MULLAPERIYAR DAM

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Mullaperiyar Dam

The Mullaperiyar Dam is a masonry gravity dam on the Periyar River in the Indian state of Kerala [1][2][5] It is located 881 m (2,890 ft) above mean sea level, on the Cardamom Hills of the Western Ghats in Thekkady, Idukki District of Kerala, South India. It was constructed between 1887 and 1895 by the British Government to divert water eastwards to the Madras Presidency area (present-day Tamil Nadu). It has a height of 53.6 m (176 ft) from the foundation, and a length of 365.7 m (1,200 ft).[1] The Periyar National Park in Thekkady is located around the dam's reservoir. The dam is located in Kerala on the river Periyar,[1][6] but is operated and maintained by Tamil Nadu state.[1][7][8] Although the Periyar River has a total catchment area of 5398 km2 with 114 km2 in Tamil Nadu,[9][10] the catchment area of the Mullaperiyar Dam itself lies entirely in Kerala.[11][12][13]

History

The unique idea of harnessing the westward flowing water of the Periyar river and diverting it to the eastward flowing Vagai river was first explored in 1789 by Pradani Muthirulappa Pillai, a minister of the Ramnad king Muthuramalinga Sethupathy, who gave it up as he found it to be expensive.[18] The location of the dam had first been scouted by Captain J. L. Caldwell, Madras Engineers (abbreviated as M.E.) in 1808 to reconnoitre the feasibility of providing water from the Periyar river to Madurai by a tunnel through the mountains. Caldwell discovered that the excavation needed would be in excess of 100 feet in depth and the project was abandoned with the comment in his report as "decidedly chimerical and unworthy of any further regard".[14]

The first attempt at damming the Periyaar with an earthen dam in 1850 was given up due to demands for higher wages by the labour citing unhealthy living conditions.[5] The proposal was resubmitted a number of times and in 1862, Captain J. G. Ryves, M.E., carried out a study and submitted proposals in 1867 for another earthwork dam, 62 feet high. The matter was debated by the Madras Government and the matter further delayed by the terrible famine of 1876-77. Finally, in 1882, the construction of the dam was approved and Major John Pennycuick, M.E., placed in charge to prepare a revised project and estimate which was approved in 1884 by his superiors.

Etymology

Earlier known as the Periyar Dam as it was basically meant to dam the Periyar river,[14] the present name Mullaperiyar is derived from a portmanteau of Mullayar River and Periyar River, at the confluence of which the dam is located below.[15]

Design

The Mullaperiyar Dam is a gravity dam made with concrete prepared from limestone and "surkhi" (burnt brick powder), and faced with rubble.[17] Gravity dams use their weight and the force of gravity to support the reservoir and remain stable.[2][5] The main dam has a maximum height of 53.6 m (176 ft) and length of 365.7 m (1,200 ft). Its crest is 3.6 m (12 ft) wide while the base has a width of 42.2 m (138 ft). It consists of a main dam, spillway on its left and an auxiliary dam (or "baby dam") to the right. Its reservoir can withhold 443,230,000 m3 (359,332 acre·ft) of water, of which 299,130,000 m3 (242,509 acre·ft) is active (live) storage.

Dam Safety

After the 1979 Morvi Dam failure which killed up to 15,000 people,[31] safety concerns of the aging Mullaperiyar dam's and alleged leaks and cracks in the structure were raised by the Kerala Government.[32] A Kerala government institution, Centre for Earth Science Studies (CESS), Thiruvananthapuram, had reported that the structure would not withstand an earthquake above magnitude 6 on the Richter scale.[32] The dam was also inspected by the Chairman, CWC (Central Water Commission). On the orders of the CWC, the Tamil Nadu government lowered the storage level from152feet to 142.2 feet then to 136 feet, conducted safety repairs and strengthened the dam.[16]

Strengthening measures adopted by Tamil Nadu PWD from 1979 onwards include cable anchoring of the dam's structure and RCC backing for the front slope. During a recent scanning of the Mullaperiyar dam using a remotely operated vehicle by the Central Soil and Materials Research Station on directions from the Empowered Committee of the Supreme Court, the Kerala Government observer opined that "mistakes in the strengthening works carried out by Tamil Nadu" in 1979 damaged the masonry of the dam.[33]

Current safety concerns hinge around several issues. Since the dam was constructed using stone rubble masonry with lime mortar grouting following prevailing 19th century construction techniques that have now become archaic, seepage and leaks from the dam have caused concern.[34][35] Moreover, the dam is situated in a seismically active zone.[36] An earthquake measuring 4.5 on the Richter scale occurred on 7 June 1988 with maximum damage in Nedumkandam and Kallar (within 20 km of the dam).[citation needed] Consequently several tremors have occurred in the area in recent times. These could be reservoir-induced seismicity, requiring further studies according to experts.[37] A 2009 report by IIT Roorkee stated that the dam "was likely to face damage if an earthquake of the magnitude of 6.5 on the Richter scale struck its vicinity when the water level is at 136 feet".

Purpose

The Periyar river which flows westward into the Arabian sea was diverted eastwards to flow towards the Bay of Bengal to provide water to the arid rain shadow region of Madurai in Madras Presidency which was in dire need of a greater supply than the small Vaigai River could give.[14] The dam created the Periyar Thekkady reservoir, from which water was diverted eastwards to via a tunnel to augment the small flow of the Vaigai River. The Vaigai was dammed by the Vaigai Dam to provide a source for irrigating large tracts around Madurai. Initially the dam waters were used only for the irrigation of 68,558 ha (169,411 acres).[16]

Currently, the water from the Periyar (Thekkady) Lake created by the dam, is diverted through the water shed cutting and a subterranean tunnel to Forebay Dam near Kumili (Errachipalam) in Tamil Nadu. From the Forebay dam, hydel pipe lines carry the water to the Periyar Power Station in Lower Periyar, Tamil Nadu. This is used for power generation (175 MW capacity) in the Periyar Power Station.[citation needed] From the Periyar Power Station, the water is let out into Vairavanar river and then to Suruliyar and from Suruliyar to Vaigai Dam.

Protected area

The Periyar National Park in Thekkady, a Protected area of Kerala, is located around the dam's reservoir, the 26 km2 (10 sq mi) Periyar lake. 62 different kinds of mammals have been recorded in Periyar, including many threatened ones. Periyar is a highly protected tiger reserve and had an estimated 53 tigers (2010) in the reserve.[citation needed] Declared an elephant reserve on 2 April 2002,[28] the population of Indian elephants in 2005 was estimated at 1100,[28] however Periyar suffers greatly from poaching of elephant being the worst affected of South Indian sanctuaries.[29]

Other mammals found here include gaur, Bison, sambar (horse deer), barking deer, mouse deer, Dholes (Indian wild dogs), mongoose, foxes and leopards. Four species of primates are found at Periyar - the rare Lion-tailed macaque, the Nilgiri Langur, the common langur, and the Bonnet Macaque. According to a report by the Kerala Forest Research Institute, the protected area surrounding the dam and reservoir is classified as a biodiversity hot spot

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