Seite - 574 - in Book of Full Papers - Symposium Hydro Engineering

is divided into four stages, level1 to level4, according to the degree of water shortage. The critical inflow can be calculated by “Eq. [1],” and “Fig. 3” shows critical inflows of Chungju Dam for each month. Fig. 3 Critical Inflows of Chungju Dam “Fig. 4” shows observed monthly inflow of Chungju Dam, and the difference between the observed inflow and the critical inflow can be calculated by “Eq. [2].” “Fig. 5” shows the difference during entire periods. The 𝐶 𝐷 𝐼 can be calculated by adding up the 𝐷 𝐼 of “Fig. 5” in a cumulative manner. However, if the upper limit of the 𝐶 𝐷 𝐼 is not set, 𝐷 𝐼 continuously increases. Therefore, a threshold for 𝐶 𝐷 𝐼 is needed to estimate optimal DIDI. To determine the threshold of 𝐶 𝐷 𝐼 , this study performed ROC analysis. Dam operation simulation was implemented from 1987 to 2015 using observed monthly inflow data and volumes of WSAC’s level1. “ A threshold value for maximum ROC score was determined as optimal threshold value, which was 630 × 106 m3. “Fig. 6” shows the cumulative difference between the observed inflow and the critical inflow when adapting the optimal threshold. “Fig. 7” shows DIDI and the point at which water supply is reduced. This Figure indicates that DIDI adequately expresses the water reduction timing of Chungju Dam. Fig. 4 Observed Monthly Inflows of Chungju Dam 574