Photo credit: N.Panton San Gregorio Creek Watershed Management Plan San Gregorio Creek Watershed Management Plan JUNE 2010 Prepared for the Natural Heritage Institute By: Stillwater Sciences 2855 Telegraph Avenue, Suite 400 Berkeley, CA 94705 Stockholm Environment Institute 11 Curtis Avenue Somerville, MA 02144 San Gregorio Environmental Resource Center Post Office Box 49 San Gregorio, CA 94074 With an appendix on Groundwater Influences Affecting Aquatic Habitat Potential, San Gregorio Creek Watershed by Robert Zatkin and Barry Hecht Project Managers: Carson Cox Elizabeth Soderstrom, PhD Natural Heritage Institute 100 Pine Street, Suite 1550 San Francisco, CA 94111 Funding provided by: State Water Resources Control Board, under Proposition 40, the California Clean Water, Clean Air, Safe Neighborhood Parks, and Coastal Protection Act of 2002 Table of Contents Table of Contents 1 Introduction.....................................................................................1 1.1 Goal and Objectives of the Watershed Management Plan........................................... 1 1.2 Limiting Factors and Watershed Approach ................................................................. 2 1.3 Funding ........................................................................................................................ 3 1.4 Technical and Stakeholder Process.............................................................................. 3 1.5 Geographic Setting of the Watershed Management Plan ............................................ 3 1.6 Supported Agency Goals and Objectives .................................................................... 4 1.7 Other Programs in the Watershed................................................................................ 5 1.8 Updating the Management Plan................................................................................... 6 2 WATERSHED CHARACTERIZATION...........................................................7 2.1 Physical Setting and Location...................................................................................... 7 2.2 Sub-basins.................................................................................................................... 7 2.2.1 Mindego Creek.................................................................................................... 11 2.2.2 La Honda Creek .................................................................................................. 11 2.2.3 Harrington Creek................................................................................................. 13 2.2.4 El Corte de Madera Creek................................................................................... 14 2.2.5 Clear Creek.......................................................................................................... 14 2.2.6 Seasonal lagoon................................................................................................... 14 2.3 Land Use.................................................................................................................... 15 2.3.1 Historical land use............................................................................................... 15 2.3.2 Current land use .................................................................................................. 16 2.4 Climate and Hydrology.............................................................................................. 21 2.4.1 Climate ................................................................................................................ 21 2.4.2 Hydrology............................................................................................................ 21 2.4.3 Groundwater........................................................................................................ 24 2.5 Geology and Geomorphology.................................................................................... 25 2.5.1 Geology and tectonics ......................................................................................... 25 2.5.2 Sediment sources................................................................................................. 28 2.5.3 Geomorphology................................................................................................... 34 2.6 Water Quality............................................................................................................. 40 2.6.1 Aquatic bioassessment ........................................................................................ 43 2.6.2 Bacteria................................................................................................................ 43 2.6.3 Temperature ........................................................................................................ 44 2.6.4 Turbidity.............................................................................................................. 46 2.6.5 Beneficial use attainment .................................................................................... 48 2.7 Vegetation.................................................................................................................. 48 2.7.1 Vegetation types.................................................................................................. 49 2.7.2 Special-status plant species ................................................................................. 51 2.7.3 Non-native invasive plant species ....................................................................... 52 2.8 Fish and Wildlife ....................................................................................................... 54 2.8.1 Special-status species .......................................................................................... 54 2.8.2 Non-native invasive species ................................................................................ 55 2.9 Watershed Characterization Synthesis....................................................................... 56 2.9.1 Water quantity..................................................................................................... 57 2.9.2 Fine sediment ...................................................................................................... 57 2.9.3 Water temperature and bacteria levels ................................................................ 57 2.9.4 Non-native invasive species ................................................................................ 58 i Table of Contents 3 Hydrologic Assessment...................................................................... 59 3.1 Background and Approach ........................................................................................ 59 3.2 The Water Evaluation and Modeling (WEAP) System ............................................. 61 3.2.1 Modeling approach.............................................................................................. 61 3.2.2 Measured precipitation and streamflow .............................................................. 63 3.2.3 Hydrography........................................................................................................ 67 3.2.4 Hydrology............................................................................................................ 68 3.2.5 Climate ................................................................................................................ 71 3.2.6 Water use............................................................................................................. 72 3.2.7 Model schematic ................................................................................................. 74 3.3 Model Calibration and Results................................................................................... 75 3.4 Evaluation of Management Strategies ....................................................................... 76 3.4.1 Minimum bypass flows ....................................................................................... 77 3.4.2 Off-stream storage............................................................................................... 79 3.5 Hydrologic Assessment Summary and Recommendations ....................................... 82 4 Limiting Factors Analysis ................................................................... 84 4.1 Approach.................................................................................................................... 84 4.2 Focal Species Selection ............................................................................................. 85 4.2.1 California red-legged frog................................................................................... 85 4.2.2 Coho salmon........................................................................................................ 85 4.2.3 Steelhead ............................................................................................................. 86 4.2.4 Tidewater goby.................................................................................................... 86 4.3 Focal Species Limiting Factors Analyses.................................................................. 87 4.3.1 California red-legged frog limiting factors analyses........................................... 87 4.3.2 Coho salmon limiting factors analyses................................................................ 91 4.3.3 Steelhead limiting factors analyses ..................................................................