taken to prevent or warn of future failures (electric warning fences, shotcrete, cement walls, bolts, terracing, grading, catchditch, scaling)  Table 4.3 Relevance of slope attributes measured in the f i e l d study. 76 TERRAIN UNIT AIR PHOTO AND MAP SOURCES FIELD SURVEY SOURCE r material genesis, modifying processes, bedrock geology seepage, material, Jointing, angle,fines TRACKSIDE SLOPE 1 TERRAIN| UNIT L _ Fig. 4.1 Slope attributes considered i n the study. of 70° i s used to segregate stable bedrock slopes from unstable ones i n t h i s study. The surface angle of unconsolidated deposits depends on p a r t i c l e s i z e , genesis and surface-modifying processes. Slopes underlain by unconsolidated materials were divided into three categories: those greater than 41°, those between 30° and 41°, and those less than 30°. In unconsolidated material, slopes greater than 41° are not maintained unless there i s cohesion. Failure i n slopes greater than 41° requires a disturbing force greater than the cohesive strength of the material Csee Chapter 3, p. 50). Forty-one degrees i s the maximum angle of p a r t i c l e accumulation for non-cohesive material (Evans, 197 6, p. 79). Loose unconsolidated material on slopes becomes r e d i s t r i -buted at angles ranging from 30° to 41°, where 30° i s an approximate lower l i m i t for the angle of repose of the material (Evans, 19 76). The mean angle of repose for talus slopes, for example, i s approximately 35°. Generally, slopes of which the angle i s less than 30° are stable. Angles of slopes adjacent to the tracks were measured with an Abney hand-level from the base to the top of the exposure. Typical trackside slope conditions are depicted i n Figure 4.2. Where the o r i g i n a l slope had not been cut or excavated, or where the track was b u i l t on f i l l , the slope angle was not recorded. The hazard, due to slope geometry, of f a i l e d material being contributed to the right-of-way was estimated i n terms 78 UNCONSOLIDATED MATERIALS W c u t s l o p e no c u t s l o p e t r a c k c u t s l o p e BEDROCK SLOPES >70Wtrack " 1 no c u t s l o p e X < 7 0 A t r a c k SLOPE AT A DISTANCE FROM THE TRACK F i g . 4.2 T y p i c a l t r a c k s i d e slope c o n d i t i o n s encountered i n thej F r a s e r Canyon. 79 of two dichotomous variables, the slope height above, and basal distance from, the track i t s e l f . These estimations are semi-quantitative and are made on the basis of p a r t i c l e size and range, angle of the natural slope, and degree of basal excavation i n the case of unconsolidated slopes and of steepness arid degree of overhang i n bedrock slopes. The trajectory of rock- or d e b r i s - f a l l from the slopes to the track was v i s u a l l y assessed. When the hazard of obstruction to the tracks i s high because of the "height" and/or "distance", the attribute(s) i s s a i d to be at the c r i t i c a l l e v e l . Where the slope i s gentle or removed from the track, i t s height and distance are n o n - c r i t i c a l , and the hazard i s low. The degree of j o i n t i n g of rock slopes adjacent to the rights-of-way was recorded. Coarsely jointed faces were those wherein spacing between jo i n t s was greater than about 20 feet (6 m). This attribute was chosen as a meso-scale surrogate f;or.. the rock cohesion parameter at the micro-scale. In slopes comprising jointed dr faulted bedrock, cohesion i s e f f e c t i v e l y zero across j o i n t planes. ...the cohesion even of a moderately jointed rock i s very much smaller than the cohesion... of the same rock i n an i n t a c t state...the influence of cohesion on the s t a b i l i t y of slopes on jointed rock i s r e l a t i v e l y unimportant... we could not determine i t s value by any other practicable means (Terzaghi, 1962, p. 257) Weakening of rock by j o i n t i n g i s aggravated by upward and outward groundwater pressure and by the 9% volume expansion of thi s water upon freezing. Slopes i n unconsolidated material were examined for the 80 presence of fines as an i n d i c a t i o n of t h e i r cohesion. In few cases was evidence of s i l t or clay found. This attribute i s considered one of the least r e l i a b l e i n the study. Groundwater seepage v i s i b l e on the face of unconsolidated and rock slopes was recorded, though t h i s was not frequently observed during the f i e l d study. The seepage variable was chosen as the indicator of hydrostatic pressure. A low incidence of observed seepage does not adequately r e f l e c t groundwater conditions; at the base of one recent s l i d e scar which appeared dry at the surface, a weephole d r i l l e d into the slope was l e t t i n g water under considerable pressure. Where steps had been taken to s t a b i l i z e slopes or i n s t a l l warning systems along the right-of-way, the nature of the work was recorded as the "remedial measures" variable. This included terracing, grading, scaling, b olting, and shotcreting of slopes, i n s t a l l a t i o n of a cement retaining wall, catchditch, or e l e c t r i c fence, or i n the most severe cases, tunnelling beneath the natural slopes. Further discussion of these methods i s made by Piteau and Peckover (1978) . This information was recorded to reinforce slope f a i l u r e data. ANALYSIS  Objectives The aims of the a n a l y t i c a l portion of the project were several: i) to highlight i n t e r - r e l a t i o n s h i p s between slope attributes using frequency d i s t r i b u t i o n and basic s t a t i s t i c s , 81 i ) to measure the amount of " e x p l a n a t i o n " of t o t a l v a r i a t i o n i n the i n c i d e n c e of slope f a i l u r e c o n t r i b u t e d by the twelve s l o p e a t t r i b u t e s c o nsidered, i i ) to e v a l u a t e the c o n t r i b u t i o n of each of the slope a t t r i b u t e v a r i a b l e s t o the v a r i a t i o n i n the i n c i d e n c e of slope f a i l u r e and to e l i m i n a t e the l e a s t i n f l u e n t i a l ones, i i i ) t o group the samples i n t o c a t e g o r i e s whose c h a r a c t e r i s s i m i l a r , iv) t o check whether the c a t e g o r i e s generated on the b a s i s of the p r i n c i p a l a t t r i b u t e s have s i g n i f i c a n t l y d i f f e r e n t slope f a i l u r e i n c i d e n c e and thus are d i s t i n c t , and v) to compare a slope c l a s s i f i c a t i o n based s o l e l y on f a i l u r e i n c i d e n c e with t h a t based on slope a t t r i b u t e s . H i s t o r i c a l Slope F a i l u r e Records The i n c i d e n c e of slope f a i l u r e along the e a s t bank of the F r a s e r R i v e r has been determined u s i n g Canadian N a t i o n a l Railway t r a c k maintenance r e p o r t s . These are compiled as f a i l u r e events occur and d i s r u p t t r a i n movement. Although such records have been kept f o r over f o r t y y e ars they were not r e l e a s e d f o r use i n t h i s study. Instead, the f a i l u r e frequency histograms p u b l i s h e d by P i t e a u (.1977, p. 104-5) have been used as an i n d i r e c t data source. Frequency data used i n t h i s study d e r i v e from records maintained d u r i n g the p e r i o d 194 8 t o 196 8 ( F i g . 4.3) . The frequency i n f o r m a t i o n i s taken from three d i f f e r e n t sources, and s u p p l i e d a t 0.1 m i l e (0.16 km) i n t e r v a l s along the t r a c k . The data s e t has three main l i m i t a t i o n s . F i r s t , snow s l i d e s are recorded as w e l l as rock, d e b r i s and s o i l s l i d e s . While these are suspected to be i n s i g n i f i c a n t i n terms of volume 701 0 ,20 f a i l u r e incidence including snowslides 0: 201 4 mile 6 . 4 km 7 11 .3 8 1 2 . 9 9 1 4 . 5 • A -10 1 6 . 1 1 1 1 7 . 7 1 • a 1 2 P - 9 . 3 -r 1 3 2 0 . 9 1 4 2 2 . 5 = 1 — 15 2 4 .1 1 16 2 5 . 1 1 7 2 7 . 3 18 2 9 . 0 T 1 9 3 0 . 6 4-end of the study area 20 3 2 . 2 2 1 3 3 . 8 T 2 2 3 5 . 4 2 5 4 0 . 2 2 6 4 1 . 8 Pig. 4 . 3 Number of slope f a i l u r e s per 0 . 1 mile ( 0 . 1 6 km) of track as recorded by the Canadian National Railway from 1 9 4 8 to 1 9 6 8 (after Piteau, 1977 , p. 1 0 4 - 1 0 5 ) . Mileages (kilometres) are measured southward from Boston Bar, B.C. Refer to the t e r r a i n c l a s s i f i c a t i o n map enclosed i n t h i s volume. 83 or damage, t h e i r r e l a t i v e frequency w i t h r e s p e c t to rock and d e b r i s f a i l u r e s i s not known. Secondly, f a i l u r e s c o n t r i b u t i n g s m a l l amounts of d e b r i s or rock may not be recorded as the m a t e r i a l i s removed by the t r a i n engine or p a t r o l c a r s . Only 3 f a i l u r e s i n v o l v i n g more than one c u b i c y a r d (1 m ) of d e b r i s are recorded, though an estimate of volume of m a t e r i a l on the t r a c k s i s r a r e l y g i v e n . T h i r d l y , slope f a i l u r e s which do not a f f e c t the right-of-way are not recorded, so t h a t the r e c o r d i s incomplete. F i n a l l y , the accuracy of the r e c o r d i s s u b j e c t to the d i l i g e n c e of the r e p o r t e r ( s ) . The f a i l u r e s may not be recorded u n t i l s e v e r a l weeks a f t e r t h e i r o c c u r r e n c e . While t h i s data s e t i s incomplete, i t may be used t o i n d i c a t e areas prone to i n s t a b i l i t y , though not i n a p r e d i c t i v e sense. The Canadian P a c i f i c Railway has not maintained records of slope i n s t a b i l i t y along the west bank to the same extent, and thus i n f o r m a t i o n about f a i l u r e s i s very sparse t h e r e . Since 19 74, r e p o r t s on slope f a i l u r e s have been made where more 3 than roughly 1 c u b i c y a r d C l m ) has e f f e c t e d t r a c k blockage. The l e n g t h of the r e c o r d i s s h o r t and snow avalanches were not considered; the t o t a l number o f events r e p o r t e d i s very s m a l l . T h e i r value i n subsequent a n a l y s i s , except as an i n d i c a t o r of a c t i v e l y f a i l i n g s l o p e s , i s so s m a l l t h a t the west s i d e of the canyon i s c o n s i d e r e d to have an inadequate r e c o r d of slope f a i l u r e ( F i g . 4.4). Because the r e c o r d of f a i l u r e s i s l o n g e s t on the e a s t e r n s i d e of the canyon, a l l of the i n i t i a l s t a t i s t i c a l work has been c a r r i e d out on the Canadian N a t i o n a l Railway data, and subsequently p r o j e c t e d to the western s i d e . 20\ 0 20 f a i l u r e Incidence excluding snowslides 0 20 4 mile 6 . 4 km 12 1 9 . 3 5 8 . 0 11 13 2 0 . 9 — i 21 3 3 . 8 6 9 .7 -P-7 11 .3 J Z L 8 12.9 9 1 4 . 5 10 1 6 . 1 11 17 .7 14 2 2 . 5 15 2 4 . 1 16 2 5 . 7 17 2 7 . 3 18 2 9 . 0 19 3 0 . 6 — i — 22 35 .4 — i — 25 4 0 . 2 JZL end of the study area n 20 3 2 . 2 23 3 7 . 0 24 3 8 . 6 26 4 1 . 8 F i g . 4 . 4 Number of slope f a i l u r e s per 0 . 1 mile ( 0 . 1 6 km) of track as recorded by the Canadian P a c i f i c Railway from 1974 to 1978. Mileages (kilometres) are measured southward from North Bend, B.C Refer to the t e r r a i n c l a s s i f i c a t i o n map enclosed in this volume. 8 5 D e s c r i p t i v e S t a t i s t i c s The data c o l l e c t e d d u r i n g the f i e l d study and from the t e r r a i n c l a s s i f i c a t i o n are s e m i - q u a n t i t a t i v e and r e q u i r e treatment by non-parametric s t a t i s t i c a l methods. The i n c i d e n c e of f a i l u r e i s an i n t e r v a l v a r i a b l e . The other twelve slope a t t r i b u t e s are nominal v a r i a b l e s , and f i v e of them are dichotomous. Because of t h e i r aggregated nature, the a t t r i b u t e s were s u b j e c t e d to b a s i c d e s c r i p t i v e s t a t i s t i c a l treatment (Appendix I I I . A and B ) . Histograms f o r each of the twelve a t t r i b u t e s were generated to i n d i c a t e the frequency of occurrence of the a t t r i b u t e s ' l e v e l s . C r o s s t a b u l a t i o n o f some o f the v a r i a b l e s was used to r e v e a l common a s s o c i a t i o n s between slope a t t r i b u t e s . Mean valu e s of the i n c i d e n c e of f a i l u r e were generated f o r each l e v e l of the slope a t t r i b u t e s . The o b j e c t i v e i n performing the d e s c r i p t i v e s t a t i s t i c s was to augment d e s c r i p t i o n o f observed t e r r a i n c h a r a c t e r i s t i c s , so t h a t a more complete image of slopes i n the F r a s e r Canyon i s o b t a i n e d . The c r e d i b i l i t y o f the s t a t i s t i c s i s dependent on the sample s i z e , the l e v e l of measurement of the a t t r i b u t e s , and on the degree of i n t e r a c t i o n between the a t t r i b u t e s . Slope A t t r i b u t e E v a l u a t i o n The purpose of t h i s stage o f the a n a l y s i s was to reduce the number of slope a t t r i b u t e s necesary i n e x p l a i n i n g v a r i a t i o n i n slope f a i l u r e frequency. The i n d i v i d u a l and combined i n f l u e n c e of the twelve slope a t t r i b u t e s i n e x p l a i n i n g the 86 v a r i a t i o n i n f a i l u r e was determined using a computer program e n t i t l e d UBC AID3, Automatic Interaction Detector (Appendix I I I . C)'. The eastern slope data were subjected to the analysis, wherein the importance of the twelve attributes was evaluated. In AID3 analysis, the dependent variable i s assumed to be normally d i s t r i b u t e d with no extreme cases. The slope f a i l u r e data along the eastern slope, however, i s considerably skewed to the r i g h t . To combat t h i s , the f a i l u r e data was log-transformed. A l l values were increased by one to eliminate the large zero- incidence class which otherwise could not be log-transformed. The AID3 program s p l i t s the data into discrete groups on the basis of c r i t i c a l variables, i n t h i s case, the slope a t t r i b u t e s . The aim i s to reduce i n t e r n a l v a r i a t i o n of the  groups while maximizing the inter-group v a r i a t i o n . The program output then may be used to decide which of the inde-pendent variables are least useful i n contributing to v a r i a t i o n i n the dependent variable, and to see where i n t e r -action between the independent variables i s present. Numerical Site C l a s s i f i c a t i o n Two methods have been employed to investigate the i n t e r n a l order, or structure, of the data; c l u s t e r i n g and multi-dimension-a l scalogram analysis (Appendix I I I . D). These analyses were made to categorize the canyon slopes using those attributes which contribute most to the explanation of v a r i a t i o n i n f a i l u r e incidence. 87 The desired endproduct of c l u s t e r i n g and scalogram analysis i s a number of slope s i t e classes, each of which may be p h y s i c a l l y discriminated from the others. In order for these classes to serve as a means of f a i l u r e c l a s s i f i c a t i o n as well, the incidence of slope f a i l u r e for the s i t e classes should be s i g n i f i c a n t l y d i f f e r e n t . Cluster analysis involves the collapsing of n variables into one-dimensional space; then the difference or s i m i l a r i t y between cases, or s i t e s , i s a l i n e a r distance which can be measured. Modes of combining and collapsing the variables and of measuring the resultant distances vary and are used to illuminate d i f f e r e n t aspects of the data structure. In this study, the aim i s to maximize inter-cluster ..distances and  i n t r a - c l u s t e r homogeneity. The method of cluster development used i s c a l l e d complete linkage, where "distances" between clusters i s maximized. Because the clustering procedure i s largely a mechanical one, assumptions of randomization and independence of samples, or s i t e s , are relaxed. In fact, i t i s stressed that the systematic choice of data points i s encouraged, either on the basis of including a rare type or of emphasizing areal association between types: . . . i f the selection of some data units promotes the candidacy of others, the e f f e c t should be exploited for the evidence of association rather than neutralized i n deference to independence (Anderberg, 1973, p. 11). Thus the l i n e a r pattern of s i t e s along the r a i l r o a d rights-of-way i n the Fraser Canyon does not invalidate the numerical 88 taxonomy generated by t h i s method. A d i f f i c u l t y of t h i s c l a s s i f i c a t i o n method i s i n d e c i d i n g on the r e s u l t a n t number of c l u s t e r s or c l a s s e s . I t i s at the d i s c r e t i o n of the r e s e a r c h e r t o choose a number of groups s u i t a b l e t o h i s purpose, and to e v a l u a t e them i n t u i t i v e l y and s t a t i s t i c a l l y i f p o s s i b l e . The m u l t i - d i m e n s i o n a l scalogram a n a l y s i s and c l u s t e r a n a l y s i s were used on data f o r the e a s t e r n , western, and combined slopes of the canyon. R e s u l t s o f the c l u s t e r a n a l y s i s f a c i l i t a t e d i n t e r p r e t a t i o n o f the scalogram p l o t s . In t h a t r e s p e c t , the two methods are complementary i n t h i s study. 89 CHAPTER 5 R E S U L T S INTRODUCTION A t e r r a i n map o f the F r a s e r Canyon, e n c l o s e d i n t h i s volume, i s the most important r e s u l t of t h i s study. I t i s the b a s i s f o r d i s c u s s i o n of the m a t e r i a l s and form of the s l o p e s . W i t h i n the context of the c l a s s i f i c a t i o n system, s u r f i c i a l m a t e r i a l r e f e r s t o a l l types o f m a t e r i a l which form the s u r f a c e of the t e r r a i n and t h e r e f o r e i n c l u d e s bedrock as w e l l as u n c o n s o l i d a t e d c o l l u v i a l , f l u v i a l , and f l u v i o -g l a c i a l d e p o s i t s . T h i s chapter comprises a d e t a i l e d d e s c r i p t i o n of the c h a r a c t e r i s t i c form and m a t e r i a l s of the canyon slopes w i t h emphasis on these f a c t o r s which r e l a t e most d i r e c t l y to slope f a i l u r e . An i n v e n t o r y of the types of mass movement i n the canyon i s presented. F i n a l l y , r e s u l t s of the d e s c r i p t i v e s t a t i s t i c s and numerical c l a s s i f i c a t i o n techniques used t o c h a r a c t e r i z e the s l o p e s w i t h r e s p e c t t o f a i l u r e are d i s c u s s e d . TERRAIN CLASSIFICATION, MAPPING, AND FIELDWORK Topographic P r o f i l e s S e v e r a l c h a r a c t e r i s t i c topographic p r o f i l e s , or topo-sequences, have been i d e n t i f i e d d u r i n g t h i s t e r r a i n a n a l y s i s . While steep rock scarps and c o l l u v i a l cones and aprons predom-i n a t e i n the canyon, t h e i r r e l a t i o n to other s u r f i c i a l 90 f e e t 6000-metres i . 4000-2000-0-RS -1000 a r ^ h / arCh or \ ^ / s g F l \ ^ . •o — • i i . 6000-4000-2000« Rs=arCv • 1 0 0 a R s / a r C ^ ^ " ^ 0- • 0 6000' i i i . 4000-2000-Rs//arCv •1000 ^ ^ ^ ^ 0" .Q S V e r t i c a l e xaggeration = 0.82 6000' i v . 4000-2000-0-•1000 a r C v ( b ) » R s ^ ^ ^ ^ * ^ ' ^ Spuzzum a l l u v i a l fan ^ — s g F l \ F i g . 5. 1 Four topographic p r o f i l e s encountered i n the F r a s e r Canyon, i ) A s s o c i a t e d with p o s t - g l a c i a l l a n d s l i d i n g . i i ) Predominantly c o l l u v i a l s l o p e . i i i ) .Steep rock with some c o l l u v i u m . i v ) A s s o c i a t e d with a l l u v i a l f a n s . (Appendix I I ) 91 m a t e r i a l s r e s u l t s i n f o u r p r o f i l e s d e p i c t e d i n F i g u r e 5.1. B e g i n n i n g w i t h t h e i r u p p e r m o s t p o r t i o n s , t h e s e a r e d e s c r i b e d as f o l l o w s : i ) P r e d o m i n a n t l y c o l l u v i a l u p l a n d s b r e a k i n g i n t o s t e e p r o c k y s c a r p s up t o 2000 f e e t (600 m) i n h e i g h t , o f t e n s h o w i n g t r a c e s o f r e c e n t f a i l u r e . A t t h e s c a r p b a s e i s an a c c u m u l a t i o n o f c o l l u -v i a l m a t e r i a l o f v a r y i n g e x t e n t and s l o p i n g t o w a r d t h e r i v e r . I n two c a s e s a s s o c i a t e d w i t h p o s t - g l a c i a l l a n d s l i d e s , t h e r e i s a p r o m i n e n t r o c k k n o l l n e a r t h e r i v e r ' s edge; e l s e w h e r e t h e c o l l u v i a l s l o p e s a r e t r u n c a t e d by t h e downward i n c i s i o n o f t h e r i v e r i n t o t h e u n d e r l y i n g b e d r o c k . i i ) M i x e d b e d r o c k and c o l l u v i a l u p l a n d s g i v i n g way t o s t e e p e r r o c k and c o l l u v i a l c a n y o n s l o p e s . The m a t e r i a l may a p p e a r u n i f o r m l y d i s t r i b u t e d . o r may a p p e a r b a n d e d i n t o s t e p s o f c o l l u v i u m s e p a r a t e d by s t e e p r o c k w a l l s . T h e r e i s a s t e e p r o c k w a l l d e s c e n d i n g t o t h e r i v e r . The a r e a l e x t e n t o f t h e c o l l u v i a l p o r t i o n s , and t h u s t h e s t e e p n e s s o f t h e o v e r a l l p r o f i l e , i s q u i t e v a r i a b l e oh t h i s t y p e o f s l o p e . i i i ) S t e e p r o c k y f a c e s f r o m t h e u p l a n d s t o t h e r i v e r , w i t h r e l a t i v e l y l i t t l e c o l l u v i a l a c c u m u l a t i o n . i v ) M i x e d c o l l u v i a l and s t e e p r o c k s l o p e s a b u t t i n g s u d d e n l y o n t o a g e n t l y s l o p i n g , t e r r a c e d a l l u v i a l f a n t r u n c a t e d a t i t s b a s e by t h e m a i n r i v e r . T h i s i s most o b v i o u s a t t h e l a r g e s t f a n a c c u m u l a t i o n s b u t o c c u r s a t s e v e r a l o f t h e s m a l l e r t r i b u t a r y c o n f l u e n c e s w i t h t h e main r i v e r as w e l l . S u r f i c i a l M a t e r i a l s As i s s e e n on t h e t e r r a i n c l a s s i f i c a t i o n map e n c l o s e d i n t h i s volume, t h e s l o p e s e x h i b i t v a r i a b l e c o m p l e x i t y r e g a r d i n g s u r f i c i a l m a t e r i a l s . Where t h e y a r e p r e d o m i n a n t l y c o m p r i s e d o f c o l l u v i u m t h e s l o p e s a r e most u n i f o r m . The s t e e p e r b e d r o c k and c o l l u v i a l s l o p e s e x h i b i t an i n t r i c a t e t e r r a i n u n i t p a t t e r n 92 and are considerably more complex. This complexity of the slopes within the t e r r a i n c l a s s i f i c a t i o n i s sometimes a r t i f i c i a l l y increased by the superimposition of roads and railway l i n e s onto the natural slopes. The canyon slopes comprise steep rock faces and c o l l u v i a l slopes of varying extent, and some f l u v i a l and f l u v i o - g l a c i a l deposits at t h e i r base. On upper slopes where the steep rock i s prevalent, there are frequent signs of r o c k f a l l and debris-flow, as well as snow avalanching. Material which i s contained within pre-existing stream or debris-flow channels appears to be transported downslope great distances, while that from sporadically f a i l i n g rockwalls may not move further away than the accumulation zone for colluvium beneath the scarp. Presumably the distance t r a v e l l e d by f a l l i n g material i s dependent upon i t s own mass, the nature of the underlying slope (angle, convexity/concavity, roughness, vegetation), and the presence or absence of a channel for the concentration of flow. Along the rights-of-way where c o l l u v i a l deposits have been cut during track construction there are many oversteepened slopes, sometimes i n the order of 50°. The colluvium i s angular and coarse at the surface, but may grade into a f i n e r matrix at depth (Photo 5.1). Remedial measures, such as catchditches, terracing, grading and retaining walls, are found i n some of these locations to prevent dry r a v e l l i n g material from reaching the tracks (Photo 5.2). Near-vertical slopes adjacent to the track commonly r e s u l t P h o t o 5 . 1 B l o c k y c o l l u v i a l m a t e r i a l i n a f i n e m a t r i x a t m i l e 2 0 . 5 ( 3 2 . 8 k m ) o n t h e e a s t e r n s l o p e . 94 from no t c h i n g of the bedrock to form the r a i l w a y r i g h t - o f - w a y . These slopes tower over the t r a c k , arid i n cases where there i s a h i s t o r y o f r e c u r r i n g f a i l u r e , are sometimes guarded by an e l e c t r i c warning fence (Photo 5.3). The rock i s o f t e n j o i n t e d c o a r s e l y , and i n some l o c a t i o n s , l a r g e j o i n t b l o c k s seem p r e c a r i o u s l y balanced above the t r a c k (Photo 5.4). Some of the rock s h a t t e r i n g along the t r a c k s i s a d i r e c t r e s u l t of c a r e l e s s "black powder" b l a s t i n g e f f e c t e d d u r i n g c o n s t r u c t i o n o f the r a i l w a y s , and t h i s tends t o r e s u l t i n a f i n e r j o i n t i n g pattern superimposed on the p r e - e x i s t i n g c o a r s e l y - f r a c t u r e d bedrock. Rock slop e s along the r i v e r and on the upper slopes e x h i b i t s i m i l a r l y coarse j o i n t i n g p a t t e r n s . The a t t i t u d e and angle o f the p r i n c i p a l j o i n t i n g planes p a r t l y determines the s u s c e p t i b i l i t y o f rock s l o p e s t o f a i l u r e . In some l o c a t i o n s the j o i n t i n g planes d i p s t e e p l y toward the t r a c k and the l i k e l i h o o d o f r o c k f a l l onto the right-of-way i s h i g h . Elsewhere the j o i n t i n g i s i r r e g u l a r and loosened b l o c k s are not as e a s i l y d i s t u r b e d . The d i f f e r e n t i a t i o n o f f l u v i o - g l a c i a l m a t e r i a l , t h a t d e p o s i t e d a t or near a g l a c i a l i c e f r o n t , from f l u v i a l l y s o r t e d f i n e s and g r a v e l s , i s d i f f i c u l t i n the F r a s e r Canyon. I t i s l i k e l y t h a t such m a t e r i a l found f u r t h e s t upslope was de p o s i t e d under f l u v i o - g l a c i a l c o n d i t i o n s , whereas the lower-slope m a t e r i a l s are l o c a l l y v a r i a b l e i n t h e i r f l u v i a l and f l u v i o - g l a c i a l o r i g i n . T h e i r s u r f a c e e x p r e s s i o n cannot be used as a d i s t i n g u i s h i n g f a c t o r s i n c e l e v e l s or t e r r a c e -l i k e d e p o s i t s d e r i v e from e i t h e r form of d e p o s i t i o n (Photos Photo 5.2 R e t a i n i n g w a l l t o prevent dry r a v e l l i n g c o l l u v i a l m a t e r i a l from r e a c h i n g the t r a c k at m i l e 10.7 (17.1 km) on the e a s t e r n s i d e of the canyon. Photo 5.3 E l e c t r i c warning fence beneath a steep rock s l o p e at m i l e 11.5 (18.4 km) on the canyon's west s i d e . 96 Photo 5 . 4 Loosened joint-blocks beside the tracks at mile 7 . 5 ( 1 2 . 0 km) on the western side of the canyon. 97 5.5 and 2.2). F l u v i o - g l a c i a l m a t e r i a l comprises s i l t - t h r o u g h t o boul d e r -s i z e d p a r t i c l e s , which u s u a l l y are p o o r l y s o r t e d . In s e v e r a l exposures the overburden p r e s s u r e has squeezed f i n e s i l t and sand i n t o p r e s s u r e r i d g e s w i t h i n the co a r s e r m a t e r i a l s . These appear as bands of v a r y i n g t h i c k n e s s and o r i e n t a t i o n w i t h i n the d e p o s i t (Photo 5.6). Where such d e p o s i t s are exposed along the t r a c k s i d e , the m a t e r i a l i s o f t e n compacted and cemented, and may f a i l i n l a r g e i n t a c t b l o c k s (Photo 5.7). A l a r g e d e p o s i t o f f l u v i o - g l a c i a l m a t e r i a l i s exposed along the e a s t s i d e of the canyon between mile 10.1 and 10.5 (16.2 and 16.9 km) and i s o v e r l a i n by a veneer of coarse c o l l u v i a l b l o c k s . W i t h i n i t are some w e l l - s o r t e d but s t e e p l y s o u t h - d i p p i n g s t r a t a of cobbles and g r a v e l , some zones of completely unsorted p a r t i c l e s from g r a v e l - to b o u l d e r - s i z e d , and s i l t y and sandy i n t e r b e d s . The d e p o s i t i s of v a r i a b l e t h i c k n e s s , appearing only as a veneer over bedrock a t the northern end o f the exposure. A p o s s i b l e j o k u l h l a u p o r i g i n i s suggested f o r t h i s m a t e r i a l (W.H. Mathews, p e r s . comm.). On t h i s b a s i s , f l u v i o - g l a c i a l d e p o s i t s along the e a s t e r n slopes south of mile 13.3 (21.4 km) might have s i m i l a r o r i g i n (Photos 5.8 through 5.11). F l u v i a l d e p o s i t s a t t r i b u t e d t o the c u r r e n t F r a s e r R i v e r regime are n o t i c a b l y uncommon along the canyon, and comprise bars of beaches o f cobbles and b o u l d e r s . Most f i n e r p a r t i c l e s are t r a n s p o r t e d out of the canyon area. Much of the f l u v i a l m a t e r i a l d e p o s i t e d under p r e v i o u s regimes has been removed by the pre s e n t r i v e r , w i t h i t s high d i s c h a r g e and steep grade. Of those remaining, most d e p o s i t s d e r i v e from a p e r i o d when 98 Photo 5.5 F l u v i o - g l a c i a l t e r r a c e a t m i l e 15.0 (24.1 km) a l o n g t h e west s i d e o f t h e canyon. Photo l o o k s southward from the A l e x a n d r a B r i d g e . Photo 5.6 D i p p i n g and c o n t o r t e d s t r a t a i n f l u v i o - g l a c i a l m a t e r i a l found at m i l e 13.4 (21.4 km) on the west s i d e of the canyon. The pen i s v e r t i c a l . Photo 5.7 Blocky f a i l u r e o f cemented f l u v i o -g l a c i a l m a t e r i a l on the western canyon s i d e at m i l e 10.5 (16.9 km). 1 0 0 Photo 5.8 View of a f l u v i o - g l a c i a l exposure along the eastern slope at mile 10.1 (16.2 km). Note the r e l a t i v e l y gentle c o l l u v i a l slope above the track, and the steep rock notch below. Photo 5.9 Poorly sorted f l u v i o - g l a c i a l material at mile 10.1 (16.2 km) on the east slope. Note s t r a t i f i e d sands between the rounded boulders, center of photo. 101 Photo 5 . 1 0 S t e e p l y d i p p i n g g r a v e l - a n d - f i n e s s t r a t a at mile 1 0 . 5 ( 1 6 . 9 km) on the e a s t e r n s l o p e . The pen i s v e r t i c a l . Photo 5 .11 Unsorted f l u v i o - g l a c i a l m a t e r i a l at m i l e 1 3 . 5 ( 2 1 . 7 km) . Note the v e r t i c a l nature o f t h i s c u t f a c e . 102 glacially deposited materials throughout the region were re a d i l y available for reworking by the Fraser River and i t s t r i b u t a r i e s . The most s i g n i f i c a n t are the Yale and Spuzzum a l l u v i a l fans mentioned previously. F l u v i a l material comprises sand, gravel and occasional cobbles, always rounded and sorted into near-horizontal s t r a t a . In some locations, dipping strata are evidence of an e a r l i e r braided channel regime. Some deposits exhibit a wide range i n grainsize and pose a continuing problem i n t h e i r c l a s s i f i c a t i o n (Photos 5.12 and 5.13). Fine sand and s i l t y capping material of aeolian o r i g i n are found very l o c a l l y , on part of the Spuzzum a l l u v i a l fan and at occasional point locations elsewhere along the canyon. While i t may have been more extensive i n e a r l i e r times, l i t t l e of t h i s fine capping has survived subsequent reworking by wind and water. At one s i t e , the aeolian material i s roughly 5 feet (1.5 m) i n thickness, and appears r e l a t i v e l y u n s t r a t i f i e d . Most l i k e l y i t s source was fresh g l a c i a l and f l u v i o - g l a c i a l sediments i n the surrounding uplands, subjected to wind erosion i n a d r i e r , p o s t - g l a c i a l period. Mass Movement The types of slope f a i l u r e encountered i n the Fraser Canyon are presented i n Table 5.1 and i l l u s t r a t e d by photos i n Appendix IV. C o l l u v i a l dry r a v e l l i n g and r o c k f a l l a c t i v i t y were evidenced on a l l parts of the slopes, but were most concentrated along the slopes adjacent to the tracks. Failures 103 Photo 5.12 F l u v i a l t e r r a c e at S t o u t , m i l e 18.1 ( 2 9 . 0 km) on the east s i d e o f the canyon. Photo 5 . 1 3 T r a c k s i d e slope cut i n t o f l u v i a l m a t e r i a l of the Spuzzum a l l u v i a l f a n , at mile 1 7 . 3 ( 2 7 . 7 km) on the west s i d e o f the canyon. A capping of a e o l i a n f i n e s i s roughly 5 f e e t ( 1 . 5 m) t h i c k here. 10 4 i n f l u v i a l , f l u v i o - g l a c i a l , and aeolian materials were not seen, except where these had been excavated during railway track construction. In general, f a i l u r e i n the unconsolidated material was very l o c a l i z e d and took the form of slow d i s i n -tegration of the trackside slope angle to the angle of repose of the material. S u r f i c i a l M O D E S O F F A I L U R E Material undisturbed slopes trackside slopes bedrock p o s t - g l a c i a l landslide r o c k f a l l r o c k f a l l slow disintegration bedrock plus slab f a i l u r e rock- and debris f a l l c o l l u v i a l rock-1ri gge re d co11uvi a1 dry r a v e l l i n g s l i d e s c o l l u v i a l debris s l i d e dry r a v e l l i n g debris flow debris s l i d e debris f a l l f l u v i o - g l a c i a l N.A. debris f a l l dry r a v e l l i n g earth f a l l f l u v i a l : N.A. dry r a v e l l i n g earth f a l l aeolian N.A. earth f a l l Table 5.1 Modes of f a i l u r e encountered on the Fraser Canyon slopes. Those which are underscored are thought to be the most s i g n i f i c a n t in contributing material to the railway rights-of-way (terminology after Varnes, 197 8) . ...... The contents of Table 5.1 r e f l e c t the comparative s t a b i l i t y of f l u v i a l and f l u v i o - g l a c i a l materials i n the undis-turbed state. More catastrophic events occur by sudden f a i l u r e 105 of rock and c o l l u v i a l slopes and may stem from the trackside slope alone, or from higher elevations on the slope. These types are thought to contribute material to the railway rights-of-way most frequently, and are underscored i n Table 5.1. Slopes exhibiting modes of f a i l u r e which occur more slowly are cleaned up before any hazardous amount of material accumulates near the tracks. ANALYSIS The general context of the numerical analyses was outlined i n Chapter 4. Reference to s p e c i f i c analyses i s made in t h i s chapter i n conjunction with the presentation of t h e i r r e s u l t s . The analyses which involve slope f a i l u r e are performed on data for the eastern slopes for which a twenty-year record i s available. The s t a t i s t i c a l analysis considers only that portion of the canyon which i s traversed by the railway l i n e s , and thus i s representative of the lower slopes below approximately 1000 feet (300 m) i n elevation. Crosstabulation of s u r f i c i a l material with slope f a i l u r e shows that slopes comprising bedrock, which usually occurs 'as- steep scarps, f a i l most frequently. The results appear i n Table 5.2 and set the stage for further discussion of slope attributes and associated f a i l u r e . 106 S u r f i c i a l Material Mean number of f a i l u r e s i n the 20-. year period Number of Cases c o l l u v i a l 1.95 125 bedrock 3.03 36 f l u v i o - g l a c i a l 0.48 21 f l u v i a l 0 .24 17 aeolian absent t o t a l 1.84 199 Table 5.2 Mean f a i l u r e incidence on of the p r i n c i p a l s u r f i c i a l found i n the Fraser Canyon slopes materials Frequency D i s t r i b u t i o n of the Slope Attributes I n i t i a l l y there were 220 and 230 sample s i t e s at 0.1 mi (0.16 km.) i n t e r v a l s along the railway tracks of the eastern and western slopes respectively. At each s i t e , each of the thirteen variables was determined during the a i r photo i n t e r -pretation of fieldwork session (refer to Table 4.2, page 74). Sites at which a rock tunnel was present were eliminated from the analysis, reducing the number of s i t e s along the eastern l i n e to 199, and along the western side, to 216. At each s i t e along the tracks, each of the twelve slope attributes was determined. Frequency d i s t r i b u t i o n s have been generated for the western and eastern slopes separately and for the combined data. These are presented i n Appendix V. For ease i n computer handling, the alphabetic t e r r a i n c l a s s i f i c a t i o n has been numerically recoded r e s u l t i n g i n 107 character strings of one through seven d i g i t s i n length. The s u r f i c i a l materials and t h e i r quantitative and p o s i t i o n a l relations to one another was retained; texture and surface expression were not considered. Eventually the seven-digit numeric strings were truncated to three d i g i t s so that the number of s u r f i c i a l material classes was reduced to twenty. This truncation retained the two most s i g n i f i c a n t materials within a t e r r a i n unit, and t h e i r r e l a t i v e areal r e l a t i o n s h i p . Generalized s t a t i s t i c s were performed with t h i s variable truncated to one d i g i t so that the predominantly c o l l u v i a l , rock, f l u v i o - g l a c i a l and f l u v i a l units could be compared. In frequency tables of the s u r f i c i a l materials i t i s seen that the west side of the canyon occupied by the Canadian P a c i f i c Railway i s considerably more gently sloping than the other bank. The eastern slopes comprise more steep rock, while western slopes show nearly twice the percentage of the more stable f l u v i o - g l a c i a l and f l u v i a l materials (Table 5.3). In Appendix V. (A)f a more detailed breakdown of the occurrence of s u r f i c i a l materials i s given. C o l l u v i a l slopes are encountered most frequently, with those classes where colluvium i s a r e a l l y predominant over steep rock being the most common (C/Rs plus C//Rs = 27.7%). Si m i l a r l y , of the bedrock-dominated slopes, those categories where steep rock i s predominant are most frequent (Rs/C plus Rs//C = 14.0%) The part of the t e r r a i n c l a s s i f i c a t i o n which indicates slope modifying processes was retained and considered as 108 S u r f i c i a l Eastern Western Combined Material Slopes Slopes Slopes (199 cases) (216 cases) (415 cases) % of t o t a l : % of t o t a l : %'.. of t o t a l : c o l l u v i a l 62.7 58.2 60 .5 (125) (126) (251) bedrock 18.0 6.5 12 .1 (36) (14) (50) f l u v i o - g l a c i a l 10 .5 17.2 14.0 (21) (37) (58) f l u v i a l 8.5 17.1 13.0 (17) (37) (54) aeolian n i l 0.9 0.5 (2) (2) Table 5.3 Summary of the frequency of occurrence of p r i n c i p a l s u r f i c i a l materials. The number of cases i n each category i s shown i n brackets. a separate slope attritube from the material i t s e l f . By d e f i n i t i o n , a l l s i t e s were modified by being crossed by the railway rights-of-way. Each s i t e may have one or more additional slope-modifying process symbols. The western slopes exhibit a smaller range of modifying conditions than the east bank. The occurrence of g u l l i e d slopes, associated with the highest slope f a i l u r e frequencies, i s also smaller on the west side than the east. Frequency of occurrence of slope modifying processes appears i n Appendix V (B), . Along both r a i l l i n e s , 77.6% of the slopes adjacent to the track have been excavated and thus oversteepened. On the eastern side of the canyon, the slopes' height above the distance from the track are estimated to be c r i t i c a l regarding 109 hazard at a majority of s i t e s . The hazard was determined by observation of the probable t r a j e c t o r i e s of f a l l i n g rock and debris from the slope above, and the associated l i k e l i h o o d of track obstruction. The hazard due to both of these geometric attributes -isj n o n - c r i t i c a l at the majority of s i t e s along the western slopes (Appendix V('G, D, E) I . The frequency d i s t r i b u t i o n of trackside slope angles again shows the predominance of steep slopes i n bedrock and unconsolidated material along the eastern canyon side. The western slopes exhibit a considerably higher percentage of slopes i n the 30° to 41° range and i n the unmeasured class, presumably due to a higher occurrence there of f l u v i a l and f l u v i o - g l a c i a l deposits, and to the building-up of the track onto f i l l . The frequency d i s t r i b u t i o n of slope angle classes appears i n Appendix V (F) . Material exposed along the trackside, a separate variable from the s u r f i c i a l material at a s i t e , again shows the rockier nature of the eastern canyon slopes (Appendix V (G)),. Roughly 40% of a l l s i t e s are characterized by steep rock adjacent to the right-of-way whether or not rock i s a component of the corresponding t e r r a i n unit. Of these, 62.7% (or 25.1% of the t o t a l number) f a l l into the coarsely jointed category. The frequency of occurrence of the j o i n t classes i s found i n Appendix V (H) , Of the f i v e l i t h o l o g i e s found i n the study area, the Spuzzum intr u s i v e quartz d i o r i t e i s the most common, ty p i f y i n g 44.1% of a l l s i t e s . The oldest unit, the Hozameen sedimentary 110 and volcanic group, i s absent from the western side of the canyon, while the Custer gneiss does not occur along the eastern slopes. Appendix V (I) gives the frequency of occurrence of the bedrock types. The occurrence of remedial measures at s i t e s along the rights-of-way were sim i l a r for both sides of the canyon (Appendix IV (J)) . While the observation of these was r e l a t i v e l y straightforward, several situations have been systematically overlooked: i) occurrence of rock scaling at lev e l s well above the tracks and i n areas where subsequent weathering has obscured the evidence, and i i ) remedial work performed below the l e v e l of the tracks, such as buttressing, retaining walls, weepholes, etc. The presence of fines and seepage were recorded for a l l s i t e s but t h e i r occurrence i s sparse (Appendix V, (K, L) ),. Subsequent SPSS investigations of the occurrence of slope f a i l u r e s for s p e c i f i c levels of each attribute were performed using the Canadian National Railway twenty-year record and thus applies to the eastern slopes only. Observations based on these data are assumed to be true on the western side as well. Although external variables e f f e c t i n g slope f a i l u r e seem to be the same from side to side of the canyon, factors which may vary include subsurface drainage, pattern, date and rate of the spring thaw, and l i t h o l o g i c structure. These factors were not investigated i n t h i s study. I l l Slope Attributes and Associated F a i l u r e Bedrock and/or c o l l u v i a l t e r r a i n units experience the highest number of slope f a i l u r e s (Table 5.2). A more de t a i l e d crosstabulation of surface material with slope f a i l u r e shows that 94.0% of a l l of the si t e s has experienced fewer than six f a i l u r e s . The remainder occur i n units where steep rock and colluvium-are present .(Table 5 v,4 ;)••-.- -A .very small number of . failures occurs on both f l u v i a l and f l u v i o - g l a c i a l materials. Several combinations of rock and c o l l u v i a l materials exhibit high mean incidence of f a i l u r e , while f l u v i a l and f l u v i o - g l a c i a l classes have the lowest occurrence (Table 5.5). A complete l i s t of mean f a i l u r e incidence for the study s u r f i c i a l material groups appears i n Appendix VI (A),. Slopes which are both crossed by the railway l i n e (X) and a c t i v e l y f a i l i n g (F) are associated with higher incidence of f a i l u r e , those which a d d i t i o n a l l y are g u l l i e d (V) having the highest occurrence of f a i l u r e s . Those s i t e s which are deforested (Y), avalanched (A), or channelled (E) show the lowest f a i l u r e occurrence (Appendix VI (B)). Table 5.6 shows the association of cutslope with f a i l u r e incidence on the eastern slopes. Only 19.1% of a l l the s i t e s have not been excavated, and a l l of these have three or fewer recorded f a i l u r e events. C o l l u v i a l slopes exhibit the largest difference i n f a i l u r e frequency between excavated and non-excavated slopes, presumably due to d e s t a b i l i z a t i o n and dry r a v e l l i n g of the base of the slopes which are cut. The e f f e c t of undercutting c o l l u v i a l slopes i s considerably more dr a s t i c 112 S u r f i c i a l Material NUMBER OF FAILURES IN THE 20-YEAR RECORD percent with: zero $1 ?$2 $ 5 Number of Cases c o l l u v i a l bedrock f l u v i o - g l a c i a l f l u v i a l 38.4 56.8 72.8 95.2 30.6 50.0 63.9 83.4 76.2 90.5 90.5 100.0 76.5 100.0 100.0 100.0 125 36 21 17 number of cases 88 125 150 187 199 Table 5.4 Fa i l u r e incidence of the p r i n c i p a l s u r f i c i a l materials, given i n percentage of the t o t a l number of, cases per category. S u r f i c i a l Material Mean Failure Incidence Number of Cases Rs // C C / Rs Rs F G R F F o r | Rs / F 3.94 HIGH 3.85 3.17 0.00 LOW 0.19 0.50 !7 20 6 4 16 2 Table 5.5 S u r f i c i a l material types showing the highest and lowest mean incidence of f a i l u r e s . 1 1 3 t h a n t h a t o f c u t t i n g i n t o b e d r o c k . B e c a u s e o f t h e p r e v a l e n c e o f c o l l u v i u m a n d t h e l i m i t e d v e r t i c a l e x t e n t o f t h e f l u v i a l a n d f l u v i o - g l a c i a l d e p o s i t s , c u t s i n t h e f o r m e r a r e o f t e n m u c h m o r e e x t e n s i v e a n d h i g h e r t h a n i n t h e l a t t e r t w o m a t e r i a l s . T h e r e i s s t r o n g a s s o c i a t i o n b e t w e e n ' f a i l u r e a n d s l o p e h e i g h t a n d d i s t a n c e f r o m t h e t r a c k ( T a b l e 5 . 7 ) . I n g e n e r a l , t h e n u m b e r o f f a i l u r e s o n s l o p e s w h o s e h e i g h t o r d i s t a n c e i s e s t i m a t e d t o b e c r i t i c a l i s t h r e e t i m e s g r e a t e r t h a n i n n o n - c r i t i c a l c a s e s . M o s t n o t i c a b l y , w h e n t h e h e i g h t o f t h e s l o p e i s e s t i m a t e d t o b e c r i t i c a l i n f l u v i o - g l a c i a l m a t e r i a l , t h e f a i l u r e i n c i d e n c e i s i n c r e a s e d 4 . 6 t i m e s . T h e s l o p e c a t e g o r y e x h i b i t i n g t h e h i g h e s t f r e q u e n c y o f f a i l u r e s a r e t h o s e g r e a t e r t h a n 4 1 ° . T h i s c l a s s c o n t a i n s c o l l u v i a l a n d f l u v i o - g l a c i a l s i t e s ; h o w e v e r , i t w a s d e m o n s t r a t e d e a r l i e r t h a t c o l l u v i a l s i t e s e x p e r i e n c e m u c h h i g h e r f a i l u r e f r e q u e n c y t h a n d o f l u v i o - g l a c i a l o n e s ( T a b l e 5 . 2 ) . T h e f a c t t h a t f l u v i o - g l a c i a l m a t e r i a l i s c o h e s i v e a n d c a n m a i n t a i n h i g h e r s l o p e - a n g l e s t h a n c o l l u v i u m i s t h e r e a s o n f o r t h e i r l o w e r f a i l u r e i n c i d e n c e . T a b l e 5 . 8 s h o w s t h e r e l a t i o n o f s l o p e a n g l e c a t e g o r i e s t o t h e i n c i d e n c e o f f a i l u r e s . T h e s t e e p r o c k c a t e g o r y ( > 7 0 ° ) e x h i b i t s t h e s e c o n d h i g h e s t m e a n i n c i d e n c e o f f a i l u r e s . A l l o f t h e c a s e s w i t h m o r e t h a n f i v e s l o p e f a i l u r e s o c c u r i n t h e > 4 1 ° a n d > 7 0 ° c a t e g o r i e s . A t d i f f e r e n t s i t e s w i t h i n e a c h s u r f i c i a l m a t e r i a l c a t e g o r y s e v e r a l s l o p e c l a s s e s may o c c u r , e s p e c i a l l y o f s t e e p r o c k a n g l e s ( > 7 0 ° ) i n c o l l u v i a l a n d f l u v i a l u n i t s . T h i s e x e m p l i f i e s t w o p o i n t s : 1 1 4 S u r f i c i a l Material MEAN FAILURE INCIDENCE on uncut slopes on cut slopes Multiplication Factor c o l l u v i a l 0.21 (24) 2.37 (101) 11.3 bedrock 0.50 (2) 3.18 (34) 6.4 f l u v i o - g l a c i a l 0.25 (4) 0.53 (17) 2.1 Fluvial 0.25 (8) 0.22 (9) 0.9 total 0.24 (38) 2.22 (161) 9.3 Table 5.6 Association between cutslope and number of cases in each category failure appears incidence. The in brackets. S u r f i c i a l Material MEAN INCIDENCE OF FAILURE on slopes whose height i s : MEAN INCIDENCE OF FAILURE on slopes whose distance i s : non-critical c r i t i c a l non-critical c r i t i c a l c o l l u v i a l bedrock flu v i o - g l a c i a l f l u v i a l total 1.03 (39) 2.36 (87) 1.00 (1) 3.09 (35) 0.14 (7) 0.64 (14) 0.13 (15) 1.00 (2) 0.70 (61) 2.35 (138) 1.12 (50) 2.51 (75) 0.50 (2) 3.18 (34) 0.63 (16) 0.00 (5) 0.19 (16) 1.00 (1) 0.83 (84) 2.58 (115) Table 5.7 Association between slope height and distance from the track with failure incidence. The number of cases i n each category appears i n brackets. 115 i) that i n c l a s s i f y i n g s u r f i c i a l material on a i r photo imagery there i s an inherent minimization of the importance of v e r t i c a l rock faces, and i i ) that the thickness of unconsolidated deposits i s variable such that, i n some locations, bedrock i s encountered in cutslopes within non-bedrock t e r r a i n units. Table 5.9 i l l u s t r a t e s the various slope angles and the i r associated f a i l u r e incidence encountered within several mixed s u r f i c i a l material categories. From the foregoing discussion i t i s apparent that s i t e s with a bedrock component exhibit the highest frequency of f a i l u r e . This i s a resu l t of i t s steep and strongly jointed nature. Bedrock i s susceptible to weakening by ice accumulation in the ;joints, expansion and contraction during freeze-thaw cycles, and the build-up of groundwater pressure behind a frozen plane p a r a l l e l to the rock face i n the winter. C o l l u v i a l slopes, while less influenced by ice - r e l a t e d processes, probably f a i l when triggered by r o c k f a l l s from the bedrock scarps above, or i n response to oversteepening of a base. Low f a i l u r e frequency i n f l u v i a l and f l u v i o - g l a c i a l materials i s attributed to the i r gentle slope and good drainage. Relative Importance of the Slope Attributes The importance of the twelve slope attributes i n explaining v a r i a t i o n i n slope f a i l u r e was investigated using the AID3 program (Appendix I I I , C). An early run of the program on the eastern slope data resulted i n a confused tree-structure, so that a l l subsequent analyses were made on log-transformed 1 1 6 Slope Angle Mean Failure Incidence NUMBER OF FAILURES 20 - YEAR RECORD percent with zero ^1 ^2 IN THE $5 Number of Cases M l 0 3.03 30.6 50.0 63. 9 89.0 36 3 0 ° - 41° 1.20 57.1 80.0 80.0 97.2 35 <30° 0.25 83.3 95.8 95.8 100.0 24 >70° 2.15 29.9 50.6 71.3 93.1 87 >70° 1.17 66.7 66.7 83.4 100.0 6 unmeasured 1.45 63.6 72.2 81.8 90.9 11 Table 5.8 Association of trackside slope angle along the eastern canyon slopes. with failure incidence SURFICIAL MATERIALS: Slope Mean Mean Mean Failure Failure Failure Angle R//C Incidence C/R Incidence F Incidence angles > 4 l ° 1 7 . 6 ? 1 0 . 0 1 5 . 9 ? 1 0 . 3 6 . 2 ? 1 . 0 associated with 3 0 ° - 4 l ° 5 . 9 * 4 . 0 3 1 . 2 ? 0 . 2 unconsolidated material < 3 0 ° — — — — 5 0 . 0 ? 0 . 1 angles >70° 76.5% 2 . 5 7 5 . 0 ? . 2 . 8 1 2 . 5 ? 0 . 0 associated with bedrock < 7 0 ° — — 5 . 0 ? 2 . 0 — — angles not measured — — 5 . 0 ? 2 . 0 — — Table 5 . 9 S u r f i c i a l materials , slope angles, and failure incidence. 1 1 7 f a i l u r e i n c i d e n c e v a l u e s a s o u t l i n e d i n C h a p t e r 4 . A s w a s d o n e f o r t h e d e s c r i p t i v e s t a t i s t i c s , t h e m a t e r i a l g e n e s i s v a r i a b l e w a s t r u n c a t e d t o t h r e e d i g i t s . T h e f i r s t A I D 3 r u n w a s m a d e u s i n g s l o p e f a i l u r e o c c u r r e n c e a s t h e d e p e n d e n t v a r i a b l e a n d t h e t w e l v e s l o p e a t t r i b u t e s : T h e p r o g r a m b e g i n s w i t h t h e e n t i r e d a t a s e t a n d s p l i t s i t i n t o t w o g r o u p s o f s i t e s . T h a t s l o p e a t t r i b u t e w h i c h e f f e c t s t h e l a r g e s t d i f f e r e n c e b e t w e e n t h e m e a n f a i l u r e i n c i d e n c e o f t h e t w o g r o u p s i s t h e b a s i s o f t h e s p l i t . T h e p r o c e s s i s r e p e a t e d f o r e a c h g r o u p u n t i l t h e s p l i t t i n g i s l i m i t e d b y g r o u p s i z e o r i n t e r n a l v a r i a t i o n . T h e p r o c e s s m a y b e p r e s e n t e d a s a t r e e - l i k e s t r u c t u r e . T h e a m o u n t o f v a r i a t i o n i n s l o p e f a i l u r e e x p l a i n e d b y t h e t w e l v e a t t r i b u t e s a f t e r s p l i t t i n g 17 t i m e s w a s 5 5 . 8 % o f t h e t o t a l . T h i s f i g u r e i s c o n s i d e r e d r e a s o n a b l e i n t h e l i g h t o f t h e g e n e r a l i z e d p r e d i c t o r a t t r i b u t e s . T e n o f t h e 18 e n d g r o u p s o f t h e t r e e w e r e p r e v e n t e d f r o m b e i n g f u r t h e r s p l i t b y t h e i r s m a l l s i z e . T h e o t h e r s w e r e " u n e x p l a i n e d " , a n d t h e i r i n t e r n a l v a r i a t i o n c o u l d n o t b e s p l i t f u r t h e r o n a n y o f t h e v a r i a b l e s p r o v i d e d . T h e r e w a s s o m e i n t e r a c t i o n b e t w e e n v a r i a b l e s , m o s t n o t a b l y o f d i s t a n c e , m o d i f y i n g p r o c e s s e s , r e m e d i a l m e a s u r e s , m a t e r i a l g e n e s i s m o d i f y i n g p r o c e s s e s b e d r o c k c u t s l o p e m a t e r i a l a n g l e h e i g h t s e e p a g e r e m e d i a l m e a s u r e s d i s t a n c e j o i n t i n g f i n e s ( 1 9 l e v e l s ) ( 1 0 l e v e l s ) (5 l e v e l s ) (2 l e v e l s ) ( 3 l e v e l s ) (6 l e v e l s ) (2 l e v e l s ) (2 l e v e l s ) (5 l e v e l s ) ( 3 l e v e l s ) (2 l e v e l s ) (2 l e v e l s ) 118 and j o i n t i n g , w i t h m a t e r i a l genesis and angle,(Appendix I I I . C). In Table 5.10, the "explanatory power of the f u l l d e t a i l of each p r e d i c t o r " , or E T A - s t a t i s t i c i s g i v e n . T h i s value i s the p r o p o r t i o n of the t o t a l v a r i a t i o n t h a t i s e x p l a i n e d by each a t t r i b u t e alone, c o n s i d e r i n g a l l i t s l e v e l s . Of the twelve slope a t t r i b u t e s , those s i x which have ETA values g r e a t e r than 0.1 were r e t a i n e d as they showed the maximum d i s c r i m i n a t o r y power. They are v a r i a b l e s which d e s c r i b e , i n a coarse way, the s u r f i c i a l m a t e r i a l and geometry of the s l o p e . The r e s u l t i s a l o g i c a l d i v i s i o n o f the v a r i a b l e s such t h a t those a t t r i b u t e s concerning the i n t e r n a l c h a r a c t e r of the slope m a t e r i a l are r e j e c t e d . They are, f o r reasons of i n c o n s i s t e n c y of o b s e r v a t i o n or s p a r s i t y o f occurrence, thought t o be u n r e l i a b l e . m a t e r i a l genesis .201 j o i n t i n g .065 modifying processes .154 f i n e s .056 d i s t a n c e .139 bedrock .047 angle .132 remedial measures .044 c u t s l o p e .130 m a t e r i a l .0 40 h e i g h t , .110 seepate :o io Table 5.10 ETA valu e s of the twelve slope a t t r i b u t e s used i n the i n i t i a l run of AID3. I n t h e s e c o n d r u n o f t h e AID3 p r o g r a m , t h e s i x h i g h - E T A v a r i a b l e s w e r e u s e d . T h e r e w a s a r e d u c t i o n i n t h e n u m b e r o f i n d e p e n d e n t v a r i a b l e s o f 50% a n d a c o r r e s p o n d i n g d r o p i n t h e p e r c e n t o f v a r i a t i o n e x p l a i n e d o f 14.4% t o 41.4%. A f t e r n i n e 119 successful s p l i t s there were ten endgroups of which four were limited by size, and the rest unexplained. The reduction i n number of s p l i t s achieved indicates that there i s more int e r n a l v a r i a t i o n within the endgroups, re s u l t i n g from fewer predictor variables. The resultant tree appears i n Appendix VII. In the tree there i s a tendency toward upward branching, indicating some pos i t i v e skewness i n the dependent variable. Wide angles between subgroups r e s u l t from large v a r i a t i o n in the parent group from which the s p l i t was made. Overall, material genesis and angle are the prominent s p l i t t i n g variables. While height was included i n the analysis on the basis of i t s previous ETA-value, i t was not used as an active s p l i t t i n g variable i n t h i s tree. The o v e r a l l v a r i a t i o n explained i s thought to be acceptable with respect to the generalized nature of the data. Frequency i s not 44.1% caused by the levels of the six predictors; rather there i s an association between the value of slope f a i l u r e incidence .and ;the. values' of: the six .attributes. E f f e c t i v e l y no in t e r a c t i o n occurs between variables i n the second tree. When material genesis was truncated to one d i g i t (thus reducing the number of levels of t h i s variable from 19 to 4), and run i n the AID3 program, there was another loss of 3.6% of the t o t a l v a r i a t i o n to 37.8%. The ETA value of that at t r i b u t e dropped as well, from .201 to .127. There i s interaction between modifying processes and distance, and amongst material genesis, angle, and distance. There are 120 eleven endgroups of which ten are explained. Clearly the ef f e c t of further aggregation of the material genesis variable has been to decrease the explaining power of that variable. The results of the AID3 runs indicate that a drop from twelve to six independent variables, maintaining material genesis at nineteen levels i s the best compromise for the available predictors. Subsequent c l a s s i f i c a t i o n and analysis therefore makes use of six predictors to generate groups of sit e s with s i m i l a r character. S t a b i l i t y C l a s s i f i c a t i o n of Sites Each time that the clustering program was employed a corresponding multi-dimensional scalogram analysis was made, and t h e i r results i n each case w i l l be considered together. In these analyses the data were organized into groups of s i t e s on the basis of the s i x slope attributes i d e n t i f i e d by the AID3 program. When the data are well-separated into groups, the c o e f f i c i e n t of contiguity of the MSA-I program approaches +1 (Appendix III, D). These two programs simply sort out structure i n the data. Whether resultant groups, or clu s t e r s , are meaningful must be interpreted by the user. Since these methods are being used to generate a framework within which to c l a s s i f y the s i t e s along the slopes, the int e r n a l v a r i a b i l i t y of the groups generated by HCLUS and MSA-I should be small i n order to be most e f f e c t i v e and p r a c t i c a l . The f a i l u r e incidence variable was not employed i n the 121 c l a s s i f i c a t i o n operation, though i t was used i n one way analysis of variance to check the s t a t i s t i c a l significance of the classes so generated. Results of the four HCLUS and MSA-I runs are summarized i n Table 5.11. The scalogram plots appear i n Appendix VIII. In a l l four runs of the HCLUS and MSA-I programs, an arbitr a r y l i m i t of sixteen clusters was adopted, with subsequent reduction to fewer groups were appropriate. The resultant clusters vary widely i n size and exhibit high i n t e r n a l v a r i a b i l i t y . When t h e i r significance with respect to slope f a i l u r e was tested with analysis of variance, the groups were marginally s i g n i f i c a n t or better. However, a closer inspection indicates that the s i g n i f i c a n t l y d i f f e r e n t mean f a i l u r e incidences occur only between several of the groups, the others having means of zero. While dropping the number of clusters from sixteen to six or four improves t h e i r s i g n i f i c a n c e , there was an associated increase i n the groups' in t e r n a l v a r i a b i l i t y . The best r e s u l t s of these analyses were obtained when the material genesis variable was truncated from three to one d i g i t , leaving each s i t e represented only by the a r e a l l y predominant s u r f i c i a l material present. The significance of the resultant clusters was improved over that of other runs, though a considerable amount of information was f o r f e i t e d . The reduction i n contribution (ETA) of the truncated material genesis variable to the explanation of t o t a l v a r i a t i o n i n the f a i l u r e incidence in the AID3 program (refer to page 119) i s METHOD OP ANALYSIS: I DUPLICATE SEARCHING HCLUS and MSA-I MSA-I UBC S P S S ;8 subprogram ONEWAY d a t a s e t number o f s i t e s number of unique cases percent s i t e s i n l a r g e s t c l u s t e r percent c l u s t e r s o f o n l y one s i t e p e r c e n t c l u s t e r s w i t h < 1 0 s i t e s c o e f f . o f c o n t i g u i t y a f t e r 2 5 i t e r a t i o n s F - r a t i o F - s t a t i s t i c o e = 0 . 1 0 « = 0 . 0 5 E a s t e r n Slopes 1 9 9 f o r 1 6 c l u s t e r s f o r 6 c l u s t e r s E a s t e r n S l o p e s * | 1 9 9 f o r 1 6 c l u s t e r s f o r 6 c l u s t e r s I f o r 4 c l u s t e r s Western Slopes I 2 1 6 f o r -16 c l u s t e r s E a s t e r n and Western Slopes | 4 1 5 for- 1 6 c l u s t e r s 9 0 6 3 9 0 1 5 7 5 1 . 7 9 3 . 5 4 5 . 2 7 6 . 9 7 7 . 9 33.8 7 1 . 8 5 0 . 0 5 0 . 0 1 8 . 7 3 3 . 3 n i l 2 5 . 0 3 1 . 2 6 8 . 7 8 3 . 3 6 8 . 7 5 0 . 0 1 6 . 7 5 6 . 2 4 3 . 7 0 . 9 9 9 9 0 . 9 9 9 2 0 . 9 8 5 7 0 . 9 9 1 0 1 . 6 7 3 0 . 5 4 5 3 . 9 7 8 2 . 1 6 2 4 . 1 7 5 N.A N . A . 1 . 5 2 1 . 7 2 1 . 8 8 2 . 2 6 1.52 1.72 1.88 2.26 1.97 2.42 N.A N.A. T a b l e 5 . 1 1 R e s u l t s of the c l a s s i f i c a t i o n methods. An a r b i t r a r y number o f 1 6 f i n a l c l u s t e r s was chosen. A s t e r i s k (*) i n d i c a t e s the case wherin the m a t e r i a l g e n e s i s v a r i a b l e was t r u n c a t e d from three to one d i g i t . 123 evidence of the importance of the three-digit l e v e l of th i s variable. Thus, despite improved significance, the truncated one-digit form was abandoned i n further analysis. Alternate Means of Site C l a s s i f i c a t i o n Two alternative methods of c l a s s i f y i n g the slopes of the study area were considered, i n which categories were formed on the basis of only one of the slope a t t r i b u t e s . In the f i r s t , the si t e s along the eastern slopes were grouped according to f a i l u r e frequency alone. This method results i n a clear image of the d i s t r i b u t i o n of slope f a i l u r e along the right-of-way, from which a c t i v e l y f a i l i n g s i t e s can be iso l a t e d e a s i l y . However, there are several disadvantages of th i s scheme. F i r s t , the c l a s s i f i c a t i o n i s dependent upon a reasonably long slope f a i l u r e record. These are ra r e l y available. Second, within this c l a s s i f i c a t i o n there i s no ind i c a t i o n of the physical nature of the slopes., Last, t h i s c l a s s i f i c a t i o n cannot be extended to other slopes or to other areas. While this c l a s s i f i c a t i o n may be of in t e r e s t to Canadian National Railway, i t i s of l i t t l e p r a c t i c a l use as a generally applicable method. The second categorization of the slopes was made using the material genesis variable alone. In this case, the variable was truncated to one d i g i t so that s i t e s were i n i t i a l l y grouped according to the i r predominant s u r f i c i a l material. One-way analysis of variance shows that there are s i g n i f i c a n t 1 2 4 DESCRIPTION OF THE CATEGORIES: Su r f i c i a l Material Mean Number of Number of Failures Cases Per Site Maximum Number of Failures at One Site Standard Deviation co l l u v i a l 1 2 5 1 . 9 5 1 7 2 . 76 bedrock 3 6 3 . 0 3 2 1 4 . 4 9 f l u v i o - g l a c i a l 2 1 0.48 4 1.08 f l u v i a l 1 7 0.24 1 0 . 4 4 total 1 9 9 1.84 2 1 3 . 0 3 ANALYSIS OF VARIANCE: Source Degrees of Freedom Sum of Mean Squares Squares F-ratio F - s t a t i s t i c ( <* = 0 . 0 1 ) between 3 1 3 5 . 1 9 4 5 . 0 6 5 .24 3 . 8 8 within 1 9 5 1 6 7 1 . 9 6 8.60 total 1 9 8 1 8 1 2 . 1 6 Table 5 . 1 2 Classification and analysis of variance of site categories based on s u r f i c i a l materials encountered along the eastern slopes of the canyon. DESCRIPTION OF THE CATEGORIES: Su r f i c i a l Material Number Cases Mean Number of of Failures Per Site Maximum Number of Failures at One Site Standard Deviation co l l u v i a l 2 5 1 1.04 1 7 2 . 1 7 bedrock 5 0 2 . 2 8 21 4.01 fluvio - g l a c i a l 5 8 0 . 2 2 4 0 . 7 0 f l u v i a l 5 4 0 . 0 7 1 0.26 total 4 1 3 0 . 9 5 2 1 2 . 2 9 ANALYSIS OF VARIANCE: Source Degrees of Freedom Sum of Mean Squares Squares F-ratio F - s t a t i s t i c ( « = 0.01) between 3 162.64 3 3 . 4 7 1 1 . 0 9 3 . 3 2 within 4 0 9 1 9 9 8 . 3 5 4 . 9 5 total 412 2 1 6 1 . 0 0 Table 5 . 1 3 Classification and analysis of variance of site categories based on s u r f i c i a l materials encountered along the eastern and western slopes. 125 d i f f e r e n c e s between the mean number of f a i l u r e s i n each category. Table 5.12 i s a summary of the a n a l y s i s . A n a l y s i s of v a r i a n c e was repeated f o r the combined d a t a s e t of s i t e s along the e a s t e r n and western s i d e s of the canyon. The r e s u l t was t h a t the groups were s t i l l s i g n i f i c a n t l y d i f f e r e n t , even though the r e c o r d of f a i l u r e s along the western slopes was sparse. An e f f e c t of the s h o r t p e r i o d of r e c o r d on the western s i d e was to reduce d r a s t i c a l l y the values of mean s l i d e occurrence due to a l a r g e number of s i t e s w i t h zero or low i n c i d e n c e of f a i l u r e . The outcome of the a n a l y s i s i s presented i n Table 5.13. C l e a r l y the value of these groups to a c l a s s i f i c a t i o n scheme i s seen. A broad g r a d a t i o n of the r e s u l t s i n Tables 5.12 and 5.13 i n t o f a i l u r e hazard c a t e g o r i e s can be made as o u t l i n e d i n Table 5.14. Hazard Due to F a i l u r e S u r f i c i a l M a t e r i a l h i g h i n t e r m e d i a t e low bedrock c o l l u v i a l f l u v i o - g l a c i a l and f l u v i a l Table 5.14 General slope f a i l u r e hazard c a t e g o r i e s . A problem with t h i s form of c l a s s i f i c a t i o n i s t h a t c e r t a i n combinations of m a t e r i a l s are m i s l e a d i n g l y a s s i g n e d w i t h i n i t . For example, on the e a s t s i d e of the canyon the t e r r a i n u n i t s where c o l l u v i u m predominates over steep bedrock (C/Rs) have 126 a mean, i n c i d e n c e of f a i l u r e of 3.85 events per s i t e ( i . e . per 0.1 m i l e o r 0.16 km segment of track) over the r e c o r d p e r i o d . Although t h i s i s the second h i g h e s t i n c i d e n c e amongst the s u r f i c i a l m a t e r i a l c a t e g o r i e s , i t would f a l l i n t o the int e r m e d i a t e hazard category presented i n Table 5.14. An a l t e r n a t i v e i s t o r e t a i n the t h r e e - d i g i t m a t e r i a l genesis and to generate c a t e g o r i e s each comprising a range o f mean f a i l u r e i n c i d e n c e s . However, the r e s u l t i s s e v e r a l groups c o n t a i n i n g somewhat u n r e l a t e d m a t e r i a l s with no i n t u i t i v e p a t t e r n o r connec t i o n between them. A p o s s i b l e scheme r e s u l t i n g from s p l i t t i n g the e a s t e r n slope data i n t o f a i l u r e i n c i d e n c e c a t e g o r i e s o f m a t e r i a l types appears i n Table 5.15. T h i s c l a s s i f i c a t i o n i s the combined r e s u l t of i n f o r m a t i o n gathered a t a l l stages o f t h i s r e s e a r c h : a i r photo i n t e r p r e t a t i o n , f i e l d survey, and numerical a n a l y s i s . F a i l u r e : Incidence Hazard Due to F a i l u r e S u r f i c i a l M a t e r i a l s 3 high Rs ; Rs//C ; C/Rs C 2 .00-2 .99 int e r m e d i a t e C=R; F G ; Rs/C 1.00-1.99 low C; C//Rs ; § ; § ; F//C 0.00-0.99 very low FG G | ; C=F ; R/F ; F ; F Table 5.15 Slope f a i l u r e hazard c a t e g o r i e s based on the s u r f i c i a l m a t e r i a l v a r i a b l e a t the t h r e e -d i g i t l e v e l . I t i s j u s t i f i e d on the b a s i s of the r e s u l t s of those stages 127 and on i n t u i t i o n . The f a i l u r e ranges and t h e i r a s s o c i a t e d s u r f i c i a l m a t e r i a l s can be a p p l i e d to the e a s t e r n s l o p e s f o r which they were g e n e r a t e d . F o r the wes tern s l o p e s o r o u t s i d e o f the s tudy a r e a , these h a z a r d l e v e l s need t o be t e s t e d f u r t h e r . 128 CHAPTER 6 C O N C L U S I O N S OVERVIEW Despite i t s heavy use as a transport corridor, the Fraser Canyon has been overlooked as far as t e r r a i n analysis and hazard evaluation are concerned. This study was designed to c l a s s i f y the t e r r a i n and investigate the d i s t r i b u t i o n of slope f a i l u r e s along the railway rights-of-way.. Conclusions drawn from the results presented i n Chapter 5 f a l l into three related, but d i s t i n c t , categories, namely: i) the nature of t e r r a i n i n the Fraser Canyon i i ) the r e l a t i o n of meso-scale t e r r a i n variables to slope f a i l u r e incidence along the railway l i n e s , and i i i ) the implementation of slope attributes i n c l a s s i f y i n g t e r r a i n with respect to slope f a i l u r e incidence. On the basis of a i r photo analysis, fieldwork, and slope attribute frequency d i s t r i b u t i o n s , the following general conclusions are made: i) Fraser Canyon slopes are dominated by c o l l u v i a l and steep bedrock t e r r a i n , i i ) f l u v i a l and f l u v i o - g l a c i a l materials are found sporadically along the lower canyon sides, i i i ) the nature of the western side of the canyon i s considerably gentler than the eastern side, iv) steep rock slopes exhibit the highest incidence or slope f a i l u r e , followed by c o l l u v i a l slopes, v) f l u v i a l and f l u v i o - g l a c i a l materials have very low f a i l u r e incidence, and vi) 80% of the slopes have been excavated (and over-steepened) during railway construction 129 The two railway routes make maximum use of the more stable unconsolidated deposits by maintaining low elevation along the canyon slopes, and where rock and c o l l u v i a l t e r r a i n units are traversed, the hazard due to slope f a i l u r e i s increased. Results of the numerical analyses give r i s e to the following conclusions: i) that material genesis (derived from the t e r r a i n unit terminology) i s the single most useful index of slope f a i l u r e , i i ) that the most s i g n i f i c a n t slope attributes i n explaining f a i l u r e incidence are material genesis, modifying processes, cutslope, angle, height above the right-of-way, and distance from the track. i i i ) that the variables l i s t e d i n ( i i ) account for 41.4% of the variance i n slope f a i l u r e incidence, iv) that variables chosen as surrogates for micro-scale parameters are i n e f f e c t i v e i n adding to the explanation of variance in f a i l u r e occurrence, and v) that clusters generated on the basis of variables l i s t e d in ( i i ) were inappropriate as a means of s i t e c l a s s i f i c a t i o n with respect to f a i l u r e incidence. Information contained i n the t e r r a i n c l a s s i f i c a t i o n , then, i s the best index of f a i l u r e at i n d i v i d u a l s i t e s , though s p e c i f i c f a i l u r e frequencies cannot be attached to i t . This conclusion contests Piteau's claim that r i v e r channel plan-form and a l l u v i a l fan impingement alone influence f a i l u r e incidence along the right-of-way of the eastern canyon slopes (Piteau, 1973, 1977). The importance of the bedrock-controlled Fraser River i n determining upslope f a i l u r e occurrence i s thought by this author to be small. Rather, slope material and l o c a l geometry, including a l t e r a t i o n of the natural slope during 130 railway construction, are atrributed major d i r e c t influence on slope f a i l u r e d i s t r i b u t i o n along the tracks. IMPLICATIONS OF THE RESULTS The c l a s s i f i c a t i o n scheme effects storage of t e r r a i n c h a r a c t e r i s t i c s for useful r e t r i e v a l by geomorphologists, engineers, and environmental planners. As well as a series of e a s i l y distinguished topographic p r o f i l e s , s p e c i f i c geomorpho-log i c information r e s u l t i n g from t h i s study includes: i) the areal extent and d i s t r i b u t i o n of t e r r a i n units i n a l a t e r a l and v e r t i c a l sense, i i ) detailed c l a s s i f i c a t i o n of the s u r f i c i a l material, by i t s texture, genesis, surface expression, and modifying processes, i i i ) an inventory of past and present slope f a i l u r e processes as evidenced i n the canyon, iv) an inventory of semi-quantitative slope attributes, and v) the association of slope f a i l u r e incidence with material genesis and other slope a t t r i b u t e s . The regional or meso-scale t e r r a i n c l a s s i f i c a t i o n map of the Fraser Canyon and the associated slope f a i l u r e characteris-t i c s are complementary to the engineers' s i t e - s p e c i f i c f a m i l i a r i t y with slopes along the tracks. As such, they merit consideration i n planning and a l l o c a t i o n of funds for remedial work, and w i l l be useful i n the l i g h t of plans to increase railway t r a f f i c and f a c i l i t i e s i n the canyon area (Duncan Wyllie, pers. comm.). Additional construction along the slopes w i l l increase hazard due to f a i l u r e by c r i t i c a l l y a l t e r i n g four of the variables considered i n t h i s project; cutslope, angle, 131 distance and height. The aim of t h i s project was the reconnaissance of Fraser Canyon t e r r a i n with respect to s u r f i c i a l materials and slope f a i l u r e . There were three stages within the work; a i r photo interpretation and t e r r a i n c l a s s i f i c a t i o n , f i e l d v e r i -f i c a t i o n , and numerical analysis of the data. From within this framework, there are several recommendations for the design of similar studies. Two aspects of the Fraser Canyon study which might be improved i n other regional-scale studies, and which a f f e c t a l l stages of the investigation are: i) Slope attribute s e l e c t i o n . Variables which describe meso-scale slope properties (eg. material genesis, slope geometry) prove to be more closely related to slope f a i l u r e incidence at the regional scale of investigation than surrogates of micro-scale variables. The purpose of the reconnaissance w i l l dictate some or a l l of the slope attributes to be considered. i i ) Slope f a i l u r e records. Recording of the type and extent of f a i l u r e s should be improved. Ideally, the recording of f a i l u r e events should be controlled by the designers of the reconnaissance, but t h i s i s usually at the expense of the duration of the record period. Generally, such records derive from secondary sources, and thus are uncontrolled. When no record of slope f a i l u r e history i s available, a method for determining the ranking tendencies of the p r i n c i p a l s u r f i c i a l materials with respect to p o t e n t i a l f a i l u r e i s necessary. In mountainous t e r r a i n s imilar to that found i n the Fraser Canyon region, variable importance of f a i l u r e i n bedrock, c o l l u v i a l , f l u v i a l and f l u v i o - g l a c i a l slopes can be assumed to hold. However, the i r f a i l u r e behavior undoubtedly changes \ 132 where variables which were i n s i g n i f i c a n t at the scale of th i s analysis (such as lithology) take on greater importance. Where the t e r r a i n i s considerably d i f f e r e n t and no h i s t o r i c record i s available, the po t e n t i a l for f a i l u r e i n the p r i n -c i p a l material types can be estimated by (in decreasing order of effectiveness): i) comparison of old and current a i r photos for v i s u a l evidence of slope f a i l u r e , i i ) f i e l d investigation i i i ) laboratory tests on material strength, iv) evidence of f a i l u r e behavior of sim i l a r materials i n other locations, or v) i n t u i t i v e evaluation. The methods of numerical analyses used were i d e a l for the semi-quantitative Fraser Canyon slope data. A wide range of similar methods i s available, those including quantitative parameters y i e l d i n g the most r e l i a b l e r e s u l t s . Where feasible, a p i l o t study involving the measurement and analysis of slope variables and i t s subsequent analysis would be useful i n determining the s u i t a b i l i t y of the variables selected, t h e i r interactions, and t h e i r power i n explaining the d i s t r i b u t i o n of slope f a i l u r e s . The most important contribution of th i s thesis i s the i d e n t i f i c a t i o n of a method for rapid inventory and assessment of t e r r a i n c a p a b i l i t y to support routeways i n the face of natural slope hazards. The t e r r a i n c l a s s i f i c a t i o n map i s useful to planners i n the i d e n t i f i c a t i o n of hazardous slopes at the regional scale and i n the development of t r a i l s , roads, r a i l 133 l i n e s , and p i p e l i n e s . The method requires refinement and testing but i t s eventual application i n remote and poorly mapped regions would be of considerable p r a c t i c a l value to planners responsible for selecting optimum alignments for routeways. 134 R E F E R E N C E S AITCHISON, G.D. and K. GRANT, 1968, " T e r r a i n E v a l u a t i o n f o r E n g i n e e r i n g , " Land E v a l u a t i o n . E d i t e d by G.A. Stewart. MacMillan of A u s t r a l i a . 392p. ANDERBERG, Michael R., 1973, C l u s t e r A n a l y s i s f o r A p p l i c a - t i o n s . Academic Press. 359p. ARMSTRONG, J.E., D.R. CRANDELL, D.J.EASTERBROOK, and J.B. NOBLE, 1965, "Late P l e i s t o c e n e S t r a t i g r a p h y and Chronology i n Southwestern B r i t i s h Columbia and Northwestern Washington," Geol. Soc. Am. B u l l . ,. V o l . 76, pp. 321-330. BECKETT, P.H.T. and R. 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WATER SURVEY OF CANADA, 19 78, H i s t o r i c a l Sediment Data Summary, B r i t i s h Columbia. F i s h e r i e s and E n v i r o n . Canada, Ottawa. WATER SURVER OF CANADA, 1977, H i s t o r i c a l Streamflow Summary, B r i t i s h Columbia. F i s h e r i e s and E n v i r o n . Canada, Ottawa. WHEELER, J.O. ( e d i t o r ) , 1970, " S t r u c t u r e of the Southern •{'•. Canadian C o r d i l l e r a , " Geol. Assoc. Can., S p e c i a l Report No. 6. 166p. 140 Appendix I. CLIMATIC DATA FOR LYTTON, HELL'S GATE, AND HOPE, B.C. • P 5? CO < 3 »"3 rn c— o\ cr. o o 1 I c\j m co m cn -=r ni m fl-o o\ o rH rH ON VO VO . . . vo in in rH rH rH m m n . . . H D \ CO 01 o OJ OJ in vo 00 00 co o o t— VO r o LH CM . . . in rn rn o vo -=r o co o\ c_> in -=r in O M J3- CM -=3" X • * ' 3 rH CM r n En < Xvo a- vo W • CLi rn CM O S i l l E-i 5H M Q C o < - P w >> g J cu •p ta o cu a o a 1-1 -=r m . . . in m _r co co cr\ . . . H • H m m vo 00 . . . vo in t— c— r— co 3- oj *r rH rH rH m vo m . . . m O rH CM CM CM O VO rH . . . co in -a-CM CM CM OV VO -=J-CM CM CM rH m m in OJ rH CM CM CM rH OJ G\ OJ CT\ CO CM rH rH o\ rn c— in m _r rH m O CO o CO CM rH . . . 4 in in t— m co m CM o I I I rH Cr. CO O O I VO CM rH in vo vo rn vo t— o o o\ r n o -=r . . . .=T -=T CM co CM in 3 3 M -=r vo t— OJ rH o in N in co t— t— H ( J \ H =3- m _r O ON O O O rH O O _r -=r a-rH O rH vo in vo cn co o\ co t— co co vo m s in co CM CM CM vo cn t— m m m vo rn o co •a- m o\ m o o o o co vo m m -co vo vo m m m o vo co rn oj CM rn oj o in CM CM i-t t— a-rn O J CM I I I vo co -=r o t - a-m CM CM I I I m rH . 0 co vo in rH rH rH I I I rH m vo I C— rH OV . . . vo vo m CM vo a-• • • c- m a-a- o\ co a- m oj c n CM I I m m I I rH VO C— rH O VO CM CVI rH I I I O o\ H I « o\ EH < ' " C3 «) M 3 • P rd U CO x o. e « cu 2 EH S rH et) E f. O c cd •a: -H EH T3 c n ON •a- 0 c— rH >H O ~ O * CM rH 0 0 CM CO OJ • • • • • " PC a . • ^ c o m ON rH rH < _• in in f - 0 1 0 0 * 0 rH •rH 0 ™ 0 1 CM 1 OJ 1 MM s S co O vo CM rH as t— VO OJ 0 rH ON ^ c— CO s • . 2 • . . • . • • M O 0 OJ M V O a - m S in rH m 2 t - a - CM X 1 1 2 1 1 1 =3 rH rH rH D r n CM OJ • < H s S 1 1 1 < 2 H M a> CD X CU z CU • X • P X • P < •p H H ed ij ed S cd s ed M O M O 0 CJ3 X < <C •H Q C ca a c CO s c to _ c CO T3 O 0 w 0 — w 0 — C 2 - P rH Ct) 2 - P rH CO 05 - P rH cu rH CU CU < - P rH O. < - P rH a EH 40 H a EH - P rH a a U >> CD O w >> 01 0 X >> CU 0 X >> CU 0 0 . S J x x _ J X W J ac X Cd J X X < X rd c cd o c cu E C o u • H > c Station Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. Year MEAN RAINFALL (mm.) Lytton 30.5 29.7 20.3 18.3 14.7 20.6 12.2 Hell's Gate 119.1 98.6 108.0 59-9 38.4 34.3 24.4 Hope 165.6 149.6 125.0 107.2 6 1 . 5 55.1 35.6 18.8 23.4 49.5 51.6 45.0 334.6 27.9 69.6 140.2 153.4 152.7 1026.8 46.0 104.4 181.9 204.2 212.3 1448.4 MEAN SNOWFALL (cm.) Lytton 5 0 . 8 2 2 . 4 8 . 4 1 . 0 Hell's Gate 5 5 . 9 2 3 . 4 8 . 1 1 . 5 Hope 6 6 . 8 2 7 . 4 1 1 . 9 1 . 0 0.8 17.8 40.4 141.6 1.3 18.5 40.1 148.8 13.7 41.1 161.9 MEAN TOTAL PRECIPITATION (mm.) Lytton 7 4 . 9 5 1 . 1 2 8 . 4 1 9 . 1 14.7 2 0 . 6 1 2 . 2 Hell's Gate 1 7 5 . 3 1 2 1 . 9 1 1 6 . 1 6 1 . 5 3 8 . 4 3 4 . 3 24.4 Hope 2 2 7 . 3 1 7 7 . 0 1 3 6 . 9 1 0 8 . 2 6 1 . 5 5 5 . 1 3 5 . 6 18.8 23.4 50.3 68.6 80.8 462.9 27.9 69.6 141.5 172.0 192.8 1175.7 46.0 104.4 181.9 217.7 249.4 1601.1 GREATEST RAINFALL IN 24 HOURS (mm.) Lytton 42.2 6 9 . 9 2 1 . 1 2 2 . 9 3 1 . 0 1 8 . 8 1 9 . 3 24.9 24.6 7 6 . 7 5 1 . 8 3 2 . 5 7 6 . 7 Hell's Gate 8 8 . 6 9 3 - 5 3 6 . 8 5 5 . 6 2 1 . 6 3 7 . 1 2 9 . 2 2 1 . 1 42.2 8 6 . 1 8 6 . 9 6 6 . 8 9 3 . 5 Hope 9 7 . 7 1 0 5 . 7 6 9 . 9 6 8 . 6 3 8 . 1 41.1 3 9 . 1 2 9 . 7 6 6 . 3 1 0 1 . 3 8 5 . 9 8 6 . 4 105.7 Appendix I. B. SUMMARY OF PRECIPITATION DATA FOR LYTTON, HELL'S GATE, AND HOPE, B.C. (Environment Canada, Canadian Normals: Precipitation, 1 9 4 1 - 1 9 7 0 ) . 142 APPENDIX II T H E E L U C T E R R A I N C L A S S I F I C A T I O N T e r r a i n u n i t s are i s o l a t e d by the i n t e r p r e t e r on the b a s i s of t h e i r form and m a t e r i a l types. T h e i r boundaries normally are c l e a r l y v i s i b l e , but are i n f e r r e d i f obscured by shadow or v e g e t a t i v e cover. A s t r i n g of a l p h a b e t i c symbols i s then assigned to the u n i t . The order and case l e v e l of the a l p h a b e t i c components s p e c i f y the a t t r i b u t e to which they r e f e r . P r o p e r t i e s of the t e r r a i n u n i t are r e p r e s e n t e d i n t h i s sequence: i-): c l a s t i c t e x t u r e (lower case) A i i ) '• genesis of the m a t e r i a l (upper case) i i i ) s u r f a c e e x p r e s s i o n (lower case) iv) q u a l i f y i n g d e s c r i p t o r (upper case s u p e r s c r i p t ) v) modifying process (upper case preceded by a hyphen) The f u l l l i s t o f t e r r a i n a t t r i b u t e s and t h e i r symbols appear on page 14 3 and each i s e x p l a i n e d i n the c l a s s i f i c a t i o n handbook prepared by ELUC (1976) . The q u a l i f y i n g d e s c r i p t o r i s used f o r those u n i t s f o r which there i s a d d i t i o n a l i n f o r m a t i o n as to g l a c i a l , o r g a n i c , or process p r o p e r t i e s . These are i n d i c a t e d by upper case l e t t e r s f o l l o w i n g the m a t e r i a l or process symbols. Thus water-deposited m a t e r i a l (F) a s s o c i a t e d w i t h g l a c i a l meltwater Q ( ) i s w r i t t e n , while i n a c t i v e ( ) c o l l u v i a l s lopes (C) i n a l a n d s l i d e area are l a b e l e d 143 I . TEXTURE S p e c i f i c C l a s t i c Terms Common C l a s t i c Terms Org ;anic Terms b b o u l d e r y a blocky e f l b r i c k cobbly r r u b b l y m mesic p pebbly g g r a v e l l y h humic s sandy f f i n e s 4 s i l t y c c l a y e y I I . GENESIS A anthropogenic 0 o r g a n i c C c o l l u v i a l R bedrock E a e o l i a n S s a p r o l i t e P f l u v i a l V v o l c a n i c I i c e W marine L l a c u s t r i n e u u n d i f f e r e n t i a t e d M m o r a i n a l I I I . SURFACE EXPRESSION a apron m subdued b b l a n k e t r r i d g e d f fan s steep h hummocky t t e r r a c e d 1 l e v e l v veneer I V . QUALIFYING DESCRIPTORS C l a s t i c Process Organic G A g l a c i a l a c t i v e B bog 1 i n a c t i v e F fen S swamp V . MODIFYING PROCESSES - A avalanched - F f a l l i n g - S s o l i f l u c t e d - B b e v e l l e d - H k e t t l e d - V g u l l i e d - C c r y o t u r b a t e d - K k a r s t m o d i f i e d -W washed -D d e f l a t e d -N n i v a t e d * - X r o a d , r a i l w a y - E c h a n n e l l e d - P p i p i n g * -Y d e f o r e s t e d D e s c r i p t i v e t e r m i n o l o g y o f the ELUC t e r r a i n c l a s s i f i c a t i o n scheme. A s t e r i s k (*) denotes a d d i t i o n s made by the w r i t e r . 144 c 1 . F i n a l l y , where f i e l d observation shows that the s u r f i c i a l geology i s more complex than indicated by i t s surface expression, stratigraphic relations between materials may be shown. For example, where a thin layer of blocky colluvium o v e r l i e s gravelly f l u v i a l deposits, the unit i s described as, arCv gFl When several s u r f i c i a l materials occur within a single t e r r a i n unit, t h e i r areal proportions may be indicated by equality or slash symbols. If one type of material occupies 90 to 100% of the area, i t alone represents that u n i t . In a unit wherein a c o l l u v i a l apron i s much more extensive than steep bedrock, the c l a s s i f i c a t i o n i s , arCa // Rs Areal proportions of materials on ve r t i c a l l y - t a k e n photography i s not to be confused with t h e i r r e l a t i v e predominance i n l a t e r a l viewing of the t e r r a i n . This applies p a r t i c u l a r l y to steep rock slopes of which the actual v e r t i c a l extent i s hidden i n a e r i a l photographs. Symbols for areal relationships used i n composite units appear i n the following table: 145 dominant proportional symbol secondary material r e l a t i o n material (% cover) (% cover) 55 - 45 i s equivalent to = 45 - 55 70 - 55 i s greater than / 30 - 45 90 - 70 i s much greater than / / 10 - 30 Descriptive terminology for t e r r a i n units i n the Fraser Canyon i s i l l u s t r a t e d i n the following examples: descriptive t e r r a i n unit terminology c h a r a c t e r i s t i c s arCa - FA Blocky and rubbly c o l l u v i a l apron, showing recent f a i l u r e scars and avalanche tracks. arC Ih(r) - X Blocky, rubbly colluvium derived from inactive r o c k f a l l or landslide processes whose surface appears hummocky and s l i g h t l y ridged, and which i s traversed by a road and/or railway track. fgCv(b) Fine and gravelly c o l l u v i a l veneer or blanket. r gF l ( t ) Gravelly f l u v i o - g l a c i a l l e v e l or terrace. sgFt Sand and gravel f l u v i a l terrace. •",E-FX Fine inactive aeolian veneer overlying a sand and gravel f l u v i a l terrace. 146 APPENDIX III M E T H O D S 0 F A N A L Y S I S APPENDIX III.A DESCRIPTIVE STATISTICS A computer program set c a l l e d UBC SPSS:8, " S t a t i s t i c a l Package for the Social Sciences", was used. It i s a large program designed to do descriptive analyses on large-volume data, accommodating both parametric and non-parametric s t a t i s t i c s . The SPSS program was chosen i n the study to handle the semi-quantitative attributes used to characterize the slopes adjacent to the tracks. Frequency of occurrence of each of the slope attributes was generated by SPSS subprogram FREQUENCIES i n both tabular and histogram form. Joint frequency tables or crosstabulations, involving two or more slope attributes simultaneously, are available i n SPSS using subprogram CROSSTABS. The s t a t i s t i c a l significance of the CROSSTABS d i s t r i b u t i o n i s tested by the chi-square s t a t i s t i c , and measures of association between variables are also available. SPSS subprogram BREAKDOWN provides a crosstabulation of independent variables with respect to a dependent one. In thi s study a BREAKDOWN of s u r f i c i a l geology by slope angle results i n a mean slope f a i l u r e incidence for each possible combination of those a t t r i b u t e s . An example of the SPSS FREQUENCIES, CROSSTABS, and BREAKDOWN subprograms i s found i n Appendix I I I ( B ) . Further information on the SPSS programs i s found i n Nie et a l . ..(2nd ed., 1975) and i n Kita (.1978) . 147 Appendix III.Bi Sample SPSS Program SPSS BATCH SYSTEM HTS/SPSS, VERSION H , RELEASE 8.0, DECEMBER 17, 1979 DEFAULT SPACE ALLOCATION.. WORKSPACE 71630 BYTES TRANSPACE 10240 BYTES ALLOWS FOR.. 102 TRANSFORMATIONS 409 RECOOE VALUES • LAG VARIABLES 1641 IF/COMPUTE OPERATIONS 5 6 7 PAGESIZE VARIABLE LIST INPUT MEDIUM INPUT FORMAT NOEJECT MILE FREQ SURFGEOL MODI TO M0D6 BR1 3R20 BR24 BRCUS CUTSLOPE MATROCK MATUN ANGLE 1 TO ANGLES HEIGHT 01 STANCE JOINTNGl TO JOINTNG4 SILTPRES SILTABS SEEPAGE FIXED MEASURE 1 TO MEASURE9 DISK FIXED(F4.0,1X,F2.0,IX,F7.0,10F1.0» 1K,F1.0,IX,2F1.0.1X,5F1.0, 1X,F1.0,1X,F1.0,1X,4F1.0,1X,2F1.0, IX.F1.0,IX,F1.0,IX,9F1.0I ACCORDING TO YOUR INPUT FORMAT, VARIABLES ARE TO BE READ AS FOLLOWS VARIABLE FORMAT RECORD COLUMNS MILE F 4. 0 I 1- 4 FREQ F 2. 0 1 6- 7 SURFGEOL F 7. 0 1 9- 15 MODI F 1. 0 1 16- 16 MOD 2 F 1. 0 1 17- 17 MO 03 • F 1. 0 1 18- 18 MQD4 F 1. 0 1 19- 19 M0D5 F 1. 0 1 20- 20 M0D6 F 1. 0 1 21- 21 BR1 F' 1. 0 1 22- 22 BR20 F 1. 0 1 23- 23 BR24 F 1. 0 1 24- 24 BRCUS F 1. 0 1 25- 25 CUTSLOPE F 1. 0 1 27- 27 HATROCK F 1. 0 1 29- 29 MATUN <"F 1. 0 1 30- 30 148 ANGLE 1 F 1. 0 1 32- 32 ANGLE2 F 1. 0 l 33- 33 ANGLE3 F 1. 0 1 34- 34 ANGLE4 F 1. 0 X 35- 35 ANGLES F 1. 0 1 36- 36 HEIGHT F 1. 0 1 3 8- 38 DISTANCE F 1. 0 1 40- 40 J0INTNG1 F I . 0 1 42- 42 J0INTNG2 F 1. 0 1 43- 43 J0INTNG3 F 1. 0 1 44- 44 J0INTNG4 F 1. 0 1 45- 45 SILTPRES F 1. 0 1 47- 47 SILTABS F 1. 0 1 48- 48 SEEPAGE F 1. 0 1 50- 50 FIXED F 1. 0 l 52- 52 MEASURE I F 1. 0 l 54- 54 MEASURE2 F 1 . 0 1 55- 55 MEASURE3 F 1. 0 1 56- 56 MEASURE4 F 1. 0 1 57- 57 MEASURES F 1. 0 1 58- 58 MEASURE6 F 1. 0 1 59- 59 MEASURE? F 1. 0 1 60- 60 MEASURE8 F 1. 0 i 61- 61 MEASURE"? F 1. 0 1 62- 62 9 N OF CASES 10 COMPUTE 11 RECODE 12 13 14 15 COMPUTE 16 COMPUTE 17 COMPUTE 18 COMPUTE 19 COMPUTE 20 COMPUTE 21 COMPUTE 22 COMPUTE 23 COMPUTE 24 COMPUTE 25 COMPUTE 26 COMPUTE 27 COMPUTE 28 COMPUTE 29 COMPUTE 30 COMPUTE 31 COMPUTE 32 COMPUTE 33 COMPUTE UNKNOWN SURFGEOL=TRUNC(SURFGEOL/100001 SURFGEOL!400=1)(415,514=2»I 416 = 3)(417=4) (425=51(435=6) (495=7)(496=8)(497=9)(500,515=10)(517=11) 1524=12) (527=13)(534=14)(600=15)(634=16)(695=17) (700,795=18)(734=19)(897=20) NSURF=SURFGEOL NFREQ=FREQ>1 M0DIFIER=l*M0Dl+2*M0D2«-4*M0D3*8*M0D4<-16*M0D5 •32*M0D6 NMOD=MODIFIER+1 BEDROCK=1*BR1*2*BR20+3*BR24*4*BRCUS NR0CK=BEDR0CK+1 NCUT=CUTSL0PE+1 MATERIAL=1*MATR0CK+2*MATUN NMAT=MAT£RIAL»1 ANGLE=1*ANGLE1+2*ANGLE2*3*ANGLE3+4*ANGLE4* 5*ANGLE5 NANGLE=ANGLE+1 NHEIGHT=HEIGHT*1 NDIST=DISTANCE+l J0INTNG=l*J0INTNGl*2*J0INTNG2«-3*J0INTNG3* 4*J0INTNG4 NJ0INT=J0INTNG+1 SILT=1«SILTPRES+2*SILTABS NSILT=SILT*l NSEEP=SEEPAGE*l NFIX=FIXED+l 149 34 COMPUTE 35 36 RECODE 37 COMPUTE 38 RECODE 39 40 FREQUENCIES 41 STATISTICS MEASURES=1*MEASURE1+2*NEASURE2+4*NEASURE3* 8*MEASURE4+ 16*MEASURE5*32*MEASURE6*64*MEASURE7* 128*MEASURE8+256*MEASURE9 MEASURES (1=1)(2=2)(4=3)(8=4)(16 = 5)(32=6) (64=7)(128=8)(256=9) NMEAS=MEASURES+l NMODI 2=1 M4=2)(6=3M 8=4) (10=5 )(12=6) (18=7) 122=81 (26=9)(34=10) INTEGER=NCUT(1,2) NANGLE!l?6I ALL AFTER READING 199 CASES FROM SUBFILE NONAME , END OF DATA WAS ENCOUNTERED ON LOGICAL UNIT # 8 SPSS BATCH SYSTEM NONAME (CREATION DATE = 06/23/80) FILE NCUT CATEGORY LABEL CODE uncut 1 cut 2 TOTAL RELATIVE ADJUSTED CUMULATIVE ABSOLUTE FREQUENCY FREQUENCY ADJ FREQ FREQUENCY (PERCENT)(PERCENT) (PERCENT) 33 161 199 19.1 80.9 100.0 19.1 100.0 MEAN MODE KURTOSIS MINIMUM 1.809 2.000 0.516 1.000 STO ERR STD DEV SKEWNESS MAXIMUM 0.028 0.394 -1.585 2.000 MEDIAN 1.882 VARIANCE 0.155 RANGE 1.000 VALID CASES 199 MISSING CASES 150 NANGLE CODE ABSOLUTE FREQUENCY RELATIVE FREQUENCY IPERCENT) ADJUSTED FREQUENCY (PERCENT) CUMULATI ADJ FR (PERCEN NA. 1 11 5.5 5.5 5.5 > 70° 2 87 43. 7 43.7 49.2 <70°3 6 3.0 3.0 52.3 <30°4 24 12.1 12.1 64.3 30°41°5 35 17.6 17.6 81.9 36 18.1 18.1 100.0 TOTAL 199 100.0 100.0 MEAN 3.467 MODE 2.000 HURTOSIS -1.513 (MINIMUM 1.000 MEDIAN 2.750 VARIANCE 2.907 RANGE 5.000 STD ERR STD DEV SKEWNESS MAXIMUM 0.121 1 .705 0.282 6.000 VALID CASES 199 MISSING CASES 0 -43 CROSSTAB'S VARIABLES=FREQI0,22 ) NCUT(1,2) NANGLE(1*61/ 44 TABLES=NCUT BY NANGLE/ 45 OPTIONS 9 46 STATISTICS 1,3,7 151 * * C R O S S T A B U L A T I O N O F * * NCUT BY NANGLE NANGLE COUNT ROM PCT COL PCT TOT PCT N.A. 1 I>70 2 *CUT 1 6 1 1 15.8 I 2.6 uncut 54.5 I 1.1 3.0 1 0.5 2 5 1 cut COLUMN TOTAL 3.1 45.5 2.5 11 5.5 86 53.4 98.9 43.2 <70" 3 2 5.3 33.3 1.0 4 2.5 66.7 2.0 I<30° -I 4 I30^f5 87 43.7 6 3.0 23 60.5 95.8 11.6 1 I 0.6 I 4.2 I 0.5 I I > 0 ° 6 5 I 1 13.2 I 2.6 14.3 I 2.8 2.5 I 0.5 1 ROW TOTAL 30 18.6 85.7 15.1 35 21.7 97.2 17.6 38 19.1 161 80.9 24 12.1 35 17.6 36 199 18.1 100.0 *A* CHI SQUARE = 126.08058 HITH 5 DEGREES OF FREEDOM. SIGNIFICANCE = 0.0000 CONTINGENCY COEFFICIENT = 0.62277 KENDALL'S TAU C = -0.01717 SIGNIFICANCE I2-TAILEDJ>= 0.8047 47 BREAKDOWN 48 49 STATISTICS VARIABLES=FREQ(0,22) NCUT(1,2) NANGLEt1,6)/ CROSSBREAK=FREQ BY NANGLE BY NCUT/ ALL 152 * * * * * C R O S S B R E A K D O W N O F * * * * * N A N G L E B Y N C U T * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * V A R I A B L E A V E R A G E D . . . F R E Q N C U T M E A N C O U N T S U M S T O D E V M A N G L E N.A. >70° <70u <30" 3CP-41° > « 1 ° C O L U M N T O T A L uncut l o.o 6 0.0 0.0 0.0 1 0.0 0.0 0.0 2 0.0 0.0 0.26 23 6.00 0.69 0.40 5 2.00 0.55 1.00 1 1.00 0.0 0.24 38 9.00 0.59 I CUt 2 I 3.20 I 5 I 16.00 I 3.96 I 2.17 I 86 187.00 I 2.81 I 1 1.75 I 4 I 7.00 I 2.36 I 1 0.0 I 1 I 0.0 I 0.0 I 1 1.33 I 30 1 40.00 I 2.28 I 1 3.09 I 35 I 108.00 I 4.58 I — I 2.22 161 358.00 3.24 ROW T O T A L 1.45 11 16.00 3.01 2.15 87 187.00 2.81 1.17 6 7.00 2.04 0.25 24 6.00 0.68 1.20 35 42.00 2.14 3.03 36 109.00 4.53 1.84 199 367.00 3.03 153 RAW CHI SQUARE = 126.08058 WITH 5 DEGREES OF FREEDOM. SIGNIFICANCE = 0.0000 CRAMER'S V = 0.79597 CONTINGENCY COEFFICIENT = 0.62277 LAMDA (ASYMMETRIC) = 0.19643 WITH NANGLE DEPENDENT. = 0.60526 WITH NCUT DEPENDENT. LAMDA (SYMMtTRIC) = 0.30000 JNCERTAINTY COEFFICIENT (ASYMMETRIC) =0.19160 WITH NANGLE DEPENDENT. = 0.58840 WITH NCUT DEPENDENT. UNCERTAINTY COEFFICIENT (SYMMETRIC) = 0.28907 KENDALL'S TAU B = -0.01812. SIGNIFICANCE = 0.3520 KENDALL'S TAU C = -0.01717. SIGNIFICANCE = 0.3594 GAMMA = -0.02938 SOMERS'S D (ASYMMETRIC) = -0.02779 WITH NANGLE DEPENDENT. = -0.01181 WITH NCUT DEPENDENT. SOMERS'S D (SYMMETRIC) = -0.01658 ETA = 0.00155 WITH NANGLE OEPENDENT. = 0.63358 WITH NCUT DEPENDENT. 50 FINISH NORMAL END OF JOB. 50 CONTROL CARCS WERE PROCESSED. 0 ERRORS WERE OETECTED. 154 A P P E N D I X I I I . C S L O P E A T T R I B U T E E V A L U A T I O N A n " A u t o m a t i c I n t e r a c t i o n D e t e c t o r " p r o g r a m (AID3) w a s u s e d t o d e t e r m i n e t h e i n f l u e n c e o f t h e a t t r i b u t e s i n e x p l a i n i n g t h e v a r i a t i o n i n s l o p e f a i l u r e . AID3 s e a r c h e s a m o n g a s e t o f p r e d i c t i n g c h a r a c t e r i s t i c s a n d i d e n t i f i e s t h o s e w h i c h b e s t i n c r e a s e t h e r e s e a r c h e r ' s a b i l i t y t o a c c o u n t f o r t h e v a r i a n c e o f a d e p e n d e n t v a r i a b l e ( L e , 19 75, p . 2 ) . I n t h i s s t u d y , t h e p r e d i c t i n g c h a r a c t e r i s t i c s a r e s l o p e a t t r i b u t e s d e r i v e d f r o m t h e t e r r a i n c l a s s i f i c a t i o n m a p a n d f r o m t h e f i e l d i n v e s t i g a t i o n . T h e AID3 p r o g r a m w a s d e s i g n e d f o r l a r g e d a t a b a t c h e s s o t h a t t h e r e l i a b i l i t y o f t h e s p l i t t i n g / r e s p l i t t i n g p r o c e d u r e i s m a x i m i z e d . I t s a p p l i c a t i o n t o t h e e a s t e r n s l o p e d a t a c o m p r i s i n g 199 c a s e s i s j u s t i f i e d b y r e s t r i c t i n g t h e p o w e r o f t h e s e a r c h i n g p a t t e r n s o t h a t r e s u l t a n t e n d g r o u p s a r e n o t t o o s m a l l . T h e i m p o r t a n c e o f t h e i n d i v i d u a l v a r i a b l e s i n e x p l a i n i n g o v e r a l l v a r i a n c e i s s t r e s s e d . F u r t h e r d i s c u s s i o n o f t h e n a t u r e o f AID3 o u t p u t a n d t h e i n t r i c a c i e s o f i t s i n t e r p r e t a t i o n a r e p r e s e n t e d b y S o n q u i s t e t a l . ,1974). B e g i n n i n g w i t h t h e c o m p l e t e d a t a s e t , t h e p r e d i c t o r v a r i a b l e c l a s s e s a r e f i r s t o r d e r e d b y a m e a n v a l u e o f t h e d e p e n d e n t v a r i a b l e , s l o p e f a i l u r e i n c i d e n c e . A n u m b e r o f s p l i t s o n e a c h v a r i a b l e i s e v a l u a t e d a n d t h e b e s t , o r m o s t s i g n i f i c a n t , i s c h o s e n . T h e s p l i t i s m a d e s o t h a t a l l . m e a n s i n o n e c l a s s a r e l e s s t h a n o r e q u a l t o a l l m e a n s i n t h e o t h e r 155 c l a s s . Subsequently, each subgroup undergoes the same tre a t -ment u n t i l the t o t a l v a r i a t i o n i s reduced as much as possible. The AID3 user imposes l i m i t s on the analyses which terminate the s p l i t t i n g procedure. These are, i) the minimum variance explained i n each group, set i n these analyses to 2% of the t o t a l variance, i i ) the minimum number of cases i n each group, set here to f i v e , and i i i ) to maximum number of s p l i t s allowed, set here to an a r b i t r a r i l y high value of 89. A tree diagram showing the succession of s p l i t groups may be generated and i t s form used as an ind i c a t i o n of variable i n t e r a c t i o n and d i s t r i b u t i o n . F i n a l groups r e s u l t i n g from the s p l i t t i n g process may be of three types. Small groups cannot be s p l i t further as the resultant groups contain fewer cases than the minimum number set by the programmer. Explained groups contain more than the minimum number of. cases but have l i t t l e i n t e r n a l v a r i a t i o n , so that further s p l i t t i n g on the independent variables cannot occur. Irt unexplained groups, though the in t e r n a l v a r i a t i o n i s large, a further s p l i t cannot be made on the independent variables used i n the analysis. Inconsistency i n the structure of the tree i s evidence of interaction between variables. Where no inte r a c t i o n occurs, the variance i s s p l i t on the same variable at corresponding l e v e l s , or branches, of the,tree. When there i s inte r a c t i o n between several variables the r e s u l t i s a skewed, asymmetric tree structure. 156 APPENDIX III.D. CLUSTER ANALYSIS AND MULTI-DIMENSIONAL SCALOGRAM ANALYSIS A h i e r a r c h i c a l c lustering program, HCLUS, developed by Frank Flynn at the University of B r i t i s h Columbia, was used on the Fraser Canyon slope data. I t employs an agglomerative method by which a nested tree i s constructed from the ind i v i d u a l cases, or branches, to the root. The data are organized into groups within which variables used to describe each datum are s i m i l a r . In th i s study, s i t e s along the railway l i n e s are described i n terms of slope a t t r i b u t e s . The s i m i l a r i t y between cases and/or clusters i s evaluated on the basis of a pre-determined linkage procedure. Several of the merging sequences are between - closest members (single linkage) - most distant members (complete linkage) - average distance within or between members (average linkage). The complete linkage method was employed i n thi s study as i t increases the difference between resultant c l u s t e r s . Further discussion of HCLUS i s made by Flynn (1976). Although slope f a i l u r e was not considered i n the clustering procedure, i t has been used i n the s t a t i s t i c a l j u s t i f i c a t i o n of the groups. SPSS subprogram ONEWAY, the analysis of variance, was employed i n the cases along the eastern slopes where the f a i l u r e history i s known. Results of the s t a t i s t i c a l testing of clusters generated with the eastern slope are ;-•.<•.:' •" v tentatively.extrapolated to the western slopes as well. A second method used to group the s i t e s was the Guttmann-Lingoes multidimensional scalogram analysis, MSA-I. In t h i s 1 5 7 analysis, data described by n variables f a l l s into a m-dimensional Euclidean framework. Within this each case occupies a d i s t i n c t position determined by the n variables. A c o e f f i c i e n t of contiguity i s generated, ranging from -1 to +1, which indicates the degree of s p a t i a l association of the data i n the m-dimensional space. The c o e f f i c i e n t has a value of +1 when the association i s perfect. When the data cannot be separated i n m-dimensional space on the basis of the variables used, the c o e f f i c i e n t has a value of -1. F i r s t the data are placed i n an orthogonal co-ordinate system from which the i n i t i a l Euclidean distances are calculated. A pre-set number of it e r a t i o n s ensues by which the c o e f f i c i e n t of contiguity i s maximized using a scalar m u l t i p l i e r for the i t e r a t i o n s . F i n a l l y the m-dimensional co-ordinates of the data are l i s t e d and a plot(s) produced showing two dimensions at a time. The data may be separated into groups of si m i l a r character by (m-1)-dimensional cutting surfaces. Further discussion of the Guttmann-Lingoes MSA procedure i s made by Lingoes (19 7 3). Before HCLUS and MSA-I were used, the data were subjected to a duplicate-searching program, which i s o l a t e d cases with unique combinations of the variables employed. This was done in order to save computing time i n the lengthy search procedures within the two c l a s s i f i c a t i o n operations. The duplicated s i t e s were reinstated a f t e r the programs were complete. 1 5 8 Appendix IV. TYPES OF SLOPE FAILURE IN THE FRASER CANYON Appendix IV. A. MODES OF FAILURE IN ROCK SLOPES Undisturbed Slopes  (above) Kuthlath p o s t - g l a c i a l landslide upslope from mile 25.0 (40.2 km) on the east side of the canyon. Steep rock scarps extend up to 2000 feet (600 m) i n height. (below) Recent rock-f a l l s i t e s on the upper slope and i n the bedrock notch i n c i s e d by the Fraser River. Photo taken of mile 9.6 (15.4 km) on the east side of the canyon. 1 5 9 T r a c k s i d e S lope S i t e o f o r i g i n o f a r e c e n t r o c k f a l l onto the t r a c k s . Note the j o i n t i n g and f r a c t u r i n g p a t t e r n at the r o c k f a l l s c a r . Photo taken at m i l e 16.7 (26.9 km) on the e a s t s i d e o f the c a n y o n . ti. FAILURES IN ROCK-AND-COLLUVIAL SLOPES U n d i s t u r b e d S lopes F a i l u r e o f a b e d r o c k - a n d - c o l l u v i a l s l a b above the T r a n s Canada Highway, ups lope from m i l e 13.0 (20.9 km) on the e a s t e r n s l o p e . 160 Rock-triggered c o l l u v i a l s l i d e above mile 19.2 (30.9 km) on the western slope. Trackside Slope Debris f a l l of c o l l u v i a l material overlying bedrock exposed i n the trackside slope at mile 13.9 (22.4 km) on the western slope. 161 C. MODES OF FAILURE ON COLLUVIAL SLOPES. Undisturbed Slopes D e b r i s s l i d e from the upper slope at m i l e 6 . 4 ( 1 0 . 3 km) on the e a s t e r n s l o p e . T r a c k s i d e Slope Dry r a v e l l i n g o f a c o l l u v i a l s l o p e oversteepened at i t s base d u r i n g r a i l w a y c o n s t r u c t i o n . Photo taken on the east s i d e o f the canyon at mile 1 1 . 4 ( 1 8 . 3 km). 162 Appendix V. FREQUENCY DISTRIBUTIONS OF THE SLOPE ATTRIBUTES The upper figure represents the percentage of s i t e s i n that class of the t o t a l number of s i t e s ( = 199). The actual number of s i t e s appears'in brackets below. A. Eastern Western Eastern Material Genesis Slopes Slopes Western predominantly c o l l u v i a l : C 8.5 8.3 8.4 (17) (18) (35) C=R 8.0 7.9 8.0 (16) (17) (33) C=F° 3.7 1.9 (8) (8) C=F 4 . 0 _ _ 1.9 (8) (8) C/R 10.1 10.6 10.4 (20) (23) (43) C//R 17.6 20.8 19.3 (35) (45) (80) C R 4.0 4.6 4.3 (8) (10) (18) C F G 3.0 1.4 2.2 (6) (3) (9) C V 7.5 0.9 4 . 1 r (15) (2) (17) t o t a l c o l l u v i a l 62.7 58.2 60.5 slopes (125) (126) ( 2 5 D 163 Appendix V. A. cont. E a s t e r n Western E a s t e r n and M a t e r i a l Genesis Slopes Slopes Western Slopes predominantly bedrock R 3.0 2.3 2.7 ( 6 ) (5) (11) R=F — 0 . 9 0.5 (2) (2) R/C 5.5 1 . 9 3 . 6 (11) (4) (15) R/F 1.0 0.5 (2) (2) R//C 8.5 1.4 4.8 (17) (3) (20) t o t a l bedrock 18.0 6.5 12.1 sl o p e s ( 3 6 ) (14) (50) predominantly f l u v i o - g l a c i a l F G 8.5 5 . 6 7.0 (17) (12) ( 2 9 ) F G//C _ — _ . 2.3 1.2 (5) (5) F G - 2.0 9.3 5.8 R (4) (20) (24) t o t a l f l u v i o - 10.5 17-2 14 .0 g l a c i a l s l o p e s (21) (37) (58) 164 Appendix V. A. cont. Eastern Western Eastern and Material Genesis Slopes Slopes Western Slopes predominantly f l u v i a l F F//C t o t a l f l u v i a l slopes aeolian capping present E 0.9 0.5 F (2) (2) 8.0 13.9 11.1 (16) (30) (46 ) 0 . 5 3.2 1.9 (1) (7) (8) 8.5 17.1 13.0 (17) (37) (54 ) 1 6 5 Appendix V. B. Eastern Western Eastern and Modifying Processes Slopes Slopes Western Slopes X 5 8 . 3 5 8 . 3 5 8 . 3 ( 1 1 6 ) ( 1 2 6 ) (242) XF 2 2 . 6 3 2 . 4 2 7 . 7 ( 4 5 ) ( 7 0 ) ( 1 1 5 ) XA 2 . 5 1 . 9 2 . 2 ( 5 ) ( 4 ) ( 9 ) XFA 2 . 5 2 . 3 2 . 4 ( 5 ) ( 5 ) ( 1 0 ) XV 1 . 5 0 . 7 ( 3 ) ( 3 ) XFV 4 . 5 2 . 2 ( 9 ) ( 9 ) XY 4 . 5 2 . 2 ( 9 ) ( 9 ) XAY 1 . 5 0 . 7 ( 3 ) ( 3 ) XVY 2 . 3 1 . 2 ( 5 ) ( 5 ) XE 2 . 0 2 . 8 2 . 4 ( 4 ) ( 6 ) ( 1 0 ) Appendix V. C. Eastern Western Eastern and Cutslope Slopes Slopes Western Slopes uncut 19.1 2 5 . 5 2 2 . 4 ( 3 8 ) ( 5 5 ) ( 9 3 ) cut 80 . 9 7 4 . 5 7 7 . 6 ( 1 6 1 ) ( 1 6 1 ) ( 3 2 2 ) 1 6 6 Appendix V . D. Eastern Western Eastern and Height Slopes Slopes Western Slopes n o n - c r i t i c a l 3 0 . 7 5 6 . 5 4 4 . 1 ( 6 1 ) ( 1 2 2 ) ( 1 8 3 ) c r i t i c a l 6 9 . 3 4 3 . 5 5 5 . 9 ( 1 3 8 ) ( 9 4 ) ( 2 3 2 ) Appendix V. E. Eastern Western Eastern and Distance Slopes Slopes Western Slopes n o n - c r i t i c a l 4 2 . 2 6 4 . 8 5 4 . 0 ( 8 4 ) ( 1 4 0 ) ( 2 2 4 ) c r i t i c a l 5 7 . 8 35 . 2 4 6 . 0 (115) (76) ( 1 9 D 1 6 7 Appendix V. F. Eastern Western Eastern and Angle Slopes Slopes Western Slopes not a p p l i c a b l e 5.5 15.7 10.8 (11) (34) (45) 70° 43.7 35.2 39.3 (87) (76) (163) 70° 3.0 1.9 2.4 (6) (4) (10) 3 0 ° 12.1 7.4 9.6 (24) ( 1 6 ) (40) 3 0 ° - 41° 17.6 29.2 23.6 (35) (63) ( 9 8 ) 1*1° 18.1 10.6 14.2 (36) (23) (59) Appendix V. G. Eastern Western Eastern and M a t e r i a l Slopes Slopes Western Slopes bedrock and 2.5 0.9 1.7 unconsolidated (5) (2) (7) bedrock 46.7 36 . 6 41.4 ((93) (79) (172) unconsolidated 5 0 . 8 ( 1 0 1 ) 6 2 . 5 ( 1 3 5 ) 5 6 . 9 ( 2 3 6 ) 168 Appendix V. H. Eastern Western Eastern and Jo i n t i n g Slopes Slopes Western Slopes not applicable 54.3 6 3 . 0 58.8 (108) (136) (244) coarse 24.6 25.5 25.1 (49) (55) (104) intermediate 12.6 5.1 8.7 (25) (11) ( 3 6 ) fine 7.0 6.0 6.5 (14) (13) (27) intact 1.5 0.5 1.0 (3) (1) (4) Appendix V. I. Eastern Western Eastern and Bedrock Slopes Slopes Western Slopes Scuzzy Pluton 1 2 . 1 2 0 . 8 1 6 . 6 (24) ( 4 5 ) ( 6 9 ) Yale Intrusives 2 3 . 6 1 8 . 1 2 0 . 7 ( 4 7 ) • ( 3 9 ) ( 8 6 ) Spuzzum Intrusives 4 2 . 2 3 5 . 8 4 4 . 1 (84) ( 9 9 ) ( 1 8 3 ) Custer Gneiss 1 5 . 3 8 . 0 ( 3 3 ) ( 3 3 ) Hozameen Group 2 2 . 1 ( 4 4 ) 10 . 6 ( 4 4 ) 169 Appendix V. J. Eastern Western Eastern and Remedial Measures Slopes Slopes Western Slopes absent 8 1 . 4 ( 1 6 2 ) 8 1 . 9 ( 1 7 7 ) 8 1 . 7 ( 3 3 9 ) present 1 8 . 6 ( 3 7 ) 1 8 . 1 ( 3 9 ) 1 8 . 3 ( 7 6 ) Appendix V. K. Eastern Western Eastern and Pines Slopes Slopes Western Slopes not applicable 48 .2 ( 9 6 ) 3 6 . 6 ( 7 9 ) 42 .2 ( 1 7 5 ) absent 46 .2 ( 9 2 ) 5 8 . 3 ( 1 2 6 ) 5 2 . 5 ( 2 1 8 ) present 5 . 5 ( 1 1 ) 5 . 1 ( 1 1 ) 5 . 3 ( 2 2 ) Appendix V. L. Eastern Western Eastern and Seepage Slopes Slopes Western Slopes absent 94.0 ( 1 8 7 ) 9 4 . 4 (204) 9 4 . 2 ( 3 9 1 ) present 6 . 0 ( 1 2 ) 5 . 6 ( 1 2 ) 5 . 8 (24) 9 170 Appendix VI. MEAN SLOPE FAILURE INCIDENCE FOR CATEGORIES OF SURFICIAL MATERIALS AND OF MODIFYING PROCESSES (Eastern slope data only) Appendix VI. A. s u r f i c i a l mean f a i l u r e number of material incidence cases C 1.06 17 C=R 2 . 3 8 16 C=F 0 . 7 5 8 C/R 3 . 8 5 20 C//R 1 . 7 1 35 C R 1 . 5 0 8 C F G 2 . 0 0 6 C F 1.40 15 R 3 . 1 7 6 R/C 2 . 0 0 1 1 R/F 0 . 5 0 2 R//C 3 . 9 4 17 F G 0 . 5 9 17 F G 0 . 0 0 4 R F 0 . 1 9 • 16 F//C 1 . 0 0 1 t o t a l 1.54 1 9 9 171 Appendix VI. B. modifying mean f a i l u r e number of processes incidence cases X 1 . 3 6 1 1 6 XF 2 . 9 1 45 XA 0.40 5 XFA 3.00 5 XV 2 . 6 7 3 XFV 5.00 9 XY 0 . 5 6 9 XAY 0 . 6 7 3 XE 0 . 2 5 4 t o t a l 1.84 1 9 9 172 Appendix V I I . AID3 TREE DIAGRAM AID3 was used with the e a s t e r n slope d a t a , u s i n g log-transformed s l o p e f a i l u r e as the dependent v a r i a b l e , and twelve or fewer slope a t t r i b u t e s as independent v a r i a b l e s . T h i s appendix c o n t a i n s the t r e e diagram r e s u l t i n g from an AID3 run where the s i x most Important s l o p e a t t r i b u t e s ( i e . those with ETA values g r e a t e r than 0.1), i n c l u d i n g the m a t e r i a l genesis v a r i a b l e at the t h r e e - d i g i t l e v e l , were used. Key to the Diagram: mean f a i l u r e i n c i d e n c e (log-transformed) parent group number of s i t e s i n t h i s group ( a s t e r i s k denotes endgroups). . 3 5 4 62 .217 4 8 Appendix VII. 174 Appendix VIII. MSA-I SCALOGRAMS. A. Eastern slope data including 199 s i t e s . B. Eastern slope data including 199 s i t e s and with the material genesis variable truncated to one d i g i t . C. Western slope data including 216 s i t e s . D. Combined eastern and western slope data including 415 s i t e s . Key to the Scalograms O 1 - 4 si t e s O 5 - 9 s i t e s # 1 0 - 2 4 s i t e s 25 + s i t e s Six slope attributes are used to describe each s i t e , and define i t s p o s i t i o n i n six-dimensional space. For ease i n in t e r p r e t a t i o n , the scalogram of the data i s presented i n two-dimensions, represented by vectors 1 and 2. 175 176 rH U O -P o > O ° o o o ° o o o « n 0° < ° fc ° ° o v e c t o r 2 O Cr O O 0 0 o o ° o # o 3 o o o o o 1 O 9§ co ° o o °o o ° o % * ° o o n © 0 ° o ° o c t o ro v e c t o r 1 O® o 0 ^ O 8 % o O Appendix V I I I . C. to <8 O° 0 D o o o o o c £ 9 o o o @ o 8 o 8 ( M © O S o o o " © o o o o r—1 - j CO v e c t o r 1 

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