Runoff Analysis for Urban Unit Subbasin Based on its Shape

Hur, Sung Chul / Park, Sang Sik / Lee, Jong Tae Abstract In order to describe runoff characteristics of urban drainage area, outflow from subbasins divided by considering topography and flow path, is analyzed through stormwater system. In doing so, concentration time and time-area curve change significantly according to basin shape, and runoff characteristics are changed greatly by these attributes. Therefore, in this development study of FFC2Q model by MLTM, we aim to improve the accuracy in analyzing runoff by adding a module that considers basin shape, giving it an advantage over popular urban hydrology models, such as SWMM and ILLUDAS, that can not account for geometric shape of a basin due to their assumptions of unit subbasin as having a simple rectangular form. For subbasin shapes, symmetry types (rectangular, ellipse, lozenge), divergent types (triangle, trapezoid), and convergent types (inverted triangle, inverted trapezoid) have been analyzed in application of time-area curve for surface runoff analysis. As a result, we found that runoff characteristic can be quite different depending on basin shape. For example, when Gunja basin was represented by lozenge shape, the best results for peak flow discharge and overall shape of runoff hydrograph were achieved in comparison to observed data. Additionally, in case of considering subbasin shape, the number of division of drainage basin did not affect peak flow magnitude and gave stable results close to observed data. However, in case of representing the shape of subbasins by traditional rectangular approximation, the division number had sensitive effects on the analysis results. keywords : basin shape, urban runoff, time-area curve, FFC2Q, ILLUDAS 요 지도시 배수구역의 유출특성을 해석하기 위하여서는 유역의 지형특성 및 유출경로를 고려하여 소유역을 분할하고 배수계통에 대한 유출량을 분석하게 되며, 이 과정에서 각 소유역의 도달시간과 시간-면적곡선은 유역형상에 따라 상이하게 구성되므로, 이로 인한 유출특성 또한 크게 변화하게 된다. SWMM 및 ILLUDAS 모형에서는 유역형상을 단순 직사각형으로 가정하여 해석함으로써 유역의 기하학적 형상이 지표면 유출에 미치는 영향을 충분히 반영하지 못하는 한계를 개선하기 위하여, 국토해양부의 FFC2Q 모형 개발연구에서는 유역형상을 고려하여 지표면 유출해석