Study of Urban Water Demand and Distribution System Reliability – A Case Study of Maharagama Water Supply Scheme, Sri Lanka

Abstract

Significant variation of flow could be identified during the day for Maharagama water supply scheme. Diurnal problem curve indicates that there is a significant problem level, which is more than 40% of service level, during the day. The system operates at a low Hourly Peak Factor (HPF) value of 1.5, moderate Minimum Night Flow Factor (MNF) of 0.4 and Daily Peak Factor (DPF) of 1.1. Water supply system pumping capacity was found to be inadequate to cater the peak demand of the scheme. It reveals that elevation and the distance have a considerable effect on Level of service for Maharagama WSS and Service level has a significant effect on consumption quantity as well, affecting overall revenue. Aim of this study is to assess water demand, evaluate distribution performance of semi urban water supply scheme, and propose management recommendations as an initial approach that will eventually lead to the development of established guidelines for system assessment and operation. In the present study, monthly consumption per connection derived for the past 13 years from 2002 to 2014 and the daily average flow obtained for Mondays through Sunday for five weeks were studied by applying multiple statistical analysis using Small Samples Theory (SMT). A System Water Balance Model was used to generate the instant flow rate time series of demand from the available service reservoir level data and pumping data. Generated out-flow time series was analyzed using Large Sample Theory of statistics. Level of service variation with the proposed parameters was assessed with Principle Component Analysis (PCA) and simple tabular methods. Results were verified with field surveys con-ducted across the study area. The purpose of a water supply distribution system is to provide safe drinking water to each consumer with adequate quantity and acceptable quality. For the operational as well as designing aspects, it is crucial to estimate water demand that is how much water is needed and the variation in demand that is when it is needed. Every year, more than 100,000 new consumers are added to the National Water Supply and Drainage Board (NWSDB) database and the demand for pipe borne water is ever increasing. Out of the piped schemes maintained by NWSDB, only 36% has the capacity to provide 24 hour supply (NWSDB, 1998). Hence, the demand is a very important parameter which requires due consideration when considering urban water supplies.