POTENTIALITIES FOR RE-USE OF DRAINAGE WATER IN DOWN STREAM OF YELLOW RIVER BASIN; SIMULATIONS FOR BOJILI IRRIGATION DISTRICT USING SWAP MODEL

摘要

With a view to assess the potential for re-use of drainage water for sustainable production of crops in the down stream of Yellow river basin, water and salt balances were analyzed with the transient moisture-solute flow model SWAP. Initially, a standard set of irrigation scenarios were tested using multiple-year meteorological data (1990-97) as required for the model and the soil and crop data from Bojili irrigation district. Predictions show that maize yields can be sustained with the re-use of saline drainage waters having salt contents up to 4 mg cm"3 whereas the adverse impacts of salts even at 2 mg cm"3 could be predicted on wheat right from the first year. As sufficient irrigation supplies are available during maize growth and deficit are expected during wheat season only, the scenario of utilising only surface waters during maize and drainage waters during wheat growing season was also tested. Such an option was found to have slight edge over continuous use of drainage waters. Major interest of simulations was to predict long-term build up of salts in soils. Predictions demand for the restricted use of drainage waters may be only up to < 3 mg l'1 salts. Since the surveys on water quality of drainage waters show that the most of waters fallwith in this category, indications are that re-use options can considerably augment the surface water supplies for irrigation. However, social-economic-water conveyance constraints and the drainage policy need are to be precisely understood before suchinitiatives are undertaken.