NATIONAL

Groundwater overuse sinks riverbed

depleting water table:The sinkhole in Chitravathi riverbed, Anantapur.— PHOTO: R.V.S. PRASAD

depleting water table:The sinkhole in Chitravathi riverbed, Anantapur.— PHOTO: R.V.S. PRASAD  

Overexploitation of ground water, coupled with virtually no recharge of the water table in the absence of good rains for the last six years, appears to have triggered the geological event known as “sinkhole” in this perennially drought-prone district of Andhra Pradesh.

In a first of its kind phenomenon, the sinkhole was noticed on the dried Chitravati riverbed near the Goddumarri village of the district. It had a depth of 30 feet and a diametre of 25 feet.

“I heard a deafening sound and saw a depression developing fast into a large cavity. Although we were away from it, we ran fearing it might drag us in,” said Obula Reddy, a farmer who owns an orchard close to the sinkhole on the outskirts of the Goddumarri village.

Sinkholes usually form in soils characterised by rocks of gypsum or dolomite or limestone which melt in water available in the sub surface channels, leading to a sudden collapse, said Manikanta, senior geologist.

On Chitravati riverbed case too, the formation of cavity was triggered by depletion of ground water.

Deputy Director of Groundwater Department P. Purushottam Reddy confirmed the development and said the intensity of drawing ground water through a string of agriculture borewells was high in the vicinity of the river, where there were a number of sweet lime orchards.

Lack of good rains in the last six years only added to the problem.

“Limestone occurs at a depth of 250 ft below the surface in the Chitravati river belt which is where the water table also starts. With the water depleting to around 750 to 850 ft, the cavernous limestone zone develops into a layer, collapsing into itself,” Mr Reddy explained.



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