Applying a GIS-based geomorphological routing model in urban catchments

This paper discusses using a GIS-based geomorphological routing model to simulate urban stormwater runoff as an alternative to physically based routing models. Hydrological measurements have been carried out (1982–1984) in the urban catchment El Batan (52 km2), which forms part of the city of Quito (Ecuador). As detailed data on the drainage network were available, a first attempt was made using, on the one hand, complete Barre de Saint-Venant equations in the network and, on the other, the linear reservoir model for the sub-catchments. Knowing both the geometry and hydraulics of the network was proved to achieve accurate simulations. However, collecting the network data and building the whole topology (reaches, nodes, sub-catchments) of this large urban catchment is very time-consuming work. Thus, grosser representations of the network to simulate runoff were tested, but it was found that the estimation of the concentration time becomes predominant, and may result in a significant loss of accuracy. Using a GIS-based geomorphological routing model is shown to be an efficient alternative: first, physical velocities in the reaches can be derived from slopes and upstream areas; second, the integration of these velocities in a distributed lag and route model produces flood simulations that are equivalent to the physically based routing model; third, Digital Elevation Models avoid most of the tedious preliminary tasks in building the catchment topology. Further investigation is required in order to evaluate variations in the lag parameter from one catchment to another.