OPTIMIZATION OF FURROW IRRIGATION SCHEDULES, DESIGNS AND NET RETURN TO WATER

A seasonal furrow irrigation model consisting of irrigation scheduling and kinematic-wave-based hydraulic submodels was modified to incorpor ate an economic optimization submodel. The model used a systematic sim ulation technique to optimize furrow irrigation schedules and designs assuming 80% irrigation adequacy at cutoff time. The irrigation schedu les and designs were optimized for the homogeneous and heterogeneous i nfiltration under the mean and observed ET0 (grass reference crop ET) conditions. The optimal management allowable depletion (MAD) level cha nged with the variation in ET0 condition, and with the consideration o f spatial and temporal (seasonal) variability in infiltration characte ristics. Irrigation design changed with both infiltration conditions a nd MAD level. infiltration variability did not influence the bean yiel d. However, the return to water decreased when spatial variability in infiltration conditions was considered. Using mean ET0 resulted in sli ghtly higher yield and net return to water as compared to using observ ed ET0. A small variation in daily mean ET0 values with respect to dai ly observed ET0 values caused a change in both irrigation schedules an d designs. Therefore, mean ET0 cannot be used to forecast irrigation s chedules and designs at the beginning of crop season. The net return t o water increased (1.7 to 3.6%), and the seasonal inflow, losses, and bean yield decreased in the case of variable interval scheduling (hold ing MAD constant) as compared to the fixed interval scheduling (MAD va ries). (C) 1998 Elsevier Science B.V.