| Abstract
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An approach for obtaining the optimal design of level basin irrigation systems based upon the maximum net benefit was developed. Zero-inertia simulation results of Clemmens and Dedrick were used to establish the relationships between DU and the design variables, and flow depth and the design variables. An analytical soil water stress model was developed that was used to simulate the daily actual evapotranspiration for corn. The relative corn yields were estimated by the Jensen multiplicative yield model. Relating the cost, income and appropriate constraints to the design variables, a maximization of the net benefits problem was formulated. A simulation procedure was used to obtain the optimal designs for a clay loam soil and a fine sandy loam soil, for a field of 32.36 ha. The optimal soil water depletion, DU, basin length and basin width of 50 percent, 83 percent, 339 m and 198 m, respectively, for a clay loam soil and 70 percent, 73 percent, 131 m and 132 m, respectively, for a fine sandy loam soil were obtained. The net benefit obtained from a fine sandy loam soil was 23 percent of that from a clay loam soil. The near-optimal DU (usd\geusd90 percent of maximum net benefit) ranged from 70 to 90 percent for a clay loam soil and from 68 to 79 percent for a fine sandy loam soil. Sensitivity analyses showed the changes in net benefits (USusd) of about 251, 97, 94, 27, 18, 16 and 6 for one percent change in crop price, available flow rate, cost of water, cost of levee construction, cost of ditch construction, cost of labor, Manning's n and cost of ports, respectively, for a clay loam soil. For a fine sandy loam soil, the changes in net benefit (US\usd) were about 224, 106, 97, 43, 38, 17, 16 and 10 for one percent change in crop price, cost of water, available flow rate, cost of levee construction, cost of ditch construction, Manning's n, cost of labor and cost of ports, respectively. For a given soil, the net benefit and design variables are more sensitive to underestimation than overestimation of intake rates.
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