Tiruvarur Collector comes up with the idea to augment water supply
A sub-surface dyke has been constructed upstream of Vennar at Munar head near Needamangalam for augmentation of groundwater. The dyke, running 140 metres across the river, five metres in width and 14 ft in depth, is made of nearly 38,000 sand bags arranged in a pyramid-like structure and covered by plastic sheet.
The dyke will act as a recharge structure. “The imbalance in the demand for water and natural recharge of groundwater in Tiruvarur district has necessitated the district administration to take up a series of artificial recharge methods, including this sub-surface dyke to augment groundwater,” said S. Natarajan, Collector, who is the brain behind the scheme.
A conservative estimate prepared by TWAD Board officials show net demand for water usage in a particular year is 54.69 tmcft for all purposes, including agriculture in the district. Current natural recharge level is 29.6 tmcft. The imbalance is 25.04 tmcft.
Inadequate rainfall, reduction of number of water flow days in rivers, and overexploitation of groundwater for various purposes had caused the depletion of groundwater and intrusion of saline water into first and second aquifers, the Collector said.
“Munar head is the entry point of Vennar, Koraiyar, and Baiminiyar into Tiruvarur district and which form the main irrigation and drainage systems. So, we decided to put this sub-surface dyke in the upstream of Vennar at Munar head. Groundwater is normally found in two aquifers. One is found at a depth of 5.5 metres which is a broad and continuous aquifer. Second is found at a depth of 30 metres in a semi-confined and confined location. In Vennar, there is 14 ft of sand at the surface level, upon which the surface water flows. Then there is 30-foot clay and then comes another thick formation of sand which is the second aquifer. The clay does not allow the surface water flowing in the river to recharge the second aquifer. By constructing the sub-surface dyke, we punctured the clay and formed the way for recharging the second aquifer,” Mr. Natarajan said.
Now, the dyke will act as a bed dam at the sub-surface level and impound flowing water in the river when water is released and help recharge the second aquifer. Thus, the water will not flow only at the surface level because of the thick clay formation without recharging the second aquifer.
The dyke will impound water in an area of about 200 acres of land. In another dimension, it will impound water to a distance of five km upstream of Vennar. It will store 43 million cubic ft of water. The sub-surface plastic sheet will not be damaged for 100 years as it is specially prepared and there is no maintenance cost.
“We started the work on May 15 and completed it on June 1 with available local material. This is only a pilot demonstration project taken up under Agricultural Technology Management Agency (ATMA) scheme. While this is a major recharge exercise done in the main river of Vennar, the district administration has taken up artificial recharge in the first aquifer in 1,620 village tanks and 1,415 locations in rivers to a distance of 145 km.
“Success of the schemes have been studied. For drought-stricken, water-starved Tiruvarur district, these measures will go a long way in sustaining groundwater,” said S. Ranganathan, Secretary, Cauvery Delta Farmers’ Welfare Association.