Abstract
Groynes are recognized to have role of preventing bank erosion because they act as flow resistance and decrease velocity near banks. In general, water surface is elevated under larger flow resistance. However, if groynes are installed, river bed at the main channel part is scoured. So, groynes has those two opposite effects on affecting water elevation. Interaction between those two opposite effects seem to have key factor for determining water level though such features have not yet been fully discussed. In this study, we try to clarify the effects of groyne interval on flow resistance by both experimental and numerical approaches under fixed bed condition. The results showed that the apparent roughness changes considerably according to the groyne interval and it takes a peak at a certain value of the aspect ratio. It is also shown that the structure of vortex between groynes can be classified into three different types, which also have close influence of determining flow resistance due to groynes.
