Understanding the Poor Performance of Urban Sewerage Systems:A Case of Coldstream High Density Suburbs, Chinhoyi, Zimbabwe

The population of Coldstream High Density Suburbs in Chinhoyi, Zimbabwe is increasing and the sewerage system shows signs of poor performance. The frequency of reported sewerage system blockages in the suburb increased from 43 per month to 65 per month between April 2012 and March 2013. The suburb has also been experiencing water shortages. An increasing population and low water supply versus overflowing sewage is a potential health risk. The main objective of this paper was to investigate the causes of the sewer system poor performance. This was achieved by assessing the sewer system infrastructure as well as the operation of the system. The impact of the behaviour of residents on the performance of the system was also discussed. The main components of the infrastructure (manholes and sewers) were physically checked for soundness. The operation of the system was assessed by a hydraulic analysis of discharge, depth of flow and velocity of flow in the sewers. Questionnaires were used to investigate the impact of the behaviour of residents on the performance of the sewer system. It was found that 4% of the components of the sewer system infrastructure were below standard and the collector main sewer was the one mainly affected. 68% of the sewers along the collector main had velocity of flow below 0.6m/s and all the sewers had depth of flow below 50%. Of the residents interviewed, 90% dumped solid wastes in the sewers and 43% did so because they were unaware of the impact. It was concluded that the sewer system failed to meet standard because the sewer system fails to self-cleanse the solid waste dumped by residents in the sewers due to water shortages. It is recommended that the municipality raises awareness among residents and some of the infrastructure should be