Periyar river basin.
Periyar ( meaning: big river) is the longest river and the river with 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 of utmost significance to the economy of Kerala. It generates a significant proportion of Kerala's electrical power via the Idukki Dam and flows along a region of industrial and commercial activity. The river also provides water for irrigation and domestic use throughout its course besides supporting 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 river Periyar. These are mostly crowded within a stretch of 5 kilometres in the Eloor-Edayar region (Udhyogamandal), about 10 kilometres north of Cochin harbor.
The Periyar 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 and 114 square kilometres (44 sq mi) is in Tamil Nadu. Its source lies high in the Western Ghats