GUWAHATI, Aug 22 - The hydroelectric power generating companies operating in Northeast India should draw lessons from the recent Kerala flood havoc. They should scientifically overhaul the present adverse reservoir operation schedules adopted for the Ranganadi, Doyang and other hydel dams in the region, including the Kurichhu dam in Bhutan on the Manas river, and turn their monopurpose dams into multipurpose ones with the use of latest technologies.
This was the observation made by Prof Nayan Sarma, a renowned river expert, who is now an Honorary Professor at the University of Nottingham, UK. Prof Sarma, also a former professor of the Indian Institute of Technology, Roorkee, was talking to The Assam Tribune on the lessons of Kerala flood in respect to reservoir operations.
�The grim lesson to be learnt here is that in the 42 dams of Kerala, extremely adverse reservoir operation policy was practised. The gates of 35 of these dams were fully opened at once, during the unprecedented rains in the southern state aggravating the flood situation there,� he said.
Prof Sarma said this year, on July 9, the spillways of Ranganadi dam of the North Eastern Electric Power Corporation (NEEPCO) had to release flood flows much in excess of the safe carrying capacity of the river. Reportedly, inflows to the Ranganadi reservoir attained a high level of 1,500 cumec, when the 160-cumec-capacity power tunnel outfalling into the Dikrong river was also not operating on that day.
Due to continuous sediment flushing operations at Yazali, the downstream river morphology of Ranganadi has undergone progressive deterioration in the form of unrelenting bed aggradation thereby reducing its flood-carrying capacity, he said.
To aggravate the situation further, the winter stream flow falls below 160-cumec level, thereby causing the downstream river sections to practically dry up. Evidently, such a shallow aggraded form of Ranganadi river geometry is incapable to safely carry the dam releases or flood flows during monsoon months, which culminates into occurrence of devastating floods in Lakhimpur district.
The story for Doyang and Kopili is also identical. Ranganadi and other hydel dams � Doyang, Kopili, Karbi Langpi, Umiam � are all operated on a single purpose mode devoid of any flood cushion to hold back flood flows. Thus, they are made to wreak havoc in the downstream areas almost regularly. Under such a situation, it is not hard to guess for one to get an idea of devastation they would cause if an excess rainfall is received in the catchment areas of these rivers in a Kerala-like situation, he said.
Therefore, it is imperative to scientifically analyse the glaring weaknesses in these single purpose dams, primarily of run-of-the-river type, to explore technical solutions, which may be out-of-box, to alleviate the recurring misery and hardship of the flood-hit people living downstream, by remodelling the existing project configuration.
In the first place, it is an instance of glaring suboptimal water resources planning to have conceived these single purpose hydel projects as against multipurpose reservoir planning based on the principle of integrated water resources management with storage space for flood cushion, irrigation and ecology, besides hydropower.
For mitigation of the almost similar flood devastation caused in downstream areas of Ranganadi, Doyang, Kopili, Karbi Langpi and Kurichhu hydel dams due to the inherent deficiencies, some solutions that would make use of recent advances in technology, can be suggested. Creation of necessary flood cushion in the reservoirs, ensuring constant release of requisite ecological flow for sustainability of aquatic flora and fauna as well as river flow regime conditions and implementation of river restoration scheme for developing required channel flood conveyance capacity (without flood spillage) along downstream river sections are some of the solutions.
Besides, undertaking catchment area treatment schemes in the watershed areas for reducing sediment ingress to the reservoir and putting in place state-of-the-art satellite-based early warning system, with maximum possible lead time, are the other solutions, Prof Sarma said.
