An integrated approach to irrigation system assessment and management of selected projects in Tha Chin Basin, Thailand

This study evaluates the sustainability of two irrigation projects located in Tha Chin Basin, Thailand, namely Kamphaengsaen operation and maintenance project (KPP), and Phophraya operation and maintenance project (PPP). It focuses on the development of irrigation sustainability index (ISI) based on key indicators and provides a basis in formulating management options for improving irrigation sustainability. The assessment of the two projects is based on the investigation of sustainability indicators. These indicators are analyzed using principal component analysis (PCA), whereby dominant indicators influencing irrigation sustainability are identified. Afterwards, the indicators are weighted and computed to obtain an irrigation sustainability index (ISI). The index is used to classify the sustainability of each irrigated area (zone) into five levels. The results for KPP show that net farm income, awareness on irrigation water use, matching of farm operations with RID water delivery, and field application ratio are the major sustainability indicators. Among the 27 zones in KPP, six zones show very low sustainability level, five zones are low, 11 zones are medium, four zones are high and one zone is very high. Four key indicators are found in PPP, which include perception of drained water quality, satisfaction on adequacy of water distribution, flow ratio, and net farm income. Among the 11 zones in PPP, there are four zones that show very low sustainability level; one zone is low, four zones are medium, one zone is high and another one zone is very high. Based on the results of the study, it is evident that each zone or project can be vulnerable to different causal indicators influencing sustainability of irrigation system so there is a need to improve the sustainability of some zones in the two projects. Therefore, this study adopts a modified Driving forces-Pressures- State-Impacts-Responses (DPSIR) framework to describe the links among the indicators influencing sustainability of irrigation system, status and impacts of problem and to formulate management options. The common management options to both projects are establishment and strengthening of water user groups, provision of support and promotion of mutual help, establishment of rules and regulations on water use and collection of irrigation water fee. The specific management strategies for KPP are improvement and flexibility of water distribution schedule. Legislation of agricultural wastewater law and improvement of water delivery plan on the other hand, are the specific management options for PPP. The key indicators identified and the irrigation sustainability map developed based on ISI can be used to formulate management strategies for some zones in the basin which are showing low sustainability levels. It is envisioned that the methodological approach adopted in this study for identifying key indicators influencing sustainability of irrigation system and for evaluating and improving irrigation sustainability might be useful to irrigation managers, policy makers, water users and researchers. (Résumé d'auteur)