An Application of the A-PDA Model For the Interconnected Operation Among Adjacent Blocks of Water Distribution Systems In Case of Emergency

Abstract

The water distribution system is an important social infrastructure providing customers with stable and safe water supply. The fact, however, is that it is not free from various abnormal situations arising from internal / external factors. In case of a water supply failure due to abnormal situations, the emergency interconnected operation between adjacent blocks in the system is one of the most effective countermeasures. To simulate these types of emergency operations, existing hydraulic analysis models, which are based on the infinite water supply assumption, may simulate unrealistic results such as satisfying sufficient water supply for more demand nodes than actual ones. If they want to have more realistic hydraulic simulation result for these situations, it is required to adopt a new hydraulic analysis which is able to consider insufficient water supply for all demand nodes. Demand Driven Analysis (DDA) and Pressure Driven Analysis (PDA) are most commonly used hydraulic analysis. DDA performs a hydraulic analysis based on the assumption that the demand at demand nodes is always 100% satisfied which derives unrealistic results in abnormal situations. In the case of the PDA, it considers the relationship between hydraulic pressure and available flow rate, which is more reliable than the DDA for abnormal operating conditions. However, since DDA and PDA are basis on the infinite water supply assumption, unrealistic hydraulic analysis results may be obtained when they are applied to the insufficient water supply condition such as the emergency interconnected operation between adjacent blocks due to one or more reservoirs may not be working properly. Therefore, Lee et al. (2018) has proposed the Advanced-Pressure Driven Analysis (A-PDA) applying the concept of limited source to the existing PDA. In this study, we apply the PDA and the A-PDA to simulate the hydraulic condition of the emergency interconnected operation between adjacent blocks for a water supply network in Korea and compare the results from them. The target network supplies water to 84,000 households and it consists of 3 reservoirs, 1,492 nodes, 1,937 pipelines, 8 pumps and 10 interconnected emergency pipes. Each reservoir takes responsible for its individual block. When one of the reservoirs cannot supply water to its individual block, the block will be supplied water through the emergency pipes from the adjacent reservoir. Fig 1 shows the layout of target network and Table 1 shows the properties of each reservoir. To explore the effect of the limited water supply condition, we generate an operation scenario: RES1 stops water supply at 00:00hr (mid night) and RES2 and RES3 supply water to Block1 for the emergency. Then, the PDA and the A-PDA are used to simulate this emergency operating condition. The initial water depth of RES2 and RES3 is 3m and 2.7m, respectively. Fig. 2 shows the available supply ratio (ASR, = available demand/required demand) with time by the PDA and the A-PDA for Block1. The ASR with time by the PDA for Block1 show us that emergency water supply to Block1 from RES2 and RES3 can be maintained through the simulation period even though the ASR are 20% to 40%. On the other hand, The ASR with time by the A-PDA for Block1 show us that the emergency water supply to Block1 ceases after 16:00hr. The reason we obtain two different water supply results for Block1 is due to the assumption of the PDA which is that the amount of water supply is unlimited during the simulation period. In the PDA, the water depth of a reservoir is always maintained at the initial set value so that the amount of water demand at demand nodes should be provided. However, for the emergency operating condition we generate for this study, the amount of water from RES2 and RES3 is insufficient to supply water for the entire network without RES1. As shown in Fig. 3, the water depths of RES2 and RES3 are continuously decreased and RES2 is empty at 16:00hr and RES3 is depleted after 39:00hr. After 16:00hr, RES3 is the only water source for the entire network and Block1 cannot be supplied water from RES3 sufficiently. From this simulation results, the A-PDA simulates this type of the water supply situation more realistic than the PDA does since without RES1, obviously, the entire network cannot be provided with sufficient water from RES2 and RES3. Therefore, in the case of the hydraulic analysis which needs to consider water supply quantity such as the interconnection operation required, the application of the A-PDA model is indispensable. Additionally, the application of the A-PDA can anticipate the possible water supply time and the possible emergency interconnected operating time in the abnormal operating condition, which is impossible to obtain by the existing hydraulic analysis. These two values will be used to design or to establish the emergency operating plan for a water supply network for better service quality.