DISTRIBUTION NETWORK IN URBAN WATER -SUPPLY

Abstract

Water is essential for sustaining all types of life forms. In fact, all human civilizations have evolved around water. The world has entered the 21't century with an enormous challenge-safe drinking water for all. Nearly 3.4 million people in the world, most of the children, die every year from diseases associated with lack of safe drinking water, inadequate sanitation and poor hygiene (WHO, Water quality may vary within a water distribution system due to internal degradation/ growth or external intrusion. Efficient water quality monitoring is thus one of the most important tools to provide adequate and reliable water supply. A decline in pressure at one or more of the system nodes can cause a reduction of the quantities supplied, while an accidental entry of a contaminant or self deterioration of water quality within the network itself is a severe damage to public health. The present study is an Endeavour to throw light on transformation in quality of water during its transit through the distribution system using modeling and monitoring methods. Recent developments in computer software now provides a capability to build representative models, which can simulate the propagation and concentration of water quality parameters under steady and dynamic flow conditions. The water quality models are essentially based on hydraulic characteristics of flow in the distribution system. Hence, study of the basic principles and techniques of hydraulic simulation is fundamental for any water quality model. In order to model spatial and temporal concentration of various water borne substances, it is desired to know the kinetics of these substances, basic equations of mixing at nodes, mixing regimes and residence time in storage tank and advective transport in the pipes. Monitoring in the WDS can determine the quality of water delivered to consumer and provide an indication of the risk of waterborne diseases. To obtain 100% information on water quality, monitoring would be required at practically all the nodes of the WDS, which is highly infeasible because of cost, time and other constraints. The number of sampling can be significantly reduced if the following assumption is made: In the absence of any quality boosting measures (such as BC stations), the quality of water deteriorates with the passage of time as it flows in the network work from source to the various demand nodes. Under this assumption, it is possible to identify optimal monitoring locations for maximum demand coverage. The term 'demand coverage' denotes the total Department of [Vater Resources Development and Management iii Indian Institute of Technology, Roorkee Dish,ibution Network in Urban Rater Supply Abstract quantity of water whose quality can be inferred from the samples taken at a particular monitoring station. The monitoring locations are selected in the descending order of demand covered by them. The method of selection of monitoring locations for maximum demand coverage applies efficiently for detection of routine internal decay of quality in Water Distribution System (WDS). However, in case of distribution systems having high vulnerability to intrusions of external contaminants, it is essential to design the monitoring network for a level of service capable of indicating the level of damage. It is possible to define the level of service in terms of the contaminated water consumed or the time lapse between the entry and detection of external contaminants termed as the "volume consumption level of service" and "T hour level of service" respectively. The monitoring network can be such identified that the required level of service can be achieved with minimum number of monitoring locations. Performance evaluation of various WDSs can be carried out using reliability analysis. Reliability analysis is essential in decision making for design, operation, maintenance and up-gradation of a WDS. Two types of reliability measures, viz, mechanical and hydraulic have extensively been used for reliability analysis of WDS. In mechanical reliability, physical connectivity of demand nodes and source nodes(s) is assessed and in hydraulic reliability the probability of receiving the desired discharge at the nodes is evaluated. With the growing comprehensive of relationship of water quality and WDS, a new dimension associated to quality issues needs to be added to the reliability analysis. The probability of receiving the desired residual chlorine concentration at the nodes has been estimated for when pipelines of the network are subject to failure.