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Water level in India�s major reservoirs on lower side: CWC

By AJIT PATOWARY

GUWAHATI, Nov 10 - The total water available in the live storage of 91 major reservoirs across the country, which is being monitored by the Central Water Commission (CWC), was 109.247 billion cubic metres (BCMs) as on November 1. This is 67 per cent of the total live storage capacity of these reservoirs and 97 per cent of the average storage in the last ten years, said the CWC.

The overall storage position of these reservoirs is less than that of the corresponding period of the last year in the country as a whole and is also less than the average storage of the last ten years during the corresponding period, it added.

The CWC is monitoring the live storage status of 91 reservoirs across the country on weekly basis. Of these reservoirs, 37 have hydropower benefit and each of them has the installed capacity of more than 60 MW. The total live storage capacity of these 91 reservoirs is 161.993 BCM, which is about 63 per cent of the live storage capacity of 257.812 BCM estimated to have been created in the country.

However, the CWC has not made any statement on the cause that has led to this reduced storage position of the reservoirs.

Meanwhile, the CWC has said in the guidelines it has issued for sediment management in hydropower and water resources projects that the sediment in dams is critical. Leaving sediment management as it is may lead to not the only reduction but also full loss of reservoir functions. With proper treatment of sediment, it is possible to maintain its function economically along centuries.

As the progress of sedimentation is slow in general, possible long-term solutions should be analysed initially and partly implemented from the beginning as they may impact the full design.

Planning and management of hydropower schemes should incorporate structural measures to manage reservoir sedimentation and prevent sediment ingress into the intakes in order to ensure the long-term viability of a project. It is also necessary at the planning level to incorporate costs for the control of reservoir sedimentation.

The sedimentation management may impact not only the design of the structures but also the choice of the dam site and even the general layout. The studies should take care of uncertainties involved in the evaluation of the siltation. Permanent diversion tunnels, flushing, sluicing and/or dredging may be cost efficient according to specific local conditions.

Desilting the water inflow to powerhouses deserves an analysis of the true efficiency of existing structures. Using the reservoir itself for desilting may be cost-efficient. Combining solutions is often suitable. A long-term sustainability analysis is advisable even if the risk is rather low. It may justify early small investments, such as bottom gates increased capacities, pipes through dams for future dredging, intakes for possible tunnels, etc. All these will considerably reduce future investments by adjusting siltation treatment to the actually measured siltation.

The current trend of providing large sized outlets/sluices that are assigned with the dual functionality of flood discharge and sediment management has given successful results, based on limited dataset available, in managing both reservoir sediment and flood.

Dredging of reservoirs for storage recovery should only be carried out after evaluating all other control measures. Progress in siltation mitigation will improve by obtaining more data and information on the true cost and efficiency of various worldwide solutions that have been used successfully.

The above mentioned guidelines are applicable for irrigation dams also where the level of sluices will be governed by the long-term live storage capacity that is required to be maintained, said the CWC.

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Water level in India�s major reservoirs on lower side: CWC

GUWAHATI, Nov 10 - The total water available in the live storage of 91 major reservoirs across the country, which is being monitored by the Central Water Commission (CWC), was 109.247 billion cubic metres (BCMs) as on November 1. This is 67 per cent of the total live storage capacity of these reservoirs and 97 per cent of the average storage in the last ten years, said the CWC.

The overall storage position of these reservoirs is less than that of the corresponding period of the last year in the country as a whole and is also less than the average storage of the last ten years during the corresponding period, it added.

The CWC is monitoring the live storage status of 91 reservoirs across the country on weekly basis. Of these reservoirs, 37 have hydropower benefit and each of them has the installed capacity of more than 60 MW. The total live storage capacity of these 91 reservoirs is 161.993 BCM, which is about 63 per cent of the live storage capacity of 257.812 BCM estimated to have been created in the country.

However, the CWC has not made any statement on the cause that has led to this reduced storage position of the reservoirs.

Meanwhile, the CWC has said in the guidelines it has issued for sediment management in hydropower and water resources projects that the sediment in dams is critical. Leaving sediment management as it is may lead to not the only reduction but also full loss of reservoir functions. With proper treatment of sediment, it is possible to maintain its function economically along centuries.

As the progress of sedimentation is slow in general, possible long-term solutions should be analysed initially and partly implemented from the beginning as they may impact the full design.

Planning and management of hydropower schemes should incorporate structural measures to manage reservoir sedimentation and prevent sediment ingress into the intakes in order to ensure the long-term viability of a project. It is also necessary at the planning level to incorporate costs for the control of reservoir sedimentation.

The sedimentation management may impact not only the design of the structures but also the choice of the dam site and even the general layout. The studies should take care of uncertainties involved in the evaluation of the siltation. Permanent diversion tunnels, flushing, sluicing and/or dredging may be cost efficient according to specific local conditions.

Desilting the water inflow to powerhouses deserves an analysis of the true efficiency of existing structures. Using the reservoir itself for desilting may be cost-efficient. Combining solutions is often suitable. A long-term sustainability analysis is advisable even if the risk is rather low. It may justify early small investments, such as bottom gates increased capacities, pipes through dams for future dredging, intakes for possible tunnels, etc. All these will considerably reduce future investments by adjusting siltation treatment to the actually measured siltation.

The current trend of providing large sized outlets/sluices that are assigned with the dual functionality of flood discharge and sediment management has given successful results, based on limited dataset available, in managing both reservoir sediment and flood.

Dredging of reservoirs for storage recovery should only be carried out after evaluating all other control measures. Progress in siltation mitigation will improve by obtaining more data and information on the true cost and efficiency of various worldwide solutions that have been used successfully.

The above mentioned guidelines are applicable for irrigation dams also where the level of sluices will be governed by the long-term live storage capacity that is required to be maintained, said the CWC.

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