Standing on the bridge on river Papagni in Andhra Pradesh’s YSR Kadapa district, Chirutani Pratap factors to the shimmering rivulets in the dry river mattress beneath. “We have begun seeing this only in the past two years. Usually, the river flows like a stream just for four months during the rainy season every year,” says the 50-year-old environmental engineer of the Andhra Pradesh water assets division about the distinctive transformation.
The change has been caused by a string of subsurface dams (SSDs) on the Papagni, a non-perennial river which joins the Penna river in Kadapa. The function of SSDs, constructed throughout streams or valleys, is to ascertain an underground reservoir and to recharge groundwater. The construction depends on piling know-how that drives zig-zag-shaped metal sheets 18 metres deep into the sand to kind a wall of types throughout the groundwater channel and impound water in reservoirs beneath to extend the groundwater storage. In Kadapa, the dams had been constructed between May 2017 and March 2018 at six slopes alongside a 34 km stretch of the river. By 2019, the elevated water ranges ranged from 5.19 metres at Gandi district to 14.64 metres at U Rajupalem.
“They are cost-effective, unlike the conventional concrete dams, and allow for minimal evaporation, which prevents the loss of stored water,” says Pratap. The SSDs have raised the groundwater desk and allowed farmers in the neighborhood to faucet into this useful resource for not less than 4 months even after the trickle on the river floor has dried. The price of setting up SSDs is barely a tenth of that of standard dams with the similar storage.
In YSR Kadapa, since 80 per cent of the geological space is roofed with sedimentary (shale and limestone) deposits which are impervious in nature, groundwater tends to deplete shortly. As a end result, pure recharge may be very sluggish. Data exhibits that since the building of SSDs, the water ranges in borewells in river-adjacent areas have been augmented and contribute to sustainable irrigation in the drought-prone district. As a end result, the development of the paddy crop throughout the kharif season has stabilised and a second crop, largely sunflower, can also be being grown throughout the rabi season.
The United Nations Convention to Combat Desertification urged groundwater dams, akin to SSD, as a know-how appropriate for financial storage of water in arid and semi-arid areas.
In the absence of budgetary allocations, YSR Kadapa district collector C. Hari Kiran banked on the mineral cess collected in the district and accessible for discretionary use to search out the Rs 26 crore required for the building of SSDs. “There have been many inquiries about SSDs from drought-prone areas,” says Kiran. “A minimum topographic riverbed slope of five to six metres is required. Suitable gradients, between 0.2 per cent and 4 per cent, which is usually the case in the transition zones between hills and plains, are the essential geographical circumstances.” Further, SSDs may be constructed the place rivers are slender, lower than 500 metres vast, or in areas with already developed farms however ones that lack water for irrigation.
SSDs have modified the face of farming in YSR Kadapa inside two years, and benefitted an space of round 8,000 acres.