Field observations and predictions of bed shear stressesand vertical suspended sediment concentration profiles in wave-current conditions

Williams, Jon J.; Rose, Christopher; Thorne, Peter D.; O’Connor, Brian A.; Humphery, J.D.; Hardcastle, P.J.; Moores, S.P.; Cooke, J.A.; Wilson, Donald W.

doi:10.1016/s0278-4343(98)00098-3

Cited by 55 publications

(22 citation statements)

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“…For medium to fine sand (grain size of 4 × 10 −4 m) w s ∼ 0.05 m s −1 and u ∼ 10 m s −1 , hence c a ∼ 10 −3 . This yields dimensional reference concentrations of the order of 0.1 kg m −3 , which are of the same order as measured reference concentrations near the Middelkerke Bank (North Sea, near Belgium) reported by Williams et al (1999).…”

Section: Model Formulationsupporting

confidence: 82%

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Modelling the formation of shoreface-connected sand ridges on storm-dominated inner shelves

et al. 2001

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A morphodynamic model is developed and analysed to gain fundamental understanding of the basic physical mechanisms responsible for the characteristics of shorefaceconnected sand ridges observed in some coastal seas. These alongshore rhythmic bed forms have a horizontal lengthscale of order 5 km and are related to the mean current along the coast: the seaward ends of their crests are shifted upstream with respect to where they are attached to the shoreface. The model is based on the two-dimensional shallow water equations and assumes that the sediment transport only takes place during storms. The flux consists of a suspended-load part and a bed-load part and accounts for the effects of spatially non-uniform wave stirring as well as for the preferred downslope movement of sediment. The basic state of this model represents a steady longshore current, driven by wind and a pressure gradient. The dynamics of small perturbations to this state are controlled by a physical mechanism which is related to the transverse bottom slope. This causes a seaward deflection of the current over the ridges and the loss of sediment carrying capacity of the flow into deeper water. The orientation, spacing and shape of the modelled ridges agree well with field observations. Suspended-load transport and spatially non-uniform wave stirring are necessary in order to obtain correct e-folding timescales and migration speeds. The ridge growth is only due to suspended-load transport whereas the migration is controlled by bed-load transport.

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Section: Model Formulationsupporting

confidence: 82%

“…From field data, see e.g. Williams et al (1999), it follows that δ ∼ 0.15 for strong waves superimposed on a mean current. It is further assumed that this parameter is a constant.…”

Section: Model Formulationmentioning

confidence: 99%

Modelling the formation of shoreface-connected sand ridges on storm-dominated inner shelves

et al. 2001

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“…This method is widely applied in oceanography (Stapleton and Huntley, 1995;Williams et al, 1999;Kim et al, 2000;Huthnance et al, 2002). Surprisingly, although it is mentioned in at least one paper as a means to obtain u * (McLelland and Nicholas, 2000), it has never been used or tested to our knowledge in fluvial studies.…”

Section: Main Methods For Bed Shear Stress Estimatesmentioning

confidence: 99%

Comparing different methods of bed shear stress estimates in simple and complex flow fields

Biron

Robson

Lapointe

et al. 2004

Earth Surf Processes Landf

272

207

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Bed shear stress is a fundamental variable in river studies to link flow conditions to sediment transport. It is, however, difficult to estimate this variable accurately, particularly in complex flow fields. This study compares shear stress estimated from the log profile, drag, Reynolds and turbulent kinetic energy (TKE) approaches in a laboratory flume in a simple boundary layer, over plexiglas and over sand, and in a complex flow field around deflectors. Results show that in a simple boundary layer, the log profile estimate is always the highest. Over plexiglas, the TKE estimate was the second largest with a value 30 per cent less than the log estimate. However, over sand, the TKE estimate did not show the expected increase in shear stress. In a simple boundary layer, the Reynolds shear stress seems the most appropriate method, particularly the extrapolated value at the bed obtained from a turbulent profile. In a complex flow field around deflectors, the TKE method provided the best estimate of shear stress as it is not affected by local streamline variations and it takes into account the increased streamwise turbulent fluctuations close to the deflectors. It is suggested that when single-point measurements are used to estimate shear stress, the instrument should be positioned close to 0·1 of the flow depth, which corresponds to the peak value height in profiles of Reynolds and TKE shear stress.

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“…These projects include CODE (Coastal Ocean Dynamics Experiment) (Cacchione et al, 1987;Grant et al, 1984), STRESS (Sediment Transport on Shelves and Slopes) (Sherwood et al, 1994), STRATAFORM (Nittrouer, 1999), and EuroSTRATAFORM (Fain et al, 2007;Nittrouer et al, 2004). Some scholars carried out boundary layer water and sediment observations in different coastal areas and collected waves, currents, and sediment concentration data under normal or stormy weather conditions (Madsen and Wood, 1993;McClennen, 1973;Williams et al, 1999;Wright et al, 1991). Zhao and Han (2007), Yang and Hou (2004), Sun et al (2010) andWang et al (2012) collected field data in Huanghua port, Jingtang port and Jiangsu coast, and analyzed the sediment transport in silt-dominated coasts.…”

Section: Introductionmentioning

confidence: 99%

Modelling and Analysis of Fine Sediment Transport in Wave-Current Bottom Boundary Layer

Zuo¹

2018

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Although all care is taken to ensure integrity and the quality of this publication and the information herein, no responsibility is assumed by the publishers, the author nor IHE Delft for any damage to the property or persons as a result of operation or use of this publication and/or the information contained herein. A pdf version of this work will be made available as Open Access via http://repository.tudelft.nl/ihe. This version is licensed under the Creative Commons To my family AbstractThe evolution and utilization of estuarine and coastal regions are greatly restricted by sediment problems. Inspired by the Caofeidian sea area in Bohai Bay, China, this study aims to better understand silty sediment transport under combined action of waves and currents, especially in the wave-current bottom boundary layer (BBL), and to improve our modelling approaches in predicting estuarine and coastal sediment transport.Field observations were carried out in northwestern Caofeidian sea area of Bohai Bay and field data were collected on several other silt-dominated coasts. Analysis shows that silt-dominated sediments are sensitive to flow dynamics: the suspended sediment concentrations (SSCs) increase rapidly under strong flow dynamics (i.e., waves or strong tidal currents which can stir up sediments), and high concentrations cause heavy sudden back siltation in navigation channels. In the following, details of silty sediment transport are studied, focusing on the BBL and high concentration layer (HCL).From laboratory experiments and theoretical analysis, an expression for sediment incipient motion is proposed for silt-sand sediment under combined wave and current conditions. The Shields number was revised by adding the cohesive force and additional static pressure, leading to an extended Shields curve.To study the HCL, a process based 1DV model was developed for flow-sediment dynamics near the bed in combined wave-current conditions. Based on the physical processes, special approaches for sediment movement were introduced, including approaches for different bed forms (rippled bed and 'flat-bed'), hindered settling, stratification effects, mobile bed effects, reference concentration and critical shear stress. The HCL was simulated and sensitivity analysis was carried out by the 1DV model on factors that impact the sediment concentration in the HCL. The results show that the HCL is affected by both flow dynamics and bed forms; the thickness of the HCL is about twice the height of the wave boundary layer; bed forms determine the shape of the concentration profile near the bottom, and flow dynamics determine the magnitude. For finer sediment, stratification effects and mobile bed effects impact the sediment concentration greatly.Finally, based on the 1DV model, the formulations of the mean sediment concentration profile of silty sediments were studied. By solving the time-averaged diffusion equation for SSC and considering the effects of bed forms, stratification and hindered settling, expressions for time-averaged SSC profile...

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Field observations and predictions of bed shear stressesand vertical suspended sediment concentration profiles in wave-current conditions

Cited by 55 publications

References 0 publications

Modelling the formation of shoreface-connected sand ridges on storm-dominated inner shelves

Modelling the formation of shoreface-connected sand ridges on storm-dominated inner shelves

Comparing different methods of bed shear stress estimates in simple and complex flow fields

Modelling and Analysis of Fine Sediment Transport in Wave-Current Bottom Boundary Layer

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