2002 Volume 8 Pages 261-266
The Ninoarate weir is constrncted at a junction between the Asahi River and the beginning of the Hyakken River in Okayama City. This weir was severely damaged due to local scour under flood flows on October 18th, 1998. The purpose of this study is to clarify the mechanism of the local scour that occurred downstream of the Ninoarate, which has a broad crest and three culverts in the low water course. The surveying of bed morphology and the boring investigation around the weir were carried out to estimate the local scour depth. Also, the scour profiles caused by the flow of water over the weir and water jets from the culverts were measured using the hydraulic channel model. As a result of the experiments. it was found that the scour depth is governed by the discharge from the culverts. The flow over the weir makes the position of the maximum scour depth shift to downstreain of the channel. Furthermore, reasonable dimensions of bed protection works were proposed to reduce the local scour at downstream of the weir.
