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check Dam

Case study of check dam constructed at Kosavankuttai village of Valavanthi combai panchayat in Sendamangalam union of Namakkal district

 Title:

Type of structure:Check Dam
Village Name:Kosavankuttai
Panchayat:Valavanthi Combai
Union :Sendamangalam
District:Namakkal

 Programme:

Programme    : NRDWP 2009 -2010

 Introduction:

 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 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:


A detailed investigation was carried out by studying rock type, weathering thickness, slope, soil type, catchment area, flow details during monsoon period etc in Kosavankuttai area. Based on the study, a check dam to a length of 15 m was recommended near the existing open well source across (for Bommasamutram village) the local stream originating from Kolli hills. A Check Dam (a length of 15 m) was constructed in the recommended location. The check dam is located on the upstream side of the existing water supply open well in the local stream. The flow direction of the stream is from East to West.





The Geographical Co-ordinates of the Check Dam as measured by GPS Instrument Trimble Juno SB –Terra sync is 110 19’ 04.094” N and 780 18’ 15.029”E and Altitude is 224.76m. The catchment area of the check dam is 7.5 km2 .The location of check dam, catchment area map, field photos before and after construction of the check dam are presented below.

   

   

 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.

Aug-09 Sep-09 Oct-09 Nov-09 Dec-09 Jan-10 Feb-10 Mar-10 April-10 May-10 June-10 July-10 Aug-10 Sep-10 Oct-10 Nov-10
230 92 53 108 45 0 0 0 18 154 114 82 121 114 258 259

 Ground water 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

(Before Construction Aug-09) Oct-09 Dec-09 Jan-10 May-10 Sep-10 Oct-10 Nov-10 Dec-10
8.6 8.2 8.5 9.0 9.6 9.1 4.6 4.0 3.0

   

 Cost:

The Estimated cost:Rs. 4.07lakhs
The executed cost:Rs.3.98 lakhs
The Date of commencement:31.7.2009
The date of completion :15.1.2010

 Analysis:

 Cost Benefit Analysis for the Check Dam:

a) Details of the Check Dam:

Length of the Check Dam:15 m
Height of Check Dam:1.2 m
Cost:Rs.3.98 lakhs
Nearest Raingauge Station:Sendamangalam

b) Storage Capacity of the Check Dam:

Maximum length of the water spread area :250 m
Width:15 m
Effective Height:0.5 m
Volume of water stored:250 X 15 X 0.5 = 1875 m3

c) Calculation:

Taking Evaporation loss as 10 %

then balance quantity of water available in the check dam =1875 - ( 1875 X 0.1 ) = 1687 m3

Hence a quantity of 1687 m3 of water will be infiltered into the ground on construction of the check dam.

If the check dam has not been constructed , only a little quantity of water ( say 10 % of 1687 m3 = 169 m3 would have recharged into the ground.

Hence the additional quantity of water recharged to ground water storage by the check dam =1687 – 169 = 1518 m3

d) Benefit from the check dam:

Generally, the check dam will be filled up twice in a year under normal rainfall.

Hence a quantity of ( 2 X 1518) of 3036 m3 of water will be added to the ground water storage. Out of the above storage ,

Agriculture usage ; 80%
Water supply usage :20 % shall be allotted

Because of the check dam , 20 % of 3036 m3 , say 607 m3 of additional quantity of water is available for drinking purpose in a year.

 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.

Parameter in mg/l Before Construction of
CD during summer
After construction of
CD during monsoon
TDS 765 345
Total Hardness 348 96
Calcium (Ca) 86 22
Magnesium (Mg) 32 10
Sodium (Na) 29 52
Pottasium (K) 19 9
Iron (Fe) 0.15 0.15
Nitrate (NO3) 14 7
Chloride (Cl2) 140 52
Flouride ( F) 0.4 0
Sulphate (SO4) 76 42

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

 ANY OHER 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.

 Conclusion :

Construction of such recharge structures will help augmenting the ground water resources both for drinking and agriculture requirements.

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