Optimum Use of Water Resources [antikvár]

Preface Nowadays, problems of water resources operation, design, and planning are often solved by a systems approach. This was not so some 10 years ago when we, the authors of this publication, joined the FAO-UNDP Project: Integrated Planning of Irrigated Agriculture in the Varamin Plain, Iran. Our task was to draw up plans for the optimum supply of irrigation water. During our work, we became more and more interested in the systems approach, as we became aware of the complicated economic .^'agronomic, and hydrologie problems involved. A storage dam was under constructiôn in the main river, but as it controlled only a portion of the river's catchment, we were facing the problem of a stochastic supply of surface water. Surface water was a limiting and variable resource, and much more land than could be irrigated was available. The solution therefore had to be sought in the conjunctive use of the surface water resources and those of the groundwater basin. To help" bs-W^ith t^r problem, we developed a computerized groundwater model of the'_basln f-or use as a simulation tool. Although the number of possible plans" for'.ttte^'j oint use of the two water resources is infinite, only a few plans are physically.feasible. A primary objective in such plans is the continued use of the groundwater basin into the indefinite future. The mere development of its resources would not, in itself, solve the region's irrigation supply problem; they must be properly managed as well. The groundwater basin must be operated at a safe-yield constraint level to prevent the inflow of saline groundwater from adjacent areas. That constraint could be released in water-deficient years to maintain the optimum area under irrigation, but any mining of the groundwater must be compensated for by artificial recharge with the excess river flow in spring. Another problem we were facing was the economy of the operation; irrigation water must be supplied at reasonable cost. The costs of providing surface water or groundwater differ; they also differ as to the site in the Plain where water is to be supplied. The idea was therefore born to apply linear programming as a tool to determine optimum solutions of irrigation water supply. The groundwater model could then be used to test these solutions for the impact they might have on the water table.