Periyar River

thumb|Periyar river in Monsoon 2025 at Abhayaranyam Kaprikkadu Ecotourism

The Periyar (, meaning: big river) is the longest river and has the largest discharge potential in the Indian state of Kerala. It is one of the few perennial rivers in the region and provides drinking water for several major towns. The Periyar is vital to the economy of Kerala because it generates a significant proportion of Kerala's electrical power via the Idukki Dam and it flows along a region of industrial and commercial activity. The river also provides water for irrigation, domestic water use, and supports a rich fishery. Due to these reasons, the river has been named the "Lifeline of Kerala". Kochi city, in the vicinity of the river mouth, draws its water supply from Aluva, an upstream site sufficiently free of seawater intrusion. Twenty five percent of Kerala's industries are along the banks of the Periyar. These are mostly crowded within a stretch of in the Eloor-Edayar region (Udhyogamandal), about north of Kochi harbor. The state of Kerala asserted during the hearings on the Mullaperiyar Dam issue in the Supreme Court of India that the Periyar originates in Kerala, flows entirely through Kerala and joins the sea in Kerala. This was also admitted by the state of Tamil Nadu in the court. Periyar originates at the southeastern border of Idukki district. The source of the river lies in the remote forests of the Periyar Tiger Reserve. The river originates from Chokkampatti Mala, a peak on the southern boundary of the Periyar Tiger Reserve.

Course

In its early course, the river flows in a narrow north sloping valley starting from the Chokkampatti hills and extending north about , with a number of sharp lateral ridges running down to it from east and west. After flowing from its origin and on reaching Mount Plateau at its eastern end, it is joined by the west-flowing Mullayar—an important tributary—at Mullakudy. During this journey the Periyar traverses 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.

The main Periyar below the Idukki reservoir flows due north parallel to the western edge of the Idukki plateau and is joined by the Perinjakutty from the east and Muthirapuzha from the north. After the confluence with Muthirapuzha, the river flows northwestwards and enters Ernakulam district at Neriamangalam. It is joined by its major tributary, the Idamalayar, upstream of the Bhoothathankettu barrage. After receiving the waters of the Idamalayar river, the Periyar flows west along the midlands of Ernakulam district.

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, again dividing into two near Kunjunnikkara island, going through the Udhyogamandal area and finally draining into the Cochin backwater system (part of Vembanad Lake) at Varappuzha. The Vembanad backwaters are connected to the Lakshadweep Sea at Cochin and Kodungallur.

Basin

thumb|right|300px|[[Anamudi peak, on the right, is the highest point of the Periyar basin at .]]

The Periyar basin spreads over an area of , most of it in central Kerala. It lies between latitudes 9°15’30"N and 10°21’00"N and longitudes 76°08’38"E and 77°24’32"E. The river drains parts of Idukki, Ernakulam and Thrissur districts in Kerala The basin has an inverted "L" shape with a maximum width at the intersection. The length-width ratio is 6:1. Most of the streams flow in deep gorges with steep valleys along the highlands of the basin. to Varapuzha and Munambam.

Anamudi, at the highest peak in South India, is the highest point in the basin.

Source – Southern Cardamom Hills

The southernmost part of the Cardamom Hills i.e. the source of Periyar River is a narrow valley extending south of Kumily. This is the southern extreme of the Periyar basin. It is less than wide and is about long. The most industrialized zone of Periyar lies in this part of the basin between Angamaly and Cochin, with over 50 large and medium scale industries. The Edayar branch of Periyar caters to the needs of these industries.

Dams

Hydro-electric projects

thumb|right|300px|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

There are other hydro-electric generation facilities on the river at Pallivasal, Chenkulam, Panniyar, Neriyamangalam and Lower Periyar.

Reservoirs

The important reservoirs in the Periyar basin within Kerala are Bhoothathankettu, Idamalayar, Lower Periyar, Mattupetty, Anayirangal, Kundala, Ponmudi, Kallarkutti, Idukki (formed by construction of three dams—Idukki, Cheruthoni and Kulamavu), Sengulam, Kallar, Erattayar and Mullaperiyar. The dams falling within Tamil Nadu in the Periyar basin are the Upper Nirar Weir and the Lower Nirar Dam. These dams help divert water from the Nirar tributary of Periyar to the adjacent Sholayar basin.

Irrigation

The Periyar valley Irrigation project in Ernakulam district envisages the utilization of the tail race discharge from the completed Hydel scheme in the Muthirapuzha tributary of river Periyar together with the controlled release from Ennackal dam constructed by Kerala State Electricity Board under Hydel scheme across the Idamalayar tributary and the dependable run off from the uncontrolled catchment of Periyar river, for irrigating an area of of land lying on the left bank of Periyar river through a network of canal system and controlling devices. The scheme consists of the Periyar Barrage at Bhoothathankettu with a catchment area of along with a network of canals.

The Parambikulam Aliyar Project (PAP) agreement was conceived to harness and share the waters in the inter-State rivers in Bharathappuzha, Chalakkudypuzha and Periyar basins. Nirar and Anamalayar, tributaries of Periyar are covered under this agreement. Water from these rivers are transferred to the adjacent Sholayar basin as part of the PAP agreement.

Due to all the diversions in its basin, the Periyar has lost 22 per cent of its average flow.

Ecological significance

thumb|300px|Thattekad Bird Sanctuary is an evergreen low-land forest located between the branches of Periyar River

South of the Mullaperiyar reservoir, at the source of Periyar River, there is an unbroken stretch of about 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 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.

The Periyar Tiger Reserve (PTR) is also one of the most ecologically diverse regions in India. The flora of the reserve is very rich and diverse. Out of the estimated 3,800 species of angiosperms of Kerala, 1,966 have been reported from within the reserve. Nowhere in the subcontinent, has such a large number of taxa been reported from an area comparable to that of the PTR. Apart from this, the reserve also contains an estimated 323 species of birds, 38 species of fish and 44 species of reptiles.

The Periyar plateau forms a part of the Project Elephant Reserve 10, which also includes the Agasthyamalai-Mahendragiri hills. The landscape on the Periyar Plateau portion of Elephant Reserve 10 maintains the most intact elephant range in Southern India. This area is believed to harbour about 2,000 elephants and is one of the potential landscapes for the long-term conservation of the species. This population is genetically more diverse and distinct from the much larger elephant population further north in the Ghats. This region is also known for its rich biodiversity. On the other hand, the landscape has also witnessed a variety of developmental activities including commercial plantations, hydroelectric and irrigation projects and other forms of infrastructural development that impede the movement of elephants.

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, bird sanctuary, located about 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 use of wetlands. It is home to more than 20,000 waterfowls—the third largest such population in India.

Religious and cultural significance

There are several places of religious significance along the banks of the Periyar. The famous Aluva Sivarathri festival is celebrated on the banks of the Periyar River in Aluva. The temple festival is conducted every year on Sivarathri day of the Kumbham month of Malayalam calendar. The Siva temple on the sand bank of Periyar River throngs with devotees every year on Mahasivarathri day.

Kalady is a town located on the banks of the Periyar river. It is the birthplace of Sri Adi Shankara, the Hindu philosopher who consolidated the doctrine of Advaita Vedanta. Kalady started featuring in the spiritual map of India only after its rediscovery in the late 19th century by the then Shankaracharya of Sringeri and the subsequent consecration of a temple for Sri Adi Shankara in 1910.

Located from Kochi, the Malayatoor Church is situated atop the high Malayatoor Hill. The church is dedicated to St. Thomas, who is believed to have prayed at this shrine. One of the most important Christian pilgrim centres in Kerala, it attracts devotees in very large numbers not only from Kerala but also from the neighbouring states. This famous church is situated at Kurisumudi, a verdant hill in the Western Ghats girdled partially by the Periyar (river). The Church has a life-size statue of St. Thomas and the imprint of the feet of the Apostle on a rock. This shrine has now been accorded an international pilgrimage station.

Environmental issues

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". Several studies have pointed out that the riverbed has deposits of heavy metals like lead, cadmium, mercury, chromium, nickel, cobalt and zinc and the ecosystem of the river has many dead zones. Some of the major recommendations are ensuring zero effluent discharge from the industrial units in the Eloor-Edayar stretch and zero emission from companies. Pollution of the river and surrounding wetlands has almost wiped out traditional occupations, including fishing and farming.

Illegal sand mining

thumb|250px| Sand mining

Illegal sand mining from the Periyar is another major environmental issue. Studies have pointed out that the quantity of sand being mined from the Periyar is at least 30 times the actual quantity that can be taken out without causing damage to the river’s environmental system. In the Periyar river basin, land sand mining is widespread in the plateau region in the highlands. Mining of sands from these areas impose severe environmental problems to the river basin environment.

Environmental protection efforts

Efforts have been made to prevent soil erosion on the banks of river periyar at Aluva Sivarathri manappuram (sand bank) through afforestation programs headed by renowned environmentalist, Prof. S. Sitaraman, since 1992. The Aluva Environmental Protection Forum started by Sitaraman and others have played a pivotal role in the prevention of illegal sand mining and water pollution in the lower reaches of the river.

Dispute

The control and safety of the Mullaperiyar dam on the river and the validity and fairness of the corresponding lease agreement have been points of dispute between Kerala and Tamil Nadu states. Intertwined with this, there is a dispute as to whether the Periyar should be classified as an inter-state river or not. Kerala states that the Periyar is an intrastate river since no part of it flows through Tamil Nadu. The river originates in Kerala, flows entirely through Kerala and joins the Arabian Sea in the Kerala. Although these facts have been admitted by Tamil Nadu, it counters that the Periyar should be considered an inter-state river since a part of the catchment of the river lies in Tamil Nadu. It has also cited a 1950 report signed by the then Kerala state irrigation minister V R Krishna Iyer recording that Periyar is an inter-state river since some of its drainage area lay in Madras state. Essentially, the dispute over the status of the river comes down to the definition of an inter-state river, with Kerala supporting the definition to be according to the course of the river,