Sensitivity analysis of the SWMM Runoff-Transport parameters and the effects of catchment discretisation

The use of the SWMM model to simulate the Runoff-Transport phenomenon necessitates the proper calibration of the different parameters involved in the process and the effect of these parameters on the routed hydrograph. A detailed sensitivity analysis is conducted on the main parameters of the Runoff-Transport Blocks to establish which are the most sensitive parameters affecting the Runoff-Transport simulation. The result of the study indicates a relative influence of the major parameters used in both the Runoff and Transport Blocks. Hence, the SWMM default values can be used adequately. The costs of setting up and running a SWMM simulation are largely determined by the level of discretisation used for a particular catchment. The purpose of this part of the study is to investigate the level of discretisation needed to adequately represent an urban watershed and to illustrate the effects of reducing the number of subcatchments on the accuracy of runoff simulation. A methodology is defined to achieve a representative equivalent catchment from theoretical considerations. Verification of the procedures involved a series of applications on both hypothetical and real areas.