Water shifted from one reservoir to another to save it from evaporation

On an average, every day, one million cubic feet of water evaporates from each reservoir

Chennai, 16-09-2012: Birds resting on a sand dunes in the middle of the Red hills reservoir near Chennai. The Red Hills Lake, is located in Ponneri Taluk of Thiruvallur district, Tamilnadu, South India. It is one of the two rain-fed reservoirs from where water is drawn for supply to Chennai City, the other one being the Chembarambakkam Lake. The full capacity of the lake is 3,300 million ft. The reservoir was built in 1876. The reservoir was originally a small tank with a capacity of 500 million cubic feet (mcft) and two masonry weirs, built using locally available laterite stones, then functioned as surplus weirs to release excess water from the water body. Today, these masonry weirs are water-retaining structures as they have been replaced by two shutters. In 1997, the storage capacity of the reservoir was increased to 3,300 mcft and the depth to 21.20 ft to cater to the drinking water needs of Chennai and also to store Krishna water received from Andhra Pradesh. Until 2012, the Water Resources Department (WRD) has only taken up maintenance work worth 500,000 every year.There are two masonry weirs in the reservoir. One weir is 178 m long and the other is 220 m long and 15 ft deep. The bund measures 5 m and runs to a distance of 7 km. Photo:S_R_Raghunathan

After 2012’s dismal northeast monsoon, 2013 too, has not fared very well as yet.

One month in, the city is yet to receive any rainfall, leading to a strain on the four reservoirs that cater to the city’s daily drinking water needs. In addition, these water bodies are struggling under the everyday loss of water due to evaporation.

Officials said that on an average, every day, one million cubic feet (mcft) of water evaporates from each reservoir. While generally this amount is negligible, at a time when the city is staring a water crisis in the face, it is essential to conserve as much of the resource as possible for summer needs, they said.

To minimise the loss, the Water Resources Department (WRD) has started diverting water from the reservoirs in Poondi and Cholavaram, which are primarily used as storage facilities, to the others in Red Hills and Chembarampakkam.

At present, these four reservoirs are less than half full and WRD officials said it was crucial to preserve the water in them.

Officials are now diverting nearly 300 cubic feet per second of water (cusecs) from Poondi reservoir to Red Hills reservoir from where it is treated and fed into the drinking water network. From Cholavaram reservoir about 150 cusecs are being sent to Chembarampakkam.

In summer, each of the water bodies generally suffers a minimum loss of five mcft of water daily. “Instead of allowing water to evaporate in Cholavaram and Poondi, we decided to transport the water to reservoirs in Red Hills and Chembarampakkam to use for drinking water supply,” an official said.

This will help maintain storage and minimise further decline, to tide over a possible water crisis until June, he added.

At present, the city is supplied with 831 million litres of water a day through various facilities, including from the reservoirs, the Minjur desalination plant and from the Veeranam tank in Cuddalore district as well as Krishna water from Andhra Pradesh.

On an average, every day, one million cubic feet of water evaporates from each reservoir