OPTIMIZATION OF FURROW IRRIGATION SYSTEM-DESIGN PARAMETERS CONSIDERING DRAINAGE AND RUNOFF WATER-QUALITY CONSTRAINTS

The design problem of furrow irrigation systems considering runoff and drainage water quality was formulated as an optimization problem, wit h maximization of net benefits as the objective. A power advance funct ion with an empirically derived relationship between the furrow irriga tion design variables and relative crop yield were used in the formula tion. The generalized geometric programming technique was used to solv e for the optimal values for the design variables that maximized the n et benefits from a furrow irrigation system. The optimal efficiency fo r which the system must be designed under a given set of soil, crop, a nd economic conditions is not known in advance. In the design, the app lication efficiency was not specified a priori. It was an output from the optimal design. The analysis suggested that it might not be econom ical to design surface irrigation systems to achieve a high applicatio n efficiency that is specified a priori. In the absence of environment al degradation problems from irrigation, it may sometimes be profitabl e to design surface irrigation systems to operate at less than the sta ndard application efficiency (55%-90%) that is routinely used in the d esign. Formulation of the design problem as an optimization problem wo uld yield the optimal application efficiency that would maximize the n et benefits to the farmer under any given set of conditions.