Using SWMM as a tool for floodplain management in ungauged urban watershed

Abstract

Mathematical modelling is a powerful tool for arriving at best water resources management. But it is necessary to possess gauged data for model calibration and verification. However most of the urban watersheds are not gauged and does not have high resolution terrain data when designing drainage infrastructure. There are many tools for urban stormwater modelling, but out of limited free tools, EPA SWMM5 has a good record of applicability in many locations elsewhere. The present work shows the applicability of SWMM5 for an urban land extent in the Matara Municipal Council area which is ungauged. This study used literature reported values and data collected during field visits to runoff modeling to obtain order of magnitude values with easy comparison of engineering alternatives for stormwater management. It is thought that possibility of using a systematic and extensive data collection program for parameter identification using simple field measurements and engineering judgment together with stakeholder information for historical record verification provides opportunity to initiate structured and solution oriented data collection programs and modelling. Kotuwegoda area with land extent of 0.475 km2 and 22 sub catchments draining via 8 outlets was modeled for a single event. It was identified that the most sensitive parameter is channel roughness and that engineering options by means of changing channel roughness and incorporating detention storage, could reduce the peak flow by approximately 30%