Reso25 16341 - Laserfiche WebLink

Browse Search

Executive Summary City of Redwood City (0011239.02)5 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 collected at 40 sites during the 2018/19 wet weather season and additional pump station sites in Redwood Shores and Seaport/Pacific Shores previously monitored during the 2015/16 season. For this Master Plan, a 24-hour, 10-year return frequency rainfall event was selected as the “design storm”. A 10-year storm has a 10 percent chance of occurring in any given year. Table ES-1 summarizes existing and future average and peak dry and wet weather flows in the City’s sewer system (including flows from tributary SMDs). Table ES-1:Summary of Wastewater Collection System Flows Model Scenario1 Maple St. Pump Station2 (mgd) Redwood Shores (mgd) Seaport/Pacific Shores (portion)3 (mgd) Existing Sewer Network Existing Average Dry Weather Flow 6.4 1.2 0.1 Existing Peak Dry Weather Flow 9.9 1.9 0.3 Existing Peak Wet Weather Flow4 38.6 5.6 1.1 Future Average Dry Weather Flow 9.7 2.1 0.1 Future Peak Dry Weather Flow 15.0 3.2 0.3 Future Peak Wet Weather Flow4 43.0 6.6 1.1 Future Sewer Network5 Future Peak Wet Weather Flow 47.1 7.0 1.1 1.Dry weather flow includes BWF plus wet season GWI; peak wet weather flow includes RDI/I from 10-year design storm event. 2.Main City area flow (including County SMDs tributary to Redwood City collection system) plus the portion of flow from Seaport/Pacific Shores that is tributary to Maple St. PS. 3.Portion of flow from Seaport/Pacific Shores that discharges directly to SVCW conveyance system. 4.Peak flows in existing sewer network may be reduced due to attenuation from upstream pipe capacity limitations and flow volume lost in model-predicted overflows. 5.With capacity improvement projects implemented. Proposed Improvement Projects Address the Potential Capacity Deficiencies Model results were examined to determine where capacity relief projects would be needed to alleviate capacity deficiencies. Due to the extent of surcharged pipes under the design storm conditions, surcharging up to 5 feet below ground level was considered acceptable during the 10-year design event (no capacity improvement project needed). These surcharge criteria allow the City to focus capital spending on areas most likely to cause sanitary sewer overflows. Where capacity improvements were determined to be needed, new pipes were sized to not exceed approximately 75 percent full under future peak wet weather conditions. Proposed sewer improvements were tested in the model to confirm that they would eliminate the identified capacity deficiencies and to confirm that sewers downstream of the upsized pipes could handle the higher peak flows. ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 94 of 317