Modeling irrigation canal network flow for return flow on agricultural watershed using EPA-SWMM

Abstract. Agricultural water is mostly consumed for rice farming, and irrigation water supplied to paddy fields is consumed as evapotranspiration, infiltration, and drainage. The amount of irrigation water supplied to the water well that is returned to the river through infiltration or drainage without being consumed is called irrigation return flow. Irrigation return flow is defined as the sum of the quick return flow flowing into the river and the delayed return flow returning to the river through deep penetration. Irrigation return flow is an important component that constitutes the flow rate of rivers in agricultural basins, and plays a major role in basin water resource management such as water supply and demand planning, water intake facility design and irrigation organization operation, and rational water supply and demand management plans. According to the results of previous research studies in South Korea, the irrigation return flow rate shows a large difference in the range of about 32% to 86% by region depending on various factors such as weather conditions, crop cultivation methods, water supply conditions, and water management plans. Therefore, it is essential to study the estimation of the regression quantity reflecting the local water management system and topographical characteristics in order to establish a water supply plan for the basin and determine the amount of irrigation water used. In this study, we developed a model for estimating irrigation return flow by using the United States Environmental Protection Agency Storm Water Management Model (EPA-SWMM) that can simulate irrigation canal networks. This irrigation canal network modeling can be simulated reflecting the water management characteristics of each reservoir, and it is possible to analyze the water level-flow of the canal, water supply, drainage, and infiltration. This study proposes a modeling method for calculating irrigation return flow using the EPA-SWMM model that can simulate agricultural water supply and estimates quick return flow and delayed return flow by analyzing water supply, drainage, and infiltration.