This study was conducted to assess and optimize the conveyance performance of major irrigation systems in the case of the NIA-Magat River Integrated Irrigation System in the Philippines. Options Analysis in Irrigation System (OASIS) was used to evaluate and optimize the conveyance efficiency of the system. Management and modernization scenarios were undertaken in the irrigation system assuming that the rehabilitation projects exerted efforts on improving efficiencies and reduced losses in the conveyance and distribution systems. Based on the results, the actual condition of the irrigation system as the reference of improvement will have 1,365,759 million cubic meters diversion supply from MARIIS and Baligatan diversion dams. Having been improved from 76% of conveyance efficiency to 95% assumed result of the improvement measures, approximately 84,303 million cubic meters or 6% increase from the actual diversion requirement can be realized. With every 1% increase in conveyance efficiency, there will be approxim
