Programme:

General:

Namakkal district is one of the interior districts of Tamil Nadu and is bounded by North latitude 110 00’00”N and 110 36’ 10”N & East longitude 770 40’ 00”E and 780 30’ 00”E. The river Cauvery is fringing the western and southern boundary of the district and is bordered by Kolli hills in eastern side. The average annual rainfall is 775.7 mm.

The groundwater potential as well as the groundwater quality may be improved by the construction of check dams across the small tributaries to rivers, streams, odais etc. By these methods, the rainwater can be impounded by the recharge structures and thereby recharge the groundwater. The TWAD Board has constructed numerous recharge structures like Check dams across streams and small rivers near water supply sources to augment its quantity and quality in Namakkal district.

In order to recharge the existing ground water sources in this district, check dams, Ooranies, and recharging through defunct borewells have been constructed under various programmes such as PMGY, NABARD, ARWSP, AGWRS, NRDWP etc.

A check dam has been constructed across the local stream near Kosavankuttai village in order to augment the water supply source ie open well source for Bommasamutram. This check dam has been taken for a case study.

Existing Water Supply Infrastructure:

Water supply is being effected to Bommasamutram village Sendamangalam union from an existing openwell available near local stream near Kosavankuttai of Valavanthi Combai Panchayat in Sendamangalam Union. The Geographical Co-ordinate of the openwell is 11”19’02.964”N and 78” 18’14.665”E and the altitude is 215.91 m above MSL.

At present, water supply is being supplied through 60,000 litres capacity over head tank to Bommasamutram with open well near Kosavankuttai as source.(Location of Overhead tank : 11017’40.489” N and 78015’35.095”E and Altitude 201.27m).

Location of Structure:

Hydrogeology:

The study area comprises hard crystalline rock which includes granite, garnetiferous gneisses and charnockite.

The weathered zone thickness noticed from well sections is ranging from 15m to 30 m. The soil cover noticed is red soil. The area has medium slope and it is a bazada zone.

Rainfall:

The month wise rainfall recorded in Sendamangalam rain gauge station for the year 2009 and 2010 is tabulated. The rainfall measured by this rain gauge actually reflects the rainfall in the area of the Check Dam. Normal annual rainfall to be received is 775.7mm.

Ground Sater Level:

The ground water level from the open well (water supply source) in the downstream side of the check dam has been measured periodically to study the water level fluctuation in the area before and after construction of Check Dam. The water level data is tabulated. The water level is in m bgl.

 

Cost:

Analysis:

Cost-Benefit Analysis for the Check Dam:

a) Details of the Check Dam:

Pumping Rate/ Energy Savings:

After construction of check dam, during monsoon the ground water level rises and hence the potential for drinking water sources is improved and due to this, the consumption of electricity is considerably reduced since the hours of pumping is reduced.

Water Level Analysis:

During monsoon period all the rain water is drained as run-off. Due to the construction of check dam some portion of the rain water is retained and allowed to percolate in to the ground and thereby the water level in the nearby area is substantially increased. This is being observed periodically from an open well available near to the check dam. The observed data show that the water level is being maintained for an additional period of four to five months. The impact of check dam on water level during rainy periods is improvement of ground water level rise considerably and to maintain the level for a certain period even after the monsoon period.

Water Quality Analysis:

The ground water samples from the observation well near the check dam have been collected before (August 2009) and after construction of the check dam (December 2010) and tested for important chemical parameters.

Water sample analysis result – Kosavankuttai Observatoion well is given below.

The analysis shows that there is an improvement in water quality because of the construction of check dam.

Any Other Relevant Aspect:

View of the Public

The public are happy to have this recharge structure in this area and they have expressed their satisfaction. The farmers have also expressed their gratitude by saying that due to the construction of this Check dam, the storage of water in this area is retained for an additional period of 2 to 3 months which helps for their effective cultivation.