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Theoretical solutions for the wave bottom boundary layer (WBL) over a sloping bed are compared with field measurements in the nearshore zone. The WBL theory is constructed using both viscoelastic-diffusion and conventional eddy viscosity turbulent closure models. The velocity solutions are then matched with those of the interior flow, given by Chu and Mei potential theory for surface gravity waves over a sloping bottom. The field measurements were obtained with a coherent Doppler profiler over a 2° bed slope. Results are presented for both flat and rippled bed conditions, the latter being characterized by low steepness, linear transition ripples. Close to the bed, the observed velocity profiles change rapidly in amplitude and phase relative to potential flow theory, indicating the presence of a wave boundary layer with a thickness of 3-6 cm. The observed velocity and shear stress profiles are in good agreement with the theory. The sloping bottom has significant effects on the vertical velocity, but not on the horizontal velocity and shear stress. Bottom roughness and friction velocity are estimated from optimizing the model-data comparisons. The friction velocities and wave friction factors are found to be consistent with values obtained from the momentum integral method and from the nearbed turbulence intensity, and with Tolman's semiempirical formulation. [ABSTRACT FROM AUTHOR]

Wave friction factors are estimated from vertical profiles of near-bed turbulence and horizontal velocity spanning the wave bottom boundary layer. Measured values are partitioned by bed state, which ranged from irregular ripples to flat bed, and are examined as a function of two traditionally selected parameters—physical bed roughness and outer flow Reynolds number. The measurements are from two field experiments in very different nearshore environments: a relatively protected unbarred pocket beach and a linear barred beach exposed to the open shelf (Duck). Measured wave friction factors are remarkably similar for the two beaches and are highest for low-energy rippled beds and lowest for the high-energy flat bed conditions. The reduction in the friction factor for high-energy conditions corresponds to a decrease in the physical roughness of the bed as wave energy increases. As a function of relative roughness, measured friction factors are generally consistent with previous laboratory results and theoretical results for the high-energy cases, but the predicted values for the low-energy rippled beds show some significant differences. A new expression is derived for the bed roughness and is found to have a stronger dependence on ripple steepness than previously suggested laboratory-based relationships. Estimated friction factors exhibit a power-law dependence on Reynolds number and occupy a narrow band within the rough turbulent and transition regions. [ABSTRACT FROM AUTHOR]

An extreme weather event (Hurricane Juan) made landfall in Nova Scotia, Canada, in September 2003. The storm produced an ∼70-cm storm surge and ∼40 cm s-1 coastal currents in Lunenburg Bay, registered by a coastal observing system. A fine-resolution (60 m) coastal circulation model is used to examine the response of Lunenburg Bay to Hurricane Juan. The model is forced by local wind stress at the sea surface, and tides and remotely generated waves specified at model open boundaries. The model performance is assessed in terms of γ2, the variance of the model errors normalized by the observed variance. The model reproduces very well the observed surface elevations with γ2 values of less than 0.05, and reasonably well the observed currents with γ2 values between 0.2 and 1.1 in the bay during Hurricane Juan. The model–data comparisons demonstrate that the coastal circulation in the bay is significantly affected by local wind associated with the storm. The model results are also used to demonstrate the importance of nonlinear dynamics in the barotropic response of the bay to the storm. [ABSTRACT FROM AUTHOR]