Wildcat Creek Watershed Erosion and Sediment Control Project Prepared for: Prepared by: February 11th, 2016 ii Contents Executive Summary ..................................................................................................................................... vii Background and Purpose ........................................................................................................................ vii Project Description.................................................................................................................................. vii Historical Sedimentation Analysis .......................................................................................................... viii Alternatives .............................................................................................................................................. ix Recommendations .................................................................................................................................... x 1. Introduction and Project Setting ........................................................................................................... 1 Introduction .............................................................................................................................................. 1 Report Format ........................................................................................................................................... 2 Project Location ........................................................................................................................................ 3 Geology ..................................................................................................................................................... 4 Climate and Hydrology .............................................................................................................................. 6 Land Cover and Ownership ....................................................................................................................... 6 Geomorphology ........................................................................................................................................ 8 2. Project GIS Development .................................................................................................................... 11 3. Stakeholder Involvement .................................................................................................................... 12 First Stakeholder Meeting ....................................................................................................................... 14 Second Stakeholder Meeting .................................................................................................................. 15 Third Stakeholder Meeting ..................................................................................................................... 15 4. Jewel Lake and Lake Anza Capacity Analysis ...................................................................................... 17 Purpose ................................................................................................................................................... 17 Methods .................................................................................................................................................. 17 Results ..................................................................................................................................................... 21 5. Sediment Analysis ............................................................................................................................... 28 Purpose ................................................................................................................................................... 28 Background ............................................................................................................................................. 28 Methods .................................................................................................................................................. 28 Field Assessment ................................................................................................................................. 29 Integration of Field Data into the Project GIS ..................................................................................... 31 Results ..................................................................................................................................................... 33 Field Analysis ....................................................................................................................................... 33 iii Sediment Contribution Segments ....................................................................................................... 34 Subwatershed Sediment Totals .......................................................................................................... 36 Sediment Storage Sites ....................................................................................................................... 37 Sediment Source Categorization ......................................................................................................... 38 Watershed Scale Management ............................................................................................................... 41 Jewel Lake Sedimentation................................................................................................................... 41 6. Erosion Control Alternatives ............................................................................................................... 45 Dredge Jewel Lake............................................................................................................................... 46 Reconnect Wildcat Creek (Bypass Jewel Lake) to Restore Sediment Continuity and Fish Passage ... 47 Stabilize Gullies Initiated at Stormwater Runoff Outfalls ................................................................... 51 Construct Additional Sediment Detention Basins ............................................................................... 53 Re-grade Dirt Roads ............................................................................................................................ 55 Install Permeable Parking Areas and Implement LID Treatments ...................................................... 57 Excavate Multi-stage Channels for Sediment Deposition and Floodplain Restoration ...................... 59 Install Check Dams to Stabilize Tributaries to Wildcat Creek ............................................................. 60 Summary of Costs of Erosion Control Alternatives ................................................................................. 61 7. Sediment Control Alternatives, Prioritization, and Recommendations.............................................. 63 Ranking Criteria ....................................................................................................................................... 63 Recommended Projects .......................................................................................................................... 65 Reconnect Wildcat Creek (bypass Jewel Lake) ................................................................................... 65 Stabilize Stormwater Outfalls ............................................................................................................. 65 Sediment Detention Basins ................................................................................................................. 66 Re-grade Roads ................................................................................................................................... 66 Additional Considerations ....................................................................................................................... 66 References .................................................................................................................................................. 67 Appendix A .................................................................................................................................................. 68 GIS Layers Compiled for this Project ................................................................................................... 68 Sediment Point Features ..................................................................................................................... 69 Sediment Line Features....................................................................................................................... 70 Subwatershed Summary ..................................................................................................................... 72 Excel Spreadsheet ............................................................................................................................... 73 iv List of Figures Figure 1: Sediment supply rate into Jewel Lake from the watershed that is trapped behind the dam was determined by using the long-term rate (1921-2013) developed from bathymetric surveys of Jewel Lake, while the reach downstream of Jewel Lake sediment supply rate (1832-1999) was developed from Wildcat Creek bed and adjacent bank sources (Collins et al. 2001). ........................................................... ix