Prospects of Groundwater Recharge of Thumbli Formation in its Exposed Area in Barmer District, Rajasthan

Geological mapping of northern part of Barmer district has revealed an area of 800 km² where Thumbli Formation, an arenaceous lithounit of Tertiary period is exposed on the surface with isolated thin cover of wind blown sand. Thumbli Formation when extending in south becomes a productive aquifer having potable water in an area of 1200 km² and is intensively exploited by large number of tubewells for urban and rural drinking water supplies and for irrigation. There is general impression among the scientists that due to low and erratic rainfall, high evapo-transpiration and deep water levels, there are hardly any prospects of this aquifer being recharged.

An attempt has been made by the author to analyze the rainfall pattern and its erratic nature in this area from daily rainfall values recorded at Sheo, Barmer and Baitu tehsil headquarters for the period of 12 years, from 1992 (when rainfall recording was started at Baitu) to 2003. The daily rainfall values when studied in relation to daily potential evapo-transpiration values and soil moisture requirement indicate that there is rainfall surplus available for groundwater recharge. The presence of bicarbonate type water in its exposed area confirms the local groundwater recharge. An attempt has been made to quantify the recharge component after determining the rainfall surplus which, however could not be correlated with the actual increment in groundwater storage due to absence of daily/weekly measurements of water levels from a close net work of piezometers in the area.