While the main purpose of irrigation reservoirs is to supply agricultural water, the needs of environmental flow and flood control has been expanded. The agricultural reservoirs have been operated in the form of carry-over system until now. Therefore, the supply of agricultural water is difficult whenthe storage rate is not sufficiently secured after large volume of irrigation. In addition, there are regulation of the upper storage rate for some largereservoirs during the flood season, but lower storage rate is not regulated. Accordingly, this study aims to evaluate the capacity of agricultural waterand environmental flow supply by setting the management lower storage rate of reservoir. The changes in the supply of agricultural and environmentalflow was simulated according to the three different regulating lower storage rate scenarios. As a result, it was judged effective in terms of water supplymanaging the lower storage rate up to 30% when the initial storage rate of farming period is above annual average for the Naju reservoir consideringexisting water management practice. If the lower storage rate would have been controlled above 30%, the supply of agricultural water might beincreased and non-effective discharge amount would be decreased compared to other scenarios during dr...