Installation and adaptive management of T-shaped and L-shaped spur dikes to control bed deformation and diversify physical environment in rivers

Abstract This study concerns a method to install spur dikes in the Yodo River, for the purpose of bed deformation control and diversification of physical conditions around the spur dikes. The effects on the physical conditions around the installed spur dikes are evaluated, based on numerical analysis and field survey. The numerical analysis results show that, by installing spur dikes with a focus on hydraulic conditions when not forming sand bars, sediment deposition is suppressed in the main channel. The field survey results demonstrate that sediment deposition in the channel is also suppressed. By installing the spur dikes, some physical conditions around the installed spur dikes can be diversified. By installing spur dikes using large movable sandbags and changing the height of them after several years for the purpose to maintain the effect of the spur dike installation longer as adaptive management, it is possible to maintain diverse bed material conditions for a long period. (For example, by changing the height of the spur dikes 0.3 m lower, about 0.5 m bed degradation is produced downstream of the spur dikes at most.) As a result, spur dike in case 8 (shape(c), height 0.7m from average water level) is better for the present. After several years, changing the height of the spur dikes would be better.