By Our Reporter
SHILLONG: Power Minister James Sangma said on Wednesday that siltation of the Umiam Lake has not affected power generation.
In reply to a supplementary query raised by Independent MLA SK Sunn in the Assembly on Wednesday, Sangma said, “The increasing urbanisation of Shillong and its neighbouring areas has substantially increased the silt load in the two main tributaries of the River Umiam, namely the Wah Umkhrah and the Umshyrpi, both of which flow through the heart of Shillong.”
He said the siltation has mostly affected the dead storage zone of the reservoir that is below the Minimum Draw Down Level (MDDL), which is 960.12 m, and the reservoir capacity for generation of power would not be substantially affected even after 100 years.
To assess the siltation of the Lake after its construction in 1965, studies were conducted by M/S WAPCOS in 1990 and M/S Tojo Vikas International Pvt Ltd, New Delhi in 2004.
Sangma said the design of the Umiam Stage-I Hydro Electric Project provides for dead storage to accommodate 100 years of sedimentation assuming that the entire sediment deposit would be below 960.12 m.
“The dead storage of the Umiam reservoir below MDDL is 39.47 million cubic metre which corresponds to a sedimentation rate of 17.8 hectare metre/100 sq.km/year,” he added.
The studies conducted by M/S Tojo Vikas (India) Private Limited revealed that the volume of sediment collected in the reservoir over 39 years (from 1965 to 2004) works out to be 20.551 million cubic metre, which corresponds to a sedimentation rate of 23.79 hectare metre/100 sq.km/year.
Sangma added that as per the study, dredging of the Umiam Reservoir “does not appear to be an attractive proposition”.
As per the report, the dredging is proposed for 2.17 million cubic metre, which is only 1.53 per cent of the live storage capacity of the reservoir.
The report stated that the cost of dredging even of the insignificant volume of 1.53 per cent of the live storage will involve a cost of about Rs 41 crore at the rate of Rs 189 per cubic metre (2004), which is not economically viable.