Abstract
Tanks are small storage reservoirs impounding the runoff from monsoon rains to regulate the supply of water mainly for irrigated command areas that are typically less than 200 ha. They account for one-third of the irrigated areas in Tamil Nadu, Karnataka and Andhra Pradesh. Years of neglect and indifference in tank maintenance and management have eroded their functional efficiency and jeopardized their multifarious benefits. In Tamil Nadu, this has resulted in a decline in their contribution to irrigation from 40% in 1995 to 25% in 2000. The modernization of these tanks requires prioritization and investment. Remote sensing technology, with its unique advantages and the latest high-resolution sensors, can provide the information on the agricultural, hydrological and structural conditions of the tank irrigation systems necessary for prioritization. The National Remote Sensing Centre (NRSC) has carried out a study of the Nanjur tank cascade in Tamil Nadu using high-resolution data from the IKONOS satellite during the crop season of 2003-2004. This study demonstrated the use of high-resolution satellite images to obtain an inventory of the different components of a tank irrigation system such as tank bunds, surplus weirs, supply channels and distribution networks. It was also found useful in updating the road-rail network at village level. The 1-m merged satellite data were useful in mapping open wells and minor roads in a tank cascade. The cropping pattern in a tank system can be mapped at cadastral level using these images, which will be useful for micro-level water and agricultural management. The 4-m multispectral image was found to be sufficient for mapping different crops at field level. The high-resolution image also provided information on intrafield variability in crop condition. The reliability and cost-effectiveness of high-resolution images from Indian satellites provide scope for the generation of information for tank system studies as well as for micro-level natural resource management.