Toutle/Cowlitz River Sediment Budget The Biedenharn Group, LLC May 18, 2010 Draft Report • August 31, 2009 Table of Contents Table of Contents .......................................................................................................................................... 2 List of Figures ................................................................................................................................................ 4 List of Tables ................................................................................................................................................. 7 1.0 INTRODUCTION ................................................................................................................................. 1 1.1 Background ................................................................................................................................... 1 1.2 Project Description ........................................................................................................................ 3 1.3 Purpose and Approach .................................................................................................................. 6 1.4 Description of Toutle/Cowlitz Basin .............................................................................................. 7 1.5 Sediment Budget Methodology .................................................................................................... 8 1.6 Previous Studies ............................................................................................................................ 9 1.7 Data Collection ............................................................................................................................ 10 1.7.1 Field Reconnaissance .......................................................................................................... 10 1.7.2 Aerial Photography ............................................................................................................. 10 1.7.3 Survey Data ......................................................................................................................... 11 1.7.4 USGS Gage Data .................................................................................................................. 11 1.7.5 Bed and Bank Material Gradations ..................................................................................... 13 2.0 HYDROLOGIC AND HYDRAULIC ANALYSES ...................................................................................... 15 2.1 Hydrology .................................................................................................................................... 15 2.2 Specific Gage Analysis ................................................................................................................. 16 2.3 Hydraulics .................................................................................................................................... 18 2.3.1 Stream Power Assessment .................................................................................................. 18 2.3.2 Critical Shear Analysis ......................................................................................................... 20 3.0 SUSPENDED SEDIMENT DATA ANALYSIS ......................................................................................... 24 3.1 Suspended Sediment Concentration .......................................................................................... 24 3.2 Annual Suspended Sediment Data ............................................................................................. 25 3.3 Suspended Sediment Gradations ................................................................................................ 28 3.3.1 North Fork Toutle River ....................................................................................................... 28 3.3.2 Green River ......................................................................................................................... 30 3.3.3 South Fork ........................................................................................................................... 31 3.3.4 Toutle River at Tower Road................................................................................................. 33 3.3.5 Cowlitz at Castle Rock ......................................................................................................... 35 3.4 Suspended Sediment Data Variability ......................................................................................... 37 4.0 TERRAIN ANALYSIS AND SEDIMENT SOURCE/SINK DEVELOPMENT ............................................... 40 4.1 USGS Repeat Cross Section Analysis ........................................................................................... 40 4.2 Bank Erosion ............................................................................................................................... 47 4.3 Surface Comparisons of North Fork Toutle Basin above the SRS ............................................... 51 4.3.1 Surface Comparison Results................................................................................................ 53 4.3.2 Variability of Surface Comparison ....................................................................................... 62 4.4 Debris Avalanche Erosion ........................................................................................................... 64 4.4.1 Annual Debris Avalanche Erosion ....................................................................................... 65 4.4.2 Debris Avalanche Erosion Rates and Decay ........................................................................ 67 4.4.3 Debris Avalanche Gradations .............................................................................................. 70 4.5 SRS Sediment Plain Deposition ................................................................................................... 71 4.5.1 SRS Sediment Plain Deposition by End Area Method ......................................................... 72 4.5.2 Sediment Plain Deposition by Surface Comparison ............................................................ 78 4.5.3 Sediment Plain Gradations .................................................................................................. 79 4.6 Sediment Output from the SRS ................................................................................................... 87 4.7 Toutle Watershed Sediment Sources ......................................................................................... 92 4.7.1 North Fork Toutle River ....................................................................................................... 92 4.7.2 South Fork Toutle River ....................................................................................................... 93 4.8 Cowlitz River................................................................................................................................ 94 4.8.1 Cowlitz Volume/Mass Analysis ........................................................................................... 95 4.8.2 Cowlitz Bed Gradation Analysis ........................................................................................ 101 4.8.3 Recommendations for Future Data Collection ................................................................. 112 4.8.4 Variability of Cowlitz Deposition ....................................................................................... 112 5.0 SEDIMENT BUDGET ....................................................................................................................... 113 5.1 Sediment Budget Results .......................................................................................................... 114 5.2 Comparison to USGS Gage Data ............................................................................................... 128 5.3 Uncertainty Analysis ................................................................................................................. 133 5.4 Forecasting of Sediment Load at Mouth of Toutle River .......................................................... 143 5.5 Conclusions and Recommendations ......................................................................................... 149 6.0 References .................................................................................................................................... 151 List of Figures Figure 1.1 Project Vicinity Map ..................................................................................................................... 2 Figure 1.2 Cowlitz Levee Location Map ....................................................................................................... 5 Figure 1.3 Watershed Map with USGS Gage Locations .............................................................................. 13 Figure 2.1 Annual peak discharges for the Toutle River at Tower Road and Cowlitz River at Castle Rock 15 Figure 2.2 Total annual discharge for 7 USGS gage sites ........................................................................... 16 Figure 2.3 Specific gage for the Toutle River at Tower Road, 1980 – 2008 ............................................... 17 Figure 2.4 Specific Gage for the Cowlitz River at Castle Rock, 1970 - 2009 ............................................... 18 Figure 2.5 Specific stream power as a function of distance