RELIABILITY ANALYSIS OF WATER DISTRIBUTION NETWORK A CASE OF ADDIS ABABA ETHIOPIA

Abstract

Water is the essential commodity required to maintain life. So, it should be available to the consumer at the lowest possible cost, in adequate quantity, and of the desired quality. A network of pipes that are used to transport water from storage reservoirs to consumer points is called “Water Distribution Network” (WDN). It consists of pipes, nodes, pumps, valves, storage tanks. Reliability is defined as the probability that a system performs its mission within specified limits for a given period of time in a specified environment. In this study, a water distribution network of Bole and Yeka Sub-City of Addis Ababa, which is an old city in Africa, is considered to check the performance of the systems. Bole and Yeka water supply system is vulnerable due to aging and corrosion. Due to climate change, rapid urbanization, irregular timing of distribution of water, and further, the system is utilized beyond its design period. Thus, it needs great attention to check the performance of the systems and assessment of the capacity of the network to deliver the required quantity of water as well as quality, i.e., hydraulic reliability of the network as well as water quality reliability. The main objective of this study is to carry out a detailed study of the existing water distribution system (WDS) of Bole and Yeka Sub-City of Addis Ababa, then modeling of the systems in ArcGIS and Simulate the existing water supply system using hydraulic simulation software WaterGEMS in order to know the existing condition of the system. The model simulation results for 24 hours are used for obtaining velocity and pressure with an interval of 1-hour simulation. These results are further used for obtaining the hydraulic and water quality reliability of the distribution network. Hydraulic reliability evaluation requires nodal demands and heads. The methodology uses to calculate hydraulic reliability requires the calculation of the volume-reliability factor and the node-reliability factor. Further mechanical reliability is calculated considering one pipe failure condition. The projected population of the case study network is 278488 in 2034, and the total demand of 42113.30 m 3 /s. The source is from a ground water well field with a capacity of 45792m 3 /s. There are 168 pipes with a diameter ranging from 100 mm to 800 mm with a total length of 81.22 km and 123 junctions, and the demand pattern runs in the interval of 1hr in the 24hr. The simulation of WDN analysis is computed in the steady-state and extended period simulation; it was observed that the hydraulic system reliability analysis is 0.95 in the normal scenario and 0.475 in the failure scenario and also maintains the desirable disinfection residual chlorine concentration for all nodes in a day. The further study discusses the water quality reliability to supply safe drinking water.