DYNAMICS OF FLOOD FLOWS AND BED VARIATIONS IN RIVER SECTIONS REPAIRED TO SHIP-BOTTOM SHAPED CHANNELS FROM COMPOUND CHANNLS

摘要

Compound channels have caused some undesirable problems on flood controls and river environments in recent years. In order to deal with these problems, one of the authors has proposed that the ship-bottom-shaped channel is a desirable cross-section of rivers for both flood controls and river environments. The Onga River in Japan challenged to change a part of channel sections to ship-bottom shaped channels from compound channels in the view of river environments. However, there have been no ideas how much the ship-bottom shaped channels improve the discharge capacity and channel stability against large floods. A large flood occurred in 2010 after completion of the ship-bottom shaped channel in the Onga River. In this study, effects of river improvements to ship-bottom shaped channels were investigated and clarified by comparing observed data and flood computation results. Velocity distributions of flood flows are improved and longitudinal bed variations decreased markedly in the ship-bottom-shaped channels compared to compound channel.