Evaluation of Water Quality and Supply System Performance of Gefersa By Pass Sub System (Case Study of Kolfe)

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Addis Ababa University


This research focused on the performance of water supply network of Kolfe keraniyo areas found in Kolfe keraniyo sub city of Addis Ababa Ethiopia. The main objective of this research was to evaluate the supply performance and chlorine concentration level of existing network of Gefersa by-pass sub system in Kolfe keraniyo areas. The area is known with high number of yearly diarrhea cases with average of 850 children with age of under-five. The basic tasks done in the research are measurement of sample data for pressure and chlorine residual from different locations of the study area followed by bottle test analyses for the chlorine residual, and use of simulation model of Bentley Water GEMS Software to identify the pressure effect on residual chlorine in the water supply distribution system. The model is used to identify the zone of high pressure and low pressure in junctions and the level of chlorine residual and velocity through pipes. The study results showed that the water supply coverage of the study area is 66.24% as GTPII set per capita demand of level I towns. This indicates that there is high gap between demand and supply. Aged pipes are observed on the area, 43% and 71.3% of the pipes are greater than 25and 15 years respectively which can be the cause for leakage and water quality problems. The conducted simulation result shows chlorine residual is inversely related with water age in the system. The aggregated bill consumption data and NRW estimated from the branch office and review of recent research result is used. As it is estimated 40% of the production i.e. 1492220.667m3/year is lost as NRW. 7 to 8mg/l of Chlorine is being added in Gefersa treatment plant reservoir as disinfectant and the model for water quality is based on it and adopted 8 mg/l for the source for the model simulation. The residual chlorine was calibrated by adjusting wall reaction coefficient. It is modeled with first order reaction based on the test of sample data by resulting -0.75/day of bulk reaction rate and -0.55 /day of first order wall reaction rate the effect of pressure can be seen in both ways either increasing or retarding chlorine consumption based on the scope and hydraulics of the system. Majority of the simulation results for the area showed that residual chlorine has direct relationship with the change of pressure in the distribution systems. For the improved system, 8958.3m3/d should be added on the existing network in order to fill the gap with introducing some pressure reducing valves to minimize excess loaded pressure.