Bed shear stress estimation on an open intertidal flat using in situ measurements

Zhu, Qin; Prooijen, Bram C. van; Wang, Z.B.; Ma, Yanyan; Yang, S.L.

doi:10.1016/j.ecss.2016.08.028

Cited by 55 publications

(43 citation statements)

References 43 publications

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“…To evaluate the validity of different algorithms for wave orbital velocity, especially the linear wave theory method and JONSWAP method, we introduced several indices including slope, correlation coefficient ( R ), root‐mean‐square error ( RMSE ), index of agreement ( I ), (Willmott et al,; Zhu et al, ) and Brier skill scores (BSS) (Brier, , Table ). The index I varies between 0 and 1, with I = 0 indicating no agreement and I = 1 indicating perfect agreement.…”

Section: Discussionmentioning

confidence: 99%

“…To remove the influence of turbulence, the turbulence spectrum is first calculated by energy spectrum analysis (Soulsby and Humphery, ; Zhu et al, ) and then subtracted from the whole spectrum ( u wave + u turbulence ). The frequency of turbulence and wave interact with each other during certain range (Bricker and Monismith, ), so the influence of turbulence cannot be totally removed due to the limitation of the method.…”

Section: Discussionmentioning

confidence: 99%

“…Relating bottom orbital velocity directly to the variance of wave‐induced near bed velocity (Wiberg and Sherwood, ), U w was calculated by integrating the contributions of each frequency component of S uv ,i

U_{normalw_Spectrum} = \sqrt{2 \sum_{i} S_{uv, i} Δ f}

where S uv = S uu + S vv is the combined horizontal spectrum of eastern and northern velocity. In addition, turbulence influence shall be removed (Soulsby and Humphery, ; Zhu et al, ), or the orbital velocity would be highly overestimated. Since the frequency of turbulence and wave interact with each other (Bricker and Monismith, ), the influence of turbulence cannot be totally removed due to the limitation of the method.…”

Section: Methodsmentioning

confidence: 99%

“…Wave friction factor was calculated according to Jonsson (), as modified by Nielsen ():

f_{w} = ({, \begin{matrix} exp ([], 5.213 {(k_{normalb} / A_{normalb})}^{0.194} - 5.977), A_{b} / k_{b} > 1.7 \\ 0.28, A_{b} / k_{b} \leq 1.7 \end{matrix})

where A b (= U w T /2π) is the near‐bed wave orbital amplitude, k b is the bottom roughness height. Usually, k b is expressed as grain size roughness height or Nikuradse roughness height k g (=2.5 d 50 ) (Nielsen, ; Soulsby, ; Zhu et al, ), which was introduced by Nikuradse () to simulate the hydraulic roughness of arbitrary roughness elements of the bottom boundary. To investigate the effect of ripples on wave‐induced shear stress, the ripple‐related roughness height ( k br_van ) is calculated as (van Rijn, )

k_{br_van} = ({, \begin{matrix} 150 f_{cs} d_{50}, normalψ \leq 50 ((),, lower wave - current regime, small - scale ripples) \\ 20 f_{cs} d_{50}, normalψ > 250 (();, upper wave - current regime, sheet flow) \\ ((), 182.5 - 0.652) f_{cs} d_{50}, 50 < normalψ \leq 250 (();, transitional regime, linear approach) \\ 20 d_{silt}, d_{50} < d_{silt} \end{matrix})

where ψ (= U wc 2 /[( s ‐1) gd 50 ], ( U cw ) 2 = ( U w ) 2 + ( U c ) 2 ) is current‐wave mobility parameter; s = ρ s / ρ w , ρ s is the density of primary particle (=2650 kg m −3 ); d silt = 32 μm; f cs = (0.25 d gravel / d 50 ) 1.5 ; f cs = 1 for d 50 ≤0.25 d gravel ; and d gravel = 0.002 m. The low limit is k br_van = 20 d silt for particles ≤32 μ m.…”

Section: Methodsmentioning

confidence: 99%

“…Several algorithms to calculate U w have been summarized in Wiberg and Sherwood (), but their validity has not yet been well understood for different water depths, especially in very shallow waters. The most widely used algorithm to calculate wave orbital velocity is based on the simple linear wave theory (Soulsby and Smallman, ; Soulsby, ; Zhu et al, ; Yu et al, ). Errors arise when only particular statistical parameters such as significant wave height ( H s ) and peak period ( T p ) rather than the full wave spectrum are utilized.…”

mentioning

confidence: 99%

See 4 more Smart Citations

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

Xiong

Wang

Gao

et al. 2018

Limnology & Ocean Methods

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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.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%