Estimation of the Flood Warning Rainfall Threshold Considering Agricultural Reservoirs

Most flood forecasting and warning systems provide flood predictions without considering the storage effects of reservoirs for small and mid-sized watersheds in Korea. It is due to lack of data available for the flood routing in most agricultural reservoirs, leading to flood control functions. Therefore, this study has estimated the flood warning rainfall amount for the threshold runoff considering the reservoir storage effects in the Nam River watershed located in Gyeongsangnamdo. The watershed delineation and basin characteristics are constructed using HEC-GeoHMS and ArcGIS, and the flood runoff is simulated by HEC-HMS. For flood warning rainfall estimates, this study has characterized agricultural reservoirs located in Gyeongsangnamdo and performed regression analysis of their four main factors that have significant impacts on runoff in small and mid-sized watersheds, based on results from the previous research. The analysis of agricultural reservoir characteristics analyzed for city/county/town units in Gyeongsangnamdo show that the average of reservoir storage rate is 79.2%, and the actual additional water storage capacity is approximately 20% in the rainy season from June to September. As a result of the new method proposed in this study, the flood warning rainfall threshold for 20-minute duration is obtained from the threshold runoff estimated by the flood simulations considering agricultural reservoir effects.