Influence of rainfall estimation error and spatial variability on sewer flow prediction at a small urban scale

Legislative drivers for water quality and urban flood risk are driving a growing need to accurately determine the performance of urban drainage systems in near real time. Rainfall data are clearly a key input to urban drainage system models. Historically rain gauge data have been used, however radar rainfall data are now widely available and benefits from significantly higher spatial coverage than rain gauges in most UK urban catchments. This paper describes a detailed study based on a small (11 km2) urban catchment in West Yorkshire, England. Radar and rain gauge data have been compared and used as the input to hydrodynamic sewer flow simulations, and the results of these simulations have been compared with measured flows in the sewer system. The results showed that for this size of catchment, there can be significant differences in simulated peak flows and combined sewer overflow spill volumes due to inherent uncertainties between the two rainfall estimates.