ON THE BOTTOM SHEAR STRESS DURING LONG WAVE RUNUP AND BACKWASH

Abstract

Laboratory experiments were performed to examine flow characteristics during runup and backwash of a breaking solitary wave. Boundary layer flows were measured by LDV at two locations landward of the still shoreline under different bed conditions. Temporal variations of the bottom shear stress were estimated from nearbed velocity profiles with different methods. The shear stress determined through the logarithmic fitting roughly agreed with that deduced from a depth-integrated momentum balance during turbulent flow phases. The friction factors during the active phases of the runup and backwash were similar in magnitude except in the leading tip where the value sharply increased. A movable bed experiment was also carried out under the same geometry to discuss relations between the bottom shear stress and sediment transport. The result indicated clear dependencies of bed deformations on the magnitude and duration of the exerted shear stress.