## 4 Application and Results
### Decision Result of Water Sensor Installation Pipeline  
Based on the methodology proposed in this study, the sensitivity of the flow direction in the pipeline under normal and abnormal conditions is calculated and the priorities for water sensor installation are determined. Results are shown in Figure 6. A graph was generated by estimating the sensitivity in each of the established normal and abnormal situations, and a virtual quadrant was created based on the point (0.5, 0.5) due to the large number of target pipelines. The distance was calculated around the pipeline located in the lower right corner near the ideal point. The size of the generated quadrant may be changed according to the weight. However, there may be cases in which they are not included in the assumed range. For this situation, the pipeline with the highest possibility of water quality contamination was selected for presentation. Figure 6a is a scenario in which the water supply comes from an emergency connection supply pipeline (one) that is connected to RES 2 due to an outage in drainage block 1. It shows that the LG-96 pipeline was the most sensitive to the change in flow direction in an abnormal situation. In this scenario, negative pressure was generated in block 1 during the supply process. However, as shown in Figure 7a, the LG-96 pipeline was included in block 2, not the block where the negative pressure was  
Figure 5: Hydraulic analysis results for pressure status by case. generated, and this node formed proper water pressures of 39.48 m and 40.06 m at each end of the pipeline. Therefore, for Case 1, the pipeline requiring water quality measurement was determined to be LG-96. Figure 6b is a scenario in which the water supply comes from an emergency connection supply pipeline (one) that is connected to RES 1 due to an outage in drainage block 2. It shows that LG016(2) pipeline is the most sensitive to the change in flow direction in an abnormal situation. In this scenario, there are very few connected pipelines for emergency supply compared to the large number of users. Therefore, a large negative pressure was generated in the block 2 region and the value reached \(-\)89.22 m. In addition, the relevant pipe was excluded from consideration for a water sensor because Case 1 pipeline belonged to the location where negative pressure was formed as seen in Figure 7b. Figure 6c is a scenario in which the water supply comes from the emergency connection supply pipelines (nine) that are connected to RES 3 due to an outage in drainage block 2, the same as for Case 2. In this case, LE-90, LE-108, and KG056(4) pipelines changed the flow direction most frequently in an abnormal situation. The above three pipelines are all located in block 2 as seen in Figure 7c. In Case 3, the pressure of the whole system tended to drop by about 10 m but because of the large number of pipelines available from other reservoirs compared to Case 2, no negative pressure was generated. Therefore, the installation of a water sensor should be considered. Figure 6d is a combined scenario of Cases 2 and 3 in which the water supply comes from the emergency connection supply pipelines (ten) connected to RES 1 and 3 due to a rupture in RES 2. In this case, five pipelines (#D744, #568, #680, SA-25, and LE-99-3) were determined to have the highest sensitivity to the flow direction. Case 4, like Case 3, also received water through a relatively large number of ten emergency connection supply pipelines and although the water pressure tended to drop by about 6 m compared to a normal system, no negative pressure was generated. Therefore, it is determined that the installation of water sensors should be considered in the five pipelines. When the pipelines chosen for the water sensor installation were depicted spatially in a network as seen in Figure 7d, four pipelines were distributed in block 1 and only one pipeline (LE-99-3) was distributed in block 2 where the outage occurred.