A nonlinear model of urban catchment response

One of the prime requisites for the efficient design of flow capacities of storm water sewerage systems is the ability to simulate mathematically the physical phenomena of the urban runoff process. The purpose of this study is to investigate the above-ground phase of the urban runoff process, and a lumped-parameter nonlinear model is postulated for its simulation, in addition to two simpler models (linear and time of entry) for the purposes of comparison. Two models of differing complexity for the simulation of the below-ground phase are also postulated. Two mall catchments (.6 and .8 ha) in the Lordshill area of Southampton have been monitored continuously for rainfall and runoff since June 19:''i,, and suitable storm events reduced to a condition suitable for analysis. It is considered that the two catchments are of small enough. size that the performance. of the above-ground model should not be. obscured by possible inaccuracies of the below-ground model.The model performance is demonstrated with the monitored rainfall as input, and the modelled and observed outfall hydrographs compared for 19 storm events on the two catchments. It is. concluded that the nonlinear surface routing submodel provides a better synthc_is of the above-ground.' phenomena than the linear or time of entry submodels.