TRIAL DESIGN OF A RUNNING WATER TYPE RETARDING BASIN FOR A CLOSED FLOODPLAIN IN THE UPPER REACH OF THE OMONO RIVER

Abstract

 By concerns about an increase in excess floods due to climate change, there is a growing need to increase the flood detention function in river upstream area. On the other hand, closed floodplains, which are common in the upper reaches, are mainly used as rice paddies, such lands possibly to be used as temporary "running water type retarding basins" during excess floods. In this study, we designed a running water type retarding basin at a closed floodplain in the upper reaches of the Omono River in Akita Prefecture by assuming that a tentative levee development plan with a flood flow rate of 2800 m³/s has been completed. A numerical simulation about its performance of retarding basin against an excess flood of 4400 m³/s showed that it is possible to reduce the peak flow rate of the excess flood by approximately 12%.