Green-Ampt 식을 이용한 SWMM의 유역 유출 해석 방안에 관한 연구

Abstract

Watershed runoff simulation results are different according to infiltration methods. There are three major infiltration methods: the Green-Ampt method, the U.S. NRCS (Natural Resource Conservation Service) method, and the Horton method. The NRCS method and the Horton method are derived from experience or experiment, on the other hand, the Green-Ampt method is derived from physical mechanism of groundwater flow. Most Korean engineers prefer to use the NRCS method rather than the Green-Ampt method, as the parameters of the NRCS method are easily determined from land use and soil maps. The NRCS method, however, was derived from the soil types and the land use classifications of U.S.A. and it may produce a little bit different results from the soil types and the land use classifications of Korea. The purpose of the study is to find more suitable method between the Green-Ampt method and the NRCS method and estimation procedure of the Green-Ampt parameters applied. An automatic calibration of SWMM for watershed runoff continuous simulation was performed for the Milyang Dam Basin. The results show all indexes for model evaluation obtained from the Green-Ampt method are better than those of the NRCS method. A proper estimation of Green-Ampt parameters is needed to simulate watershed runoff from an ungaged basin. There are three parameters in the Green-Ampt method: the saturation hydraulic conductivity, the wetting front suction head, and the initial moisture deficit. The saturation hydraulic conductivity and the wetting front suction head were estimated from soil and land use maps for Milyang Dam Basin utilizing a geographic information system. Each parameter estimated from the soil and land use maps is little different from that obtained by the automatic calibration. The Green-Ampt infiltration method may produce smaller errors than the NRCS method for watershed runoff continuous simulation. The two parameters of the Green-Ampt method can be reasonlly estimated from soil and land use maps. The estimation procedure of the Green-Ampt parameters determined in the study would be helpful for a watershed runoff continuous simulation model and a water balance analysis.