scholarly journals NEARSHORE SEDIMENT TRANSPORT: ESTIMATES FROM DETAILED MEASUREMENTS OF THE NEARSHORE VELOCITY FIELD

1984 ◽  
Vol 1 (19) ◽  
pp. 115
Author(s):  
A.J. Bowen ◽  
J.C. Doering
Keyword(s):  
Sediment Transport ◽  
Velocity Field ◽  
Conceptual Models ◽  
Relative Importance ◽  
Rip Currents ◽  
Velocity Measurements ◽  
Wave Drift ◽  
Nearshore Sediment Transport ◽  
Incident Waves

A very wide variety of conceptual models has been used to explain the movement of sediment in the nearshore region. While there is general agreement that the incident waves are primarily responsible for the mobilisation of sediment, many processes have been proposed as the transport agents, for example, wave drift velocities, wave assymetry, longshore and rip currents, undertow, the downslope component of gravity. As it is currently difficult to make reliable point measurements of sediment transport, many of these ideas can not be tested directly. However, in many cases, detailed measurements of the velocity field in the water can be used to examine at least the relative importance of these possible processes. The situation is complicated by the lack of accepted formulae for sediment transport. The result is that the velocity measurements are also being used to examine the 'reasonability' of the various formulations.

Sedimentation and equilibrium in wave-formed bars: a review and case study

1979 ◽  
Vol 16 (2) ◽  
pp. 312-332 ◽  
Author(s):  
Brian Greenwood ◽  
Robin G. D. Davidson-Arnott
Keyword(s):  
Sediment Transport ◽  
Hydrodynamic Instability ◽  
Field Measurements ◽  
Theoretical Models ◽  
Break Point ◽  
Rip Currents ◽  
Group Vi ◽  
Process Factors ◽  
Incident Waves ◽  
Bar Formation

A tentative classification of wave-formed bars is presented based on available evidence of both morphological and process factors. One specific group of bars (group VI), which has been described by numerous studies in the Great Lakes, the Mediterranean, and the Gulf of St. Lawrence, is examined in detail; models of bar formation and equilibrium, which may be relevant to this group, are reviewed and evaluated. These include (1) vortex action under plunging breakers; (2) interaction of incident waves with standing waves generated by reflection; (3) interaction of incident waves with standing edge waves; and (4) hydrodynamic instability of a uniformly long wave setup produced by incident waves.Results of field measurements of one set of crescentic group VI bars in Kouchibouguac Bay, New Brunswick, indicate that none of the theoretical models adequately explains the characteristics of these bars: (a) the stability of the bar form in an area of high longshore sediment transport; (b) sediment transport patterns, which reveal a continuous circulation of sediment through the bar; and (c) the occurrence of spilling rather than plunging breakers. A conceptual model of bar formation and equilibrium is proposed based upon: (a) landward sediment transport by shoaling waves, increasing towards the break point; (b) gradual reduction of transport rates associated with spilling breakers leading to a buildup of the bar; (c) maintenance of the trough through removal of sediments by longshore and rip current circulation; (d) seaward transport of sediment by rip currents; and (e) landward transport of sediments under reformed waves landward of the trough. The application of this model to other group VI bars, particularly straight bars, is discussed.

scholarly journals Artificial Intelligence Application on Sediment Transport

2021 ◽  
Vol 9 (6) ◽  
pp. 600
Author(s):  
Hyun Dong Kim ◽  
Shin-ichi Aoki
Keyword(s):  
Sediment Transport ◽  
Numerical Models ◽  
Beach Nourishment ◽  
Hydraulic Model ◽  
Alternative Methods ◽  
Cross Sectional ◽  
Sand And Gravel ◽  
Incident Waves ◽  
Artificial Intelligence Application ◽  
Deep Learning Model

When erosion occurs, sand beaches cannot maintain sufficient sand width, foreshore slopes become steeper due to frequent erosion effects, and beaches are trapped in a vicious cycle of vulnerability due to incident waves. Accordingly, beach nourishment can be used as a countermeasure to simultaneously minimize environmental impacts. However, beach nourishment is not a permanent solution and requires periodic renourishment after several years. To address this problem, minimizing the period of renourishment is an economical alternative. In the present study, using the Tuvaluan coast with its cross-sectional gravel nourishment site, four different test cases were selected for the hydraulic model experiment aimed at discovering an effective nourishment strategy to determine effective alternative methods. Numerical simulations were performed to reproduce gravel nourishment; however, none of these models simultaneously simulated the sediment transport of gravel and sand. Thus, an artificial neural network, a deep learning model, was developed using hydraulic model experiments as training datasets to analyze the possibility of simultaneously accomplishing the sediment transport of sand and gravel and supplement the shortcomings of the numerical models.

scholarly journals SURVEY TECHNIQUES/PROCEDURES AND DATA PROCESSING FOR MONITORING NEARSHORE SEDIMENT TRANSPORT

1982 ◽  
Vol 1 (18) ◽  
pp. 97
Author(s):  
J. Zacks
Keyword(s):  
Sediment Transport ◽  
Surf Zone ◽  
Survey Techniques ◽  
The Past ◽  
Bed Elevation ◽  
Innovative Methods ◽  
Survey Error ◽  
Nearshore Sediment Transport ◽  
The Many ◽  
The Cost

The cost of many coastal projects is often increased by the expensive beach repair and maintenance required to remedy the destabilising effects of structures on the adjoining coastline. Physical and/or mathematical models have been developed for use in planning these projects in order to predict and quantify the effects of marine sediment transport on the coastal topography. Such models need to be calibrated against prototype data and one method of gauging volumetric sediment movement is by successive bathymetric/ topographic profiting surveys which are performed seasonally and annually. Since large quantities of sediment are related to small changes in bed elevation it is clear that this profiling needs to be done with the utmost precision* The areas most affected extend from the beach through the surf zone to water depths of about 25 metres. The surf zone in particular is a dynamic and hostile area which falls outside the traditional activities of both the hydrographic and land surveyors. Consequently innovative methods, deficient in sound survey principle and practice, have often been pursued in this area without any attempt being made to assess the tolerance on the data. This paper attempts to show that it is possible to produce reliable and verifiable results to the required accuracy by using conventional survey equipment and techniques, also by taking the necessary precautions against the many possible sources of survey error. The procedures and techniques described have evolved from NRIO's involvement over the past decade in major projects at Richards Bay, Durban, Koeberg and in False Bay. The results of a recent verification investigation are fully reported in this paper.

scholarly journals GROIN LENGTH AND THE GENERATION OF EDGE WAVES

1976 ◽  
Vol 1 (15) ◽  
pp. 85 ◽  
Author(s):  
Michael K. Gaughan ◽  
Paul D. Komar
Keyword(s):  
Incident Wave ◽  
Wave Length ◽  
Critical Length ◽  
Beach Erosion ◽  
Rip Currents ◽  
Edge Waves ◽  
Normal Waves ◽  
Wave Basin ◽  
Incident Waves ◽  
Selection Of

A series of wave basin experiments were undertaken to better understand the selection of groin spacings and lengths. Rather than obtaining edge waves with the same period as the normal incident waves, subharmonic edge waves were produced with a period twice that of the incoming waves and a wave length equal to the groin spacing. Rip currents were therefore not formed by the interactions of the synchronous edge waves and normal waves as proposed by Bowen and Inman (1969). Rips were present in the wave basin but their origin is uncertain and they were never strong enough to cause beach erosion. The generation of strong subharmonic edge waves conforms with the work of Guza and Davis (1974) and Guza and Inman (1975). The subharmonic edge waves interacted with the incoming waves to give an alternating sequence of surging and collapsing breakers along the beach. Their effects on the swash were sufficient to erode the beach in some places and cause deposition in other places. Thus major rearrangements of the sand were produced between the groins, but significant erosion did not occur as had been anticipated when the study began. By progressively decreasing the length of the submerged portions of the groins, it was found that the strength (amplitude) of the edge waves decreases. A critical submerged groin length was determined whereby the normally incident wave field could not generate resonant subharmonic edge waves of mode zero with a wavelength equal to the groin spacing. The ratio of this critical length to the spacing of the groins was found in the experiments to be approximately 0.15 to 0.20, and did not vary with the steepness of the normal incident waves.

scholarly journals Analytic reconstruction of a two-dimensional velocity field from an observed diffusive scalar

2019 ◽  
Vol 871 ◽  
pp. 755-774
Author(s):  
Arjun Sharma ◽  
Irina I. Rypina ◽  
Ruth Musgrave ◽  
George Haller
Keyword(s):  
Velocity Field ◽  
Ocean Circulation ◽  
Incompressible Flows ◽  
Circulation Model ◽  
Scalar Fields ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Velocity Measurements ◽  
Ocean Circulation Model ◽  
Spatial Domains

Inverting an evolving diffusive scalar field to reconstruct the underlying velocity field is an underdetermined problem. Here we show, however, that for two-dimensional incompressible flows, this inverse problem can still be uniquely solved if high-resolution tracer measurements, as well as velocity measurements along a curve transverse to the instantaneous scalar contours, are available. Such measurements enable solving a system of partial differential equations for the velocity components by the method of characteristics. If the value of the scalar diffusivity is known, then knowledge of just one velocity component along a transverse initial curve is sufficient. These conclusions extend to the shallow-water equations and to flows with spatially dependent diffusivity. We illustrate our results on velocity reconstruction from tracer fields for planar Navier–Stokes flows and for a barotropic ocean circulation model. We also discuss the use of the proposed velocity reconstruction in oceanographic applications to extend localized velocity measurements to larger spatial domains with the help of remotely sensed scalar fields.

Patterns of nearshore sediment transport along the Nile Delta, Egypt

1991 ◽  
Vol 15 (5-6) ◽  
pp. 409-429 ◽  
Author(s):  
Omran E. Frihy ◽  
Alfy M. Fanos ◽  
Ahmed A. Khafagy ◽  
Paul D. Komar
Keyword(s):  
Sediment Transport ◽  
Nile Delta ◽  
Nearshore Sediment Transport

Mathematical modelling of shallow flows: Closure models drawn from grain-scale mechanics of sediment transport and flow hydrodynamicsThis paper is one of a selection of papers in this Special Issue in honour of Professor M. Selim Yalin (1925–2007).

2009 ◽  
Vol 36 (10) ◽  
pp. 1605-1621 ◽  
Author(s):  
Rui M. L. Ferreira ◽  
Mário J. Franca ◽  
João G. A. B. Leal ◽  
António H. Cardoso
Keyword(s):  
Sediment Transport ◽  
Mathematical Modelling ◽  
Conceptual Models ◽  
Numerical Solutions ◽  
Shear Stresses ◽  
Shallow Flows ◽  
River Modelling ◽  
Morphologic Evolution ◽  
Sediment Mixtures ◽  
Selection Of

Mathematical modelling of river processes is, nowadays, a key element in river engineering and planning. River modelling tools should rest on conceptual models drawn from mechanics of sediment transport, river mechanics, and river hydrodynamics. The objectives of the present work are (i) to describe conceptual models of sediment transport, deduced from grain-scale mechanics of sediment transport and turbulent flow hydrodynamics, and (ii) to present solutions to specific river morphology problems. The conceptual models described are applicable to the morphologic evolution of rivers subjected to the transport of poorly sorted sediment mixtures at low shear stresses and to geomorphic flows featuring intense sediment transport at high shear stresses. In common, these applications share the fact that sediment transport and flow resistance depend, essentially, on grain-scale phenomena. The idealized flow structures are presented and discussed. Numerical solutions for equilibrium and nonequilibrium sediment transport are presented and compared with laboratory and field data.

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