There is a 15- 30 centimetre rise in groundwater levels: SPPU study
Under the study, a total 103 villages across 13 talukas of Pune district were selected where trench-cum-recharge shaft structures were proposed to tackle drinking water scarcity issues
According to a research report on ‘Impact Assessment of Trench-cum-Recharge Shaft Structures constructed in water-stressed villages across 13 talukas of Pune’ – submitted by the geology department of the Savitribai Phule Pune University (SPPU) to the Pune Zilla Parishad (ZP) – there is a nearly 15 to 30 centimetres’ rise observed in groundwater levels depending on the locations of these structures and the topography of the villages housing them.
Professor Bhavana Umrikar, associate professor of Geology, SPPU, said, “Rainwater harvesting is one of the leading programmes being implemented in the country. Moreover, under the ‘catch the rain’ umbrella, there is continuous engagement to save every drop of rain and use water resources judiciously to mitigate drought. Particularly in rural Maharashtra, which is totally dependent on groundwater as the prime source for drinking, there is a need to keep these sources perennial.”
“A majority of water supply wells tap phreatic aquifers that get replenished in every hydrological year, and these wells are located near second- or third-order streams. Keeping this in view, trench-cum-recharge shafts have been constructed on priority at 222 locations in tanker-fed villages of Pune district, Maharashtra. This report incorporates the impact assessment of these structures with an aim to find out whether the drinking water supply issues have been resolved in these water-scarce villages,” professor Umrikar said.
Under the study, a total 103 villages across 13 talukas of Pune district were selected where trench-cum-recharge shaft structures were proposed to tackle drinking water scarcity issues. This is the most efficient and cost-effective technique to recharge unconfined aquifer overlain by poorly permeable strata. The recharge shaft is placed in a recharge pit surrounding the filter media. A shaft of 0.5 metres’ diameter and depth ranging from 25 to 30 metres is constructed, where the shallow aquifer is located or where the upper layer of soil is alluvial or less permeable.
About the conclusions of the study, professor Umrikar said, “The current study related to impact assessment of trench-cum-recharge shafts constructed in water-stressed villages across 13 talukas of Pune district depicts that there is a nearly 15 to 30 cm rise observed in groundwater levels depending on the locations of these structures and the topography of the village. As this is the first year of assessment and there has been a delay in the monsoon in the year 2023, it has been suggested to opt for assessment of one or two more hydrological cycles to confirm the rise in groundwater levels. There is also a need for regular maintenance of these trench-cum-recharge shaft structures so that the maximum benefit out of these structures could be drawn in terms of elevated recharge to aquifers and perennial supply of drinking water in these villages.”
“Apart from the rainfall analysis and observation of groundwater level trends, there has to be continuous monitoring of the number of tankers that have been provided to the water-stressed villages, and for how long these tankers have been needed is also very important to actually quantify the role of recharge shafts in mitigating the water scarcity. And it is recommended that the installation of these trench-cum-recharge shafts is locale-specific, and there is a need to undertake area treatment so that the entire village would be benefitted and that would help in achieving the sustainable goal of providing safe drinking water throughout the year,” professor Umrikar said.
According to the Pune ZP to which the research report has been submitted, there are various artificial recharge techniques successfully planned and executed in many parts of Maharashtra, Pune district being among them. There is an urgent need to undertake impact assessment studies in areas where the recharge structures are constructed; the before and after scenario has to be generated to understand the changes that have taken place in terms of reduced number of tankers, groundwater availability in summer etc.
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Study of hydrographs
The comparison of current groundwater levels with the previous hydrologic year and trend analysis also helps in understanding the impact of recharge structures on water table aquifers. Therefore, some hydrographs generated at representative locations have been studied to find out the recent trends and increase in groundwater levels or availability of groundwater in severe summer months.
