Evaluation of measures to meet future supply demand gap in Chennai city, India

Availability of water forever has daunted all the major cities of the world and the cities of India are no exception. Even with high annual average rainfall of 1200 mm the Chennai city has an availability of just 108 lpcd of water, which is much lower than 150 lpcd prescribed by the World Health Organisation. The water requirement presently is met mainly from five reservoirs and partly from groundwater pumping which has given rise to seawater intrusion. The objective of this study is to find effective measures for overcoming the chronic demand supply gap and to predict the results of such measures quantitatively by modelling with the Water Evaluation and Planning System(WEAP). The modelling of city's water demand and supply system was carried out using WEAP and calibration was done using PEST. The data required for this study was obtained from various sources as well as by field investigations. There has been a continuous decrease in the actual water supply even with high availability as predicted by the model. About 60 percent of the city's supplied water ends in sewage and after treatment is presently supplied to industries, on its reuse it is found to meet completely the city's demand alone. The modelled heavy rainfall scenario demonstrates an increase in the water availability up to 20 percent during the years of heavy rainfall. The rejuvenation of existing water bodies in the outskirts of Chennai will increase the water availability for agriculture by 60 percent and hence more groundwater can be pumped for city's water supply. With addition of a new desalination plant over the existing two, the city's water supply-demand gap can be reduced by about 80%. If all the measures are implemented the water availability will exceed the demand. Thus, the WEAP model was successfully used to suggest means for sustainable water management plans for the Chennai city.