Bed shear stress distribution over beach profiles

Abstract

The mechanism of cross-shore movements of the bottom sand and the local bed movement around marine structures can be better understood by defining the bed shear stress distribution along the bed. In order to obtain the variation of the bed shear stress over rigid uniform and barred beaches from intermediate to shallow water conditions, a series of measurements were done to clarify the structure of the wave boundary layer along the beach by using a Constant Temperature Anemometer (CTA). The bed shear stress measurements were made on both the uniform beaches which are different slopes (1:10 and 1:5) and the barred beaches which reached dynamically stable condition after a certain time, their initial slopes were 1:10. The maximum bed shear stress varied with the depth parameter (d/H-0). The maximum value of bed shear stress was found at the plunging point due to strong vortex generation and the turbulent structure. However, the periodic component of the bed shear stress was still of the periodic character at breaking points as non-breaking waves. The magnitudes of bed shear stress at given depth was found depending on wave characters. The maximum bed shear stress distribution over barred beach was larger than that of the initial uniformly sloped due to larger wave breaks on steeper slope over bar crest.