MULLAPERIYAR DAM - HISTORY

BRIEF HISTORY OF THE MULLAPERIYAR DAM:

The Periyar dam is the first Surkhi concrete dam in a “V” shaped gorge in the Western Ghats over the west flowing Periyar River. This Periyar River is a perennial river which rises from the Sivagiri group of hills in Kerala state and flows through Kerala state and joins the Arabian sea. Out of its total catchment of 4976 sq.km only 114sq.km at the origin of the river lies in Tamil Nadu. It is built of concrete in Surkhi motor (brick powder in lime) with a thick masonry facing and is 173m high above foundation rock with a base width of 144.5ft Its length is 200ft at foundation level and 1241 ft at top. On both sides of the main valley there are smaller depressions and the one on the left side was blocked by a second dam of the same time with 221ft length and 53ft height which is connected with the high ground by means of an earthen dam. The depression on the right flank is utilized as an escape channel and it was originally cut down to a level 11ft below the crest of the main dam and it functions as an open weir escape for discharge of flood flows. But doubts were expressed about the spillway capacity during heavy floods and in 1908 the level of the escape was reduced by 8ft and a regulator was constructed upon it with 10 spans each of 36ft width, fitted with gates of 16ft height. There is an extremely huge quantity of Dead Storage provided merely to raise the remainder water to the level at which it can be passed through the tunnel into the Eastern side of the river basin watershed. The level of the sluice through which the water drawn by the Tamil Nadu is 48ft below the crest of the dam which leaves a Dead Storage water depth of 125ft When full, the lake holds 15.661 TMC of water out of which 9.176 TMC is utilizable as it is lying above the level of the sluice. From the Northern most arm of the reservoir the water is led for about a mile through a deep open cut channel and then through a tunnel of 5700ft length into another open cut channel on Eastern side of Western Ghats which leads into the Surulivar rivulet which discharges into Vaigai river. After irrigating about 1,27,000 acres in the Surulivar river valley the water is picked up at the Perani regulator across the Vaigai river about 80 miles downstream of the tunnel and flows into the Periyar main canal of 35 miles length. The main canal of 35 miles length is 100ft wide at its head and discharges 2000 cusecs of water. The rainfall occurs in 4 out of 5days during June to November when the rain is practically continuous. Sudden floods from 10,000 to 1,20,000 cusecs are constantly experienced during most of the year. Sometimes 3 inches of rain is recorded in a period of 4 hours ,resulting in heavy floods. The project sanctioned in 1884 and started in 1887 was completed by 1897. Where formerly 66,000 acres of land in Tamil Nadu was irrigated from scanty and unreliable water sources 1,85,000 acres was provided with unfailing water supply at a cost of Rs.1.048 crores and the project returns about 6% on capital outlay and proved a financial success.

ENSURING SAFETY OF THE DAM WITHOUT JEOPARDISING INTERESTS OF BOTH STATES

In order to resolve the controversy between Tamil Nadu and Karnataka, a scientific assessment of the problem must be made from several aspects

The probability of failure of a dam depends on factors like seismicity of the area, spillway capacity, nature of foundations, seismic design quality of construction, and feasibility of disaster management, bombing by terrorists or enemy countries. About 10% of the dams failed in India and abroad and about 2% of them are reported to have collapsed. The Valiant dam in Italy failed in 1963 due to the collapse of the mountain slopes around the reservoir basin due to a series of medium earthquakes. Some dams in the Western Ghats of Maharashtra and Karnataka have also collapsed. About 2000 dams have been identified by the US experts as unsafe and it is estimated to cost $1000 million to rehabilitate them. Under the dam Safety Acts in USA and Canada, the risk analyses and dam-break scenarios are used as tools to assess the hazard potential of a dam as it provides firstly the data required for scientific estimation of spill way capacity and secondly to predict the flood wave depth and flood wave arrival times for identifying the villages and towns that could be drowned by the flash floods due to the collapse of the dam. Thus flood management in preventive terms means dam safety and in protective terms flood plains management. According to the International Standards (ICOLD –57, Bulletin46) seismic safety of the dam ensures that firstly the dam does not suffer significant damage due to an anticipated earthquake and secondly the damage to the dam is limited and no catastrophic failure occurs leading to uncontrolled release of water due to a maximum credible earthquake.While studying the Environmental safety of Mulaperiyar dam, two expert committees, one appointed by the Kerala state and another by the union Government presented contradictory recommendations on safety aspects of the dam. A perusal of Newspaper reports on the findings of Expert Committee of the Central Government indicates that the report gives a false impression about the safety of Mulaperiyar dam and naturally the farmers of Tamil Nadu have become suspicious about the genuine grave concerns of Kerala on the colossal environmental damaging impacts consequent to the proposed increase in the height from 136ft to 152 ft of the century-old Mulaperiyar dam. Safety and Environmental hazards of Mullaperiyar and other dams like Iddukki are questions of life and death to Kerala and such issues are too serious to be blindly left in the hands of Experts since they involve not only the technical but also the major social problems. Since most Keralites are intellectual giants, it is necessary to create proper environmental awareness on this controversial problem so that the people can safeguard their right to life and the environment as envisaged under section 51(A) of the constitution of India.