Sharp variations in groundwater levels at the same location: a case study from a heavily overexploited, fractured rock aquifer system near Bengaluru, South India.

Analyses of 83 borehole camera video scans revealed that (i) measured groundwater levels show variations of up to about 200 m, even in borewells located in close proximity to each other; (ii) water-bearing joints located at shallow depths in deeper borewells often produce cascades of water which flow down-hole till they meet the water level; (iii) the downward flow of recharging waters directly through the existing borewell shafts leads to the formation of a dewatered zone below the recharge zone and above the saturated zone, and (iv) the borewells completed in the dewatered zone show a direct relationship between water level and well depth – deeper the borewell, deeper is the water level. Only the currently yielding borewells, with at least one water-yielding joint below the water level give a fair estimate of the regional groundwater table.