On estimation of coastal wave parameters and wave‐induced shear stresses

Abstract

Wave parameters, e.g., wave height, near-bed wave orbital velocity, and wave-induced shear stresses, are important hydrodynamic parameters for sediment processes in coastal oceans. Wave orbital velocity is particularly critical in sediment resuspension. Several algorithms to calculate wave orbital velocity have been proposed, including linear wave theory, spectrum, and Joint North Sea Wave Project methods, but the validity of these algorithms in relatively shallow waters is not well understood. In this study, we compared the wave parameters obtained by different instruments and algorithms at four sites, one within the intertidal zone with a mean depth of 1 m and the remainder three in deeper offshore water with mean depths of 15-30 m. We found a high consistency of the estimated wave height, peak wave period, and wave orbital velocity among different datasets and different algorithms at the offshore sites, while there were significant discrepancies at the shoreline site. Using Ursell number, our study suggests that it is reliable to apply any of the three algorithms and different instruments (acoustic Doppler velocimeter and buoy) in deeper water. However, for very shallow water, it is recommended to use the measured highfrequency velocity and spectrum method to calculate wave orbital velocity, and use wave gauge instrument or zero-crossing algorithm to obtain wave height and period information. Finally, the effect of turbulence and bedform morphology on wave-induced shear stress is discussed: without removing the turbulence or taking onto account bedforms (e.g., ripples), the orbital velocity will be remarkably over-estimated or under-estimated.

Impacts of Currents and Waves on Bottom Drag Coefficient in the East China Shelf Seas

“…There are patchy distributions of the sea floor mud (e.g., Hu et al, 2011;Qiao et al, 2017), resulted from the transport of sediments from the inputs of the Yellow and Changjiang Rivers by the ocean flows. The ECSS presents strong tidal flows (e.g., Liu et al, 2009;Lozovatsky et al, 2008a), and the coastal waters are often affected by significant waves (e.g., Xiong et al, 2018;Yang et al, 2014). There have been several previous studies on Cd in the ECSS based on observations, for example, in the Jiaozhou Bay of the Yellow Sea (Liu & Wei, 2007;Lozovatsky et al, 2008b) and in the Xiangshan Bay of the East China Sea (Xu et al, 2017).…”

Experimental Investigation on Characteristics of Sand Waves with Fine Sand under Waves and Currents

“…It is important to describe the topography of ripple pattern properly since it determines the net shear stress over the flow field. Xiong et al [42] calculated the wave height of ripples based on the formulas of Boyd et al [43] and Allen [44]. The scales are comparable to the results of Zhao et al [45] at Dongtai.…”

Small-scale bedforms and associated sediment transport in a macro-tidal lower shoreface

“…The near-bottom wave orbital velocity, 𝑈 𝑤 , was then calculated following small-amplitude linear wave theory considering regular waves (Soulsby, 2006;Wiberg and Sherwoord, 2008). This approach is sufficient when the wave height is small compared to the waves wavelength and the water depth and the water is shallow with respect to the wavelength (Wiberg and Sherwood, 2008;Xiong et al, 2018) as was the case at our study site. The Newton-Raphson iteration method was used to determine the wave number 𝑘 from the dispersion equation following the Fenton and McKee (1990) algorithm.…”