Model Calibration of a Large Urban Sewer System using Radar Precipitation Information
This chapter describes the development and calibration of an XP SWMM Project Model of the City of Ottawa’s major interceptor and collector sewers. The Project Model was developed to confirm the size and assist in the development of an operating strategy for the Somerset Wastewater Storage Facility (SWSF). Significant temporal and spatial variability of rainfall over the large West Nepean sewershed area precluded the calibration of the entire Project Model utilizing precipitation information from the area rain gauges alone. Rainfall data was developed for a virtual rain gauge network, which provided 5-minute rainfall volume estimates for each 1 km2 of the drainage area, utilizing data from the existing rain gauges and the weather radar information. Final Project Model calibration was performed using the flow data collected at six flow monitoring stations in the West Nepean portion of the collection system and the virtual rain gauge data averaged over the Project Model sub-catchment areas.
In general, measured and modelled peak flows and event volumes matched well, with 17 out of 24 events having peak flows within the 15% envelope. Measured and modelled event volumes were within a 15% envelope for all 24 model calibrations. Rainfall estimates for the large West Nepean sewershed area based on radar imaging enabled the calibration of the Project Model, which would not have been possible using data obtained from the area rainfall gauges alone.
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