Reservoir sedimentation is one of the most important problems being faced by many existing Irrigation projects around the world. Rapid silting up of the reservoirs well before completing their useful life has drastically reduced their storage capacity. Reduced storage capacity means less water to lesser command areas resulting in the wide gap between irrigation potential created and irrigation potential utilized. This further lowered the food production and the overall economy of the region.
There are two kinds of measures available for tackling this problem. One is curative and the other is preventive. Curative measures include physical removal of accumulated silt from the reservoir by dredging. While this could be a feasible option for small scale reservoirs, huge costs are required in the case of large reservoirs meant for irrigation purposes. The second option of prevention of reservoir sedimentation involves studying land use pattern that causes silting and taking appropriate biotic and non-boitic measures to reduce generation and transport of silt in to the reservoirs. This concept has come to be known as ‘Catchments Area Treatment’.
In this method, the crucial steps are identifying the most vulnerable areas of sediment generation in the catchment of a reservoir and suggesting various measures which can be taken up at required locations so that little silt is generated in the basin. This helps the reservoir to function till its full designed life. Obviously this requires collection of huge quantity of data pertaining to various characteristics of the catchments such as land use, land cover, geology, topography, soils, geomorphology, slopes, existing agronomic practices.
Conventional methods of collecting data of such nature and magnitude prove to be cumbersome and time consuming. Remote sensing with its synoptic view, multi-spectral, and multi-date coverages of the Earth''''s features provides necessary inputs from the scale of a ‘watershed’ to the ‘whole of a river basin’ in different thematic layers required. The catchment area then can be graded into different classes of silt proneness using empirical numerical models such as Universal Soil Loss Equation (USLE).
Suitable agronomic, structural, land use and soil conservation practices are adopted that help reduce transport of silt in large quantities into the dams. Many of the Governments existing soil & water conservation, afforestation programmes can be integrated into the Catchment Area Treatment projects for effective implementation. In many countries, these form part of Environmental Impact Assessment (EIA) and Environmental Management Plans (EMP) submitted to their governments, before a new irrigation project is taken up for construction.