Chennai: Indian Institute of Technology Madras Researchers have designed and overseen the construction of a check dam across Palar River that has resulted in the significant increase in storage of surplus rainwater in the river.
The innovative design of IIT Madras Researchers also resulted in a savings of nearly Rs. 49.5 crore for this project, which was funded under Corporate Social Responsibility (CSR) activities of the Madras Atomic Power Station (MAPS) at Kalpakkam.
While a conventional weir-type check dam costs around Rs. 82 crore and takes up to one year for construction, this project was completed with a funding of Rs. 32.5 crore in six months. The construction of this innovative check dam began in March 2019 and the structure was completed by August 2019, before the onset of monsoon.
Speaking about the unique features of this check dam, Prof R. Sundaravadivelu, Institute Chair Professor, Department of Ocean Engineering, IIT Madras, who lead the efforts from IIT Madras, said, “This unique project was implemented successfully using the diaphragm wall as a deep foundation for check dam, ensuring safety and arresting seawater intrusion. The funding of MAPS, encouragement of the District Collector and cooperation of PWD is greatly acknowledged.”
Palar River supplies drinking water to Chennai, Vellore and Kanchipuram. The impact of climate change in recent years has affected the river, which has resulted in a water crisis in the region. To overcome the water scarcity and prevent the seawater intrusion, it was proposed to construct a check dam across Palar River (at Vayalur, tail end of the river).
The main function of the check dam was to obstruct the flow of water and create a ponding to conserve the rainwater that allows infiltration to the Aquifer beneath to improve the groundwater levels.
At this juncture, Tamil Nadu Public Works Department (PWD) approached Prof. R. Sundaravadivelu, Department of Ocean Engineering, IIT Madras, to evolve an innovative design concept with faster construction technology at a lesser cost.
The following points are considered while planning of the innovative concept for Check dam over conventional concept:
Ø To arrest the seawater intrusion into the freshwater aquifer
Ø To create a subsurface reservoir in the upstream of the check dam
Ø To prevent piping and quicksand condition
Ø To allow the surplus water flow with minimum velocity i.e., Non-Scouring Velocity.
Ø To prevent scour and notch of the soil particles at the river bed
Considering the above points, a deep dyke like structure with 1.2 km length across the river having gentle concrete slope was planned with the stone apron on the upstream and downstream. The deep dyke using diaphragm wall was faster to construct and arrest seawater intrusion.
Its salient features include:
Ø The concrete slope allows the surplus water flow with a minimum velocity
Ø Two launching apron with the packed stones of the size of 300mm weighing 40kg on both the upstream and the downstream prevents eddy formation so that scouring of the soil particles is minimized
Upon completion of the project, the river is now brimming with surplus rainwater. It is a huge success for the IIT Madras, PWD and the Madras Atomic Power Station (the CSR funding agency).
Palar River runs 390 km, including parts of Karnataka, Andhra Pradesh and Tamil Nadu but 80 per cent of the river is in Tamil Nadu – commencing in Vellore district. Nearly 1 tmc of water can be conserved and this can increase the groundwater potential along sand strata.
In the recent years because of climate change effects, the rainfall is varying along the basin. The lower reach adjacent to Chennai is experiencing annual rainfall of about 1200 mm while it varies to nearly 650mm in the upper reaches. The number of rainfall days is about 25 days a year.
Hence, water resources engineers have to evolve suitable conservation measures. Detailed rainfall analyses and hydrogeological studies using GIS were undertaken. Based on the studies a weir of height of 1.5m with a dyke like penetration into the subsurface strata was evolved. A suitable location was identified in the lower reach of the river and structure was installed. The post monitoring of the project indicate the improvements through these conservation measures.