A methodology and computer model is developed to determine economically optimum closed subsurface drainage systems in irrigated areas. The model maximizes net benefits, by comparing profit driven by crop yield to drain system cost and selects an optimum drain layout. The optimization methodology used, is the SIMPLEX method, Neider and Mead. The SIMPLEX model was linked to the subsurface drainage model DRAINMOD Skaggs [10], and to the surface hydraulic model KINE, Walker and Skogerboe[14]. The selected optimum drainage system maximizes the difference between total revenue, and the total cost of installation, operation and management of a particular drainage system. The optimization sub-program provides a workable and simple procedure for optimizing water management simulation models
