Evaluation of Applicability for Nonpoint Discharge Coefficient using Watershed Model

Abstract

Abstract Total maximum daily load have been implemented and indicated that nonpoint dischargecoeffients in flow duration curve were 0.50 of Normal flow duration (Q 185 ) and 0.15 of low flowduration(Q 275 ). By using SWAT, nonpoint discharge coefficients are studied with the conditionsof the instream flow and the rainfall in two study areas. The nonpoint discharge coefficientaverage of BOD and TP for normal flows duration in 3 years are 0.32_0.36 and 0.28_0.31. Forthe low flow duration, the nonpoint discharge coefficient avergae of BOD and TP were0.10_0.12 and 0.10_0.11. These are lower than the coefficients of total maximum loadregulation. There are big differences between one of regulation and one of SWAT for thenormal flow duration. With the consideration of rainfall condition, the nonpoint dischargecoefficient of flood flow duration are influenced on the amount of rainfalls. However, thenonpoint discharge coefficients of normal flow duration and low flow duration are not effectedby the rainfall condition. Since the spatial distribution and geomorphological characteristicscould be considered with SWAT, the estimation of nonpoint discharge coefficient in watershedmodel is better method than the use of the recommended number in the regulation.Keywords : Nonpoint discharge coefficient, SWAT model, TMDL