Observations of large infragravity wave runup at Banneg Island, France

Sheremet, A.; Staples, Tracy; Ardhuin, Fabrice; Suanez, Serge; Fichaut, Bernard

doi:10.1002/2013gl058880

Cited by 40 publications

(38 citation statements)

References 30 publications

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“…Measurements with arrays of instruments reveal that free waves generally dominate the bottom pressure records in water depths larger than 20 m or so [ Webb et al ., ; Herbers and Guza , , ]. Integrated over 5 to 30 mHz, the heights of IG waves strongly vary with the local water depth, ranging from an average of 0.5 to 2 cm in 4000 m depth [ Aucan and Ardhuin , ] to several meters during extreme events near the shoreline where they play an important role in coastal flooding [ Sheremet et al ., ]. The possible resonant excitation of harbors [e.g., Okihiro et al ., ] and ice tongues [ Bromirski et al ., ] means that even small amplitudes IG waves can be important.…”

Section: Introductionmentioning

confidence: 99%

Infragravity waves across the oceans

Rawat

Ardhuin

Ballu

et al. 2014

Geophysical Research Letters

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Ocean infragravity (IG) waves are low-frequency waves generated along shorelines by incident seas and swell and with heights of the order of 1 cm in the open ocean. Despite these small amplitudes, they can be of much importance for ice shelf break up and errors in measurements of sea level by future satellite altimeters. A combination of numerical model results and in situ data is used to show that bottom pressure signals in the infragravity frequency band can be dominated by bursts of energy that travel across ocean basins, and can last for several days. Two particularly strong events recorded in 2008 are studied, one in the North-Pacific and the other in the North-Atlantic. It is shown that infragravity waves can travel across whole oceans basins with the signal recorded on the western shores often dominated by IG waves coming from the opposite shore of that same ocean basin.

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Section: Introductionmentioning

confidence: 99%

Infragravity waves across the oceans

Rawat

Ardhuin

Ballu

et al. 2014

Geophysical Research Letters

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“…Of particular interest is the identification of the respective contribution of the wave setup, the incident swash, and the infragravity swash components to the total runup (Guza & Thornton, ; Holman & Sallenger, ; Stockdon et al, ). On Banneg Island, very high infragravity waves, up to 2 m, have been observed (Sheremet et al, ). Such infragravity waves are likely to contribute to the occasional flooding of the island and the displacement of cliff‐top storm deposits (Autret et al, ; Suanez et al, ).…”

Section: Discussionmentioning

confidence: 99%

“…However, in the absence of runup measurements, these guesses rely on the extrapolation of the runup formula proposed by Stockdon et al () for beaches. Another study on the Banneg cliff hydrodynamics used data from the 2008–2009 winter and focused on infragravity waves which were found to be exceptionally high (Sheremet et al, ) and are expected to form a significant fraction of the runup. Here we use more recent and more extensive data to provide runup measurements and explore the physical processes that control wave runup over steep rocky cliff.…”

Section: Banneg Islandmentioning

confidence: 99%

Wave Runup Over Steep Rocky Cliffs

et al. 2018

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Wave runup is known to depend on offshore wave conditions and coastal morphology.While most field studies on wave runup have focused on low-to-mild-sloping sandy beaches, runup measurements on steep and irregular rocky cliff profiles are still very scarce. Here we investigate the physical processes controlling wave runup in such environments and the range of applicability of empirical runup formula. This study focuses on the steep rocky cliffs (0.1 < tan < 0.4) of Banneg Island, a small island located in the Molène archipelago, Brittany, France, occasionally flooded during extreme water level events. A statistical parameter for extreme runup is derived from the measurements of pressure sensors deployed in the intertidal zone. Deep water wave parameters are used to force a high-resolution wave model, and nearshore wave parameters and high-resolution topographic data are analyzed concurrently with runup time series in order to assess the dependence of the runup on hydrodynamic conditions and morphological parameters. The wave runup is shown to be strongly related to the square root of the offshore significant wave height times the offshore wavelength. The measurements also reveal the depth dependence of the runup, which is mainly attributed to the curvature of the foreshore profile. In comparison to empirical relation obtained for a mild-sloping beach, the present data show a significant reduction in normalized wave runup, that is attributed to enhanced bottom friction over the rocky bottom. Plain Language SummaryWhen waves reach the shores, they travel up and down the beach before being reflected seaward. The maximum vertical excursion of the waterline relative to the still water level, called the wave runup, is a key parameter for the design of coastal structures and the prediction of overtopping volumes during storm events. Most runup studies in natural environments have focused on smooth and mild-sloping sandy beaches, and empirical formula to predict the wave runup has been derived for these environments. Here we study the process of wave runup over steep rocky cliffs. Using pressure sensors deployed in the intertidal zone of Banneg Island-a small island located west of Brittany, France, exposed to very high waves-we measured runup events. Then we investigated the link between these runup data, offshore wave parameters, and cliff slopes. Our results reveal that the wave runup is linearly dependent to the square root of the offshore wave height times the offshore wavelength. In addition, a significant reduction of the runup is found compared to sandy environments, which is attributed to the frictional effect exerted by the rocky bottom on the flow.

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“…2. A second and distinct type of nonlinear effect, demonstrated to occur on the rocky Atlantic coast of Banneg Island, France, involves large infragravity waves of low-frequency (300 s period) that become trapped against the shore during storms (Sheremet et al, 2014). Such focusing of wave energy increases the probability of encountering large waves in these areas.…”

Section: Giant or "Rogue" Wavesmentioning

confidence: 99%