Modelling urban flooding integrated with flow and sediment transport in drainage networks

Abstract

Drainage networks play an essential role in mitigating urban flooding, which, nevertheless, are prone to suffer sediment deposits. To date, however, the effects of sediments in drainage networks on urban flooding remain poorly understood. Here an integrated model is proposed for urban flooding. It is composed of a hydrological module for surface runoff integrated with a one-dimensional hydro-sediment-morphodynamic module for coupled open-channel or pressurized flow and sediment transport in drainage networks. The governing equations are solved synchronously using a well-balanced finite volume method. The model is tested against two laboratory cases involving mixed flow and sediment transport in pipes, and the results agree well with observed data. A new residential area with virtually pervious surface and an established urban area with essentially impervious surfaces are studied using the present model to unravel how sediments in drainage networks affect urban flooding under different extreme rainfall and sediment scenarios. The results reveal that sediments alter the discharge hydrographs in the drainage networks to distinct extents under different storm return periods. As far as the present computational cases are concerned, when a third of the pipe diameter is occupied by sediment deposits, the peak pipeline flow discharge decreases by up to 25 %. Accordingly, the surface inundation depth increases by up to 18 %, and the inundation area expands by up to 12 %, characterizing a considerably higher flooding risk. The present findings provide insight into the influences of sediment transport in drainage networks on urban flooding.