Wetlands and Water Resources, Inc. 818 Fifth Avenue, Suite 208 San Rafael, CA 94901 Tel 415.457.0250 Fax 415.457.0260 www.swampthing . org Aramburu Island Shoreline Protection and Ecological Enhancement Project Draft Enhancement Plan April 19, 2010 Prepared for: Richardson Bay Audubon Sanctuary 376 Greenwood Beach Road Tiburon, CA 94920 In Partnership with: Marin County Department of Parks and Open Space 3501 Civic Center Drive, Room 260 San Rafael, CA 94903 Project No. 1145 Prepared in Collaboration with: Roger Leventhal, PE, FarWest Restoration Engineering Peter Baye, PhD Planning Assessment Design Implementation Applied Science This page intentionally left blank Aramburu Island Shoreline Protection and Ecological Enhancement Project Draft Enhancement Plan 19 April 2010 Table of Contents 1 INTRODUCTION ......................................................................................................................................... 1 2 SITE DESCRIPTION ..................................................................................................................................... 3 2.1 HISTORY OF RICHARDSON BAY ................................................................................................................................ 3 2.2 HISTORY OF ARAMBURU ISLAND AND HARBOR SEAL HAUL‐OUT .................................................................................... 3 2.3 SURROUNDING LAND USES AND HABITATS ................................................................................................................ 5 2.4 CURRENT PROJECT SITE CONDITIONS ....................................................................................................................... 5 2.4.1 Topography and Bathymetry ................................................................................................................. 7 2.4.2 Geology and Soils ................................................................................................................................... 8 2.4.3 Hydrology ............................................................................................................................................... 9 2.4.4 Erosion and Sediment Transport ............................................................................................................ 9 2.4.5 Biological Resources ............................................................................................................................ 10 2.4.6 Jurisdictional Wetlands, Tidelands, and Shorelines ............................................................................. 14 2.4.7 Cultural Resources and Infrastructure ................................................................................................. 15 2.5 OPPORTUNITIES AND CONSTRAINTS ....................................................................................................................... 15 2.5.1 Ecological Resources ............................................................................................................................ 15 2.5.2 Topography and Hydrology ................................................................................................................. 16 2.5.3 Soils ...................................................................................................................................................... 17 2.5.4 Invasive Plants ..................................................................................................................................... 17 2.5.5 Considerations for Adjacent Land Uses ................................................................................................ 18 3 PROJECT GOALS AND DESIGN OBJECTIVES ................................................................................................ 18 3.1 PROJECT GOALS ................................................................................................................................................. 18 3.1.1 Reduce Erosion along the Eastern Shoreline ........................................................................................ 19 3.1.2 Enhance Island Resilience to Sea‐Level Rise ......................................................................................... 20 3.1.3 Enhance Habitats for Shorebirds, Waterbirds, and Wading Birds ....................................................... 20 3.1.4 Enhance Suitability of Haul‐Out Habitats for Harbor Seals.................................................................. 20 3.1.5 Enhance Habitats for Rare Salt Marsh Plants ...................................................................................... 21 3.1.6 Establish Native Vegetation on the Island Terrace .............................................................................. 21 3.2 DESIGN OBJECTIVES ............................................................................................................................................ 21 4 SHORELINE PROTECTION AND ECOLOGICAL ENHANCEMENT DESIGNS ...................................................... 22 4.1 SHORELINE PROTECTION AND ECOLOGICAL ENHANCEMENT ........................................................................................ 23 4.1.1 Design Rationale .................................................................................................................................. 23 4.1.2 Design Elements ................................................................................................................................... 24 818 Fifth Avenue, Suite 208, San Rafael, CA 94901 tel 415.457.0250 • fax 415.457.0260 • www.swampthing.org Aramburu Island Shoreline Protection and Ecological Enhancement Project Draft Enhancement Plan, 19 April 2010 4.1.3 Habitat Benefits ................................................................................................................................... 30 4.1.4 Construction Methods .......................................................................................................................... 30 4.2 ISLAND TERRACE ENHANCEMENTS ......................................................................................................................... 34 4.2.1 Palette of Enhanced Habitat Types ...................................................................................................... 34 4.2.2 Habitat Enhancement Construction Elements ..................................................................................... 37 4.3 ENHANCEMENT ALTERNATIVES ............................................................................................................................. 45 4.3.1 Alternative 1: Lowland Wetland‐Grassland Matrix ............................................................................. 46 4.3.2 Alternative 2: Saline Backshore ........................................................................................................... 46 4.3.3 Alternative 3: Mixed Design ................................................................................................................. 46 4.3.4 Enhancement Alternative Construction ............................................................................................... 47 4.3.5 Alternative Comparison ....................................................................................................................... 48 REFERENCES ...................................................................................................................................................... 51 Tables TABLE 1. LANDSCAPE UNIT ACREAGES, EXISTING CONDITIONS .................................................................................................... 6 TABLE 2. TIDAL DATUMS, SAUSALITO ..................................................................................................................................... 9 TABLE 3. SHORELINE PROTECTION AND ENHANCEMENT CONSTRUCTION ELEMENTS ...................................................................... 25 TABLE 4. SHORELINE ENHANCEMENT IMPORTED MATERIAL QUANTITIES AND SOURCES ................................................................. 33 TABLE 5. ISLAND TERRACE ENHANCEMENT CONSTRUCTION ELEMENTS ....................................................................................... 38 TABLE 6. ISLAND TERRACE HABITAT TYPES IN ENHANCEMENT ALTERNATIVES ............................................................................... 45 TABLE 7. CONSTRUCTION QUANTITIES AND ESTIMATED DURATIONS ........................................................................................... 48 TABLE 8. CHANGE IN PROJECT SITE HABITAT CONFIGURATION .................................................................................................. 49 TABLE 9. ALTERNATIVE COMPARISON MATRIX ....................................................................................................................... 50 Figures Figure 1. Vicinity Map Figure 2. Historical Richardson Bay: 1883 Coast Survey Figure 3. Aramburu Island, 1950‐2004 Figure 4. Surrounding Habitats and Sensitive Resources Figure 5. Landscape Units Figure 6. Topography and Bathymetry 2009 Figure 7. Soil Types Figure 8. Soil Pit Locations Figure 9. Subsurface Profiles Figure 10. Shoreline Erosion Figure 11. Native/Non‐Native Vegetation Stands, 2009 Figure 12. Jurisdictional Waters of the U.S. Figure 13. Wetland Habitats Delineated on Site Figure 14. BCDC Jurisdictional Areas Figure 15. Study Beaches Figure 16. Shoreline Enhancement Features Figure 17. Shoreline