Effectiveness assessment of reservoir projects for flash flood control, water supply and irrigation in Wangmo Basin, China.

Most flash floods in countries around the world occur in poor rural mountainous areas and typically cause more casualties and economic losses due to monitoring challenges and early warning difficulties. In mountainous regions, reservoir projects are a very effective measure for mitigating the risk of flash floods and can also be used for water supplies and irrigation, but there is a lack of research on the comprehensive benefit assessments of reservoirs. In this paper, we simulate the inundation extents of flash floods for the Wangmo Basin in China, where flash floods frequently occur, under different return periods using the HEC-HMS (HEC-Hydrologic Modelling System) model and FLO-2D model and compare the resulting housing losses with and without reservoirs. The results indicate that using dam and reservoir operations for flood control in the Wangmo River Basin decreases the flooded housing area in the county centre by approximately 12.9 %-30.2 %, which results in housing losses reductions of 19.7 %-45.7 %.These dams and reservoirs will begin to make a profit during the 38th year of operation, and the average annual net benefit reaches 101.76 million RMB in 50 years, which is equivalent to 1.43 % of the GDP of Wangmo County; the net benefits of flood control, water supply and irrigation accounted for 0.4 %, 1.0 % and 0.03 %, respectively. Priority should be given to planning and building these water conservation measures to help these poor mountainous areas. The construction of dams and reservoirs can contribute to decreasing losses in poverty and disaster-prone regions. The effectiveness evaluation framework for dams and reservoirs presented in this study can be applied to other mountainous basins for flood control and local development.