Walnut Creek Sedimentation Study January 10, 2012 Prepared for: U.S. Army Corps of Engineer Sacramento District 1325 J Street Sacramento, CA 95814-2922 Prepared by: Ronald R. Copeland, Ph.D., P.E. Mobile Boundary Hydraulics, PLLC P.O. Box 264 Clinton MS 39060 1 Table of Contents LIST OF FIGURES ............................................................................................................................................ 4 LIST OF TABLES .............................................................................................................................................. 6 LIST OF PLATES .............................................................................................................................................. 7 INTRODUCTION ............................................................................................................................................. 8 Purpose ..................................................................................................................................................... 8 Study Area ................................................................................................................................................. 8 Study Approach ......................................................................................................................................... 8 Numerical Model Description ................................................................................................................... 9 NUMERICAL MODEL .................................................................................................................................... 11 Geometry ................................................................................................................................................ 11 Model Network ....................................................................................................................................... 11 Hydrographs ............................................................................................................................................ 13 Downstream water surface elevation..................................................................................................... 13 Temperature ........................................................................................................................................... 14 Sediment Removal Templates ................................................................................................................ 15 Sediment Data / Characteristics of Deposit ............................................................................................ 18 Sediment Data / Bed Material ................................................................................................................ 18 Bed-Material Transport Function ........................................................................................................... 21 Silt and Clay Transport Functions ........................................................................................................... 22 Sediment Data / Inflow ........................................................................................................................... 26 Sediment Inflow / Tributaries ................................................................................................................. 28 MODEL CALIBRATION.................................................................................................................................. 30 Sediment Inflow – USGS Sediment Load Curve ...................................................................................... 30 Sediment Inflow – Adjusted Rating Curve .............................................................................................. 35 Deposition and Erosion Limits ................................................................................................................ 37 Sensitivity of Input Parameters ............................................................................................................... 42 DISCUSSION AND CONCLUSIONS ................................................................................................................ 44 Channel Stability ..................................................................................................................................... 44 2 Model Performance ................................................................................................................................ 44 Boundary Condition Issues ..................................................................................................................... 45 Model Application ................................................................................................................................... 46 Recommendations for Additional Data and Modeling ........................................................................... 47 APPENDIX A: HYDROLOGY .......................................................................................................................... 48 Daily Hydrologic Analysis ........................................................................................................................ 48 Sub-daily Hydrologic Analysis ................................................................................................................. 50 APPENDIX B: Sediment Data Analysis and Suggested Sediment Model Parameters ................................ 52 Project Setting ......................................................................................................................................... 52 Estuarine Aspects of the System ............................................................................................................. 52 Some Field Observations ........................................................................................................................ 56 Summary of Core Sediment Data ........................................................................................................... 58 Sediment Transport Parameters ............................................................................................................. 77 Sediment Transport Parameters ............................................................................................................. 77 REFERENCES ................................................................................................................................................ 80 3 LIST OF FIGURES Figure 1. HEC-6T model schematic showing segments and control points. .............................................. 12 Figure 2. USGS reported water temperatures for Alameda Creek at Niles, Napa River at Napa, and Walnut Creek at Concord. Solid lines are daily data, points are individual measurements. ..................... 15 Figure 3. Calculated cross section changes at Station 16+00. ................................................................... 16 Figure 4. Calculated geometry before and after sediment removal in 1986 and 1989 at Station 276+46. .................................................................................................................................................................... 17 Figure 5. Calculated geometry before and after sediment removal in 1993 and 1995 at Station 330+61. .................................................................................................................................................................... 17 Figure 6. 2009 Bed material gradations between Suisun Bay and Pacheco Creek. ................................... 19 Figure 7. Initial bed material gradations used in HEC-6T model between Suisun Bay and Pacheco Creek normalized to 0.008mm. ............................................................................................................................. 19 Figure 8. Initial bed material gradations used in HEC-6T model between Pacheco Creek and Grayson Creek normalized to 0.008mm. .................................................................................................................. 20 Figure 9. Initial bed material gradations used in HEC-6T model upstream from Grayson Creek normalized to 0.008mm. ............................................................................................................................. 20 Figure 10: Erosion Rate Characteristics ...................................................................................................... 25 Figure 11: Deposition rate characteristics .................................................................................................. 25 Figure 12. Sediment inflow on Walnut Creek from Porterfield 1972 report. Total and sand load curves were scaled from report. Sand size class data and Concord 1970 data are reported measurements. ..... 28 Figure13. Annual sediment Inflow calculated using HEC-6T sediment inflow curve and 1965-2005 hydrograph at Concord. .............................................................................................................................. 31 Figure 14. Calculated Change in cross section shape at Station 378+82 during 40-year simulation. ....... 38 Figure 15. Calculated Change in cross section shape at Station 304+69 during 40-year simulation. ....... 39 Figure B-1. Bathymetry of Suisun Bay (Walnut Creek enters near the “Southern Channel” label). ......... 54 Figure B-2. Historical