Some Issues Related To Water Harvesting Ponds For Conservation Ground Water Recharge

摘要

The water harvesting ponds collect not only the surface runoff, but also have an effect over the replenishment to the deep aquifer. And when direct shafts are pierced from these ponds into the aquifers below, the aquifers too get polluted and an aquifer once polluted can never be cleaned. As a measure to combat water shortages, harvesting of rain water and runoff is practiced . This practice has certainly been successful in raising the shallow water table at many places and farmers have been able to give primary and secondary irrigation to rabi crops. Although it has been widely claimed that the ground water table has been rising due to watershed programmes at many places in India, in reality and in spite of all these programmes, the deep ground water has been declining very fast. A major factor is a drag force which is created near the pond on the ground water contained in the soil profile above the semi permeable membrane, of the deep aquifer. Specially when such pond is constructed near a natural drainage system. All the micro pores which were closed over the years get opened and the drainage of the ground water stored in the upstream profile into the pond starts. This in turn lowers the water head which forces the water to penetrate and replenish the deep aquifer. In vertisols , the lateral or horizontal hydraulic conductivity is far greater(.3cm/day) than vertical hydraulic conductivity (.05cm/day) and thus the ground water flows towards the pond at a much greater rate than earlier as the evaporation from the pond surface pulls the water from the earth profile adjacent to it.