Mojave River Bridge at Yucca Loma Road Town of Apple Valley and City of Victorville San Bernardino County, California Location Hydraulic Study Report Prepared for: Prepared by: and February 2009 Location Hydraulic Study Report Mojave River Bridge at Yucca Loma Road Town of Apple Valley and City of Victorville, San Bernardino County, California Table of Contents Executive Summary........................................................................................................... iv Acronyms........................................................................................................................... vi 1 General Description............................................................................................ 1 1.1 Project Description...............................................................................................1 1.1.1 No-Build Alternative......................................................................................... 1 1.1.2 Build Alternative ............................................................................................... 1 1.2 Need for Project ...................................................................................................5 1.3 Project History.....................................................................................................5 1.4 Creek, Stream, and River Crossings ....................................................................5 1.4.1 Geographic Location ......................................................................................... 5 1.4.2 Watershed Size .................................................................................................. 5 1.5 Geographical References.....................................................................................8 1.6 Traffic ..................................................................................................................8 1.7 Traffic Interruptions for Base Flood (Q100) .......................................................11 1.7.1 Land Use.......................................................................................................... 11 1.7.2 Soil and Bed Material...................................................................................... 11 1.8 Historic Flood Events ........................................................................................14 2 Hydrologic and Hydraulic Data........................................................................ 15 2.1 Hydrologic Stability...........................................................................................15 2.2 Federal Emergency Management Agency Data ................................................15 2.3 Map of Floodplain..............................................................................................16 2.4 Estimating Design Discharge.............................................................................16 2.4.1 Rivertech Hydrologic Data.............................................................................. 16 2.4.2 USACE Data.................................................................................................... 17 2.4.3 Peak Flows from USGS Gaging Station.......................................................... 17 2.4.4 Design Discharge............................................................................................. 18 2.5 Hydraulic Assessment........................................................................................18 2.5.1 Design Tools.................................................................................................... 18 2.5.2 Cross Section Data........................................................................................... 18 2.5.3 Manning’s n..................................................................................................... 18 2.5.4 Expansion and Contraction Coefficient........................................................... 19 2.5.5 Existing Condition........................................................................................... 19 2.5.6 Proposed Condition ......................................................................................... 20 3 Project Evaluation............................................................................................. 25 3.1 Risk Associated with Implementation of the Action .........................................25 3.2 Impacts on Natural and Beneficial Floodplain Values ......................................25 3.3 Support of Probable Incompatible Floodplain Development ............................26 3.4 Measures to Minimize Floodplain Impacts Associated with the Action ...........26 3.5 Measures to Restore and Preserve the Natural and Beneficial Floodplain Values Impacted by this Action.........................................................................27 3.6 Practicability of Alternatives to any Significant Encroachments ......................27 3.7 Practicability of Alternatives to any Longitudinal Encroachments ...................27 4 References......................................................................................................... 28 February 2009 i Location Hydraulic Study Report Mojave River Bridge at Yucca Loma Road Town of Apple Valley and City of Victorville, San Bernardino County, California Figures Figure 1. Project Location Map .......................................................................................... 2 Figure 2. Project Vicinity Map ........................................................................................... 3 Figure 3. Project Vicinity Map, Aerial View...................................................................... 4 Figure 4. Mojave River Watershed Area at the Proposed Bridge Location ....................... 6 Figure 5. Traffic Count Locations, City of Victorville, CA ............................................... 9 Figure 6. Traffic Count Locations, Town of Apple Valley, CA....................................... 10 Figure 7. Land Use Map, Town of Apple Valley ............................................................. 12 Figure 8. Land Use Map, City of Victorville.................................................................... 13 Figure 9. USGS Gaging Stations in the Project Vicinity.................................................. 14 Figure 10. FEMA Design Flow Locations along the Mojave River................................. 15 Figure 11. Water Surface Profiles, Existing Condition .................................................... 20 Figure 12. Proposed Mojave River Bridge Profile ........................................................... 21 Figure 13. Proposed Mojave River Bridge, Typical Section............................................ 22 Figure 14. Water Surface Profiles, Existing and Proposed Conditions ............................ 24 Tables Table 1. Comparisons of the 100-year Flow Characteristics for Existing and Proposed Conditions............................................................................................................ v Table 2. Watershed Size of the Tributaries at the Project Location ................................... 7 Table 3. Current and Future Traffic at the Proposed Mojave River Bridge ....................... 8 Table 4. Traffic Counts in the Local Streets, City of Victorville, CA................................ 9 Table 5. Traffic Counts in the Local Streets, Town of Apple Valley, CA ....................... 10 Table 6. Channel Bed Particle Size Distribution .............................................................. 11 Table 7. Annual Peak Flows, Before and After Completion of the Mojave River Dam.. 14 Table 8. FEMA Flood Insurance Study Hydrologic Data ................................................ 16 Table 9. Estimated Design Discharges at the Project Location........................................ 17 Table 10. Estimated Design Discharge, GEV Method ..................................................... 17 Table 11. Estimated Design Discharge............................................................................. 18 Table 12. Manning’s n value selected for the Hydraulic Analysis................................... 19 Table 13. Existing Condition, Mojave River.................................................................... 19 Table 14: Design Specification of the Proposed Mojave River Bridge............................ 20 Table 15. Proposed Condition, Mojave River .................................................................. 23 Table 16: Increase in Impervious Area............................................................................. 25 February 2009 ii Location Hydraulic Study Report Mojave River Bridge at Yucca Loma Road Town of Apple Valley and City of Victorville, San Bernardino County, California Photos Photo 1. Yucca Loma Road, Terminus at the Mojave River.......................................... D-2 Photo 2. Yates Road, Terminus at the Mojave River ..................................................... D-2 Photo 3. Mojave River, River Channel........................................................................... D-3 Photo 4. Mojave River, Debris and Vegetation at the bank............................................ D-3 Appendices Appendix A Hydraulic Analysis: Existing Condition ................................................. A-1 Appendix B Hydraulic Analysis: Proposed Condition................................................ B-1 Appendix C FEMA Floodplain Map..........................................................................