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 , exiting the Periyar Tiger Reserve and passing through Vandiperiyar, Elappara and Ayyappancoil to the Idukki reservoir formed by the Idukki, Cheruthoni and Kulamavu dams. The Idukki dam is constructed across the Periyar river on the famous Idukki gorge formed by the Kuravan and Kurathi hills. 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. 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