The Hindu : Andhra Pradesh News : Nagarjunasagar loses a fourth of its capacity

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Monday, Aug 25, 2008
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Andhra Pradesh

Andhra Pradesh

Nagarjunasagar loses a fourth of its capacity

M. Malleswara Rao

Storage capacity lost due to silt

HYDERABAD: Nagarjunasagar dam, which has been instrumental in making Andhra Pradesh a rice granary, has lost over one-fourth of its storage capacity so far due to silt.

The reservoir is no longer able to store water to its full capacity of 408 tmcft (thousand million cubic ft). Now, it can impound only 288.17 tmcft.

This implies that the dam will have to surplus soon after achieving this capacity during floods in the Krishna.

This revelation was made in a report of the Central Water Commission (CWC) submitted to the government recently after it conducted a bathymetric survey.

The world’s largest man-made reservoir spread over 110 sq km has lost nearly a fourth of its capacity working out to 119.83 tmcft.

The CWC found that the reservoir was accumulating 3.07 hectare-metre of silt annually for each 100 sq km of its water-spread.

Engineers were surprised over such heavy siltation in Nagarjunasagar as they presumed that it would, indeed, be free from the problem as the Krishna passes through rocky terrain.

Moreover, reservoirs upstream such as Alamatti, Narayanpur, Jurala and Srisailam would catch much of the silt. In contrast, it is known that reservoirs across the Godavari get silted fast as the river flows through black-cotton soils.

This is all too apparent from Sriramsagar the capacity of which has dwindled from 112 to 90 tmcft and the Nizamsagar.

Now, the Krishna appears to be no better if the fall in the storage capacity of Srisailam from 308 tmcft to 263 tmcft is any indication. If measures are not taken now, it will lose its full capacity in 70 to 80 years, says T. S. Prakasha Rao, advisor, Irrigation.

Steps suggested

The immediate steps required are construction of silt-arresting tanks on the slopes of river banks, afforestation in the catchment area and growing of grass on river margins to prevent erosion and cutting.

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