STUDY OF FLOOD CONTROL EFFECTS DUE TO RETARDING BASIN AGAINST EXCESS FLOOD -Case study of Ara River 1^st retardng basin and Ichinomiya River 2^nd retarding basin-

Abstract

 This study aims to compare flood control effect of two retarding basin against excess flood by field surveys and flood simulation. Field sites were chosen at Ichinomiya River 2^nd retarding basin and Ara River 1^st retarding basin which were flooded due to big typhoons in 2019. The results showed that the Ichinomiya River 2^nd retarding basin showed the limitation of flood control function under huge flood like typhoon no. 21 even though the height of overflow weir was changed. The Ara River 1^st retarding basin showed the flood control function in the large flood due to typhoon no. 19. Also noted that selecting appropriate heights of the overflow weir is important to reduce flood discharge and water level in the downstream reach of rivers.