## 4 Application and Results
### Decision Result of Water Sensor Installation Pipeline
As can be seen, when the spatial distribution status of all the cases is put together, it shows that the pipelines that have frequent flow direction changes in the pipeline during abnormal situations occur not only in outage regions but also in the blocks supplying water to the outage region. Therefore, there is great uncertainty about the location of potential water contamination during unpredictable emergency situations, and water sensors thus need to be installed in appropriate locations. It is expected that an emergency pipeline operation plan can be established through the application of the results of the scenarios proposed in this study. Figure 6e is a scenario in which the water supply comes from nine emergency connection supply pipelines from RES 2 due to an outage in block 3. In this case, the closest point was chosen as the red origin but due to the very low sensitivity of 0.1 in abnormal situations, it was decided that it should be excluded from consideration for a water sensor. Table 3 shows the pipelines for which water sensors should be considered as priority number 1 determined by Figure 6 for each case. One pipeline location for Case 1, three for Case 3, and five for Case 4 were determined for a total of 9 pipeline locations. As a result, as seen in Case 4, there were the most pipelines with frequent change in the flow direction when water was supplied from both reservoirs. As shown in Table 3, when looking at the number of blocks belonging to the determined water sensor points, there are four in Block 1 and five in Block 2. The reason for this can be confirmed by the difference in the ground level of the node in the block receiving the supply and the position head of the reservoir in the supplying block, as shown in Figure 8. The position head of the supply reservoir in Block 3 is 137.7 m and the average ground level of the node is 76.3 m, which is the highest value compared to other blocks, because the flow direction is most often decided to be a single direction. Of course, depending on the operation status and importance of the target network, the priority of the water sensor installation location can be set so that at least one is installed per block. In Case 4, 25 pipelines, including the determined water sensor installation pipeline, were found to have a very high change in flow direction in cases of emergency, as shown in Table 4, and it was found that they are high compared to other scenarios. Therefore, it is necessary to closely monitor the changes in water quality for scenarios similar to Case 4 when establishing an emergency pipeline operation plan. Figure 6: Normal and abnormal situation flow direction sensitivity calculation result. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Case** **Number**} & \multirow{2}{*}{**Pipe Name**} & \multirow{2}{*}{**Located Block**} & \multicolumn{2}{c}{**Abnormal**} & \multicolumn{1}{c}{**Normal**} \\ \cline{3-6}  & & & **Situation** & **Situation** & **Situation** \\  & & & **Sensitivity** & **Sensitivity** & **(1,0)** \\ \hline \multirow{2}{*}{1} & LG-96 & Block 2 & 0.64 & 0.48 & 0.6 \\ \cline{2-6}  & LE-90 & Block 2 & 0.48 & 0 & 0.52 \\ \cline{2-6}  & LG056(4) & Block 2 & 0.48 & 0 & 0.52 \\ \cline{2-6}  & LE-108 & Block 2 & 0.48 & 0 & 0.52 \\ \hline \multirow{2}{*}{4} & \#D744 & Block 1 & 0.96 & 0 & 0.04 \\ \cline{2-6}  & \#D568 & Block 1 & 0.96 & 0 & 0.04 \\ \cline{2-6}  & \#D680 & Block 1 & 0.96 & 0 & 0.04 \\ \cline{2-6}  & \#D680 & Block 1 & 0.96 & 0 & 0.04 \\ \cline{2-6}  & SA-25 & Block 1 & 0.96 & 0 & 0.04 \\ \cline{2-6}  & LE-99-3 & Block 2 & 0.96 & 0 & 0.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: A-city measuring instrument location decision priority result (all cases). Figure 7: Decision result of water sensor installation location by case.