Overland Flow Simulations in an Urban Catchment: A Straightforward Approach to Considering Culverts

Existing overland flow models tend to neglect culvert flow. The goal of the present study is to implement a straightforward and easily realizable representation of culvert flow into the overland flow module of the OpenGeoSys (OGS) multiphysics simulator. Culverts are represented as source and sink terms in the modified OGS model. As a simplification, the flow rate at the culvert is calculated based on water depth and hydraulic head at the inlet and outlet of the culverts with the Darcy-Weisbach equation for pipe and channel flow. For validation of the newly implemented culvert representation, model results of culvert flow have been compared with results from the pipe flow model HYSTEM-EXTRAN (HE). The results of this comparison agree well for fully filled pipes. However, if there is an increasing difference between water depth at the inlet and outlet of the culvert, the quality of the results is decreasing. This is due to the fact that the Darcy-Weisbach equation does not consider accelerated or delayed flow. The model has been tested on a real study area and provides reasonable results where culvert flow is qualitatively well represented. Analysis of results shows that the consideration of culverts as presented here satisfies mass conservation.