From Poondi reservoir, the river flows through Thiruvallur District, enters the Chennai metropolitan area, and joins the sea at Ennore Creek.
Vallur Anicut is a small check dam constructed near Minjur across the river to control water levels and feed irrigation channels in the 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).
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.
[7] 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.
[9] 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.