SUSTAINABLE WATERSHED PROTECTION IN SAHIBI RIVER - A CASE STUDY

Landuse and land management can significantly affect catchment water yield and peak flows from a given catchment, principally by the modification of the infiltration rate and surface storage. Streamflow in catchment is a variable that can range widely. It is correlated with rainfall and antecedent soil moisture. In tropical areas flow in small agricultural catchment often ceases in the dry season, while in the wet season large flows are recorded following heavy rainfalls. High levels of vegetative cover in agriculture areas protect the soil from raindrop impact and create conditions favourable for infiltration. At the same time vigorous growth increases evapo- transpiration rates and depletes soil moisture, and therefore may reduce the volume of ground water recharge, and hence catchment baseflow levels. The low and variable rainfall severely limits crop production. Runoff irrigation is reported to increase and stabilise crop production in arid and semi arid regions. Waterharvesting has shown to be an inexpensive and effective way of increasing biomass in many arid and semiarid regions. In runoff irrigation, the surface runoff water is guided into field reservoirs or soil conservation structures. The standing water is allowed to percolate deep into the soil profile, increasing the plant available soil moisture reserves. Crops, which are rainfed, utilise this additional water to give higher yields.In 1972-73 All India Co-ordinated Research Project on Dryland Agriculture first attempted to integrate cropping systems with soil conservation measures on a watershed basis. Success of these experiments brought Rainfed Farming Systems in centrestage. Watershed management emerged as a conservation model to prevent land degradation by reducing soil and water erosion, and provide sustainability to the Agro-Ecological systems. This has since grown as one of the most successful and popular programme. India is operating probably the world's largest programme of watershed management for dry land areas. An Integrated Watershed Management project for Sustainable Watershed Protection in the Sahibi River catchment was started in 1978 and completed in 1998. Detailed analysis was possible due to the collection of large database on sediment flow in 17 selected watersheds for their entire period of treatment covered between 1983 to 1997. Data was recorded prior to, during and after the execution of works. Time series data so collected was the basis for evaluation of effectiveness of the programme.