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 Electromagnetic power of lightning superbolts from Earth to space

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
J.-F. Ripoll ◽  
T. Farges ◽  
D. M. Malaspina ◽  
G. S. Cunningham ◽  
E. H. Lay ◽  
...  
Keyword(s):  
Low Frequency ◽  
Optical Emission ◽  
High Energy ◽  
Very Low Frequency ◽  
Electromagnetic Power ◽  
Power Spectral ◽  
High Energy Tail ◽  
Van Allen Probes ◽  
Long Time ◽  
Low Frequency Waves

AbstractLightning superbolts are the most powerful and rare lightning events with intense optical emission, first identified from space. Superbolt events occurred in 2010-2018 could be localized by extracting the high energy tail of the lightning stroke signals measured by the very low frequency ground stations of the World-Wide Lightning Location Network. Here, we report electromagnetic observations of superbolts from space using Van Allen Probes satellite measurements, and ground measurements, and with two events measured both from ground and space. From burst-triggered measurements, we compute electric and magnetic power spectral density for very low frequency waves driven by superbolts, both on Earth and transmitted into space, demonstrating that superbolts transmit 10-1000 times more powerful very low frequency waves into space than typical strokes and revealing that their extreme nature is observed in space. We find several properties of superbolts that notably differ from most lightning flashes; a more symmetric first ground-wave peak due to a longer rise time, larger peak current, weaker decay of electromagnetic power density in space with distance, and a power mostly confined in the very low frequency range. Their signal is absent in space during day times and is received with a long-time delay on the Van Allen Probes. These results have implications for our understanding of lightning and superbolts, for ionosphere-magnetosphere wave transmission, wave propagation in space, and remote sensing of extreme events.

scholarly journals Environmental controls on surf zone injuries on high-energy beaches

2019 ◽  
Vol 19 (10) ◽  
pp. 2183-2205 ◽  
Author(s):  
Bruno Castelle ◽  
Tim Scott ◽  
Rob Brander ◽  
Jak McCarroll ◽  
Arthur Robinet ◽  
...  
Keyword(s):  
Wave Height ◽  
Surf Zone ◽  
High Tide ◽  
High Energy ◽  
Water Levels ◽  
Small Scale ◽  
Beach Morphology ◽  
Environmental Controls ◽  
Flow Activity ◽  
Incident Waves

Abstract. The two primary causes of surf zone injuries (SZIs) worldwide, including fatal drowning and severe spinal injuries, are rip currents (rips) and shore-break waves. SZIs also result from surfing and bodyboarding activity. In this paper we address the primary environmental controls on SZIs along the high-energy meso–macro-tidal surf beach coast of southwestern France. A total of 2523 SZIs recorded by lifeguards over 186 sample days during the summers of 2007, 2009 and 2015 were combined with measured and/or hindcast weather, wave, tide, and beach morphology data. All SZIs occurred disproportionately on warm sunny days with low wind, likely because of increased beachgoer numbers and hazard exposure. Relationships were strongest for shore-break- and rip-related SZIs and weakest for surfing-related SZIs, the latter being also unaffected by tidal stage or range. Therefore, the analysis focused on bathers. More shore-break-related SZIs occur during shore-normal incident waves with average to below-average wave height (significant wave height, Hs = 0.75–1.5 m) and around higher water levels and large tide ranges when waves break on the steepest section of the beach. In contrast, more rip-related drownings occur near neap low tide, coinciding with maximised channel rip flow activity, under shore-normal incident waves with Hs >1.25 m and mean wave periods longer than 5 s. Additional drowning incidents occurred at spring high tide, presumably due to small-scale swash rips. The composite wave and tide parameters proposed by Scott et al. (2014) are key controlling factors determining SZI occurrence, although the risk ranges are not necessarily transferable to all sites. Summer beach and surf zone morphology is interannually highly variable, which is critical to SZI patterns. The upper beach slope can vary from 0.06 to 0.18 between summers, resulting in low and high shore-break-related SZIs, respectively. Summers with coast-wide highly (weakly) developed rip channels also result in widespread (scarce) rip-related drowning incidents. With life risk defined in terms of the number of people exposed to life threatening hazards at a beach, the ability of morphodynamic models to simulate primary beach morphology characteristics a few weeks or months in advance is therefore of paramount importance for predicting the primary surf zone life risks along this coast.

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 Studi Hindcasting Dalam Menentukan Karakteristik Gelombang dan Klasifikasi Zona Surf Di Pantai Uluwatu, Bali

2018 ◽  
Vol 5 (1) ◽  
pp. 119
Author(s):  
Karina Santoso ◽  
I Dewa Nyoman Nurweda Putra ◽  
I Gusti Bagus Sila Dharma
Keyword(s):  
Wave Height ◽  
Calculation Result ◽  
Significant Wave Height ◽  
Surf Zone ◽  
Wind Data ◽  
Wave Transformation ◽  
Breaking Wave ◽  
Significant Wave ◽  
The World

Bali is one of the islands where there are many surf zones with various characteristics. In addition, Bali is also a heaven with a classy wave for the surfers of the world. One of the most challenging places to surf in Bali is Uluwatu Beach. Uluwatu Beach is ranked the 3rd best surf spot in the world version of CNN Travel in 2012. Wind causes sea waves, therefore wind data can be used to estimate the height and direction of the waves. Wave Hindcasting with Sverdrup, Munk and Bretschneider (SMB) method is calculated based on wind data for 10 years (2001 - 2010) from BMKG Ngurah Rai Station - Denpasar to obtain a significant wave height and period. In this research, it is necessary to approach through Hindcasting procedure, wave transformation analysis and surfing Terminology in determining the type of breaking wave and classification of surf zone in Uluwatu Beach area. Wave calculation result in Uluwatu Beach dominated by wave that coming from west side with significant wave height (Hs) of 0.98 m and significant wave period (Ts) of 5.21 s. The wave height due to the influence of wave refraction and shoaling is 0.976 m. The breaking wave height obtained from the calculation is 1.04 m at a depth of 0.849 m. From the result in this research, it can be concluded that the breaking wave type that occurred at Uluwatu Beach is plunging type according to the calculation result from its Irribaren number (0.4 <Ni <2.3). The classification of the surf zone at Uluwatu Beach based on its breakup type of wave is thought to be a good zone for surfers on intermediate level.

Research and Analysis on the Wave Transformation and Irregular Wave Breaking Criterion on the Shore

2016 ◽  
Vol 858 ◽  
pp. 354-358
Author(s):  
Tao You ◽  
Li Ping Zhao ◽  
Zheng Xiao ◽  
Lun Chao Huang ◽  
Xiao Rui Han
Keyword(s):  
Theoretical Model ◽  
Wave Height ◽  
Wave Breaking ◽  
Surf Zone ◽  
Breaking Waves ◽  
Wave Transformation ◽  
Breaking Wave ◽  
Height Distribution ◽  
Flume Experiments ◽  
Irregular Wave

Within the surf zone which is the region extending from the seaward boundary of wave breaking to the limit of wave uprush, breaking waves are the dominant hydrodynamics acting as the key role for sediment transport and beach profile change. Breaking waves exhibit various patterns, principally depending on the incident wave steepness and the beach slope. Based on the equations of conservation of mass, momentum and energy, a theoretical model for wave transformation in and outside the surf zone was obtained, which is used to calculate the wave shoaling, wave set-up and set down and wave height distributions in and outside the surf zone. The analysis and comparison were made about the breaking point location and the wave height variation caused by the wave breaking and the bottom friction, and about the wave breaking criterion under regular and irregular breaking waves. Flume experiments relating to the regular and irregular breaking wave height distribution across the surf zone were conducted to verify the theoretical model. The agreement is good between the theoretical and experimental results.

scholarly journals Environmental controls on surf zone injuries on high-energy beaches

2019 ◽  
Author(s):  
Bruno Castelle ◽  
Tim Scott ◽  
Rob Brander ◽  
Jak McCarroll ◽  
Arthur Robinet ◽  
...  
Keyword(s):  
Wave Height ◽  
Surf Zone ◽  
High Tide ◽  
High Energy ◽  
Water Levels ◽  
Small Scale ◽  
Beach Morphology ◽  
Environmental Controls ◽  
Flow Activity ◽  
Incident Waves

Abstract. The two primary causes of surf zone injuries (SZIs) worldwide, including fatal drowning and severe spinal injuries, are rip currents (rips) and shore-break waves. SZIs also result from surfing and body boarding activity. In this paper we address the primary environmental controls on SZIs along the high-energy meso-macrotidal surf beach coast of SW France. A total of 2523 SZIs recorded by lifeguards over 186 sample days during the summers of 2007, 2009 and 2015 were combined with measured and/or hindcast weather, wave, tide and beach morphology data. All SZIs occurred disproportionately on warm sunny days with low wind likely because of increased beachgoer numbers and hazard exposure. Relationships were strongest for shore break and rip related SZIs and weakest for surfing related SZIs, the latter being also unaffected by tidal stage or range. Therefore the analysis focussed on bathers. Shore-break related SZIs disproportionately occur during shore-normal incident waves with average to below-average wave height (significant wave height Hs = 0.75–1.5 m) and around higher water levels and large tide range when waves break on the steepest section of the beach. In contrast, rip related drownings occur disproportionally near neap low tide, coinciding with maximized channel rip flow activity, under shore-normal incident waves with Hs > 1.25 m and periods mean wave period longer than 5 s. Additional drowning incidents occurred at spring high tide, presumably due to small-scale swash rips. The composite wave and tide parameters proposed by Scott et al. (2014) are key controlling factors determining SZI occurrence, although the risk ranges are not necessarily transferable to all sites. Summer beach and surf zone morphology is highly interannually variable, which is critical to SZI patterns. The upper beach slope can vary from 0.06 to 0.18 between summers, resulting in low and high shore-break related SZIs, respectively. Summers with coast-wide highly (weakly) developed rip channels also result in widespread (scarce) rip related drowning incidents. With life risk defined in terms of the number of people exposed to life threatening hazards at a beach, the ability of morphodynamic models to simulate primary beach morphology characteristics a few weeks/months in advance is therefore of paramount importance to predict the primary surf-zone life risks along this coast.

scholarly journals A LONG-TERM EQUILIBRIUM BEACH PLANFORM MODEL FOR COASTAL WORK DESIGN

2012 ◽  
Vol 1 (33) ◽  
pp. 43 ◽  
Author(s):  
Verónica Cánovas ◽  
Raúl Medina
Keyword(s):  
Sediment Transport ◽  
Case Studies ◽  
Wave Height ◽  
Surf Zone ◽  
Control Point ◽  
Wave Climate ◽  
Work Design ◽  
Sediment Distribution ◽  
Wave Incidence

Traditional models usually allow fitting the equilibrium beach planform of crenulated beaches knowing wave climate characteristics at a control point. However, sometimes there are shoals or bars in the surf zone which affect surf zone dynamics and longshore sediment distribution, and it is difficult to take into account these elements using those traditional models. A long-term equilibrium beach planform model is proposed here based on sediment transport equations. This model takes into account the sediment transport due to oblique wave incidence and that due to wave height gradient. Two case studies have been studied: a simple pocket beach and a beach which is sheltered by a sandstone bar. Results show the model fits reasonably well the equilibrium beach planform to the shorelines of those beaches. This model is more suitable than traditional models when there are elements affecting surf zone dynamics.

Observing Surf-Zone Dispersion with Drifters

2007 ◽  
Vol 37 (12) ◽  
pp. 2920-2939 ◽  
Author(s):  
Matthew Spydell ◽  
Falk Feddersen ◽  
R. T. Guza ◽  
W. E. Schmidt
Keyword(s):  
Wave Height ◽  
Surf Zone ◽  
Major Axis ◽  
Relative Dispersion ◽  
Inertial Subrange ◽  
Breaking Wave ◽  
Similar Distribution ◽  
The One ◽  
Non Gaussian ◽  
Particle Statistics

Abstract Surf-zone dispersion is studied using drifter observations collected within about 200 m of the shoreline (at depths of less than about 5 m) on a beach with approximately alongshore uniform bathymetry and waves. There were about 70 individual drifter releases, each 10–20 min in duration, on two consecutive days. On the first day, the sea-swell significant wave height Hs was equal to 0.5 m and mean alongshore currents |υ| were moderate (&lt;0.1 m s−1). On the second day, the obliquely incident waves were larger, with Hs equal to 1.4 m, and at some surf-zone locations |υ| was greater than 0.5 m s−1. The one-particle diffusivity was larger, with larger waves and stronger currents. On both days, the one-particle diffusivity tensor is nonisotropic and time-dependent. The major axis is initially parallel to the cross-shore direction, but after a few wave periods it is aligned with the alongshore direction. In both the along- and cross-shore directions, the asymptotic diffusivity is reached sooner within, rather than seaward of, the surf zone. Two-particle statistics indicate that relative dispersion grows like D2(t) ∼ t3/2 and that the relative diffusivity is scale-dependent as μ ∼ l2/3, with l being the particle separation. The observed scalings differ from 2D inertial-subrange scalings [D2(t) ∼ t3 and μ ∼ l4/3]. Separations have a non-Gaussian self-similar distribution that is independent of time. The two-particle statistics are consistent with a nonconstant-coefficient diffusion equation for the separation probability density functions. The dispersion is explained by neither irrotational surface gravity waves nor shear dispersion. The observations imply the existence of a 2D eddy field with 5–50-m length scales, the source of which is speculated to be alongshore gradients in breaking-wave height associated with finite crest lengths.

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.

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