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Modeling Sediment Transport, Channel Morphology and Gravel Mining in River Bends

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Modeling Sediment Transport, Channel Morphology and Gravel Mining in River Bends AN ABSTRACT OF THE THESIS OF Ili for the degree of Doctor of Philosophy in Civil Engineering presented on October 19.1995. Title: Modeling Sediment Transport. Channel Morphology and Gravel Mining in River Bends . Abstract approved: Redacted for Privacy Peter C. Klingeman A technique is developed and tested to analyze the interaction of flowing water, bed topography, and bedload sediment transport in meandering channels where gravel bars are removed. The method relates the local velocity distribution, bed shear stress and sediment transport conditions to the local bed configuration in river bends before and after gravel bar removal. Specific attention is given to pool-depth changes as an immediate result of gravel removal, the residual effects of boundary shear stress changes, and the potential long-term consequences from subsequent runoff events with brief periods of increased streamflow and sediment transport. The most significant new aspect of this work is the ability to predict whether or not periodic gravel "mining" by means of bar scalping has a residual or cumulative effect on channel morphology and pool depth, particularly in bends. This application is tested against field data collected for the Chetco River and South Santiam River in Oregon, the East Fork River in Wyoming, and the upper Rhone River in France. Some of these sites have been partially subjected to gravel mining; others offer contrasting circumstances to allow comparisons of effects. The study suggests that the maximum velocity distribution shifts inward toward the convex bank of a channel bend at high water levels after gravel removal from a point bar, assuming that sediment transport rates and resupply from upstream are the same as before bar scalping. The inward shift of the maximum velocity distribution causes changes of boundary shear stress distribution in pool zones. Weaker boundary shear stresses are expected in pool zones after bar scalping. This will result in fewer incipient motion events in pool zones over each runoff season. As a result, the pool will experience net sediment deposition as a long-term effect of sediment transport events separated by periods of bed stability. Modeling Sediment Transport, Channel Morphology and Gravel Mining in River Bends by Ilgi Nam A THESIS submitted to Oregon State University in partial fulfillment of the requirement for the degree of Doctor of Philosophy Completed October 19,1995 Commencement June 1996 Doctor of Philosophy thesis of Ilgik lam presented on October 19.1995 APPROVED: Redacted for Privacy Major Professor, representing Civil Engineering Redacted for Privacy Head of Department Civil Engineering Redacted for Privacy Dean of Graduate Sc I understand that my thesis will become part of the permanent collection of Oregon State University libraries. My signature below authorizes release of my thesis to any reader upon request. Redacted for Privacy Ilgi Nam, Author ACKNOWLEDGMENTS I wish to express my gratitude to Professor Peter C. Klingeman for his inception of the research topic, his valuable guidance throughout the study and his help in the final phase of writing this thesis. My appreciation is also expressed to the members of my graduate committee, Professors David A. Bella, Jonathan D. Istok, Robert E. Wilson, and Robert W. Collier, who helped guide me in my graduate studies and research and who read the thesis and offered valuable comments. Finally, I wish to express my deepest gratitude to my father and mother, to my wife, and to my two sons for their patience, encouragement, and support during the long years required to complete my doctoral studies. ii TABLE OF CONTENTS Page I. INTRODUCTION 1 Background of the Study 1 Research Objectives 2 Research Scope 3 Organization of Thesis 3 II. BASIC THEORY OF FLOW AND SEDIMENT TRANSPORT IN MEANDERING RIVERS 5 Open Channel Hydraulics 5 General Concepts of Sediment Transport 13 Channel Morphology 37 Behavior of Meandering Alluvial Channels 42 III. COMPUTATIONAL METHODS IN SEDIMENT TRANSPORT 53 Water Profile Modeling and Computations 54 One-Dimensional Sediment Transport Modeling and Computations 56 Two-Dimensional Sediment Transport Modeling and Computations 60 Three-Dimensional Sediment Transport Modeling and Computations 65 Channel Morphology Modeling and Computations 66 - The General Model by Bridge and Co-Workers 76 General Modeling and Experiments Concerning Sediment Transport 83 IV. RIVER GRAVEL MINING AND EFFECTS ON CHANNEL MORPHOLOGY 87 Methods for Gravel Mining 87 Studies of Mining Effects 88 V. DEVELOPMENT OF RESEARCH HYPOTHESES AND TESTING METHODOLOGY 97 Flow Assumptions for Analysis of Flow in Bends 97 Conceptual Hypothesis for Hydraulic Changes from Bar Scalping Natural Bends 98 Conceptual Hypothesis and Analysis for Hydraulic Changes from Bar Scalping an Equivalent Rectangular Bend 101 Development of Methodology to Calculate Mean Bed Shear Stresses 105 iii TABLE OF CONTENTS (Continued) Page VI. DEVELOPMENT OF COMPUTATIONAL MODEL 111 Computational Method 111 Computer Model 121 VII. SUPPORTING FIELD RESEARCH 128 Chetco River 128 South Santiam River 135 East Fork River 147 Rhone River 155 VIII. TESTING OF HYPOTHESES AND MODEL REFINEMENTS 160 Shear Stress Conditions for Artificial Cross Sections 160 Geomorphic Relationships for Artificial Cross Sections 184 Chetco River Relationships 192 South Santiam River Relationships 196 East Fork River Relationships 209 Rhone River Relationships 216 IX. APPLICATION TO LONG-TERM MORPHOLOGICAL EFFECTS OF GRAVEL MINING 223 General Aspects of Long-Term Effects 223 Specific Expectations 224 X. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS 226 Summary and Synthesis of Work 226 Main Conclusions of Work 227 Recommendations for Future Work 227 BIBLIOGRAPHY 229 APPENDICES 245 A: Comparison of Shear Stress Before and After Bar Scalping in Case 1 through Case 7 246 B: Input Data and Outputs for the Bridge Computer Program Before and After Bar Scalping in Case 1 268 iv TABLE OF CONTENTS (Continued) Page C: Hydrologic Data of the Chetco River near Brookings in 1981, 1982 and 1989, and Hydrologic Data of the South Santiam River at Waterloo in 1994 315 D: Shear Stress Calculations for the South Santiam River, East Fork River and Rhone River 342 V LIST OF FIGURES Figure Page 1. Definition sketch for channel shape 6 2. Composite cross section with variable boundary roughness 7 3. Depth-velocity relationships for four regimes of open-channel flow 12 4. Helical flow patterns flow in channel bends 13 5. Shields diagram 32 6. Critical shear stress for quartz sediment in water as function of particle size 32 7. Definition sketch for flow in channel bends and symbols used 43 8. Cross section d in the curved channel of Pacheco-Ceballos' laboratory flume 44 9. Definition sketch for Bridge's 1976 model 77 10. Definition diagram for channel bend in Bridge model 80 11. Sketch of natural channel bend with bar scalping 99 12. Hypothesized isovel pattern and boundary shear stress distribution for natural unscalped bend 99 13. Hypothesized isovel pattern and boundary shear stress distribution for scalped natural bend 100 14. Hypothesized isovel changes in natural bend due to bar scalping 100 15. Hypothesized net change of boundary shear stress distribution in natural bend due to bar scalping 100 16. Sketch of an equivalent rectangular bend with bar scalping 103 17. Hypothesized isovel pattern and boundary shear stress distribution for equivalent rectangular bend before bar scalping 103 18. Hypothesized isovel pattern and boundary shear stress distribution for equivalent rectangular bend after bar scalping 104 19. Hypothesized net change of boundary shear stress distribution for equivalent rectangular bend due to bar scalping 104 20. Schematic diagram of channel and associated specific energy curve for a scalped point bar with subcritical flow 106 21. Cross section of composite rectangular channel before and after bar scalping in subcritical flow 108 vi LIST OF FIGURES (Continued) Figure Page 22. Schematic diagram of artificial composite trapezoidal cross section 112 23. Schematic cross-sectional shape in Case 1 114 24. Schematic cross-sectional shape in Case 2 119 25. Schematic cross-sectional shape in Case 3 119 26. Schematic cross-sectional shape in Case 4 119 27. Schematic cross-sectional shape in Case 5 120 28. Schematic cross-sectional shape in Case 6 120 29. Schematic cross-sectional shape in Case 7 120 30. Plan view of the reach used in computer model 122 31. Chetco River study area .129 32. Location of the cross sections in the lower Chetco River study reach 132 33. Cross sections SCS #56 and DSL A in the lower Chetco River 133 34. Cross sections DSL B and DSL C in the lower Chetco River .134 35. Cross section SCS #14 in the lower Chetco River 135 36. South Santiam River study area .137 37. Photos of South Santiam River study area 138 38. Schematic location of transects in South Santiam River study reach .139 39. Photos of gravel bars beside transects in the South Santiam River study reach 140 40. Bed elevation and mean velocity at South Santiam River Transect 1 on June 10, 1995 141 41. Bed elevation and mean velocity at South Santiam River Transect 1 on August 3, 1995 142 42. Bed elevation and mean velocity at South Santiam River Transect 2 on June 12, 1995 143 43. Bed elevation and mean velocity at South Santiam River Transect 2 on July 31, 1995 .144 vii LIST OF FIGURES (Continued) Figure Page 44. Comparison of particle size distributions of four armor bed material samples at Transects 1 and 2 of the South Santiam River on July 31, 1995 and August 3, 1995 146 45. Location of East Fork River study area 149 46. Location of the cross sections in East Fork River study reach 150 47. Bed elevation at East Fork River Transect 0421 on May 23, 1979 151 48. Bed elevation at East Fork River Transect 1662 on May 23, 1979 152 49. Bed elevation at East Fork River Transect 2510 on May 23, 1979 153 50.
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