Bank Stability and Toe Erosion Model BSTEM Analysis

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

Introduction • Study Context – Stream. WISE program • Initial Geomorphic Investigation – Spring 2007 • Preliminary Concepts – Summer 2007 • BSTEM Modeling and Refinement – Fall 2007 • Potential ADLL Project Areas 25 -Feb-21 2

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 25 -Feb-21 3

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

BSTEM Sites Location River Station Sub-Reach Description Average Local Bed Slope Channel Status ft/ft 47115 US of Bernal 0. 0008 Constructed 42069 Bernal to B-2 -1 0. 0045 Degrading 35895 B-2 -1 to Castlewood 0. 0025 Degrading/Widening 32424 Castlewood to Verona 0. 0022 Degrading/Widening 29893 Castlewood to Verona 0. 0029 Degrading/Widening 22845 DS of Verona; SFPUC 0. 0014 Aggrading/Widening

River Station 47115 Left (East) Bank Clear Lake clay soils q Holocene basin deposits q

River Station 42069 Left (East) Bank Sycamore silt loam q Holocene stream terrace q Latest Holocene alluvial fan q

River Station 35895 Right (West) Bank Zamora silt loam q Holocene stream terrace q Early Quaternary or older bedrock q

River Station 32424 Left (East) Bank Yolo Loam q Latest Holocene stream terrace q

River Station 29893 Right (West) Bank Yolo loam q Holocene stream terrace q

River Station 22845 Left (East) Bank Yolo loam q Latest Holocene stream terrace q

BSTEM Version 4. 1 • Quantitative, predictive tests of… – Hydraulic Scour – Geotechnical Failure • Surface water • Water-table • Vegetation • Bank height • Bank composition • Bank angle Layer 1 Layer 2 Layer 3 Toe material http: //www. ars. usda. gov National Sedimentation Laboratory

Model Inputs • • Topography/Geometry Stratigraphy Bed and Bank Materials Groundwater Vegetation Hydrograph Duration Water Stage 25 -Feb-21 13

Modeled Treatments Treatment Category Treatment Type Placed Rock Bank Protection Placed Rock Toe-of-Bank Protection Geoweb Toe-of-Bank Protection Reduced Bank Height and Angle Bank Strengthening 25 -Feb-21 Bank Drainage Vegetative Bank Strengthening 14

Model Output • Toe Erosion – occurrences – retreat distances – eroded volumes • Bank Failure – occurrences – eroded volumes – peak or drawdown conditions 25 -Feb-21 15

POTENTIAL ADLL PROJECT AREAS Initial Geomorphic Inventory + BSTEM Modeling = Potential Project Areas to be considered by Stream. WISE 16

Questions? 25 -Feb-21 17