Dam Safety Act states that "it is expedient in the public interest that the Union should take under its control the regulation of uniform dam safety procedure for specified dam." It defines “specified dam” as a dam constructed before or after the commencement of this Act, which is,—(i) above fifteen metres in height, measured from the lowest portion of the general foundation area to the top of dam; or (ii) between ten metres to fifteen metres in height and satisfies at least one of the following, namely:—(A) the length of crest is not less than five hundred metres; or (B) the capacity of the reservoir formed by the dam is not less than one million cubic metres; or (C) the maximum flood discharge dealt with by the dam is not less than two thousand cubic metres per second; or (D) the dam has specially difficult foundation problems; or (E) the dam is of unusual design.
It defines “dam” as any artificial barrier and its appurtenant structure constructed across rivers or tributaries thereof with a view to impound or divert water which also include barrage, weir and similar water impounding structures but does not include—(a) canal, aquaduct, navigation channel and similar water conveyance structures; (b) flood embankment, dike, guide bund and similar flow regulation structures.
It defines “dam failure” as any failure of the structure or operation of a dam which leads to uncontrolled flow of impounded water resulting in downstream flooding, affecting the life and property of the people and the environment including flora, fauna and riverine ecology.The failure in the operation shall mean such faulty operations of the dam which are inconsistent with the operation and maintenance manual.
It defines “dam incident” as all such problems occurring to a dam that have not degraded into a dam failure, and includes–– (i) any structural damage to the dam and the appurtenant structure; (ii) any unusual reading of any instrument in the dam; (iii) any unusual seepage or leakage through the dam body; (iv) any unusual change in the seepage or leakage regime; (v) any boiling or artesian condition noticed below the dam; (vi) any sudden stoppage or unusual reduction in seepage or leakage from the foundation or body of the dam or any of its galleries; (vii) any malfunction or inappropriate operation of gates; (viii) occurrence of flood, the peak of which exceeds the available flood discharge capacity of the dam or seventy per cent. of the approved design flood; (ix) occurrence of flood, which resulted in encroachment on the available freeboard, or the approved design freeboard; (x) any unusual erosion in the near vicinity up to five hundred metres downstream of the spillway or waste-weir; and (xi) any other occurrence which a prudent dam engineer may relate to dam safety concerns.
It defines “distress condition” as the occurrence or potential development of such conditions in the dam or appurtenance structure or its reservoir or reservoir rim, which if left unattended to, may impede the safe operation of dam for its intended benefits or may pose serious risks to the life and property of people and the environment including flora, fauna and riverine ecology.
It defines “vulnerability and hazard classification” as the system or systems of classifying dams on the basis of their condition, location, damage or hazard potential.
In the backdrop of these acknowledgements in the Dam Safety Act, the query of the Parliamentary Standing Committee as to how many large dams are in India which are 100 years old and still functional assumes great significance. Responding to the query, Department of Water Resources, River Development & Ganga Rejuvenation stated, “As per the National Register of Large Dams-2019, there are 234 functional large dams in India which are 100 years old”. The report provides a list of these 234 large dams in a table at pages 45-50. The Committee's report makes recommendations with regard to safe decommissioning of these dams.
When asked to enumerate the major instances where failure or leakage from such old dams has wreaked havoc in terms of loss of lives as well as economic losses, the Department replied, “As per the records available in this office, the the list of reported failures from such old large dams include Madhya Pradesh’s Tigra (1917) in 1917 due to overtopping followed by slide, Maharashtra’s Ashti (1883) in 1933 due to slope failure, Maharashtra’s Khadakwasla (1880) in 1961 due to overtopping, Madhya Pradesh’s Jamunia (1921) in 2002 due to piping leading to breaching and Rajasthan’s Jaswant Sagar (1889) in 2007 due to piping leading to breaching.
On being asked about the mechanism put in place in India to assess the viable lifespan and performance of dams and projects which has a direct bearing upon the consideration for dam decommissioning from an environmental perspective, the Department, in its written submission, stated, “Dams in India are normally designed for approximately 100 years of useful age. The functional life of the dams gets decreased with progressive reservoir sedimentation concurrently reducing project benefits. There is no mechanism to assess the viable lifespan and performance of dams. Regular maintenance of dams is undertaken for their health assessment and their safety. As a part of maintenance activity, regular pre & post monsoon inspections, and the maintenance/rehabilitation works of the dams are carried out. These dams are mostly owned by State Govts. /PSUs/Pvt. Agencies which carry out the O&M works of the dams in their jurisdiction. However, no information/recommendation from the dam owners has been submitted for de-commissioning of any of their dams. Realizing the importance of dam safety, a Dam Safety Act has been notified in the
year 2021 to provide for surveillance, inspection, operation and maintenance of the specified dam for prevention of dam failure related disasters and to provide for institutional mechanism to ensure their safe functioning and for matters connected therewith or incidental thereto”.
On a query as to how many dams which are more than 100 years old have been decommissioned in India, the Department furnished its written reply said, “As per the information available in CWC, no such dam has been decommissioned in India”. This report creates a compelling logic for the adoption of a decommissioning policy for every dam which is constructed in India.