Assessment of the process, nature and impact of rehabilitation for development of a moderniZation strategy for national irrigation systems in the Philippines

Data on medium- to large-scale canal irrigation systems in the Philippines suggest that rehabilitation projects were not sufficient to close the gap between actual area irrigated and irrigation service area. This study analysed the underlying details of various rehabilitation and improvement works in three canal irrigation systems to identify an effective approach to close this gap. The findings show that the rehabilitation works generally focused on maintaining the original canals. Canal lining was the most common improvement work. The planning and design process adopted lacked revalidation of design criteria and assumptions used in the original system design. It did not have the benefit of diagnostic assessment studies. No technical assessments of water supply adequacy for proposed projects were carried out. The findings also indicate that the potential for increasing the actual area irrigated lay in augmentation of water supply, reuse of drainage water, use of adjustable gates at major water distribution points and strategic timing of irrigation schedules between tertiary areas to adapt to prevailing hydrological regimes. Consideration of these findings and an increased attention to consistency among available water supply, irrigation demand, physical design of structures and a realistic operational plan can greatly enhance the impacts of the irrigation modernisation plan in the Philippines. Copyright © 2015 John Wiley & Sons, Ltd.