## 2 Material and Methods
### Assessment of Hydropower Resilience  
The resilience of a hydropower reservoir can be calculated at the dam water level, which is calculated from the inflow and outflow discharges and the current water storage. Since power generation is related to dam water level and outflow discharge, these are important considerations. If resilience is high, power generation can be increased, but there is a risk of water disaster. Therefore, to suggest the optimal operation rule using resilience, the methodology should be constructed by additionally considering spillway discharge, flood risk days, and drought risk days (Figure 4). Figure 4 shows the procedure for evaluating the power production performance of the hydropower reservoir. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Dam**} & \multirow{2}{*}{**Year**} & \multirow{2}{*}{\begin{tabular}{c} **Height** \\ **(m)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Length** \\ **(m)** \\ \end{tabular} } & \multirow{2}{*}{\begin{tabular}{c} **Total Water Capacity** \\ **(106 m3)** \\ \end{tabular} } & \multirow{2}{*}{\
\begin{tabular}{c} **NWL** \\ **(EL.m)** \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} **LWL** \\ **(EL.m)** \\ \end{tabular} } \\ \hline Hwacheon & 1944 & 81.5 & 435 & 1018 & 181.0 & 156.8 \\ \hline Chuncheon & 1964 & 40 & 453 & 150 & 103.0 & 98.0 \\ \hline Uiam & 1967 & 23 & 273 & 80 & 71.5 & 66.3 \\ \hline Cheongpyeong & 1943 & 31 & 407 & 185.5 & 51.0 & 46.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The specifications of dams in study area. Figure 3: Study Area of Hydroelectric Dam. The trapezoidal symbols are hydroelectric dams located in the Bukhangang watershed. The yellow symbols are the target dams in this study. Pyeonghwa Dam is located at the most upstream. The first step is to define the operating rules for inflow and hydropower reservoirs. For inflow, there is a method using historical data and a method using predicted inflow using machine learning such as LSTM (Long Short-Term Memory), which is one of the recurrent neural network techniques. However, in this study, only historical inflow data was used. The hydropower reservoir operation rules in Korea can be stipulated as limited water level, outflow discharge by water level, outflow discharge by period, and so on. For this standard, the relevant laws, and regulations, such as the regulation on the operation  
Figure 4: Assessment Methodology of Resilience. of dams and weirs, were referred to [16]. The first step is to simulate the operation of the hydropower reservoir using the above data as input values. As the simulation results, dam water level, outflow discharge, power generation, etc. are calculated, and the program used for the simulation was HEC-5 developed by the US Army Corps of Engineers. The second step is to evaluate the power generation, which is the main performance of the hydropower reservoir. However, the operation rule was defined as maximizing the amount of electricity sales rather than maximizing the amount of power generation. As shown in Figure 5, it was confirmed that the month with the highest dam water level had the lowest SMP (System Marginal Price) unit price from August to October. SMP means the most expensive price among power sources required to meet the demand for power. All power sources in Korea received the same SMP in return for power generation. There is a possibility that even if the power generation is the most in August and October when the dam water level is high, the power sales may not be the maximum. Therefore, in this study, not the maximum power generation, but the maximum electricity sales amount was defined as the power generation performance and an evaluation methodology was presented. The third step is to evaluate the additional performances of the hydropower reservoir. Additional features are the performance of flood control and water usage.