Abstract
In the downstream tidal basin of the Kiso River, large-scale groins of about 200 m long were constructed and diverse river environment with pools and creeks was created by scouring, sedimentation and foresting in intermediate areas of groins. The scouring zone downstream of large-scale groins played an important role on creating and maintaining embayment water zone. In this study, we examined the scours formed behind the large-scale groins in the Kiso River by field observations using ADCP and other observation equipment set downstream of the groins. Then the mechanism of creating downstream scour was investigated by 2-D and 3-D numerical analyses in considering the effects of groins' lengths on the scouring. As a result, we revealed that offshore-heading streams occur behind the groins during ebb tide and flood event and it may cause the scouring downstream of the groins.
