Author(s): N. Tanaka; M. Nemoto; E. Furusato
Linked Author(s): Norio Tanaka
Keywords: Gravel bed; Armouring; Sand supply; Friction velocity; Shear stress
Abstract: This study was conducted for clarifying the turbulent structure, shear stress characteristics, and sand motion in the armoured gravel-bed layer. As the form-induced sublayer by large stones is thick, log-law cannot be applied. Using linear equation for the form-induced sublayer and exponential equation for the interfacial layer as the theoretical model, the vertical profile of double-averaged velocity can be analyzed successfully. Although the spatial-averaged Reynolds stress at the bed was very small by the sheltering effect of large size stones, the sand moved quickly in between the large stones, and transported very slowly in lateral directions in our experiments. When the sand height became a height at which the Reynolds stress equaled the critical shear stress of the sand estimated by single particle size theory, the front of the sand layer moved to the downstream. This indicates the importance in understanding the characteristics of velocity and shear stress inside the armoured layer for supplying sand to downstream of a river.