A new type of sea bed waves

Knaapen, M.A.F.; Hulscher, Suzanne J.M.H.; Vriend, H.J. de; Stolk, Arjen

doi:10.1029/2000gl012007

Cited by 46 publications

(43 citation statements)

References 10 publications

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“…The results previously described have been obtained by fixing those related to the site on the basis of the field measurements described in Knaapen et al (2001) If the tidal strength is fixed at U * 0 = 0.6 ms −1 and the ellipticity is varied, both clockwise and counterclockwise long bed waves form when e is larger than about 0.2, up to almost circular tides. Finally, runs have been made using the sediment transport rate formulations of Meyer-Peter & Muller (1948) and Soulsby and Van Rijn (Soulsby 1997) instead of that proposed by Fredsøe & Deigaard (1992).…”

Section: Robustness Of the Resultsmentioning

confidence: 99%

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Long bed waves in tidal seas: an idealized model

2009

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An idealized model is proposed to explain the appearance of the long bed waves that have been recently observed in shallow tidal seas. The model assumes that these bedforms grow due to tide-topography interaction. The water motion is described by means of the depth-averaged shallow water equations and the bottom evolution is governed by conservation of sediment mass. The sediment transport formulation includes a critical bottom stress below which no sediment moves. Also, anisotropic sediment transport, due to local bottom slopes in the longitudinal and transverse directions, is taken into account. A linear stability analysis of the flat bottom configuration reveals that different bottom patterns can emerge. In accordance with previous analyses, for strong tidal currents, the fastest growing modes are sand banks. However, if the tidal currents are elliptical and the maximum bottom stress is just above its threshold value for the initiation of sediment motion, the model shows the presence of further growing modes which resemble the long bed waves observed in the field.

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Section: Robustness Of the Resultsmentioning

confidence: 99%

“…By analysing bathymetric surveys made in the North Sea, Knaapen et al (2001) have identified new bedforms which can be classified neither as sand waves nor as sand banks. These new bedforms, named long bed waves, are characterized by crests which are 60…”

Section: Introductionmentioning

confidence: 99%

Long bed waves in tidal seas: an idealized model

2009

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“…Subaqueous dunes are bedforms produced in river channels, estuaries, and coastal zones [1][2][3]. They are formed with different sediment sizes, mostly ranging from medium sand to gravel [4], and show rhythmic patterns caused by the interaction of turbulent flow on the riverbed [5].…”

Section: Introductionmentioning

confidence: 99%

Riverbed Micromorphology of the Yangtze River Estuary, China

Cheng

et al. 2016

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Dunes are present in nearly all fluvial channels and are vital in understanding sediment transport, deposition, and flow conditions during floods of rivers and estuaries. This information is pertinent for helping developing management practices to reduce risks in river transportation and engineering. Although a few recent studies have investigated the micromorphology of a portion of the Yangtze River estuary in China, our understanding of dune development in this large estuary is incomplete. It is also poorly understood how the development and characteristics of these dunes have been associated with human activities in the upper reach of the Yangtze River and two large-scale engineering projects in the estuarine zone. This study analyzed the feature in micromorphology of the entire Yangtze River estuary bed over the past three years and assessed the morphological response of the dunes to recent human activities. In 2012, 2014, and 2015, multi-beam bathymetric measurements were conducted on the channel surface of the Yangtze River estuary. The images were analyzed to characterize the subaqueous dunes and detect their changes over time. Bottom sediment samples were collected for grain size analysis to assess the physical properties of the dunes. We found that dunes in the Yangtze River estuary can be classified in four major classes: very large dunes, large dunes, medium dunes, and small dunes. Large dunes were predominant, amounting to 51.5%. There was a large area of dunes developed in the middle and upper reaches of the Yangtze River estuary and in the Hengsha Passage. A small area of dunes was observed for the first time in the turbidity maximum zone of the Yangtze River estuary. These dunes varied from 0.12 to 3.12 m in height with a wide range of wavelength from 2.83 to 127.89 m, yielding a range in height to wavelength of 0.003-0.136. Sharp leeside slope angles suggest that the steep slopes of asymmetrical dunes in the middle and upper reaches, and the turbidity maximum zone of the Yangtze River estuary face predominantly towards tides because of the ebb-dominated currents. Sharp windward slope angles in the lower reach of the North Passage show the influence of flood-dominated currents on dunes. It is likely that the scale of dunes will increase in the future in the South Channel because of a sharp decline of sediment discharge caused by recent human activities.

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“…2014; Knaapen et al, 2001). Esses refletores geralmente não possuem continuidade lateral, porém, podem apresentar regularidade e padrão de refletividade devido à influência adquirida pelo contato com outras unidades estruturais ou pelo comportamento constante de fluxo havendo poucas alterações em um longo período de atuação (Harvey et al, 2005;Miall, 2006), além de apresentar desconformidades, assimetria e configuração caótica em sua disposição, o qual é comportamento característico de ambientes energéticos com variações abruptas de dinâmica e de forçantes de deformação do processo de sedimentação (Bourgoin et al, 2013;Wittmann et al, 2011), nota-se uma tendência de inclinação de alguns refletores de NW-SE, levando a crer que essas formas de fundo estão se deslocando perpendicularmente a direção do Canal do Norte com transporte de carga de fundo aparente para a montante (Besio et al, 2008;Komarova and Newell, 2000;Strasser, 2008 (Baas et al, 2016;Neill et al, 2012).…”

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Caracterização Das Principais Feições Superficiais De Fundo E Em Subsuperfície No Limite Sudoeste Da Baía De Macapá, Canal Do Norte, Rio Amazonas

2017

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RESUMO.A Baía de Macapá, por estar inserida a zona de médio estuário do Rio Amazonas, apresenta vestígios de alterações morfológicas diferenciadas pela forte dinâmica em um curto intervalo de tempo. O reflexo de tais alterações pode ser observado nas modificações morfoestruturais presentes no leito e subsuperfície. A análise dos perfis sísmicos em alta resolução pelo intervalo de frequência de 0,7 kHz a 12,0 kHz revela que as características apresentadas nas formas de fundo desencadeiam os processos modeladores do padrão de reflexão observados nos refletores em subsuperfície. Através desta relação foi possível identificar a predominância de cinco formas de fundo, quatro unidades estruturais e cinco sismofácies com o destaque para a identificação de uma feição de paleocanal. Observou-se que as variações morfológicas do leito são influenciadas pela constante atuação dos processos hidrodinâmicos e sedimentares ocorrentes periodicamente e vice-versa, corroborando para correlação entre as feições superficiais de fundo e as feições em subsuperfície.Palavras-Chave: Morfologia, formas de fundo, sismofácies, paleocanal.ABSTRACT. The Macapá Bay, because it is inserted in the middle estuary zone of the Amazon River, presents evidences of different changes in a short time. The reflex of such changes can be observed in morphostructural modifications present in the bed and subsurfaces. The analysis of the high-resolution seismic profiles through on frequency range of 0.7 kHz to 12.0 kHz reveals that the features presented in the bedforms trigger the reflection pattern modelers processes observed in the subsurface reflectors. Through this relationship, it was possible to identify the predominance of five bedforms, four structural units and five seismic facies with highlight for the identification of a paleochannel feature. It was observed that the morphological variations of the bed are influenced by the constant actuation of the hydrodynamic processes and sedimentary that occur periodically and vice versa, corroborating to correlation between the superficial bottom features and the subsurface features.

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A new type of sea bed waves

Cited by 46 publications

References 10 publications

Long bed waves in tidal seas: an idealized model

Long bed waves in tidal seas: an idealized model

Riverbed Micromorphology of the Yangtze River Estuary, China

Caracterização Das Principais Feições Superficiais De Fundo E Em Subsuperfície No Limite Sudoeste Da Baía De Macapá, Canal Do Norte, Rio Amazonas

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