Noyyal is a –long seasonal river in Western Tamil Nadu, India. It is a tributary of the Kaveri river. The river rises in the Vellingiri hills, a division of the Nilgiri Biosphere Reserve, in the Western Ghats, and flows westwards through the cities of Coimbatore, and Tirupur, before draining into the Kaveri at Noyyal in Karur district. The river basin covers an area of , which consists of of cultivable lands. This stretch has 23 dams and 32 tanks. It's present name refers to the name of the point where it pours into the river Kaveri, changed in 1750 AD. The Noyyal River and its interconnected tank and canal system is believed to have been built by the Chalukya Cholas, as a system of water transport, and storage. This system helped in maintaining unchanged water levels under the ground. Excess water was conveyed to the storage tanks, which also helped in refilling the spring water. After urbanisation, storage tanks were drastically removed and only 11 remained.
From the source, the river valley consists of kankar soil for a stretch of to a depth of . It extends from the origin of the river to the Ukkadam Lake in Coimbatore.
Water storage
The Noyyal River system has an extensive network of canals, and tanks. Surplus water from the river spilled into the canals and were channeled to the tanks, preventing flooding, and was used to replenish the ground water and for utilisation later. However, the system was neglected and the number of functional water bodies has reduced to eleven by 2003. This has had a profound effect on agriculture in the region.
There are two major dams–Orathuppalayam (near Chennimalai) and Aathupalayam (near Vellakoil), which were commissioned with the aim of irrigating about 20,000 acres of land in Tirupur and Karur districts. The Orathuppalayam dam has been decommissioned and acts as effluent storage tank. Another reason for pollution is the huge concentration of textile units in Tiruppur releasing industrial effluents into the river.. Despite several litigation and court orders, which ordered the closure of such units, the river continues to be polluted. The Government of Tamil Nadu announced a project to prevent pollution in July 2018. Alkalinity in the river is more than the permissible amount for drinking water fixed by the Bureau of Indian standards. Several projects have been undertaken to restore groundwater level even after the implementation of Zero Liquid Discharge