Using SWMM as a tool for hydrologic impact assessment

Hydrologic impact assessment is necessary for a planned development area in designing detention storage for urban drainage systems to minimize the effect of urbanization. It also has strong implication on pollutant loads from urban areas. For such assessment, single or two hydrologic models can be paired for pre- and post- development conditions. Typical pairings are the use of synthetic hydrograph methods for both conditions or synthetic hydrograph for pre-development and urban hydrology model for post-development condition. The former has the difficulty of accounting for drainage structure for post-development condition and the latter can run into erratic evaluation as the error can be introduced due to different model conceptualizations and parameterizations. In order to overcome the aforementioned shortcomings, the use of Storm Water Management Model (SWMM) for both pre- and postdevelopment conditions is proposed in this study. The SWMM was applied to four planned development areas in Korea. The comparison of the results with previous assessments done for the same sites showed that the new approach can resolve the irrationalities that can occur with the combination of two different models such as smaller peak flow and longer time to peak for post-development condition. It is thought that the proposed method improves the accountability of the hydrologic impact assessment on planned development areas.

Acknowledgment In this study, the use of SWMM model to assess the hydrologic impact of urbanization was proposed as an improvement to the conventional use of synthetic hydrograph-urban hydrology model combination for pre- and post-development conditions respectively. As a prerequisite to use SWMM to assess pre-development condition, it was necessary to test SWMM in the natural watershed setting as the model was originally developed to model urban setting. Applications to three different natural watersheds showed that SWMM This study was supported by the 2003 Core Construction Technology Development Project (03-Sanhakyoun-C03-01) through the Urban Flood Disaster Management Research Center in KICTTEP of MOCT, Korea. This study was also supported by the Korea University Grant in 2005.