Multipurpose Detention Pond Design for Improved Watershed Management

Peak-flow attenuation is important in urban stormwater management because runoff from post-development increases in magnitude and volume and may cause flooding to downstream areas. The standard practice in the United States is to require that the peak flow after development does not exceed predevelopment peak flow for specified design storms. The purpose of detention basins is to capture high runoff rates from post-development and control the peak discharge of the outflow using orifices and weirs. However, the use of detention basins in Korea is not used in new developments due of high land costs. As a result, many existing urban areas experience an increased frequency of flooding due to urbanization upstream in the watershed. This study investigates how variations in pond size, orifices and weirs could be used to reduce the peak-flows from a new 11 hectare development in the Ulsan-Hwabong region of Korea. This development is typical of new developments that are being constructed on the fringe of existing urban areas in Korea. In this study, the required volume and land area of a detention pond was determined in order to control the development outflow peaks for the 2-year, 10-year and 100-year design storms. Three cases detention pond designs are compared in terms of economics. The rainfall-runoff simulation model used in the design of these three detention ponds is the Storm Water Management Model (SWMM) 5, which is the latest updated version for windows.