RID had studied the FS, EIA, and SEA (Strategy Environmental Assessment) of the Mekong-Loei-Chi-Mun Water Management by Gravity in the northeastern region and it was completed in July 2012. It can be concluded that the estuary of the Loei River should be improved; diversion canal dredging, diversion tunnel boring, and distribution canal construction for irrigation and flood prevention should be carried out. The project can distribute water to most of the agricultural lands in Mekong-Chi-Mun basins, calculating as a total irrigation area of about 30.64 million rai. The study focused on the development model in Phase 1 and sought out the appropriate alternative for development, considering the budget, break-even point, development distribution, problems, urgent need and hydraulic flow of diversion tunnel in Phase 1 by using 3D hydraulic model and physical model based on the diversion system structure, starting from the Mekong River, Loei estuary (improving Loei estuary, dredging diversion canal and drilling diversion tunnel) to the tunnel exit.