Kosasthalaiyar River, also known as Kortalaiyar, is one of the three rivers that flow in the Chennai metropolitan area. The 136-kilometre (85 mi) river originates near Kaveripakkam in Vellore District and drains into the Bay of Bengal. Its northern tributary Nagari river originates in Chitoor district of Andhra Pradesh and joins the main river in the back waters of Poondy dam. Its catchment area spreads in Vellore, Chitoor, North Arcot, Thiruvallur and Chennai districts. It has catchment area in North Arcot District with a branch near Kesavaram Anicut and flows to the city as Cooum River and the main Kosasthalaiyar River flows to Poondi reservoir. From Poondi reservoir, the river flows through Thiruvallur District, enters the Chennai metropolitan area, and joins the sea at Ennore creek. There are two check dams across the river at Tamaraipakkam and Vallur. The excess discharge in the river is controlled by the Tamarapakkam Anicut located across the river in the downstream of Poondi reservoir. Vallur Anicut is a small check dam constructed near Minjur across the river to control water levels and feed irrigation channels in the area. It flows to a distance of 16 kilometres (10 mi) in the Chennai metropolitan area. The total catchment area of the river is 3,757 kilometres (2,334 mi), and the bed width ranges from 150 to 250 metres (490 to 820 ft). The discharge capacity of the river is 110,000 cubic metres per second (3,900,000 cu ft/s), and the anticipated flood discharge capacity is about 125,000 cubic metres per second (4,400,000 cu ft/s).
Every year, whenever the floodgates of Poondi reservoir are opened, a considerable volume of water gets drained into the sea through the Kosasthalaiyar river near the Ennore creek.
In 2011, the Water Resources Department (WRD) initiated the tendering process under the Irrigated Agriculture Modernisation and Waterbodies Restoration and Management (IAMWARM) project to rejuvenate nearly 200 lakes falling under Kosasthalaiyar river sub-basin. The department also proposes to construct groynes to reduce formation of sand bars near the mouth the river.
In May 2012, the Water Resources Department (WRD) planned to construct a check dam across the river near Bandikavanur village in Tiruvallur district, about 30 kilometres (19 mi) from Chennai, at a cost of ₹ 300 million. The Bandikavanur check dam, to be constructed about 500 metres (1,600 ft) upstream of the Karanodai bridge on Chennai–Kolkata National Highway, would be constructed at a height of 6.3 metres (21 ft) across the nearly 300-metre (980 ft) wide river. The check dam would recharge the water table at a radius of 10 kilometres (6 mi).
- "Check dam to meet city's needs". The Hindu (Chennai: The Hindu). 26 April 2012. Retrieved 18 May 2012.
- Session-3 River and Drainage System in CMA
- Lakshmi, K. (10 November 2011). "Life set to flow back to 200 lakes". The Hindu (Chennai: The Hindu). Retrieved 13 Nov 2011.
- Lakshmi, K. (3 December 2011). "WRD plans groynes". The Hindu (Chennai: The Hindu). Retrieved 4 Dec 2011.
- Lakshmi, K. (16 January 2013). "One check dam to save many litres of water". The Hindu (Chennai: The Hindu). Retrieved 18 Jan 2013.