Detailed investigation of sorted bedforms, or “rippled scour depressions,” within the Martha's Vineyard Coastal Observatory, Massachusetts

Goff, John A.; Mayer, Larry A.; Traykovski, Peter; Buynevich, Ilya V.; Wilkens, Roy H; Raymond, Richard; Glang, Gerd; Evans, Robert; Olson, Hilary Clement; Jenkins, Chris

doi:10.1016/j.csr.2004.09.019

Cited by 96 publications

(102 citation statements)

References 13 publications

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“…Next, a comparison of the model findings with field observations of sorted bed forms at Martha's Vineyard Coastal Observatory, Massachusetts, is performed (Goff et al 2005). At this site, the bed features are observed in depths from 8 to 18 m. They emerge shore-normal from the shoreface into the inner shelf and have wavelengths ranging from 100 to 500 m. The bottom sediment at this site is bimodal and is composed of a fine fraction with a grain size approximately equal to 0.25 mm and a coarse fraction with grain sizes between 0.5 mm and 2.0 mm.…”

Section: The Field Casesmentioning

confidence: 99%

“…These bed forms are ubiquitously observed and exhibit a broad range of characteristics (e.g. Aubrey, Twichell & Pfirman 1982;Cacchione, Grant & Tate 1984;Goff et al 2005;Ferrini & Flood 2005;Bellec et al 2010). Figure 1 shows a side scan sonar image of the inner shelf near Wrightsville Beach, North Carolina (USA), which reveals the presence of sorted bed forms in this area.…”

Section: Introductionmentioning

confidence: 99%

“…Goff et al (2005) report that the boundaries of the bed forms can migrate tens of metres in months, while the bed features observed in the German Bight, southeastern North Sea, appear essentially stable over a period of 26 years (Diesing et al 2006).…”

Section: Introductionmentioning

confidence: 99%

“…However, Ferrini & Flood (2005) report, for the bed features along the south shore of Long Island, both down-current and up-current offsets. Moreover, observations at Martha's Vineyard Coastal Observatory, Massachusetts, reveal that the relative position of the coarse patch with respect to the bottom waviness can change proceeding along a sorted bed form from the shoreline to the offshore region (Goff et al 2005).…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, sorted bed forms with relatively larger amplitude also occur. For instance, Goff et al (2005) describe bed features with heights of 3 m, where the mean water depth is ≈12 m.…”

Section: Introductionmentioning

confidence: 99%

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Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

2011

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An idealised model is presented to study the formation of sorted bed forms generated by a wind-driven along-shore current. The study employs a linear stability analysis to describe the time development of perturbations of both bottom composition and bed elevation, superimposed on a flat bed composed of a sediment mixture homogeneously distributed in space. The model considers both bed and suspended loads and takes into account the averaged influence of waves on the flow field and the transport of sediment. The results show that the positive coupling between waves, along-shore current and the erodible heterogeneous bed leads to the amplification of two modes, which exhibit distinct characteristics. A first mode is found to be dominant when moderate hydrodynamic conditions are considered and is primarily amplified by the convergence of sediment transport induced by the changes in the bed elevation. This mode has wavelengths of the order of hundred metres and has coarse (fine) sediments in its troughs (crests). By increasing the height of the waves and/or the strength of the steady current, the second mode can become dominant. This mode is characterised by shorter wavelengths and results from the interaction between the convergence of sediment transport related to changes in the bottom composition and that induced by perturbations of the bed elevation. These bed features can have an up-current or a down-current shift between the centre of the coarse-grained bands and the trough of the bottom wave. Typical growth times of the amplified features are of the order of hundreds of days and the migration rates, in the direction of the along-shore current, range between 0.1 and 10 m per day. A qualitative comparison of the model results with field observations indicates that the generation of two distinct modes provides a possible explanation for the broad range of characteristics of the natural bed features.

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Section: The Field Casesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

2011

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Direct Measurements of Mean Reynolds Stress and Ripple Roughness in the Presence of Energetic Forcing by Surface Waves

et al. 2018

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Direct covariance observations of the mean flow Reynolds stress and sonar images of the seafloor collected on a wave‐exposed inner continental shelf demonstrate that the drag exerted by the seabed on the overlying flow is consistent with boundary layer models for wave‐current interaction, provided that the orientation and anisotropy of the bed roughness are appropriately quantified. Large spatial and temporal variations in drag result from nonequilibrium ripple dynamics, ripple anisotropy, and the orientation of the ripples relative to the current. At a location in coarse sand characterized by large two‐dimensional orbital ripples, the observed drag shows a strong dependence on the relative orientation of the mean current to the ripple crests. At a contrasting location in fine sand, where more isotropic sub‐orbital ripples are observed, the sensitivity of the current to the orientation of the ripples is reduced. Further, at the coarse site under conditions when the currents are parallel to the ripple crests and the wave orbital diameter is smaller than the wavelength of the relic orbital ripples, the flow becomes hydraulically smooth. This transition is not observed at the fine site, where the observed wave orbital diameter is always greater than the wavelength of the observed sub‐orbital ripples. Paradoxically, the dominant along‐shelf flows often experience lower drag at the coarse site than at the fine site, despite the larger ripples, highlighting the complex dynamics controlling drag in wave‐exposed environments with heterogeneous roughness.

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A method for semi‐automated objective quantification of linear bedforms from multi‐scale digital elevation models

Cazenave

Dix

Lambkin

et al. 2012

Earth Surf Processes Landf

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The increasing availability of large, detailed digital representations of the Earth's surface demands the application of objective and quantitative analyses. Given recent advances in the understanding of the mechanisms of formation of linear bedform features from a range of environments, objective measurement of their wavelength, orientation, crest and trough positions, height and asymmetry is highly desirable. These parameters are also of use when determining observation‐based parameters for use in many applications such as numerical modelling, surface classification and sediment transport pathway analysis. Here, we (i) adapt and extend extant techniques to provide a suite of semi‐automatic tools which calculate crest orientation, wavelength, height, asymmetry direction and asymmetry ratios of bedforms, and then (ii) undertake sensitivity tests on synthetic data, increasingly complex seabeds and a very large‐scale (39 000 km2) aeolian dune system. The automated results are compared with traditional, manually derived, measurements at each stage. This new approach successfully analyses different types of topographic data (from aeolian and marine environments) from a range of sources, with tens of millions of data points being processed in a semi‐automated and objective manner within minutes rather than hours or days. The results from these analyses show there is significant variability in all measurable parameters in what might otherwise be considered uniform bedform fields. For example, the dunes of the Rub' al Khali on the Arabian peninsula are shown to exhibit deviations in dimensions from global trends. Morphological and dune asymmetry analysis of the Rub' al Khali suggests parts of the sand sea may be adjusting to a changed wind regime from that during their formation 100 to 10 ka BP. Copyright © 2012 John Wiley & Sons, Ltd.

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Detailed investigation of sorted bedforms, or “rippled scour depressions,” within the Martha's Vineyard Coastal Observatory, Massachusetts

Cited by 96 publications

References 13 publications

Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

Formation of rhythmic sorted bed forms on the continental shelf: an idealised model

Direct Measurements of Mean Reynolds Stress and Ripple Roughness in the Presence of Energetic Forcing by Surface Waves

A method for semi‐automated objective quantification of linear bedforms from multi‐scale digital elevation models

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