CS(AR)-20/98-99 : Performance evaluation of percolation ponds for artificial recharge - a case study

Abstract

A percolation pond is a small water storage structure constructed across a natural stream or water course to harvest the runoff from the catchment and impound for longer time to facilitate percolation of impounded water into the soil substrata both vertically and laterally, thereby recharging ground water storage in the zone of influence of the pond. With a view to assess the benefits of these ponds in terms of the artificial recharge to the aquifers, two percolation ponds are studied in the state of Tamilnadu. The study broadly aims at : assessing the quantum of seepage to the aquifers through the ponds; assessing the zone of influence of the ponds, and; correlating the quantum of seepage to the total storage loss in the pond.

The seepage losses from percolation ponds have been assessed by computing the water balance of the ponds. As far as the percolation ponds are concerned the loss in storage is entirely due to percolation and evaporation. Therefore using the available data, the inflows, the evaporation losses and the change in storage are calculated and the seepage losses are assessed for each of study pond for various observation periods. The study shows that the seepage rates in Uralipatti percolation pond vary from 34.7 to 16.3 cum per day for storages between 1500 to 300 cum during 1991 and from 180.1 to 19.7 cum per day for storages between 2700 to 260 cum during 1993. In the case of Viralipatti pond, these rates are found to vary from 137 to 20.40 cum per day for the storage amount between 10905 to 2830 cum. The average rates of seepage computed over the entire periods of study are obtained as 41.06 and 45.84 cum per day for Uralipatti and Viralipatti pond respectively. Since these seepage rates calculated on volume basis may not be representative in view of the high variability in the storage capacities due to siltation, the column of water recharging the aquifers is also calculated. It is found that these rates, expressed in terms of column of water in the pond, vary from 55.7 to 5.4 mm per day in Uralipatti pond and from 23.3 to 5 mm per day in Viralipatti pond. Over a total observation period of 123 days in Uralipatti pond, the total storage loss is observed to be about 5734 cum, of which 5051 cum percolated down and the rest 683 cum was lost through evaporation. In Viralipatti pond, the seepage and evaporation losses are computed as 5455 and 2860 cum respectively against a total storage loss of 8315 cum over 119 days. These seepage and evaporation losses account for 88% and 12% of the total storage loss in Uralipatti pond and 65.60% and 34.40% in Viralipatti pond. The zone of influence of the ponds is assessed by analysing the response of the water table in the selected wells with the start of recharge. For this purpose. the hydrographs of ponds and observation wells and the ground water table contour maps are drawn for all the recharge periods. In the case of Uralipatti pond, it is observed that the wells located within a radius of 340 m downstream of the pond get adequate recharge from the pond. While the wells located upto 840 m also show moderate recharge effect, the wells at 950 m and beyond have negligible effect of the pond storage. In the Viralipatti pond, the wells located downstream of the pond show a significant recharge upto a distance of 200 m but only a marginal recharge at 305 m.

It is concluded from the study that such percolation ponds are very useful in recharging the shallow ground water aquifers. During the field visits. the farmers in the command areas of such ponds also expressed the increased availability of water in their wells, which they utilize for irrigating the wet crops.