Sustainable Fresh Water Supply for Chennai City

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Sustainable Fresh Water Supply for Chennai city, Tamil Nadu, India A Status Update Joseph Thomas,
Chief Technology Officer, Villgro, Chennai, India
3H, IIT Madras Research Park, Kanagam Road, Taramani, Chennai, Tamil Nadu India 600113. Telephone +91 44 6663 0400, email:joseph@villgro.org, mobile +91 98840 49116 Key Words: Rain water harvesting, Sustainable water supply, Urban fresh water.

Abstract
Chennai city, one of the major metropolises of India, is situated at the northern coastal edge of the State of Tamil Nadu. The city is more well-known by its older name of Madras. Currently, Chennai is inhabited by more than 7 million people in an area of 176 sq km. Water supply for this population is maintained by tapping a combination of surface storage reservoirs and aquifers. The Chennai Municipal Water Supply and Sewerage Board (CMWSSB), a statutory body established in 1978, is responsible for water supply and sewerage services in the Chennai Metropolitan Area. The main sources of public water supply in the city are the three reservoirs — Poondi, Redhills and Cholavaram — with an aggregate storage capacity of 175 million cubic metres (MCM). The other major resource is groundwater from the well-fields in the Araniar-Kortaliyar basin and the southern coastal aquifer, and also a large number of wells and tube-wells spread all across the city (Figure 1). Over-extraction of groundwater resulted in a rapid ingress of seawater, which extended from 3 km inshore in 1969 to 7 km in 1983 and 9 km in 1987[[i]]. Groundwater levels within the city also fell and brackish water began to appear, even in localities which earlier had good quality groundwater sources. The CMWSSB calculates water availability based on surface and aquifer contributions under its direct control. Since it perceived reservoirs and other surface supply as more significant for a long time, very little attention was paid to subsurface storage or ground water recharge. As an outcome of research, done by several agencies the CMWSSB embarked on a campaign to create ground water recharge facilities in the city, and later throughout the State. This led to significant changes in ground water levels and to the quantum of water available to the population of a growing metropolis. [pic]Figure 1.

Introduction

The Chennai Municipal Water Supply and Sewerage Board (CMWSSB) is solely responsible for providing drinking water and sewerage services to the residents of Chennai. One of India’s major metropolises, Chennai is situated at the northern coastal edge of the State of Tamil Nadu. The city is more well-known by its older name of Madras. Currently, Chennai is inhabited by more than 7 million people in an area of 176 sq km. The CMWSSB depends on surface reservoirs and ground water sources to maintain water supply to the residents. Supply is maintained through multiple means. Since Chennai is essentially low-lying and water supply is intermittent, most residents build underground sumps that store the water. Subsequently, the water is pumped up to an overhead tank. In other cases, water tankers are dispatched by CMWSSB to various localities and the sumps are filled from the tankers. In other localities, CMWSSB has put in place above-ground water tanks and these are filled by the water tankers. In yet other places, residents collect water directly from the tanker, see Figure 2.

[pic]
Figure 2: Drinking water collection from tankers directly by residents.

Despite the seemingly abundant sources of water, Chennai suffers continuously from water stress since the entire basin is dependent on rainfall. The annual rainfall in Chennai is 1200 mm [[ii]]. This quantum is, given the size of the Chennai basin, sufficient to meet the needs of the population. The problem is with the distribution of the rainfall. There are two rainy seasons in Chennai. The first is the Southwest monsoon, which has patchy rains and contributes about 25% of the total rain and falls between May and...
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