A Study on the Application of Cascade Type Flood Control to the Chikugo River

The efficiency of the "Cascade" method based on a new flood-control concept was verified in a river basin. In recent years, an increase in the frequency and intensity of disaster hazards, such as heavy rainfall, has been observed in Japan, presumably due to global warming. Additionally, environmental preservation in Japan has continued to be respected even after rapid and high economic growth. However, it is extremely difficult to implement large-scale public works because budgets for such projects have been reduced. We therefore recommend the construction of multiple small-scale dams around river basins instead of a single large-scale dam in order to prevent flood disasters and preserve the natural environment. In this study, Cascade-type flood control was demonstrated using numerical simulation in which an upstream dam arranged in a series overflows from an emergency spillway while a final downstream dam is required only to use its normal spillway and never its emergency spillway. The Cascade method should strengthen the flood control capability for the lower reaches of a river, which are generally more important than the upper reaches. This study clearly demonstrated that the Cascade method of flood control is much more effective than the conventional method in the Chikugo River. Additionally, the Cascade method, which combines dams in series and in parallel, is also effective for improving the efficiency of multiple dams operated cooperatively.