Sand Bed Instability Due to Bed Load Motion

Kennedy clarified that the lag of sediment transport for bed form plays an important role for sand bed instability, but this lag could not been evaluated quantitatively to date. In this study, the role and constitution of the lag has been clarified by inspecting the instability analysis compared with theory of bed load transport process. Particularly, based on the writers’ research on bed load transport process by stochastic approaches, the lag distance of bed load transport rate for bed shear stress has been reasonably clarified. Furthermore, improving the flow model based on the potential flow theory by introducing the effect of flow acceleration or deceleration which can be expressed by local variation of flow depth, the phase lag between bed shear stress and bed form has been estimated. After clarification of these lags, an instability analysis has been conducted and the possibility of instability of bed surface has been investigated against hydraulic conditions.