Reso25 16341 - Laserfiche WebLink

Browse Search

Hydraulic Model Development and Calibration City of Redwood City (0011239.02)2-8 Woodard & Curran, Inc. Sanitary Sewer Capacity Master Plan November 2023 2.3 FLOW ESTIMATING METHODOLOGY This section describes the methodology for estimating wastewater flows for loading to the hydraulic model. 2.3.1 Wastewater Flow Components Wastewater flows include three components: base wastewater flow (BWF), groundwater infiltration (GWI), and rainfall- dependent infiltration/inflow (RDI/I), as illustrated conceptually in Figure 2-6. BWF represents the sanitary and process flow contributions from residential, commercial, institutional, and industrial users of the system. BWF varies throughout the day, but typically follows predictable diurnal patterns depending on the type of land use. GWI is groundwater that infiltrates into defects in sewer pipes and manholes, particularly in winter and springtime in low-lying areas. GWI is typically seasonal in nature and remains relatively constant during specific periods of the year. However, rainfall typically has long-term impacts on GWI rates, as evidenced by measurable increases in GWI after prolonged periods of rainfall. RDI/I is storm water inflow and infiltration that enter the system in direct response to rainfall events, either through direct connections such as holes in manhole covers or illegally connected roof leaders or area drains, or, more commonly, through defects in sewer pipes, manholes, and service laterals. RDI/I typically result in short term peak flows that recede relatively quickly after the rainfall ends. The magnitude of RDI/I flows is related to the intensity and duration of the rainfall, the relative soil moisture at the time of the rainfall event, and the condition of the sewers. Dry weather flow (DWF) consists of BWF plus GWI, while wet weather flow (WWF) adds the RDI/I component. Figure 2-6:Wastewater Flow Components ATTY/RESO.0077/CC RESO SEWER SYSTEM MANAGEMENT PLAN - EXHIBIT A REV: 07-14-25 LF Page 124 of 317