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Hydraulic Model Development and Calibration City of Redwood City (0011239.02)2-4 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 •Subcatchments were defined to define areas tributary to the modeled pipe network. Each city parcel was assigned to a modeled pipe or manhole to define where the flow from that parcel enters the modeled sewer system (referred to as its “load point”). For selected large parcels, the parcel may be loaded to more than one manhole or pipe in the network. For County SMDs (except for Fair Oaks), subcatchments were delineated to define areas tributary to the modeled network. 2.2 FLOW MONITORING PROGRAM To support the development of the hydraulic model and flow projections for the Master Plan, a temporary flow monitoring plan was conducted as part of this study during the 2018/19 wet weather season (late December through February) at 40 locations on City sewers. The flow monitoring was conducted by ADS Environmental Services (ADS) under contract with the City. Four recording rain gauges were also installed. The purpose of the flow monitoring program was to quantify the flows in the system to provide data with which to calibrate the hydraulic model (discussed later in this chapter), and to quantify the I/I response to storm events in various areas of the system. Therefore, flow meters were selected to isolate upstream basins (where feasible) and to provide downstream confirmation of flow in major trunk sewers. Of the 40 meter sites, 30 sites in the Main City Area were selected by Woodard & Curran for purposes of model calibration (identified by prefix “FM” in the meter ID), and ten sites were selected by the City (seven sites identified by prefix “RWC” in the main system, two sites with prefix “RWS” in Redwood Shores, and one site with prefix “SP” in Seaport/Pacific Shores) for other purposes. Note that the City conducted a pump station flow monitoring program in the Redwood Shores and Seaport/Pacific Shores systems during the 2015/16 winter; therefore, only limited monitoring was included for those areas in the 2018/19 program, as the 2015/16 data were available for use for model calibration. The locations of the 2018/19 flow monitoring sites and rain gauges are shown in Figure 2-3 and Figure 2-4. The figures also show the associated tributary area for each flow meter used for model calibration (in the Main City area, four of the “RWC” meters were also found to be useful for model calibration). Note that some meters were located downstream of other meters; therefore, the tributary areas shown for each of these meters are the “incremental” areas between the flow meters and tributary areas of the upstream flow meters. Note also that due to the numerous flow splits in the Main City Area, the tributary areas shown may not be precise but represent the primary flow patterns in the system. In addition to the temporary meters, the City provided flow data for the 2018/19 monitoring period from SVCW for Maple Street Pump Station and the Redwood Shores discharge to the SVCW WWTP (daily flows only for Redwood Shores); as well as flow data from the County for the Fair Oaks SMD meter. Rainfall for the largest storm events in the 2018/19 wet weather period are summarized in Table 2-1. Figure 2-5 shows a typical plot of measured flow and rainfall for one flow meter. Attachment A of the Model Development TM includes plots of the rainfall and flow data for all of the 2018/19 meters. ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 120 of 317