Final Arroyo Seco Watershed Assessment May 20, 2011
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ARROYO SECO WATERSHED SUSTAINABILITY CaMPAIGN Final Arroyo Seco Watershed Assessment May 20, 2011 Prepared for the Arroyo Seco Foundation FINAL Arroyo Seco Watershed Assessment Arroyo Seco Watershed Sustainability Campaign Acknowledgments ......................................................................................................................................... 1 1. Introduction .......................................................................................................................................... 1 1.1 Background ................................................................................................................................... 1 1.2 The Arroyo Seco Foundation......................................................................................................... 2 1.3 Purpose of the Arroyo Seco Watershed Assessment ................................................................... 4 1.4 Document Organization ................................................................................................................ 4 2. Watershed Coordination and Collaboration ......................................................................................... 5 2.1 Watershed Management and Planning: Public Involvement through the Years ......................... 5 2.2 Arroyo Seco Watershed Assessment (ASWA) Outreach: ............................................................ 14 2.3 Arroyo Seco Greenway Agreement ............................................................................................ 15 3. Assessment of Habitat Features in Relation to Watershed Function ................................................. 16 3.1 Hydrology, Hydraulics, and Sediment Management .................................................................. 16 3.1.1 Watershed Characterization ............................................................................................... 16 3.1.2 Recommendations .............................................................................................................. 20 3.2 Biological Resources .................................................................................................................... 23 3.3 Water Quality .............................................................................................................................. 41 3.3.1 Water Quality Improvements ............................................................................................. 44 3.3.2 Aquatic Habitat Improvements ........................................................................................... 47 3.3.3 Native Riparian Vegetation Improvements ........................................................................ 47 3.3.4 Stream Bank and Trail Stabilization .................................................................................... 48 3.3.5 Public Outreach Efforts ....................................................................................................... 48 i Final Watershed Assessment of the Arroyo Seco Watershed 3.4 Water Supply ............................................................................................................................... 49 3.4.1 Existing Surface Water Supply ............................................................................................ 49 4. Approach to Evaluation and Ranking of Current and Future Restoration Projects ............................ 50 4.1 Restoration Project Criteria ........................................................................................................ 51 4.2 Evaluation of Restoration Projects.............................................................................................. 52 4.3 Restoration Project Ranking ....................................................................................................... 52 5. Recommendations .............................................................................................................................. 52 5.1 Top Tier Restoration Projects ..................................................................................................... 54 5.1.1 Project 1: Upper Arroyo Seco Restoration .......................................................................... 56 5.1.2 Project 2: Arroyo Seco Channel Improvements in Hahamongna Watershed Park ............ 61 5.1.3 Project 3: Brookside Park Golf Course Arroyo Seco Channel Naturalization ...................... 65 5.1.4 Project 4: Lower Arroyo Linkages ....................................................................................... 70 5.1.5 Project 5: Confluence Gateway Multi‐use Project .............................................................. 82 5.2 Distributed Project Themes ........................................................................................................ 87 6. Data Gaps and Next Steps ................................................................................................................... 89 6.1 Process for Adding Projects to the ASWA ................................................................................... 89 7. List of References ................................................................................................................................ 90 8. Preparers and Contributors ................................................................................................................ 92 APPENDICES Appendix A Arroyo Seco Greenway Agreement Appendix B Arroyo Seco Watershed Projects Appendix C CDM Memorandum: Flood Hazard, Sediment Management and Water Feature Analyses, Hahamongna Watershed Park, Pasadena, CA Appendix D Arroyo Seco Watershed Assessment Meeting Notes A ii Final Watershed Assessment of the Arroyo Seco Watershed LIST OF TABLES Table 1: Arroyo Seco Watershed Planning Milestones Table 2: Stakeholder OrganizationsTable 3: Special-Status Species with Potential to Occur in the Arroyo Seco Watershed Table 4: Focal Species for the Arroyo Seco Restoration Project Table 5: Qualitative Description of Data Sources (NET) Table 6: Water Quality Sample Comparisons (NET) Table 7: LA River Reach 2 Study Area Grab Sample Comparisons Lower Arroyo Seco @ San Fernando Road Table 8: Arroyo Seco Restoration "Sample Project" Qualitative Ranking Approach LIST OF FIGURES Figure 1: Structure of Arroyo Seco Watershed Sustainability Campaign Figure 2: The location of current and historic observations of special-status plant and animal species in the Arroyo Seco watershed. Figure 3: Delineation of Upper and Lower Arroyo Seco Watershed Figure 4: Arroyo Seco Greenway: Five Top Tier Projects Figure 5: Short Term Impacts of Brown Mountain Dam Figure 6: USGS Erosion Monitoring Site from Station Fire Figure 7: Natural Arroyo Seco Channel Figure 8: Normal Flow Channel Alignment Figure 9: Realigned Arroyo Seco Flood Channel and Normal Flow Channel Figure 10: Schematic Diagram of the Cypress Avenue Bridge and Access Improvements Figure 11: Schematic Diagram of Avenue 43 Bridge Vicinity Improvements Figure 12: Schematic Diagram of the Southwest Museum, Sycamore Grove Park, Montecito Heights Park, Audubon Center Vicinity Linkage Projects Figure 13: Arroyo Seco Park, Bushnell Way Elementary School Pedestrian Improvements Figure 14: Avenue 64 Stairway and Open Space Improvements Figure 15: Confluence Gateway Multi-use Project Conceptual Site Plan A iii Final Watershed Assessment of the Arroyo Seco Watershed Acknowledgments The Arroyo Seco Foundation (ASF) wishes to thank the State of California Department of Water Resources for their support and funding for this Watershed Assessment. ASF also acknowledges those stakeholders who have passionately embodied the vision of a restored Arroyo Seco for many years. These supporters include the Council of Arroyo Seco Agencies, Council of Arroyo Seco Organizations, Arroyo Seco Stream Team, U.S. Army Corps of Engineers, City of Pasadena, City of Los Angeles, State Water Resources Control Board, Caltrans, County of Los Angeles, and North East Trees. ASF retained the services of Camp Dresser & McKee, Inc. (CDM) to prepare the Arroyo Seco Watershed Assessment (ASWA). 1. Introduction 1.1 Background The Arroyo Seco is one of the most spectacular and diverse watersheds in California. The Arroyo combines elements of a rough mountain watershed with an urbanized streamzone surrounded by half a million diverse residents. Over its 22-mile course, the Arroyo Seco drops from an elevation of nearly 6,100-feet at its headworks in the San Gabriel Mountains to 320-feet at its confluence with the Los Angeles River. The Arroyo passes by and through some of the most important landmarks in the Los Angeles Basin. As the Arroyo leaves its relatively natural upper watershed and descends from the San Gabriel Mountains, it passes by NASA's Jet Propulsion Laboratory (JPL) and enters the 250-acre basin within Hahamongna Watershed Park until it reaches Devil's Gate Dam. Below the dam, the Arroyo is highly impacted by urbanization, and is channelized as it runs through Brookside Park and the Rose Bowl. From this point, the Arroyo meets the Arroyo Seco Historic Parkway (Pasadena Freeway), a Federal Scenic Byway and the first freeway in the west, as it continues by the Huntington Botanical Gardens to the Audubon Center at Debs Park and from the Lummis Home and Gardens to the Los Angeles State Historic Park. The Arroyo is an environmental, cultural, and recreational oasis for all of Southern California. Upper Arroyo Seco Watershed (arroyoseco.org) 6 1 Final