Guwahati: The Central Electricity Authority has stated that it is the responsibility of the project authority to assess the upper regions, which encompass the reservoir area and dam site, to detect any faults or potential slides and implement necessary measures to ensure the stability of hydro power projects that are susceptible to such issues.
“The vulnerable projects shall include 400MW and above capacity hydro power projects located uppermost in a river or its tributary at an elevation above 1500 m in cases where the gross reservoir storage is at least 50 MCM (Million Cubic Metre). The examination of upper reaches may include study of hazards due to avalanche, GLOF (Glacier Lake Outburst Flood), landslide hazard analysis of slopes above the reservoir rim area, etc,” stated CEA.
A Glacial Lake Outburst in South Lhonak Lake in North Sikkim on the night of October 3-4 caused a devastating flood in the North Eastern State of Sikkim. The water level in the Teesta River rose about 50-60 feet in height, causing calamitous floods downstream.
Sikkim chief minister Prem Singh Tamang had said substandard quality practices followed during the construction of the Chungthang dam, Teesta Urja Ltd resulted in the situation taking a catastrophic turn and an inquiry committee will be set up and those found guilty will be brought to charge.
CEA has issued guidelines for developers of hydro power projects in hilly terrains to maintain slope stability. “The design, construction and maintenance of the slopes is one of the major challenges during planning, construction and operation of hydro power projects. “Generally slope instabilities in hydro power projects are encountered during execution as well as operation. Slope instabilities are generally caused when the force/ load equilibrium of the stable slope is disturbed due to change in geometry of the natural slope, hydrogeological regime, deforestation, and/or weathering effect,” it stated.
These guidelines are applicable guiding them to take cognizance of past slope failures and existence of unstable slopes in the project area covering the affected zones and recommend necessary remedial measures for slope stabilisation of hydro power projects prior to construction, during construction, and post commissioning of the project.
It said a careful and thorough investigation of project area prior to excavation, utilising advanced techniques covering all the aspects of slope stability can mitigate the possibility of slope failure and effective measures for slope stabilisation may be planned in advance reducing the cost of stabilisation.
The CEA said after the allocation of the site for the project development, the area needs to be studied on a regional scale (1:50,000/1:25,000) for depicting regional geological features such as geological setup/ stratigraphy of the area, major and minor thrust/ faults, folds, and other discontinuities/deformation in the rock mass, analysis of their impact to the proposed project, and delineation of vulnerable zones/ landslides/ subsidence and also land use/ land cover.
Before starting the project excavation works, detailed geological and geophysical investigations/ explorations of the slopes of the project area should be carried out to delineate various slope parameters viz. soil/ rock-mass characteristics/ class, hydrological/ hydrogeological details, and other governing parameters for slope stability as per
codes.
The CEA has also formed a technical committee to study the issues in the event of any geological surprise faced in the hydroelectric projects.
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“It has been observed that development of hydroelectric projects had been marred due to various issues/ constraints including geological uncertainties/ constraints, resulting in significant time and cost overruns. In this regard, the Techno Economic Concurrence issued by the CEA, in general, provides that the Project Developer shall systematically maintain a record of the geological surprises, which are encountered and treatment provided. At the same time, the Project Developer shall request the Ministry of Power to constitute an Expert Committee consisting of representatives from State Govt., GSI, CWC and CEA. Once this Committee is constituted, the Project Developer shall submit the proposal for enhanced cost to the Expert Committee, which in turn shall examine and recommend the cost thereof, ” stated the authority.
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