Dry Bypass Pump Station Feasibility and Alternatives Analysis (CA)
The U.S. Army Corps of Engineers (USACE), Sacramento District (SPK) has completed a conceptual design for the Dry Bypass Pump Station as part of their Final Supplemental General Design Memorandum (SGDM) for the Napa River/Napa Creek Flood Protection Project. Due to limited real estate availability in the downtown area of the City of Napa, storage of interior storm flows at the proposed location is anticipated to be insufficient to provide detention of storm flows. Therefore, a pump station is required to prevent interior flooding for Interior Drainage Area 5. The design discharge (24 hour, 1% annual chance flood event) for the pumping station was estimated to be 930 cubic feet per second (cfs). The location anticipated for the pump station in the SGDM appears to be too small to house the pumps required to effectively pump the peak 1% annual chance flood event (100-year) interior flow. Therefore, SPK contracted WEST Consultants, Inc. (WEST) and HDR to prepare a feasibility level design analysis, alternatives comparison, and report detailing the design alternatives with a recommended alternative.

As part of this study, WEST completed the hydrologic and hydraulic analysis of Interior Drainage Area 5 was completed. The analyses were completed to define the inflow hydrograph to the proposed pump station, to estimate the maximum interior flood inundation depths and boundaries, and to evaluate various alternatives for the 10%, 4%, 2%, and 1% annual channel flood events. The hydrology analysis was completed using HEC-HMS, and the hydraulic analysis was completed using HEC-RAS and FLO-2D.