The Nilgiris as a region can be divided into three strata of upper, middle and lower altitudinal zones. Each has a distinct vegetation and supports a variety of life forms and activities.
The Nilgiris district can be divided into four basins
Moyar Basin and its 24 rivers – draining mainly into the Bhavani reservoir as water supply for irrigation and drinking water in Tamil Nadu
Bhavani Basin and 26 rivers – draining again to the Bhavani reservoir along the district boundary and onwards again into the Tamil Nadu plains. Both the above basins finally feed into the Cauvery river basin.
Kabini basin and its five major rivers drain into Karnataka
Chaliyar basin and its eight rivers feed into Kerala
Inspite of 1800-2000 mm annual average rainfall, the number of rainy days has reduced drastically. Erratic and unpredictable rains have changed the water budget and utilization pattern. Water enterprises, such as private water tankers have boomed in this district.
There is a crucial linkage between Shola patches (endemic montane forest-type which occur in this region) and water resources availability. Wherever Shola forests exist, existence of water source is assured.
Large Government Water Schemes of the TWAD Board basically tap springs and infiltration systems and not ground water resources. Wells are built in swamps and marshes so that percolation from springs around the well also take place. Feeder pipelines from other springs are also brought to the well. These springs are found in various altitudes. Local land use adjacent to these water bodies is critical in maintaining year round water flow. Several spring sources have dried up or the flow has drastically reduced due to land use changes or development works (revetment walls, road enlargement, check dams, etc.). Encroachments (very common) have destroyed water bodies as they have been converted for agriculture or tea thus blocking spring routes. In marshy environments, it is important to keep the passage of flow open – this is the key to wetland management, but unfortunately decision-makers perceive these areas as vacant land for further development works.
There is field data to show that rains are failing both as the annual average and the number of rainy days. This has severe negative consequences on this fragile hill district – the livelihood of people, the plantation & agriculture economies and the ecology.
