scholarly journals FIELD MEASUREMENTS AND MODELLING OF NEARSHORE CURRENTS AT A HIGH-ENERGY GEOLOGICALLY-CONSTRAINED BEACH

2020 ◽  
pp. 18
Author(s):  
Arthur Mouragues ◽  
Philippe Bonneton ◽  
Bruno Castelle ◽  
Vincent Marieu
Keyword(s):  
Surf Zone ◽  
Low Frequency ◽  
Field Measurements ◽  
High Energy ◽  
Oblique Wave ◽  
Wave Forcing ◽  
Circulation Patterns ◽  
Wave Conditions ◽  
Nearshore Currents ◽  
Set Up

We present field measurements of nearshore currents at a high-energy mesotidal beach with the presence of a 500-m headland and a submerged reef. Small changes in wave forcing and tide elevation were found to largely impact circulation patterns. In particular, under 4-m oblique wave conditions, our measurements indicate the presence of an intense low-frequency fluctuating deflection rip flowing against the headland and extending well beyond the surf zone. An XBeach model is further set up to hindcast such flow patterns.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/EiqnjBIkWJE

scholarly journals Headland Rip Modelling at a Natural Beach under High-Energy Wave Conditions

2021 ◽  
Vol 9 (11) ◽  
pp. 1161
Author(s):  
Arthur Mouragues ◽  
Philippe Bonneton ◽  
Bruno Castelle ◽  
Kévin Martins
Keyword(s):  
Surf Zone ◽  
Low Frequency ◽  
High Energy ◽  
Width Ratio ◽  
Coastal Morphology ◽  
M Wave ◽  
Circulation Patterns ◽  
Spatial Coverage ◽  
Wave Event ◽  
Wave Conditions

A XBeach surfbeat model is used to explore the dynamics of natural headland rip circulation under a broad range of incident wave conditions and tide level. The model was calibrated and extensively validated against measurements collected in the vicinity of a 500-m rocky headland. Modelled bulk hydrodynamic quantities were in good agreement with measurements for two wave events during which deflection rips were captured. In particular, the model was able to reproduce the tidal modulation and very-low-frequency fluctuations (≈1 h period) of the deflection rip during the 4-m wave event. For that event, the synoptic flow behaviour shows the large spatial coverage of the rip which extended 1600 m offshore at low tide, when the surf zone limit extends beyond the headland tip. These results emphasize a deflection mechanism different from conceptualised deflection mechanisms based on the boundary length to surf zone width ratio. Further simulations indicate that the adjacent embayment is responsible for the seaward extent of the rip under energetic wave conditions. The present study shows that the circulation patterns along natural rugged coastlines are strongly controlled by the natural variability of the coastal morphology, including headland shape and adjacent embayments, which has implications on headland bypassing expressions.

scholarly journals LONGSHORE TRANSPORT OF SAND

1968 ◽  
Vol 1 (11) ◽  
pp. 18 ◽  
Author(s):  
Douglas L. Inman ◽  
Paul D. Komar ◽  
Anthony J. Bowen
Keyword(s):  
Energy Flux ◽  
Surf Zone ◽  
Field Measurements ◽  
Breaking Waves ◽  
Transport Rate ◽  
Wave Power ◽  
Longshore Transport ◽  
Wave Conditions

Simultaneous field measurements of the energy flux of breaking waves and the resulting longshore transport of sand in the surf zone have been made along three beaches and for a variety of wave conditions. The measurements indicate that the longshore transport rate of sand is directly proportional to the longshore component of wave power.

scholarly journals Unforced Oscillation of Rip-Current Vortex Cells

2013 ◽  
Vol 43 (3) ◽  
pp. 477-497 ◽  
Author(s):  
Joseph D. Geiman ◽  
James T. Kirby
Keyword(s):  
Incident Wave ◽  
Surf Zone ◽  
Low Frequency ◽  
Surface Gravity Wave ◽  
Wave Forcing ◽  
Forcing Function ◽  
Single Dipole ◽  
Wide Range ◽  
Simple Scaling ◽  
Good Agreement

Abstract A numerical simulation of a monochromatic surface gravity wave–driven flow over an alongshore quasi-periodic rip-channeled beach using the wave-resolving model Funwave is used to investigate coherent, very low-frequency (VLF) motions with characteristic frequencies f < 4.0 mHz inside of the surf zone generated by wave breaking. These oscillations of the nearshore cellular vorticity pattern occur for shore-normal waves over a wide range of amplitudes of the incident wave field and occur despite the wave forcing being essentially constant. The oscillations occur at the lower end of the VLF spectrum or around fp = 0.55 mHz. For small incident wave amplitudes, an equilibrium state consisting of a staggered counterrotating vortex array generates a net weak alongshore current that is also seen in drifter trajectories observed in the field. Using a simpler pseudospectral vorticity model of a single dipole generated by a smooth, stationary in time forcing function sb, this study shows show that the Strouhal number of the vortex shedding process responsible for the oscillation is dependent on the circulation strength of the vortices in the dipole, as well as the bottom friction parameter. This process includes the pinching off, advection, and eventual regeneration of the vortex in the dipole. A simple scaling argument shows good agreement with the frequencies observed in the simulations.

scholarly journals COMPUTATION OF LONGSHORE CURRENTS

1974 ◽  
Vol 1 (14) ◽  
pp. 40 ◽  
Author(s):  
Ivar G. Jonsson ◽  
Ove Skovgaard ◽  
Torben S. Jacobsen
Keyword(s):  
Surf Zone ◽  
Numerical Algorithms ◽  
Field Measurements ◽  
Breaking Waves ◽  
Bottom Friction ◽  
Rip Currents ◽  
Longshore Current ◽  
Lateral Mixing ◽  
Set Up ◽  
The Given

The steady state profile of the longshore current induced by regular, obliquely incident, breaking waves, over a bottom with arbitrary parallel bottom contours, is predicted. A momentum approach is adopted. The wave parameters must be given at a depth outside the surf zone, where the current velocity is very small. The variation of the bottom roughness along the given bottom profile must be prescribed in advance. Depth refraction is included also in the calculation of wave set-down and set-up. Current refraction and rip-currents are excluded. The model includes two new expressions, one for the calculation of the turbulent lateral mixing, and one for the turbulent bottom friction. The term for the bottom friction is non-linear. Rapid convergent numerical algorithms are described for the solution of the governing equations. The predicted current profiles are compared with laboratory experiments and field measurements. For a plane sloping bottom, the influence of different eddy viscosities and constant values of bottom roughness is examined.

scholarly journals FIELD MEASUREMENT OF WAVE SET-UP

1988 ◽  
Vol 1 (21) ◽  
pp. 38
Author(s):  
Gregory A. Davis ◽  
Peter Nielsen
Keyword(s):  
Surf Zone ◽  
Field Measurements ◽  
Break Point ◽  
Water Levels ◽  
Pressure Transducers ◽  
Cheap Method ◽  
Mean Water Level ◽  
The Difference ◽  
Set Up ◽  
Average Position

A new, efficient and cheap method is described for obtaining field measurements of surf zone mean water levels. The method applies manometer tubes rather than the traditional pressure transducers. Together with simple stilling well measurements of the water table the results obtained from manometer tubes demonstrate for the first time a complete mean water level profile, from offshore of the break-point to the back-beach region. While some previous studies have provided information about the average position of the waterline, the present study is the first to provide comprehensive field data on the position of the shoreline defined as the intersection of the mean water surface and the sand. The difference between average position of the waterline and the shoreline is not trivial.

scholarly journals Field Measurements of a High-Energy Headland Deflection Rip Current: Tidal Modulation, Very Low Frequency Pulsation and Vertical Structure

2020 ◽  
Vol 8 (7) ◽  
pp. 534 ◽  
Author(s):  
Damien Sous ◽  
Bruno Castelle ◽  
Arthur Mouragues ◽  
Philippe Bonneton
Keyword(s):  
Wave Height ◽  
Surf Zone ◽  
Low Frequency ◽  
High Energy ◽  
Winter Period ◽  
Breaking Wave ◽  
Driving Mechanism ◽  
Peak Period ◽  
Very Low Frequency ◽  
Wave Incidence

Headland rips, sometimes referred to as boundary rips, are rip currents flowing against natural or artificial obstructions extending seaward from the beach, such as headland or groynes. They can be driven either by the deflection of the longshore current against the obstacle or by alongshore variation in breaking wave height due to wave shadowing in the lee of the obstacle. The driving mechanism therefore essentially depends on the angle of wave incidence with respect to the natural or artificial obstruction. We analyze 42 days of velocity profile measurements against a natural headland at the high-energy meso-macrotidal beach of Anglet, southwest France. Measurements were collected in 6.5–10.5-m depth as tide elevation varied, during the autumn–winter period with offshore significant wave height and period ranging 0.9–6 m and 8–16 s, respectively, and the angle of wave incidence ranging from −20 ∘ to 20 ∘ . Here we analyze deflection rip configurations, corresponding to approximately 24 days of measurements, for which the current meter was alternatively located in the rip neck, rip head or away from the rip as wave and tide conditions changed. Deflection rips were associated with large offshore-directed velocities (up to 0.6 m/s depth-averaged velocities) and tide modulation for low- to moderate-energy waves. The vertical profile of deflection rips was found to vary from depth-uniform in the rip neck to strongly depth-varying further offshore in the rip head with maximum velocities near the surface. Very low frequency motions of the rip were dramatic, ranging 10–60 min with a dominant peak period of approximately 40 min, i.e., with longer periods than commonly reported. The strong offshore-directed velocities measured well beyond the surf zone edge provide new insight into deflection rips as a dominant mechanism for water and sediment exchanges between embayed (or structurally-controlled) beaches and the inner-shelf and/or the adjacent embayments.

scholarly journals SHORT WAVE BREAKING EFFECTS ON LOW FREQUENCY WAVES

2011 ◽  
Vol 1 (32) ◽  
pp. 20 ◽  
Author(s):  
Christopher Daly ◽  
Dano Roelvink ◽  
Ap Van Dongeren ◽  
Jaap Van Thiel de Vries ◽  
Robert McCall
Keyword(s):  
Wave Breaking ◽  
Surf Zone ◽  
Low Frequency ◽  
Breaking Waves ◽  
Short Wave ◽  
Frequency Wave ◽  
Wave Heights ◽  
Wave Groupiness ◽  
Set Up ◽  
Low Frequency Waves

The effect of short wave breaking on low frequency waves is investigated using two breaker formulations implemented in a time-dependent numerical model (XBeach): (1) an advective-deterministic approach (ADA) and (2) the probabilistic breaker formulation of Roelvink (1993). Previous research has shown that the ADA breaker model gives different results for the cross-shore pattern of the fraction of breaking waves, which is now shown to affect not only the short wave height but also the short wave groupiness. While RMS short wave heights are comparable to measurements using both breaker models, the ADA breaker model allows higher levels of short wave groupiness into the surf zone. It is shown that this acts as an additional forcing mechanism for low frequency waves in the shoaling and nearshore zone, which, in addition to greater levels of breaking, leads to higher values of wave set-up. These findings are dependent on the complexity of the local bathymetry. For a plane slope, the differences in the low frequency wave heights and set-up predicted by both breaker models are negligible. Where arbitrary breakpoints are present in the field of wave propagation, such as nearshore bars or reefs, the ADA model predicts higher localized set-up, indicative of greater flow over such features. Differences are even more pronounced when the incident wave regime is highly energetic.

Eels Under Standing Wave Conditions

1982 ◽  
Vol 40 ◽  
pp. 492-495
Author(s):  
O.L. Krivanek ◽  
J. TaftØ
Keyword(s):  
Standing Wave ◽  
Wave Conditions ◽  
Set Up ◽  
A Site ◽  
Complex Crystal

It is well known that a standing electron wavefield can be set up in a crystal such that its intensity peaks at the atomic sites or between the sites or in the case of more complex crystal, at one or another type of a site. The effect is usually referred to as channelling but this term is not entirely appropriate; by analogy with the more established particle channelling, electrons would have to be described as channelling either through the channels or through the channel walls, depending on the diffraction conditions.

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