Large-scale bedforms, sediment distribution and sand mobility in the eastern North Sea off the Danish west coast

Anthony, Dennis; Leth, Jørgen

doi:10.1016/s0025-3227(01)00245-6

Cited by 48 publications

(37 citation statements)

References 15 publications

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“…Consequently, sediment distribution patterns with strong grain-size contrast might remain stable for decades Goff et al, 2005) despite frequent remobilisation of sediment. Such a mechanism has been specifically attributed to sorted bedforms (Murray and Thieler, 2004), but high stability has also been described for other sediment distribution patterns with high grain-size contrast (Anthony and Leth, 2002;Schwarzer et al, 2003;Tauber and Emeis, 2005). It might therefore be reasonable to assume that the observed patterns of high grain-size contrast in our study area are generally stable over decadal timescales.…”

Section: Limitations Of the Data Setssupporting

confidence: 66%

Mapping seabed sediments: Comparison of manual, geostatistical, object-based image analysis and machine learning approaches

Diesing

Green

Stephens

et al. 2014

Continental Shelf Research

184

123

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Marine spatial planning and conservation need underpinning with sufficiently detailed and accurate seabed substrate and habitat maps. Although multibeam echosounders enable us to map the seabed with high resolution and spatial accuracy, there is still a lack of fit-for-purpose seabed maps. This is due to the high costs involved in carrying out systematic seabed mapping programmes and the fact that the development of validated, repeatable, quantitative and objective methods of swath acoustic data interpretation is still in its infancy. We compared a wide spectrum of approaches including manual interpretation, geostatistics, object-based image analysis and machine-learning to gain further insights into the accuracy and comparability of acoustic data interpretation approaches based on multibeam echosounder data (bathymetry, backscatter and derivatives) and seabed samples with the aim to derive seabed substrate maps. Sample data were split into a training and validation data set to allow us to carry out an accuracy assessment. Overall thematic classification accuracy ranged from 67% to 76% and Cohen's kappa varied between 0.34 and 0.52. However, these differences were not statistically significant at the 5% level. Misclassifications were mainly associated with uncommon classes, which were rarely sampled. Map outputs were between 68% and 87% identical. To improve classification accuracy in seabed mapping, we suggest that more studies on the effects of factors affecting the classification performance as well as comparative studies testing the performance of different approaches need to be carried out with a view to developing guidelines for selecting an appropriate method for a given dataset. In the meantime, classification accuracy might be improved by combining different techniques to hybrid approaches and multi-method ensembles.

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Section: Limitations Of the Data Setssupporting

confidence: 66%

Mapping seabed sediments: Comparison of manual, geostatistical, object-based image analysis and machine learning approaches

Diesing

Green

Stephens

et al. 2014

Continental Shelf Research

184

123

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“…The origins of sand ridges or banks are closely related to hydrodynamic conditions and generally require tidal seas with current speeds greater than 0.5 m s 1 − to move sand to form ridges (Caston 1972;Belderson et al 1982;Pattiaratchi and Collins 1987;Dyer and Huntley 1999;Anthony and Leth 2002). Of particular, importance is the role of tidal currents (Stride 1982).…”

Section: Hydrodynamicsmentioning

confidence: 99%

Morphology, Hydrodynamics and Sediment Characteristics of the Changyun Sand Ridge offshore Western Taiwan

Liao¹,

Yu²

2005

Terr. Atmos. Ocean. Sci.

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TAO, Vol. 16, No. 3, August 2005 622 Mainly medium to coarse-grained sands have accumulated on the Changyun Ridge to form sand banks. At the northern outlet of the Penghu Channel, the shoaling topography of the Changyun Ridge has caused a decrease in tidal current velocity and the subsequent deposition of sands, forming the present Changyun sand ridge. The formation of the eastern and western Changyun sand ridges is probably affected mostly by the tidal current patterns in the areas north of the Penghu Channel.

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“…Sandy beach and nearshore environments exhibit a variety of bedforms ranging in scale from small ripple marks (cm), megaripples and large sand waves or subaqueous dunes (m) to very large sand ridges or sorted bedforms (km), all caused by waves and currents interacting with sediment supply, grain size, coastal morphology and depth (i.e., Allen, 1980;Boothroyd, 1985;Ashley, 1990;Anthony and Leth, 2002;Bartholdy et al, 2002;Passchier and Kleinhans, 2005;Diesing et al, 2006;Whitmeyer and FitzGerald, 2008). There are many terms like sand waves or megaripples for large sandy bedforms and a uniform and general definition for these features is still under debate.…”

Section: Introductionmentioning

confidence: 99%

Long-term displacement of intertidal seagrass and mussel beds by expanding large sandy bedforms in the northern Wadden Sea

Dolch

Reise

2010

Journal of Sea Research

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On aerial photographs, sandy tidal flats display (1) large sandy bedforms (N10 m long, N 3 m wide), indicating effects of strong hydrodynamics on sediment relief, and (2) beds of seagrass and mussels, indicating stable sediment conditions. These physical and biogenic structures have been mapped from aerial photographs taken in a back-barrier tidal basin of the North Sea coast at low tide between 1936 and 2005. Fields of large intertidal sandy bedforms show a consistent spatial distribution in the central part of the basin, and have increased in area from 7.2 to 12.8 km 2 , corresponding now to 10% of the tidal flats. Areal expansion may be linked to a rise in average high tide level and an increase of the expansion rate from the 1960s to the mid 1990s might be traced back to an increased frequency of storm tides during this period. It is shown that expanding fields of large sandy bedforms have replaced mussel beds in the low tidal zone and displaced seagrass beds in the mid tidal zone. Fields of intertidal large sandy bedforms are expected to expand further with an accelerating rise in sea level, and it is recommended to monitor these physical indicators of sediment instability and disturbance of biogenic benthic structures by analysing aerial photographs.

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Large-scale bedforms, sediment distribution and sand mobility in the eastern North Sea off the Danish west coast

Cited by 48 publications

References 15 publications

Mapping seabed sediments: Comparison of manual, geostatistical, object-based image analysis and machine learning approaches

Mapping seabed sediments: Comparison of manual, geostatistical, object-based image analysis and machine learning approaches

Morphology, Hydrodynamics and Sediment Characteristics of the Changyun Sand Ridge offshore Western Taiwan

Long-term displacement of intertidal seagrass and mussel beds by expanding large sandy bedforms in the northern Wadden Sea

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