Noyyal River

The Noyyal River rises from the Vellingiri hills in the Western Ghats in Tamil Nadu, southeastern India and drains into the Kaveri River.The river's basin is 180 km (110 mi) long and 25 km (16 mi) wide and covers a total area of 3,500 km² (1,400 sq mi). Cultivated land in the basin amounts to 1,800 km² (690 sq mi) while the population density is 120 people per km² (311/mi²) in the countryside, and 1000 people per km² (2590/mi²) in the cities. The area is known for its scanty rainfall and the development of the Noyyal River Tanks System to hold any overflow from the rains plus the water of the Northeast and Southwest monsoon season was ecologically important. The 173 km (107 mi) long tributary of the Kaveri River filled 32 tanks. These interconnecting tanks held the water flowing from the Noyyal.

Ecology

The township of Coimbatore once was surrounded by the Noyyal river and its canals, tanks, and rivulets. The Noyyal river and its interconnected tank and canal system, believed to have been originally built by the Chalukya Cholas kings, was then an efficient system that provided water transport, storage, and maintained stable groundwater levels. Surplus water from the Noyyal river spilled into the canals and were channeled to the tanks, preventing unwanted flooding. The tanks were a major factor in replenishing the ground water through percolation of the subsoil water. As urbanisation grew, the system was neglected and the number of functional tanks was drastically reduced until only eleven were left. Today the system no longer works and water is scarce. Agriculture has significantly decreased. Lacking irrigation water, lakhs of Coconut trees in the area have dried up.