Despite marked growth in its irrigated area over the last few decades, the Asian region has not enjoyed the full-scale benefits of irrigation mainly due to inadequacy and insufficiency of on-farm irrigation facilities and lack of knowledge about and enthusiasm for irrigation management among beneficiary farmers.
In fact, the irrigation efficiency level is still rather low at 30-40%, and, as a result, the ratio of actual irrigated areas to planned irrigable areas is also low, especially in large-scale irrigation projects.
In this context, it is now commonly recognized that to improve and upgrade the level of irrigation efficiency, farmers'active participation in on-farm irrigation management through water users'associations for irrigation is essential. Several governments in Asia have recognized this fact, and the number of water users' associations has markedly increased over the last 10-20 years. In many cases, however, most of the water users' associations are still in their infancy, and some do not function fully.
The purpose of this report is to address the actual situation and mainconstraints of water users'associations in Asian countries from the technical, financial, and socio-economic viewpoints.

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A mathematical model was formulated and applied to screen water resources projects and to generate alternative river basin development plans. The water resources projects in the river basin consist of reservoir construction, hydropower energy production, irrigation development, and municipal water supply. An optimization technique of mixed integer program ming was employed for modeling the project components and a hydrologic system for the river basin.During the solution process, some problems were encountered; these are overcome by fully taking advantage of the optimization technique. The model solutions proved that the model is capable of generating alternative development plans according to capital availabilities of investment on water resources projects. Modifications to the model formulation are proposed taking into account the problems encountered in the solution process.

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