ABSTRACT
I n t h e past, irrigation and drainage systems were designed as separate and distinct entities and not as a water management system with two interactive components (U.S. Department of Interior, 1993). The irrigation system was designed and a management plan established for the proposed system based on the soils, cropping pattern, and water quality. A value of deep percolation, estimated from the irrigation sys tem design and management, was used to design the subsurface drain age system. The drainage design assumed that all the drainage water was discharged and the midpoint water table height reached the maxi mum value by the end of the irrigation season. No interactive manage ment was assumed to occur between the drainage and irrigation sys tems. In fact, the irrigation management assumed that deep percolation was lost from the system, and the crop was not using water from the shallow groundwater.
