Periyar (river)

Periyar
Location map of the Periyar River
Origin	Sivagiri Hills, Sundaramala in Tamil Nadu
Mouth	Lakshadweep Sea, Vembanad Lake
Basin countries	India
Length	244 km
Source elevation	1830 m
Avg. discharge	295 m³/s
Basin area	5398 km²

Periyar (meaning: big river) is a river that flows in the states of Tamil Nadu and Kerala, India. It is one of the few perennial rivers in the region and provides drinking water for several major towns. The river is mostly located in Kerala and generates a significant proportion of that state's electrical power via the Idukki Dam. Due to these reasons, the river has been named the ‘Lifeline of Kerala’. It is the longest river and the river with the largest discharge potential in Kerala.

Origin and path

Periyar river view at Bhoothathankettu near Kothamangalam, Ernakulam.

The Periyar originates in the Sivagiri peaks of Sundaramala, Tamil Nadu. It has a total length of approximately 244 kilometres (152 mi) and a catchment area of 5,398 square kilometres (2,084 sq mi), of which 5,284 square kilometres (2,040 sq mi) is in Kerala. The river flows northwards from its origin, for 48 kilometres (30 mi) and at Mullakudy is joined by the west-flowing Mullayar, an important tributary. During this journey the Periyar flows through the Periyar Tiger Reserve, flowing across or forming the boundaries between various sections of the reserve. Going downstream, it defines a part of the border between Periyar section of the reserve in the east and Sundaramala section in the west and then the borders between Moolavaigai and Thannikudy sections in the east and Ummikuppan, Mlappara and Aruvioda sections in the west before reaching the Periyar Lake.

The Mullaperiyar dam is constructed at the confluence of the Periyar and Mullayar to create the Periyar Thekkady lake and reservoir, as well as the Periyar National Park. The area belonging to Tamil Nadu in the Periyar basin is located far down the river from the Mullaperiyar Dam site. This area is drained by the tributary Nirar, which is diverted to Tamil Nadu as a part of inter-state Parambikulam-Aliyar Project (PAP) agreement.

From Periyar Thekkady lake and reservoir, some water is diverted eastwards to Tamil Nadu via a tunnel. The diverted water, after power generation, is let into the Suruliar river (a tributary of the Vaigai River) thereby resulting in an inter-basin transfer of water. Downstream of the Mullaperiyar dam, the Periyar continues to flow northwestward for 35 kilometres (22 mi) through Vandiperiyar, Elappara and Aiyyappankoil to the Idukki reservoir formed by the Idukki, Cheruthoni and Kulamavu dams. From there, it flows northwestwards and then westwards. At Aluva, the river bifurcates into the Marthandavarma and the Mangalapuzha branches. The Mangalapuzha branch joins Chalakudy River and empties into the Lakshadweep sea at Munambam, and the Marthandavarma branch flows southwards, through the Udhyogamandal area and joins the Cochin backwater system (part of Vembanad Lake) at Varapuzha.

Anamudi (2,695m) is the highest point of the Periyar basin.^{[citation needed]}

Tributaries

Its major tributaries are:

• Muthirapuzha River
• Mullayar River
• Cheruthoni River
• Perinjankutti River
• Edamala River

Minor tributaries are: Muthayar, Perunthuraiar, Chinnar, Cheruthony, Kattappanayar

Although the Chalakudy river in strict geological sense is a tributary of the Periyar, for all practical purposes it is treated as a separate river by Government and other agencies. Chalakudy river itself has a catchment area of 1,704 km², with 1,404 km² in Kerala and 300 km² in Tamil Nadu.

Hydro-electric projects

Idukki Dam across the Periyar river

The Idukki Dam is the largest hydro-electric project in Kerala and lies on the Periyar. It is the biggest dam of its kind (a concrete, double curvature parabolic, thin arc dam) in Asia and the second-biggest in the world. Its generators have a power output of 780 MW (6 X 130), and generate electricity through the underground facility at Moolamattam, built by an India-Canada joint venture. Power generation at Idukki is minimal during the monsoon. The dam also permits storage of water for the dry summer period when many other reservoirs in the area are low. Since the commissioning of the Idukki project in 1976, tail-race water (between 19.83-78.5 cumecs) has been diverted from the Idukki reservoir through the Moolamattom power station into the Thodupuzha tributary of the Muvattupuzha river.

There are other hydro-electric generation facilities on the river at Pallivasal, Chenkulam, Panniyar, Neriyamangalam and Lower Periyar.^{[citation needed]}

Dams

Aside from its dams used for hydro-electric purposes, the Periyar also has dams called Mullaperiyar, Bhuthathankettu, Mattupetty, Munnar, Cheruthoni, Kulamavu, Irattayar, Edamalayar, Anayirangal and Ponmudi.^{[citation needed]}

Mullaperiyar dam was one of the earliest instances of inter-basin transfers in the peninsular India. While it met the demand for water on one hand, it led to the deterioration of water quality downstream of the river. Salinity intrusion and pollution dispersion problems arose in the lower reaches of the Periyar due to non-availability of sufficient quantity of water for flushing. Another inter-basin transfer from the Periyar to the Muvattupuzha river due to the Idukki project has further adversely affected the downstream flow in the Periyar river. Due to all the diversions in its basin, the Periyar has lost 22 per cent of its average flow.

Ecological Significance

South of the Mullaperiyar reservoir, at the source of Periyar River, there is an unbroken stretch of about 350 km² of sheltered, unmodified rainforests within the Periyar Tiger Reserve. These rainforests extend further west into the adjacent Pamba basin within the Gudarakal Forest Range and continue south beyond the Gudarakal Range into the forests of the Achankovil Division. This entire stretch contains about 600–700 km² of undisturbed wet evergreen forests typical of the Western Ghats. The forests on the upper reaches of Periyar are mostly inaccessible and is one of the least disturbed evergreen forests left in the Western Ghats.

Thattekad Bird Sanctuary, one of the important bird sanctuaries of India, is an evergreen low-land forest located between the branches of Periyar River. It has a rich and varied birdlife. Several species of birds, both forest birds as well as the water birds visit the sanctuary. Dr. Salim Ali, India's greatest ornithologist, once described this tiny, 25 km² bird sanctuary, located about 60 km north-east of Kochi, as "The richest bird habitat in peninsular India".

Periyar is one of the six major rivers flowing into the Vembanad lake. Vembanad Kol Wetland was included in the list of wetlands of international importance, as defined by the Ramsar Convention for the conservation and sustainable utilization of wetlands. It is home to more than 20,000 waterfowls in India - the third largest such population in India.

Pollution

The lower reaches of the Periyar are heavily polluted. Industries in the Eloor industrial zone discharge waste into the river. Greenpeace India describes the lower Periyar as "a cesspool of toxins, which have alarming levels of deadly poisons like DDT, endosulfan, hexa and trivalent chromium, lead, cyanide, BHC."