HYDERABAD: Osmansagar and Himayatsagar, the traditional drinking water supply sources of the city, might never get full unless there is `extreme rainfall'. Despite normal rainfall in most of the last 46 years, the reservoirs got filled only a few times.

Notwithstanding more than 1,100 mm of rainfall in their catchment areas last year - it was 350 mm higher than the normal - the reservoirs could not get filled.

More startlingly, more than half of the rainfall received went into recharging the depleting groundwater levels. In fact, the groundwater level in the catchment areas rose by 15 metres!

Paradoxical situation

"Such is the situation that whatever is the rainfall in the catchment areas of the two reservoirs it is simply percolating down to recharge the groundwater table with little or no runoff to reach them," explained B. Venkateswara Rao, Head, Centre for Water Resources, Jawaharlal Nehru Technological University, who completed a study on the decreasing inflows into Osmansagar and Himayatsagar recently.

Armed with the groundwater level data of the past 20 years, the study revealed that inflows have been declining every passing year, thanks to the heavy recharge of groundwater along their course and very little left to reach the reservoirs.

In the year 2005 itself, the groundwater levels in their catchment areas had increased from 40 metres below ground level to 25 metres indicating a heavy induced recharge.

Rampant development

He said the induced recharge was also due to rampant development of the catchment areas with institutions, habitations, including farmhouses, and water conserving structures like check dams and farm ponds obstructing the natural flow of water into the reservoirs.

"This coupled with largescale groundwater withdrawal has led to a situation where there is no water left downstream to flow into the reservoirs, closing the entire upper Musi basin."

Findings to be presented

The findings of the study are being presented at an international seminar being organised by the Stockholm International Water Institute from August 20 to 28.

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