Comparison of Bed Shear under Non-Breaking and Breaking Solitary Waves

Abstract

New experimental measurements of bed shear under solitary waves and solitary bores that represent tsunamis are presented. The total bed shear stress was measured directly using a shear cell apparatus. The solitary wave characteristics were measured using ultrasonic wave gauges and free stream velocities were measured using an Acoustic Doppler Velocimeter. The measurements were carried out in laminar and transitional flow regimes (∼104 < Re < ∼105). This sort of data is sparsely available in literature. In the absence of direct measurements, shear stress is indirectly estimated using velocity profiles or is inferred using standard friction factors. However, this indirect method has its limitations, e.g., under unsteady hydrodynamic conditions and relatively large roughness the assumptions of both approaches are no longer valid. More than 168 experimental runs comprising solitary waves and bores were carried out over a smooth flat bed with wave height to water depth ratio varying between 0.12 and 0.69. Analytical modeling was carried out to predict shear stresses using Fourier and convolution integration methods. This paper presents comparison of the measured and predicted bed shear stress or skin friction stress, together with estimates of traditional wave friction factors. Overall, the models can predict the bed shear stress with a satisfactory degree of accuracy.