Bank Stability and Toe Erosion Model (BSTEM) Analysis of Arroyo de la Laguna Associated with Zone 7’s StreamWISE Program Alameda Creek Watershed Sediment Forum April 23, 2008 Virginia Mahacek Valley & Mountain Consulting for West Yost Associates

Introduction Study Context –StreamWISE program Initial Geomorphic Investigation –Spring 2007 Preliminary Concepts –Summer 2007 BSTEM Modeling and Refinement –Fall 2007 Potential ADLL Project Areas 9-May-152

Approach Representative Sites on ADLL –Initial Investigation Results Existing Geomorphic Conditions –Estimates of Parameters Future Stormwater Flows –Hydrographs with COL (provided by WYA) Alternative Treatments –BSTEM Scenarios 9-May-153

Bed and Bank Problems 4 Conceptual Projects  Bed Incision  Toe Erosion  Bank Failures  Debris Jams  Locations  Treatment Types

BSTEM Sites Location Sub-Reach Description Average Local Bed SlopeChannel Status River Station ft/ft 47115US of Bernal0.0008Constructed 42069Bernal to B Degrading B-2-1 to Castlewood0.0025Degrading/Widening Castlewood to Verona0.0022Degrading/Widening Castlewood to Verona0.0029Degrading/Widening DS of Verona; SFPUC0.0014Aggrading/Widening

River Station Left (East) Bank  Clear Lake clay soils  Holocene basin deposits

River Station Left (East) Bank  Sycamore silt loam  Holocene stream terrace  Latest Holocene alluvial fan

River Station Right (West) Bank  Zamora silt loam  Holocene stream terrace  Early Quaternary or older bedrock

River Station Left (East) Bank  Yolo Loam  Latest Holocene stream terrace

River Station Right (West) Bank  Yolo loam  Holocene stream terrace

River Station Left (East) Bank  Yolo loam  Latest Holocene stream terrace

BSTEM Version 4.1 Quantitative, predictive tests of… –Hydraulic Scour –Geotechnical Failure Surface water Water-table Vegetation Bank height Bank composition Bank angle National Sedimentation Laboratory Layer 1 Layer 2 Layer 3 Toe material

Model Inputs Topography/Geometry Stratigraphy Bed and Bank Materials Groundwater Vegetation Hydrograph Duration Water Stage 9-May-1513

Modeled Treatments 9-May-1514 Treatment CategoryTreatment Type Bank Protection Placed Rock Bank Protection Placed Rock Toe-of-Bank Protection Geoweb Bank Protection Geoweb Toe-of-Bank Protection Reduced Bank Height and Angle Bank Strengthening Bank Drainage Vegetative Bank Strengthening

Model Output Toe Erosion –occurrences –retreat distances –eroded volumes Bank Failure –occurrences –eroded volumes – peak or drawdown conditions 9-May-1515

Initial Geomorphic Inventory + BSTEM Modeling = Potential Project Areas to be considered by StreamWISE 16 P OTENTIAL ADLL P ROJECT A REAS

Questions? 9-May-1517