Turbulent suspension of sediments in the deep sea

The high-energy benthic boundary layer experiment demonstrated the existence of high energy events capable of suspending large amounts of sediment at the base of the Nova Scotian Rise. The currents that cause these storms are episodic pulses of 25-35 cm s -1 flows lasting four to seven days. The build up and decay of the currents is too rapid for local equilibrium of the suspended sediment distribution to be achieved. Therefore, a fully time-dependent model of the turbulent boundary layer and the suspended sediments was developed to describe the events in detail. The period of high flow is erosive for only a few hours. The surface erodible bed sediments are quickly removed. The dominant processes resulting in the development of the suspended sediment profile are then restricted to turbulent diffusion and entrainment. The depth of penetration of the suspended sediments into the water column is limited by stratification induced by suspended sediments. After the shear generated turbulence collapses most of the eroded sediment remained in suspension far above the expected ‘ equilibrium ’ height for a ‘ non-storm ’ turbulent boundary layer. Scaling arguments, and the model, show that fine clay particles kept in suspension by turbulent diffusion dominate settling during the low level turbulence present during ‘non-storm’ conditions. Level 2 and 2 1/2 energy closure models with stratification predict quite different structures of the nepheloid layer.

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Non-equilibrium turbulent stresses and sediment transport in the benthic boundary layer of a shallow shelf environment influenced by flow obstruction

10.5194/egusphere-egu2020-11021 ◽

2020 ◽

Author(s):

Martin Austin ◽

Ben Lincoln ◽

Guy Walker-Springett

Keyword(s):

Boundary Layer ◽

Sediment Transport ◽

Suspended Sediment ◽

High Energy ◽

Velocity Shear ◽

Benthic Boundary Layer ◽

Suspended Sediment Transport ◽

Mean Flow ◽

Turbulent Dissipation ◽

Non Equilibrium

The shallow continental shelf is increasingly used to site infrastructure for marine energy conversion and aquaculture. In this shallow typically energetic environment, tides and waves cause significant sediment fluxes, which interact with and are modified by emplaced infrastructure. This contribution presents observational field data to quantify non-equilibrium turbulent stresses caused by an obstruction in a tidal flow and its impact on suspended sediment transport.Observations of the turbulent properties of the benthic boundary layer (BBL) in an energetic nearshore environment were made over a 4-month period in Cemaes Bay, Anglesey, UK. The area experiences a high energy semi-diurnal tidal regime with a maximum range of 7.5&#160;m. Tidal current velocities were a maximum of 1.1 m s&#8722;1 during springs tides and the strength of the tides ensures that the water column was vertically well mixed. An instrumented lander deployed in 13 m depth on a region of flat sand-sheet sampled the turbulent flows in the BBL using a pulse coherent Nortek Aquadopp and a Vector ADV. An Acoustic Backscatter System was mounted coincidently to sample suspended sediment concentrations.Vertical profiles of mean flow show that during the flood tide an obstruction upstream of the sampling region modified the BBL causing the breakdown of the constant stress layer and a reduction in velocity shear compared to the opposing ebb tide currents. The turbulent dissipation rate computed using the inertial dissipation and structure functions methods illustrate an order of magnitude increase in dissipation and identify a strongly non-equilibrium relationship between turbulent dissipation and production during flood tides, which varies with elevation above the seabed. The non-equilibrium turbulence effects the suspension and transport of seabed sediments by modifying the vertical profile of sediment diffusivity. These effects are quantified and impacts discussed.

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Suspended-sediment transport and benthic boundary-layer dynamics

Marine Geology ◽

10.1016/0025-3227(81)90155-9 ◽

1981 ◽

Vol 42 (1-4) ◽

pp. 1-18 ◽

Cited By ~ 28

Author(s):

Charles E Adams ◽

Georges L Weatherly

Keyword(s):

Boundary Layer ◽

Sediment Transport ◽

Suspended Sediment ◽

Benthic Boundary Layer ◽

Suspended Sediment Transport ◽

Boundary Layer Dynamics

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An instrument system for monitoring and sampling suspended sediment in the benthic boundary layer

Marine Geology ◽

10.1016/0025-3227(86)90069-1 ◽

1986 ◽

Vol 71 (3-4) ◽

pp. 187-199 ◽

Cited By ~ 41

Author(s):

R.W. Sternberg ◽

R.V. Johnson ◽

D.A. Cacchione ◽

D.E. Drake

Keyword(s):

Boundary Layer ◽

Suspended Sediment ◽

Benthic Boundary Layer

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SEDIMENT TRANSPORT ON THE SOUTH-EAST AUSTRALIAN CONTINENTAL SHELF

Coastal Engineering Proceedings ◽

10.9753/icce.v19.131 ◽

1984 ◽

Vol 1 (19) ◽

pp. 131 ◽

Cited By ~ 1

Author(s):

Angus D. Gordon ◽

John G. Hoffman

Keyword(s):

Sediment Transport ◽

Continental Shelf ◽

Suspended Sediment ◽

Transport System ◽

Sediment Concentration ◽

High Energy ◽

Sediment Distribution ◽

Sediment Movement ◽

Shelf Sediment ◽

Sea Bed

Engineering projects on the continental shelf off Sydney, Australia, have stimulated investigation into the sediment transport system of the shelf. Investigation activities associated with these projects have included: definition of sea bed morphology, sediment distribution and bedform characteristics; monitoring of steady and wave induced currents; wind data collection; suspended sediment sampling; bottom camera sediment movement investigations and analytical studies of sediment reaction to sea bed forcing functions. Sea bed velocity exceedence relationships for both wave oscillations and steady currents have been determined at depths of 24 m, 60 m and 80 m. Thresholds of sediment movement have been defined. Relative sediment transport computations have been undertaken and studies of suspended sediment concentration profiles are in progress so that absolute transport rates can be determined. The prevailing conditions, which include a mainly south bound current, are seldom sufficient to induce entrainment of shelf sediments. Transport events mainly result from major storms in the Tasman Sea which produce both high energy waves and north bound currents. Although these events are rare and short lived, the combined wave and current shear produced at the sea bed during the events gives rise to entrainment conditions which result in their dominance of the shelf sediment transport system.

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Sebaran Sedimen Tersuspensi di Perairan Teluk Awur Jepara menggunakan Citra Landsat 8

BULETIN OSEANOGRAFI MARINA ◽

10.14710/buloma.v9i1.29111 ◽

2020 ◽

Vol 9 (1) ◽

pp. 77-82

Author(s):

Petrus Subardjo ◽

Agus Anugroho Dwi Suryoputro ◽

Ibnu Praktikto

Keyword(s):

Remote Sensing ◽

Suspended Sediment ◽

Satellite Imagery ◽

Suspended Sediments ◽

Landsat 8 ◽

Mixing Process ◽

Sea Waves ◽

Longshore Current ◽

Sediment Distribution ◽

Sediment Content

Sedimen tersuspensi dianggap sebagai sedimen yang didistribusikan oleh arus laut. Arus sepanjang pantai (longshore current) berperan besar terhadap proses perpindahan sedimen di perairan. Gelombang laut yang yang membentuk sudut terhadap garis pantai menyebabkan arus sepanjang pantai Transpor sedimen yang disebabkan oleh arus sepanjang panti sering menimbulkan permasalahan erosi pantai dan pendangkalan perairan. Perairan Teluk Awur memiliki bentuk teluk dan tanjung yang memungkinkan terjadinya arus sepanjang pantai. Potensi adanya proses erosi dan sedimentasi di perairan Teluk Awur membuat pentingnya kajian mengenai pola sebaran sedimen tersuspensi. Penelitian ini mampu menjelaskan tentang pola sebaran sedimen tersuspensi di perairan Teluk Awur, Kecamatan Tahunan, Kabupaten Jepara. Metode yang digunakan untuk penentuan sedimen tersuspensi menggunakan pengindraan jauh dan data yang digunakan yaitu citra satelit landsat-8. Kandungan sedimen tersuspensi tertinggi berada di Desa Teluk Awur dan Desa Demaan. Kandungan tertinggi sebesar ± 67,54 mg/L dan semakin menjauhi pantai konsentrasi menurun. Tingginya kadungan sedimen tersuspensi dipengaruhi oleh proses mixing dan intensitas curah hujan. Suspended sediments are considered as sediments distributed by ocean currents. Current along the coast (longshore current) plays a major role in the process of transfer of sediment in the waters. Sea waves that form angles to the coastline cause currents along the coast Sediment transport caused by currents along the orphanage often cause erosion and coastal silting problems. The waters of Teluk Awur have the shape of bays and headlands which allow currents along the coast. The potential for erosion and sedimentation in the Awur Bay waters makes it important to study the pattern of suspended sediment distribution. This research is able to explain the pattern of suspended sediment distribution in Awur Bay waters, Annual District, Jepara Regency. The method used to determine suspended sediment uses remote sensing and the data used are Landsat-8 satellite imagery. The highest suspended sediment content was in Teluk Awur Village and Demaan Village. The highest content of ± 67.54 mg / L and increasingly away from the beach decreased concentration. The high suspended sediment content is influenced by the mixing process and the intensity of rainfall.

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