Field Experiments of Beach Scarp Erosion During Oblique Wave, Stormy Conditions (Normandy, France)

Geomorphology 236 (2015) 132–147

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Geomorphology

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Field experiments of beach scarp erosion during oblique wave, stormy conditions (Normandy, France)

Yoann Bonte ⁎,FranckLevoy

Unité Morphodynamique Continentale et Côtière (M2C), Université de Caen-Basse Normandie, 24 rue des Tilleuls, 14000 Caen Cedex, France article info abstract

Article history: A field-based experimental study of beach scarp morphodynamic evolution was conducted on the shoreface of a Received 2 July 2014 macrotidal sandy beach subject to storms combined with spring tide events (Luc-sur-Mer, France). Both video Received in revised form 3 February 2015 and in-situ measurements on an artificial berm are used to understand beach scarp evolution over one tide Accepted 15 February 2015 during stormy conditions. Image time stacks are used to analyze the swash action on the beach scarp and topo- Available online 21 February 2015 graphical data of the scarp are recorded with a terrestrial scanner laser to quantify the morphodynamic response Keywords: of the beach scarp to wave action. This work provides a new and unique dataset about beach scarp changes and Beach scarp berm morphology in particular under rising tide and oblique wind-wave conditions. During one stormy event, Swash zone the berm was completely destroyed. However, contrasting alongshore changes were measured during the Berm erosion erosive phase with different crest and foot scarp retreats and eroded volumes between the west and the east Video system measurement side of the berm. The beach in front of the scarp also shows a contrasting residual evolution, indicating an evident Terrestrial laser longshore sediment transport on the study area as a consequence of incident oblique wave conditions. A strong Macrotidal beaches connection between beach evolution and beach scarp changes is clearly identified. The scarp erosion increases on the west side of the berm when the beach level is lowered and reduces when the beach surface rises on the east side. The beach slope and foreshore elevation as a result of a longshore sediment transport between east and west profiles, influence swash activity. Overall, water depth and swash activity became progressively different along the scarp during the experiment. Swash measurements indicate that the presence of the beach scarp strongly influences the swash motion. At high tide, the reflection of the uprush on the scarp front induces a collision between the reflected backwash and the following uprush dynamic. These collisions reduce and sometimes stop the motion of the following uprush, reducing the incoming swash excursion. Consequently, the scarp presence modifies the swash interaction that normally appears on a planar beach surface. With a beach scarp, the swash energy level is substantially attenuated and its spectrum is characterized by a large band. The number of uprush impacts on the scarp front calculated from video images reaches about 25 per 5 min. In spite of the swash energy attenuation due to swash/swash interactions, these impacts provoke the berm destruction in about two hours. However, the onshore migration of the swash zone induced by the rising tide appears to be important to explain scarp destruction, compensating the attenuated swash activity due to backwash-uprush interactions. © 2015 Elsevier B.V. All rights reserved.

1. Introduction et al., 2005) and cause inconvenience to beach users (Kobayashi et al., 2009; Ruiz de Alegria-Arzaburu et al., 2013). Coastal dunes protect low-lying area from flooding and must be Scarp formation has been also observed in a variety of natural sandy actively managed to prevent damage along many sandy coasts around beaches around the world (Sherman and Nordstrom, 1985; Carter, the world. The berm height constitutes an important element of the 1988; Short, 1999; Vousdoukas, 2012) and on artificial beaches natural system to control and reduce the rate of dune recession. For (Kubota et al., 1997). Scarp persistence depends of the local beach example, many beach nourishment projects include the construction conditions. A beach scarp can disappear through continued upslope of a wide berm to improve the dissipation of wave energy during migration, collapse as a result of drying of the beach, or be destroyed major storms and to limit the shoreline erosion. However, beach scarps by wave overtopping (Sherman and Nordstrom, 1985). Scarps probably after nourishment can appear unexpectedly (Nishi et al., 1994; Seymour retard post-storm recovery by waves because low steepness constructive waves during high water levels are reflected by the vertical face of this morphology (Nishi et al., 1994). ⁎ Corresponding author. Tel.: +33 231 565 744. This morphological feature is common on eroding beaches, as point- E-mail address: [email protected] (Y. Bonte). ed out by Carter and Stone (1989), and although there are numerous

http://dx.doi.org/10.1016/j.geomorph.2015.02.014 0169-555X/© 2015 Elsevier B.V. All rights reserved. Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 133 studies on the morphology and physical processes affecting the scarp of impacts induced by swash, water level and beach scarp face retreat is a dune and many conceptual models describing beach scarps on investigated. These data constitute a unique set of active scarp erosion microtidal and mesotidal environments (Wright and Short, 1983; based on field measurements helpful for calibrating/validating 3D Sunamura, 1985; Short, 1999), quantitative information about beach beach erosion modeling over short timescales also accounting for a scarp formation and evolution in macrotidal environments is still longshore sediment transport gradient. lacking. Sherman and Nordstrom (1985) give a qualitative description of beach scarp formation and evolution based on field observations, 2. Equipment and methods but without a data set to analyze the conditions for the scarp initiation and evolution. 2.1. Field site Katoh and Yanagishima (1990, 1992) studied natural berm formation and erosion using a multi-year dataset of daily surveys of An instrumental field study of the beach scarp morphodynamics was beach profiles. The authors demonstrated the role of long waves near conducted in March 2012 on a beach where natural beach scarps have the shoreline and watertable level on berm erosion. Longshore often been observed. This field site is located at Luc-sur-Mer Beach, on transport and its morphological effects are also important. For instance, the south coast of the Bay of Seine (Fig. 1). The maximum spring tidal Seymour et al. (2005) observed rapid erosion of a berm fill and that range reaches 8 m and the tidal wave is dominated by the M2 semi- scarping resulted in an alongshore quasiperiodic variability. diurnal harmonic whose amphidromic point is a virtual one located Two main field experiments studied artificial sandy beach scarp onland in the southwest of England (Pingree and Griffiths, 1979). The (respective heights of about 0.3 and 1.0 m) with hydrodynamic central English Channel is an area of strong tidal current activity, mainly measurements and topographic surveys during storm events to calcu- longshore oriented and revealing a maximum 3 hours after high and late the eroded volume of the dune as a function of the swash impact. low tide. This coast is partly sheltered from the influence of the prevail- At the Army Corps of Engineers Field Research facilities at Duck, during ing western Atlantic swells by the Cherbourg peninsula, and is mainly the SUPERDUCK experiment, an artificial dune approximately 1.0 m affected by local wind waves (Larsonneur et al., 1982). The prevailing high and 1.3 m wide (classical height for a berm scarp) was built on winds are from the north to northwest, although the strongest winds the beach and allowed to erode naturally during rising tide (Fisher are directed offshore (from the southwest). The local wind induces et al., 1986; Crowson et al., 1988; Overton and Fisher, 1988). Video waves from the north-western sector with short periods ranging from camera recorded both the changes in the artificial berm scarp and the 3to7s(Monfort et al., 2000). The mean annual significant wave height swash impact sequences through one lateral face made with a clear measured on the lower part of the foreshore at Luc-sur-Mer Beach plastic (different to the other made with plywood). Vertical stakes and between 2007 and 2012 (Fig. 2) is around 0.33 m. wave gages were placed in front of the artificial berm scarp to measure The beach slopes, expressed as tan β, vary from 0.08 for the high tidal depth and velocity of the swash. These experiments concluded that it is zone to 0.03 for the upper part of the mid-tidal zone. The sediment difficult to isolate the impact of a single swash on the amount of the comprises a variable range of grain sizes from fine sands (D50, mid = sand eroded, but the total erosion during one event is linearly correlated 0.217 mm) on the mid-tidal zone to coarse sands (D50, high = with the summation of the swash force for each individual swash. 0.622 mm) on the high tidal zone. A 20 m-wide low-amplitude sandbar Another dataset originated from Hasaki beach on the Pacificcoastof with a 6–8 m wide runnel is observed across the profile, separating the Japan where several field experiments on sediment transport and pro- high and the mid-tidal zones (Fig. 3). The runnel area is composed of file evolution in the swash zone have been performed (Kubota et al., very coarse sands, broken shells and few pebbles. The low tidal zone is 1997, 1999). During some of these experiments, an artificial beach flat, planar and partially wet, due to cropping out of the watertable, face was created by accumulating sand on the beachface using a and mainly composed of a rocky platform with a slope of 0.01 and few bulldozer. The size of the artificial mound put on the beachface was small patches of fine sands. This beach system is classified as reflective, about 30 m alongshore with an extension of 20 m offshore and a with an Iribarren number of 0.71, and more precisely as a low tide mean slope of 1/7. During these experiments, after wave action on the terrace using the Masselink and Short (1993) classification with beachface, the profile shape had the characteristics of a real beach parameters RTR and Ω of 11 and 0.33, respectively. scarp (with an estimated height of about 0.3 m), with waves causing The experiment was carried out during 6 tides with a combination of transport and erosion by direct impact. A stick array of iron bars wave characteristics and an increasing tidal range from neap tide to deployed cross-shore to the shoreline was used to manually measure spring tide. the profile change each minute during a two hour period. Traps were Natural beach scarps are ephemeral erosional features difficult to used to quantify onshore and offshore sediment transport, and swash study with a complete set of instruments. Due to these practical consid- capacitance gages were installed close to the iron bars. Video cameras erations, an artificial beach scarp had been constructed and compacted for detailed wave recording were also deployed in the front of the with a bulldozer on the foreshore at the location where a beach scarp artificial beachface as well as a pressure wave gage and an electromag- had often been observed (Fig. 4). The artificial berm is about 40 m in netic current meter (Larson et al., 2004b). the alongshore direction, with a scarp about 1 m high (Fig. 5). Buck (2007) and Kobayashi et al. (2009), using numerical models, Dimensions of this artificial beach scarp are based strictly on in situ show that the effect of the incidence wave angle on berm, but also on observations at the field site, especially its height, its face (shaped dune erosion is of the order of 20%. Previously, based on the SBeach with an important slope as observed in natural beach scarp), its length model and a longshore wave height distribution, Nishi et al. (1994) and its location. The artificial beach scarp was realized with local sand showed a longshore curved scarp suggesting that the gradient of from the natural berm. longshore sediment transport-dominated scarp generation. Using a Limited detailed quantitative information is available with respect to wave basin to study the erosion mechanism of scarping on sandy the geotechnical characteristics of the sediment used in previous field berms, Payo et al. (2008) mentioned for instance alongshore variability campaigns (Fisher et al., 1986; Crowson et al., 1988; Kubota et al., of beach changes in tests, but indicated also that this was probably due 1999; Larson et al., 2004b) and large-scale laboratory experiments to the non-uniformity of the concrete slope in the used basin. The lack of (Overton et al., 1990; Nishi and Kraus, 1996; Dette et al., 2002; Van field data to validate modeling results is also pointed out. Longshore Gent et al., 2008; Van Thiel de Vries et al., 2008; Van Rijn, 2009), even measurements are clearly scarce, especially during storm conditions. though some procedures for compacting the used sediment have been The aim of this contribution is to present and discuss a new data set detailed (use of vibrating compactor, saturation of sand with pouring of beach scarp morphodynamics exposed to increasing water levels and water, addition of sand by layers, rollers, heavy equipment, etc.). under stormy oblique wave conditions. The relationship between wave Overton et al. (1994) used laboratory experiments to show that an 134 Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147

Fig. 1. Location of the study area.

increasing dune compaction and a decreasing sand grain size improved Richard, 1995) which measures the ratio between the depth of penetra- the strength of the dune. Nishi and Kraus (1996) during the SUPERTANK tion of a calibrated rod and the strength to press it into the sand. experiments showed that compaction altered the strength of the dune Seven measurements of compaction were performed (A1–A7 on the (about 1 m height), the volume of eroded sediment, the thickness artificial berm, Fig. 6) and for the natural berm three points were of layer separation and the angle of slope failure. Geotechnical measured (N1 to N3 in Fig. 6). properties in dune or scarp erosion field or laboratory experiments Compaction of the artificial berm appears relatively homogeneous. appear fundamental for understanding the physical processes and for However, compaction close to the scarp has lower values (Fig. 7b) due reproducing realistic conditions in artificial settings. to the difficulty to ride close to the scarp with a bulldozer without During our experiment, measurements of soil compaction were provoking collapsing. This is similar to natural observations (Fig. 7a), performed on a natural berm close to the field site and on the artificial the natural compaction being higher on the inner part of the berm berm to appreciate differences. The compaction measurement was than on the outer part (which is younger and less protected). The done with a dynamical penetrometer called PANDA (Gouvrès and compaction values obtained for the artificial berm can be considered

Fig. 2. Wave heights and directions at Luc-sur-Mer between 03/22/2007 and 10/02/2012. Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 135

Fig. 3. Typical beach profile with mean grain sizes. as correct even if a longer time delay before the beginning of the conditions, often a beach scarp appears close to the groin where the experimentation would have inevitably rendered its geotechnical berm was previously wide. characteristics more similar to natural cases. About 30 m eastward of the study area, there is a low crested groin 2.2. Field measurements during the experiment which affects longshore sediment transport and impacts the upper foreshore topography with contours slightly oblique to the coastline. Low and high frequency water level measurements were obtained As mentioned by Nishi et al. (1994), these kinds of made-man from a S4DW electromagnetic current meter with a pressure sensor structures during stormy oblique wave conditions influence the beach (from InterOcean) located on the mid-foreshore (100 m offshore of the topography and possibly the longshore evolution of neighboring beach scarp at a depth of 3 m at high tide) and moored about 0.4 m beach scarps. After a long period of fair weather conditions, the berm above the beach surface (Figs. 4, 8a). This location is relatively close to was often well-developed, especially in the updrift side of the groin. the artificial berm to fully characterize incident waves (angle, period Just after this period, when the first storms occurred with wind wave and height), especially at high tide when swash motions attack the

Fig. 4. Beach topography of the study area and plan view of instrument locations, including ﬁelds of view of the cameras. 136 Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147

Fig. 5. Artiﬁcial beach scarp on the upper foreshore at Luc-sur-Mer Beach (France).

scarp toe. The S4DW continuously records pressure and horizontal sum of the scanner system precision and the RTK-DGPS precision, current fluctuations with a sampling frequency of 2 Hz. Wave character- around 6 cm for both horizontal and vertical dimensions. istics were obtained from the measured time series by spectral analysis At high tide, since the scanner was always placed at the same using a classical Fast Fourier Transform (FFT) with 16 degrees of location, topographic data can be compared in a relative coordinate freedom. system. The maximum estimated error of the topographic survey is Topographic data were collected using a Terrestrial Laser Scanner the precision of the scanner system, around 1.2 cm for both horizontal (TLS) Leica C10 deployed on a 3 m stainless-steel tripod slightly and vertical dimensions. Relative coordinates are projected to a cross- seaward of the beach scarp on the western side of the artificial berm shore/longshore reference system. (Fig. 8b). The scans were performed at each low tide, while video Swash and run-up data were collected using video techniques acquisition was performed from the beginning to the end of each high previously tested extensively (Holland et al., 1995, 1997; Stockdon tide. Compared to topographical measuring methods like DGPS, the et al., 2006; Senechal et al., 2011). The video monitoring system used laser scanner appears to be more accurate as it permits to obtain huge for the experimentation is the KOSTA System (developed by CASAGEC details with a spot size of 4.5 mm at 50 m (Leica product specifications). and AZTI-Tecnalia in 2005) (Rihouey et al., 2008). It is composed of It is possible to acquire a high density of X,Y,Z topographic points two synchronized video cameras (referred to as camera C1 and C2) (average distance between points of 10 cm) in all directions around deployed to obtain, after geo-referencing, a vertical view of beach the scanner in a minimum of time (20,000 m2 area recorded in 5 min scarp and swash zone. with a density of 100 points.m−2). Each cloud of points scanned is Video data were synchronized with in situ measurements using obtained from the same scanner location. Geographical position of universal time. Cameras C1 and C2 were fixed on a 6 m mast top the clouds is referenced with 5 targets (Fig. 8b–c) positioned by Real- (Fig. 8d) placed on the upper foreshore on the eastern side of the Time-Kinematic Differential GPS (RTK-DGPS). Digital Elevation Models artificial berm, to record images at a frequency of 2 Hz during a burst (DEM) were constructed to compare all the clouds of points with area period of 20 minutes every 30 minutes. As shown in Fig. 9, both cameras grids spacing of 0.05 m for each survey. All topographic data were were pointed in a direction parallel to the foreshore and in an area acquired in the French metric coordinate system (Lambert 93), then X covering about 15 m in the along-shore direction and 16 m in the and Y coordinates projected to a cross-shore/longshore referential. For cross-shore direction (area view of cameras is oriented to take into the low tide topographic survey, the maximum estimated error is the account the floodlight scope for night recording).

Fig. 6. Location of compaction measurements on the artiﬁcial and natural berm. Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 137

Fig. 7. Penetrograms on natural (a) and artiﬁcial berm (b).

Fig. 8. Instrumentation deployed during the ﬁeld experiment. S4DW current meter (a); Terrestrial laser scanner on the heavy ballasted stainless-steel tripod and targets (on dotted frame) (b); Mast equipped of cameras and spotlight (c). 138 Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147

Fig. 9. Map of cross-shore (a) and longshore (b) video pixel resolutions (gray line indicates location of extracted video time series).

Standard lens distortion correction and image geo-rectification number of swash on scarp. Longshore and cross-shore pixel resolutions techniques with targets were used for the transformation from of video measurements are less than 2 cm (Fig. 9). distorted image coordinates (U, V) to metric system coordinates On the video time series, the run-up edges are defined as the most (X, Y). Then, the same pixel cross-shore transect is extracted from shoreward line of water identifiable. This definition is consistent with every image to obtain a time series of swash excursion and impact swash measurements obtained with resistance wires deployed near

Fig. 10. Part of 60 s video time series with horizontal swash excursion (dotted line) and swash maximum (point) (a), and vertical run-up elevation time series (black line) with run-up maximum (point) (b). Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 139 the bed (Holman and Guza, 1984; Holland et al., 1995). The water line 3. Results variation shown on the video time series is manually digitized (Fig. 10a) and its X position along the extraction profile is saved for The results presented focus on a tidal cycle when the beach scarp each image (every 0.5 s). The X error of the digitalization is about was eroded. During the previous tides, despite high wave conditions, +/−1pixel,so+/−2 cm. Before every video acquisition, a topograph- the water level at high tide was too low to erode the toe of the scarp. ical measure with TLS is done and topographic data (X, Z) are extracted The time (in hours) used in the description of the experiment is from the same profile than video extraction. The X, Y and Z error about expressed from the beginning of the experiment. TLS measurements is about +/− 1.2 cm. A linear regression formula is calculated between each points for each topographic profile (Z = f[X]) 3.1. Hydrodynamics and the X digitized water line position is introduced in respective polynomial formula to determine the Z swash elevation and calculate 3.1.1. Shoaling zone the run-up value during all video time series (Fig. 10b). During the tide when beach scarp recession was observed, the mean Finally, time series are segmented into section of 600 s and each run- significant and mean maximum wave height were respectively of 0.6 m up elevation time series and linearly detrended. On each time series, a and 0.96 m (Fig. 11b) and waves came mainly from −30° from shore spectral analysis was realized by FFT with 16 degrees of freedom. normal direction (Fig. 11c). The spectral analysis of the waves, with a

Fig. 11. Time series of the hydrodynamic characteristics during the erosive campaign. Water level predicted (gray line) and measured (black line) (a); significant wave height (gray line) and maximum wave height (black line) (b); wave direction from shore normal (c); peak energy (black line) and significant (gray line) wave period (d); and wave spectrum calculated from the pressure time series recorded by the S4DW (e). Gray patches indicate the video burst sequences and vertical dashed lines indicate the time of the theoretical high tide. 140 Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 degree of freedom of 16, shows only one frequency peak that migrates frequency and its energy (Fig. 12b) are characterized by a large band, between 0.17 Hz (Tp = 5.9 s) and 0.21 Hz (Tp = 4.8 s); no low frequency substantially attenuated. peak was observed (Fig. 11d-e). The spread of frequencies was due to a After the destruction of the scarp, the hydrodynamics are consistent strong wind blowing on the study area before and during the tide, with with available studies on planar slopes. Compared to the incident wave a mean and maximum wind force respectively of 8 and 13 m.s−1 and a spectra in the shoaling zone (Figs. 12, 14), the swash energy shifts mean wind direction of −80° from a shore normal direction. As often towards lower frequencies, with peaks between 0.17 and 0.22 Hz for observed along the English Channel coast, short-crested waves result the incident waves and between 0.04 and 0.08 Hz for the swash. This directly from the local wind (Larsonneur et al., 1982; Monfort et al., wave frequency shifting confirms results of Erikson et al. (2005) and 2000). the 2006 Deltaflume test cases (Roelvink et al., 2009). This result The maximum water level measured during the field campaign was shows that on a reflective high beach, a low frequency band can be 3.52 m IGN69 (French vertical datum) with a duration of the high tide observed in the swash zone, even if incident band is normally more slack of about three hours. A low storm surge, not exceeding 20 cm, energetic (Holland and Holman, 1993). was observed during the second part of the high tide slack, explaining The impact number calculated from video images, recorded on the the slight elevation of the still water level between 2:30 and 4:15, just eastern profile (the video camera system configuration does not permit before the beginning of the falling tide (Fig. 11a). us to obtain data on the western profile), evolves in three steps (Fig. 15). On the mid-part of the foreshore zone, close to the mean water level Between 1:30 and 2:00, corresponding to 120 and 90 min before high contour where the current-meter was deployed, the mean current tide, the impact number increased from 5 to 30 per 5 min, then between velocities were weak (below 0.2 m.s−1), with maximum velocities 2:00 and 3:00, it stayed stable at about 25 per 5 min, and finally, just observed at the beginning and at the end of the submergence period before the end of the rising tide, it decreases from 25 to 17 per 5 min and eastward-directed, and minimum velocities at high tide (between until the destruction of the scarp (Table 2). During this last period, the 0.05 to 0.1 m.s−1). impact frequency varied from 0.085 to 0.058 Hz. This impact frequency is relatively close to the swash peak frequency, between 0.04 and 0.08 Hz, measured just after scarp destruction.

3.1.2. Swash zone characteristics and impact number on scarp face Statistics of run-up 2 % (R2)and16%(R16) have been calculated from The presence of the beach scarp strongly influences the swash video data on the eastern profile after scarp destruction at 4:40, 5:00 dynamics. Many times during the period of observation, swash charac- and 5:10. R16 and R2 values are almost constant varying respectively teristics were modified due to reflection of the uprush on the scarp between 0.34 and 0.38 m and between 0.46 and 0.52 m (Table 1). front, inducing a collision between the reflected backwash and the Between 2:00 and 3:00, when the impact number on the scarp is following uprush. This mechanism of collision is mentioned by Erikson relatively stable (Fig. 15), the difference between foot scarp height et al. (2005) as an important natural swash interaction which must be and mean water level stays stable, comprised between 0.35 and considered to improve the prediction of swash motion. As shown in 0.45 m (Fig. 20b) despite a mean water level rising of 22 cm induced Figs. 11a–band12a, during two time periods of 10 minutes, at 3:00 by tide (Fig. 15). This difference observed during the erosion of the

(with a beach scarp morphology) and 4:30 (after beach scarp destruc- beach scarp is lower than the R2 values observed after the scarp destruction), incident wave spectra and significant wave height are similar. tion and close to the R16 values. Because incident wave characteristics However, the spectrum analysis of the same two time periods of are quite stable during the main part of the experiment and the swash 10 minutes for the run-up is different (Fig. 12b). When the beach interactions due to increased collisions spreads spectra band reduce scarp is present, the run-up spectra values are spread, between 0.025 its energy, run-up values during scarp erosion must be lower than and 0.25 Hz, with several peaks. After beach scarp destruction, the after the scarp destruction. Logically, the rising tide level, about 0.2 m, run-up spectra values are between 0.025 and 0.2 Hz, but with a domi- appears really important to explain and control scarp erosion. nant peak at low frequencies around 0.05 Hz and a secondary peak at 0.13 Hz. Video recordings during the experiment show the impact of back- 3.2. Topographic changes wash/uprush collisions when the scarp is present (Fig. 13). Clearly, these collisions reduce, even stop, the motion of the following uprush Swash attack is focused at the foot of the scarp and causes undercut- reducing the incoming swash excursion. Consequently, the latter ting which leads to the creation of tension cracks parallel to the face, in could not reach the scarp and erodes its toe. The scarp’s vertical face the upper part of the scarp. This mechanism is also observed driving reflects the incoming swash and amplifies the backwash activity dune recessions (Carter and Stone, 1989). Sediment resulting from which mitigates the next uprush. The scarp presence clearly modifies mass failure landed in front of the foot of the scarp and was quickly the swash interaction that normally appears on a planar beach surface removed by swash action. Further undercutting followed by new mass (Erikson et al., 2005; Guedes et al., 2011) and consequently the swash failure continued the erosive cycle. In this study, the berm-type failure

Fig. 12. Wave spectra at the S4DW location (a) and swash spectra on the east video proﬁle (b). Black line is during scarp erosion and gray line is after scarp destruction. Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 141

Fig. 13. Time series of swash-swash collision with reﬂection on the beach scarp.

mechanism described by Erikson et al. (2007) was mainly observed maximum residual erosion of 0.3 m at the edge of the west side berm probably due to the relative low compaction of the artificial berm. and a maximum residual accretion of 0.2 m at the east side were Topographic variations between the two low tides highlight a com- measured. At the same time, the beach scarp crest was eroded by plete destruction of the artificial berm. The contrasting alongshore 0.75 m in the west and 0.5 m in the East. Also the laser scanner measure- beach changes indicate an evident net movement of sediments from ments revealed an asymmetrical evolution between the west and the north-west to south-east on the upper part of the foreshore in the east part of the berm (Fig. 17). front of the scarp (Fig. 16). The erosion of the berm was also greater On the west profile (Fig. 4), the scarp retreated landward for on the north-west side than on the south-east side, showing a possible 150 minutes and was finally deeply smoothed and the beach profile 3D effect. At the initial scarp foot location, after the collision period, a became quasi-linear. The beach elevation at the initial foot scarp

Fig. 14. Spectra of measured incident waves (black line) and measured vertical run-up elevation (gray line) just after scarp destruction at 4:40 (a), 5:00 (b) and 5:10 (c). 142 Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147

be the installation of the scanner to have a good field of view, with capabilities of deployment just outside of the studied area, no movement of the structure during acquisitions (mast, tripod or platform) and the least possible shadow zones. However, improvements could be made regarding temporal scales of data acquisitions. Continuous acquisitions at a high frequency (2 Hz) will be useful for describing short-term evolutions of beach scarps or dune fronts (wave impact time scale), and even swash activity, as recently presented by Almeida et al. (2013). Unlike classical uses of in situ video system for tracking beach evolution, which deliver decimetric to metric resolution, the proximity fi Fig. 15. Time series of impact number per 5 min on the eastern pro le of the scarp (cross) of the video measurements system to the beach scarp has made it and mean water level (gray line). possible to precisely record the horizontal scarp evolution and the swash impacts with a high definition, about 2 cm per pixel. The combi- position (12 m in the cross-shore) increased by 12 cm during the first nation of these two non-intrusive techniques has made it possible to 80 minutes of scarp retreat, then decreased by 25 cm until the end of extract good values of run-up with an accuracy better than 5 cm, the experiment (210 minutes). On the east profile (Fig. 4), the scarp which seems very good considering the space and time variability of retreated landward for 120 minutes and disappeared. The foreshore this phenomenon. beach slope on the east profile decreased a little from 0.081 to 0.074, while the west profile slope decreased from 0.104 to 0.067 (foreshore 4.2. Longshore variability of beach and scarp changes beach slope is measured between mean water level and initial foot scarp position as recommended by Stockdon et al. (2007)). On The contrasting behavior between the east and the west side of the the east profile, the beach elevation at the first foot scarp position beach scarp is firstly the result of a contrasted beach evolution in the (12 m in the cross-shore) increased by 25 cm during the first front of the scarp during the duration of the experiment. The beach 110 minutes of scarp retreat, then decreased by 15 cm until the end of elevation changes were the consequence of a west–east gradient of the experiment (180 minutes). These observations clearly show a sediment longshore transport, induced by oblique waves generated by different morphodynamical behavior between each side of the beach wind parallel to the shore. Fig. 16(b–c) shows that the east and west and of berm. beach profiles change differently between 0 and 25 m in the cross- On the two profiles, the foot scarp migrates landward (speed shore direction, but that they are stable offshore. These changes mainly between 1.5 to 4 cm.min−1) and its elevation increases regularly during on the upper part of the beach result especially from the swash motion. the experiment (Fig. 18). On the east profile, the foot scarp retreats Oblique swash, but also grazing swash observed on video images, along a mean slope βT of 0.131, while on the west profile its retreat contributes actively to move sediment alongshore. During the collision follows a steeper slope of 0.209. phase, swash activity also brings sediments eroded from the western The eroded volume evolution of the beach scarp during the experi- part of the beach scarp to the eastern part located close to a groin. The ment was calculated using laser data for each profile (Fig. 17). Large effect of the groin also seems important and its presence explains the differences in the eroded volumes are observed during the experiment contrasting initial beach slope in the front of the scarp. The groin with values on west and east profiles of 1.9 and 0.9 m3.m-1, respectively. influences the beach topography especially close to its updrift side. (Table 2). The scarp disappeared when its height decreased below The initial contours close to the groin were not parallel to the shoreline 20 cm (Fig. 20a). This destruction happened first on the east profile, but were slightly oblique, showing the impact of the groin on the then on the west profile. longshore sediment circulation. The level of the beach was always higher along the west side of the groin in comparison with the east 4. Discussion side, confirming the residual movement of sand over a long period of time but also over a stormy period. The groin induces an alongshore 4.1. Laser data and proximal video acquisitions contrasted updrift beach elevation which explains, locally, the gradient of longshore sediment transport and induced beach changes. The more Topographic acquisitions done by terrestrial laser scanning during rapid decrease of the scarp height on the east is due to the sediment the erosion period have enabled us to obtain a complete set of deposit in front of the scarp that permits overwash, which smoothed topographical data, permitting a 3D description of beach scarp changes. the rest of the scarp. On the western profile, the landward migration Terrestrial laser scanners are a very useful tool for non-intrusive of the foot scarp combined with the residual decrease of the beach measurements of an eroding foreshore with scarps and probably also elevation in front of the scarp by erosion during the tide, permits this of dune systems. Compared to topographic data acquired by stereo area to be conserved longer than on the eastern pro file. Then, after the video, this method has the advantage not to be affected by problems collision regime period (Sallenger, 2000), the scarp is destroyed by of lighting or precision due to the proximity of cameras that influences overwash processes. The evolution of the beach in front of the beach the size of the pixels and the topographic accuracy. Laser scanning scarp seems important to explain the observed scarp changes. presents no problem for distinguishing position of elements with strong The observed storm surge during the second part of the tidal cycle contrast. Its large range of measurements could permit the recording of (Fig. 11a) in particular between 2:30 and 4:30 allowed for continued large scale in-situ morphologies (tens to hundreds of metres), enabling wave action on the scarp despite a landward retreat of the scarp toe. easy analysis of 3D systems in a very small time and with centimetre This is in line with observations by Shepard (1950) and Wiegel (1964) accuracy. Like for the stereo video protocol, the principal issue would on foreshore landward migration by swash undercutting and slumping on the scarp face. However, during the period of the scarp retreat, the

Table 1 difference in height between the foot scarp and the mean water level Summary of run-up values on the eastern profile after beach scarp destruction. was stable between 0.35 and 0.45 m (Fig. 20b). For east and west profiles, this height evolves in the same manner. Moreover, impact Time (hh:mm) 4:40 5:00 5:10 numbers, recorded on the east profile follow a three-step evolution. R16 (m) 0.34 0.39 0.38 During the 60 minutes when the impacts number was stable at about R (m) 0.46 0.52 0.50 2 25 impacts per 5 min the water level increased by 22 cm, showing Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 143

Fig. 16. Topographic changes of the studied area during the experiment (a), beach topography at low tide before (blue line) and after (red line) scarp erosion atwestprofile (b) and east profile (c). that there is a parallel evolution between the water level and the scarp on the west part of the artificial berm. Further video data during oblique retreat. However, eroded volumes on the beach scarp increased wave conditions will be necessary to study longshore run-up variability differently along east and west profiles. The hydrodynamic and and its consequence on scarp and dune retreat. morphological interactions seem alongshore different. The beach slope, as mentioned by Stockdon et al. (2006),andforeshoreelevation 4.3. Longshore variability of scarp retreat and foot scarp trajectory as a result of a longshore sediment transport between east and west profiles, influence swash activity. The beach slopes between the During laboratory observations, Larson et al. (2004a) suggested that two profiles at the beginning of the experiment are quite different, the foot scarp follows a slope similar to the initial foreshore slope during respectively 0.081 on the east side of the berm and 0.104 on the west its retreat (βT/βf(0) = 1). Laboratory investigations done by Palmsten side (Fig. 16b-c). The slope changes during the experiment were more and Holman (2012) present a different result with βT/βf(0) = 0.54. important along the west profile with a decrease from 0.104 to 0.067 For this in situ experiment, the results were quite different and spatially than along the east profile where the slope decreased from 0.081 to contrasting. Along the west profile, the foot scarp evolves with a slope of 0.074. 0.131 (R2 = 0.92). Compared to the foreshore slope (taken between Swash excursions and run-up elevation were affected when mean water level and initial foot scarp position) of 0.104 (R2 =0.99), the beach topography was highly three dimensional. During the Luc- the ratio βT/βf(0) is of 1.26. On the east profile, the foot scarp evolves sur-Mer experiment, the difference of foreshore slope near the foot to a slope of 0.209 (R2 = 0.97) and the initial foreshore slope is 0.081 2 scarp at east and west part of field experiment probably affects swash (R =0.99),givingaratioβT/βf(0) of 2.58. dynamics (direction, speed, energy…) and consequently their impacts Differences between the two surveyed profiles can be ascribed to on the scarp. Video data show complex swash circulations close to various effects: from the influence of the initial topography at the scarp where longshore transport is active. Swash was primarily oblique front of the scarp to a variability in the spatial characteristics of the but in some instances swash circulating from west to east was also run-up. The residual elevation of the beach in front of the scarp is observed. Grazing swash contributes also to reinforce longshore flow opposite between the eastern and the western parts of the scarp. This and scarp formation and erosion (Sherman and Nordstrom, 1985). elevation increases in front of the foot scarp on the eastern part of the Unfortunately, data recorded during the campaign are not sufficient berm and decreases on the western part. Logically, when the beach to confirm the role of the local slope and local topography on swash level increases due to sediment deposits, the trajectory of the scarp activity because the deployed video device could not acquire images foot is steep due to the location of the foot always being higher. 144 Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147

Fig. 17. Cross-shore proﬁle evolution of the beach scarp at east (a) and west (b) part of the study area.

Inversely, when the elevation of the beach decreases and the beach with the retreat of the scarp base following a steep slope (between slope stays constant, the foot scarp trajectory follows a weak slope. 1:50 and 2:20). Thereafter, the foot scarp slope is less important due Moreover, the ﬁrst step of the upper beach changes in the front of the to the lower beach elevation in front of the scarp. These observations western scarp shows a vertical accretion which can be corroborated indicate that the slope of foot scarp retreat was not directly linked to

Fig. 18. Initial beach proﬁle and trajectory of the scarp base for east (a) and west (b) part of the study area. Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 145

eroded volume. With respect to works on dune erosion, it is interesting to test some models of dune recession with data coming from this study. In their formulation to calculate the eroded volume from the dune, Larson et al. (2004a) recognize the use of the number of waves (by

the ratio t/Tp) to quantify the inﬂuence of waves on dune erosion. Palmsten and Holman (2012) used this same number and incorporated the probability distribution of wave run-up over the foot scarp to

calculate a number of collisions. Their results show that the ratio t/Tp overestimates the real number of impacts, but also that the formulation to calculate number of collision underestimates the real number of impacts on the dune scarp. In this experiment, we analyze the number of impacts per 5 min during a 60 min period. When this number is stable, it shows an impact frequency, calculated from video images, that oscillates between 0.058 and 0.085 Hz. This rather low frequency is closer to the swash frequency recorded on the foreshore after scarp destruction whose peaks are between 0.04 and 0.08 Hz, but clearly different from the incident wave frequency with peaks between 0.17 and 0.22 Hz (Fig. 14) commonly observed for wind wave conditions. These observations suggest that swash frequency is more able to realistically characterize the Fig. 19. Cumulative volume evolution of the beach scarp between 5 and 12 m cross-shore on east and west proﬁle. number of impacts on dune or beach scarp face. Therefore, it appears more insightful to test swash frequency than incident waves frequency to the calculation of volume eroded from a dune. However, the swash the initial beach slope and clearly suggest that the contrasted vertical interactions due to the collisions between backwash and following evolution of the beach just in front of the scarp inﬂuences the trajectory uprush induced by the beach scarp affect the swash motion and, in of dune base evolution. Palmsten and Holman (2012) mentioned that particular, contribute to reduce its energy. To explain the destruction an increase in slope of the retreat trajectory is possibly related to the of the scarp during this experiment, the rising mean water level appears decrease in low frequency energy observed in run-up, but beach eleva- to be an important factor compensating the decrease of swash energy tion changes in the front of scarps and also probably for dune systems during the phase of active swash-swash interactions. can also contribute to modify this trajectory, especially with oblique wave conditions inducing a varying longshore transport. 5. Conclusions

4.4. Eroded volume variability and volume calculation Anewfield experiment was performed to study erosion of an artificial beach scarp along a macrotidal coast during oblique wind- A strong connection between beach evolution and eroded volume wave conditions. Incident wave, swash activity using video imaging of the scarp is identified. Fig. 19 shows different volume changes and topographic characteristics using a terrestrial scanner laser were between the west and east sides, a result directly related to differences measured to develop a new dataset useful to improve the knowledge in longshore sediment transport. As mentioned previously, the mecha- on the morphodynamics of beach scarp, but also of dune fronts. nisms of scarp and dune erosion are often similar but differ by their A complete destruction of the artificial berm (1 m high and 40 m long) is observed during the experiment. The duration of the erosive processes was short, only few hours, when swash activity had the capability to destroy the berm and water levels were high enough to allow swash to reach the scarp. Contrasting alongshore changes were measured: the erosion of the berm crest was greater on the west side of the berm than on the east side (0.75 m versus 0.5 m), the eroded volumes on west and east profiles were different, respectively 1.9 and 3 -1 0.9 m .m , the foot scarp retreat along a mean slope βT of 0.131 was observed on the east side, while on the west profile its retreat followed a steeper slope of 0.209. The beach just in front of the scarp showed also a different evolution during the experiment. A residual beach erosion of 0.3 m at the west edge of the artificial berm and a residual accretion of 0.2 m in the east side were measured showing a clear longshore movement of sediments from north-west to south-east on the upper part of the foreshore in front of the scarp induced by oblique wave conditions. Alongshore beach changes in front of the scarp, at a small spatial scale (tens of metres), explain the scarp behavior. The scarp front erosion increases strongly when the beach level is lowered and reduces when the beach surface rises. Overall, water depth and swash activity became progressively different along the scarp during the experiment. During most of the experiment, the collision regime described by Sallenger (2000) was principally observed. For about one hour and forty minutes, uprush strikes the scarp toe contributing to its erosion. The impact number grows with the rising tide and stays stable around 25 impacts per 5 minutes (0.08 Hz) before to decrease. This swash Fig. 20. Time series of scarp height evolution at east (gray line) and west (black line) profile (a), and difference between foot scarp and observed water level at east frequency is clearly different from the incident wave frequency (gray line) and west (black line) profile (b). (between 0.17 Hz and 0.21 Hz, stable during all the experiment 146 Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147

Table 2 Summary of hydrodynamic and morphological parameters (no impact data available for west proﬁle).

Time MWL Hs Tp East proﬁle West proﬁle (hh:mm) (m IGN69) (m) (s) Eroded volume between Foot scarp height Impacts on scarp Eroded volume between Foot scarp height 5 and 12 m cross-shore (m IGN69) (number/10 min) 5 and 12 m cross-shore (m IGN69) (m3/m) (m3/m)

01:00 2.25 0.52 5.0 0 3.3 0 3.41 01:10 2.51 0.57 4.4 0 01:20 2.72 0.59 4.1 0 3.3 0 0 3.41 01:30 2.88 0.61 3.8 0 3.3 0 3.41 01:40 3.01 0.62 3.7 20 01:50 3.10 0.69 4.6 −0.08 3.42 34 −0.02 3.44 02:00 3.18 0.68 4.9 −0.14 3.46 −0.09 3.53 02:10 3.21 0.69 4.6 58 02:20 3.24 0.66 4.8 −0.38 3.59 48 −0.27 3.7 02:30 3.27 0.69 5.0 −0.47 3.68 −0.39 3.74 02:40 3.33 0.64 4.8 49 02:50 3.38 0.67 5.2 −0.63 3.76 52 −0.74 3.75 03:00 3.40 0.71 5.4 −0.74 3.83 −0.90 3.78 03:10 3.44 0.66 4.9 (scarp destruction) 48 03:20 3.47 0.69 5.3 −0.93 18 −1.35 3.81 03:30 3.46 0.64 4.5 −1.05 −1.66 3.9 03:40 3.52 0.65 4.9 (scarp destruction) 03:50 3.50 0.64 4.6 −1.30 −2.16 04:00 3.50 0.72 5.6 duration), but within the swash peak frequency range measured just comments about the manuscript. Our thanks are expressed to Giovanni after scarp destruction (between 0.04 and 0.08 Hz). Coco, from IH Cantabria, for his tremendous help in preparing and If the eroded volume from the scarp is linearly correlated with the improving this manuscript. Thanks, also, to the two anonymous summation of the swash impacts observed during the video bursts, reviewers for useful and constructive review comments for improving swash motion is strongly affected by the presence of the scarp. Video the manuscript. recordings show clearly that the swash characteristics were modified due to reflection of the uprush on the scarp front inducing a collision between the reflected backwash and the following uprush. These References swash interactions that normally appear on free beach surface were Almeida, L.P., Masselink, G., Russell, P.E., Davidson, M.A., Poate, T.G., McCall, R.T., reinforced by the presence of the reflective scarp front. The collisions Blenkinsopp, C.E., Turner, I.L., 2013. Observations of the swash zone on a gravel between backwash and the following uprush reduce, and even stop, beach during a storm using a laser-scanner. Proceedings 12th International Coastal Symposium (Plymouth, England). Journal of Coastal Research 65, pp. 636–641. the incoming swash excursion acting on the swash frequency and/or Buck, M.A., 2007. Experiments and numerical model for berm and dune erosion. (Ph.D. its intensity. The run-up spectra when the beach scarp was present, thesis). Research Rep. No. CACR-07–03. Center for Applied Coastal Research, Univ. are spread, between 0.025 and 0.25 Hz, with several peaks and its of Delaware, Newark, Del. Carter, R.W.G., 1988. Coastal Environments. An introduction to physical, ecological and energy was rather attenuated by comparison with other spectra before cultural systems of coastlines. Academic Press, London (617 pp.). and after the phase of collision regime. With this kind of swash condi- Carter, R.W.G., Stone, G., 1989. Mechanisms associated with the erosion of sand dune tions, the scarp could be naturally protected from erosion. The scarp cliffs, Magilligan, Northern Ireland. Earth Surf. Proc. Land. 14 (1), 1–10. erosion and its complete destruction were then the result of tide- Crowson, R.A., Birkemeier, W.A., Klein, H.M., Miller, H.C., 1988. Superduck nearshore processes experiment: summary of studies CERC field research facility. Technical induced mean water level rise of about 20 cm. During this phase, the Report CERC-88-12. Coastal Engineering Research Center, U.S.Army Engineer mean impact number is maximum and relatively constant, and the Waterways Experiment Station, Vicksburg, MS (115 pp.). difference between the scarp foot height and the mean water level Dette, H.H., Larson, M., Murphy, J., Newe, J., Peters, K., Reniers, A., Steezel, H., 2002. Application of prototype flume tests for beach nourishment assessment. Coast. Eng. stays stable. The onshore migration of the swash zone induced by the 47 (2), 137–177. rising tide appears to be important to explain scarp destruction, com- Erikson, L., Larson, M., Hanson, H., 2005. Prediction of swash motion and run-up including pensating the attenuated swash activity due to backwash-uprush the effects of swash interaction. Coast. Eng. 52, 285–302. Erikson, L.H., Larson, M., Hanson, H., 2007. Laboratory investigation of beach scarp and interactions. dune recession due to notching and subsequent failure. Mar. Geol. 245, 1–19. More studies are needed to improve the knowledge of beach scarp Fisher, J.S., Overton, M.F., Chisholm, T., 1986. Field measurements of dune erosion. morphodynamics and its variability presented and discussed in this Proceedings of the 20th Coastal Engineering Conference, Taipei, Taiwan 82, pp. 1107–1115. paper. In particular, at a local scale, alongshore variability of swash Gouvrès, R., Richard, B., 1995. Le pénétromètre dynamique léger PANDA. Proceedings of conditions must be taken into account in order to analyze their implica- ECSMFE, Copenhagen, Denmark, pp. 83–88. tions on the beach scarp behavior. Works are under way to assess the Guedes, R.M.C., Bryan, K.R., Coco, G., Holman, R.A., 2011. The effects of tides on swash statistics on an intermediate beach. J. Geophys. Res. 116 (C04008), 1–13. use of our findings especially for the quantification of dune front retreat. Holland, K.T., Holman, R.A., 1993. The statistical distribution of swash maxima on natural beaches. J. Geophys. Res. 98 (C6), 10271–10278. Acknowledgements Holland, K.T., Raubenheimer, B., Guza, R.T., Holman, R.A., 1995. Run-up kinematics on a natural beach. J. Geophys. Res. 100 (C3), 4985–4993. Holland, K.T., Holman, R.A., Lippmann, T.C., Stanley, J., Plant, N., 1997. Practical use of This work was funded by the PLAMAR CNRS program and the French video imagery in nearshore oceanographic field studies. IEEE J. - Oceanogr. Eng. 22, Higher Education and Research Ministry. Thanks to Benjamin Outrey 81–92. (Leica Geosystem) for lending the terrestrial laser scanner during the Holman, R.A., Guza, R.T., 1984. Measuring run-up on a natural beach. Coast. Eng. 8, 129–140. experimentation and to the Luc-sur-Mer town council for lending Katoh, K., Yanagishima, S., 1990. Berm erosion due to long period waves. Proceedings of their bulldozer to the artificial berm building. Thanks also to Laurent the 22nd International Conference of Coastal Engineering, pp. 2073–2086. Benoit, Emmanuel de-Saint-Léger and Emilie Poullain, from Caen Katoh, K., Yanagishima, S., 1992. Berm formation and berm erosion. Proceedings of the – fi 23rd International Conference of Coastal Engineering, pp. 2136 2149. University, for their help during the eld experimentation and to Olivier Kobayashi, N., Buck, M.A., Payo, A., Johnson, B.D., 2009. Berm and dune erosion during a Monfort, from Caen University, for his help on the data treatment and storm. J. Waterw. Port Coast. Ocean Eng. 135 (1), 1–10. Y. Bonte, F. Levoy / Geomorphology 236 (2015) 132–147 147

Kubota, S., Naito, A., Matsumura, T., Takezawa, M., 1997. Field observations of topography Roelvink, D., Reniers, A., Van Dongeren, A., Van Thiel de Vries, J., McCall, R., Lescinski, J., change on an artificial beach face due to on–offshore transport. Proceedings of 2009. Modelling storm impacts on beaches, dunes and barrier islands. Coast. Eng. Combined Australasian Coastal Engineering and Ports Conference, Christchurch, 56, 1133–1152. New Zealand, pp. 325–330. Ruiz de Alegria-Arzaburu, A., Mariño-Tapia, I., Silva, R., Pedrozo-Acuña, A., 2013. Post- Kubota, S., Katori, S., Takezawa, M., 1999. Relationship between on-offshore sediment nourishment beach scarp morphodynamics. In: Conley, D.C., Masselink, G., Russell, transport rate on the beach face and wave energy. Proceedings of Coastal Sediments P.E., O’Hare, T.J. (Eds.), Proceedings of the 12th International Coastal Symposium 99. ASCE, pp. 447–462. (Plymouth, England). Journal of Coastal Research, Special Issue 65, pp. 576–581. Larson, M., Erikson, L., Hanson, H., 2004a. An analytical model to predict dune erosion due Sallenger Jr., A.H., 2000. Impact scale for barrier islands. J. Coast. Res. 16 (3), 890–895. to wave impact. Coast. Eng. 51, 675–696. Senechal, N., Coco, G., Bryan, K.R., Holman, R.A., 2011. Wave run-up during extreme storm Larson, M., Kubota, S., Erikson, L., 2004b. Swash-zone sediment transport and foreshore conditions. J. Geophys. Res. 116, 1–13. evolution: Field experiments and mathematical modeling. Mar. Geol. 212, 61–79. Seymour, R., Guza, R.T., O'Reilly, W., Elgar, S., 2005. Rapid erosion of a small southern Larsonneur, C., Bouysse, P., Auffret, J.P., 1982. The superficial sediments of the English California beach fill. Coast. Eng. 52, 151–158. Channel and its western approaches. Sedimentology 29, 851–864. Shepard, F.P., 1950. Beach cycles in Southern California. U.S. Army Corps of Masselink, G., Short, A.D., 1993. The effect of tide range on beach morphodynamics and EngineeringBeach Erosion Board Tech. Mem. 20 pp. 1–26. morphology: A conceptual beach model. J. Coast. Res. 9 (3), 785–800. Sherman, D.J., Nordstrom, K.F., 1985. Beach scarps. Z. Geomorphol. 29 (2), 139–152. Monfort, O., Levoy, F., Larsonneur, C., 2000. Beach cusp characteristics and the hydrody- Short, A.D. (Ed.), 1999. Handbook of beaches and shoreface morphodynamics. Wilez and namic conditions of formation in macrotidal environments. Bull. Soc. Geol. Fr. 171 Sons, Chichester (379 pp.). (6), 649–656. Stockdon, H.F., Holman, R.A., Howd, P.A., Sallenger Jr., A.H., 2006. Empirical parametriza- Nishi, R., Kraus, N.C., 1996. Mechanism and calculation of sand dune erosion by storms. tion of setup, swash, and run-up. Coast. Eng. 53, 573–588. Proceedings of the 25th Coastal Engineering Conference. ASCE, pp. 3034–3047. Stockdon, H.F., Sallenger Jr., A.H., Holman, R.A., Howd, P.A., 2007. A simple model for the Nishi, R., Sato, M., Wang, H., 1994. Field observation and numerical simulation of beach spatially-variable coastal response to hurricanes. Mar. Geol. 238, 1–20. and dune scarps. Proceedings of the 24th Coastal Engineering Conference. ASCE, Sunamura, T., 1985. In: Horikawa, K. (Ed.), 1988. Nearshore dynamics and coastal pp. 2434–2448. processes, theory, measurement, and predictive models. University of Tokyo Press. Overton, M.F., Fisher, J.S., 1988. Simulation modeling of dune erosion. Proceedings of the Van Gent, M.R.A., Van Thiel de Vries, J.S.M., Coeveld, E.M., De Vroeg, J.H., Van de Graaff, J., 21st International Conference in Coastal Engineering. ASCE, Costa del Sol-Malaga, 2008. Large-scale dune erosion tests to study the influence of wave periods. Coast. Spain, pp. 1857–1867. Eng. 55 (12), 1041–1051. Overton, M.F., Fisher, J.S., Stone, A.L., 1990. Large scale laboratory tests of dune erosion. Van Rijn, L.C., 2009. Prediction of dune erosion due to storms. Coast. Eng. 56, 441–457. Proceedings of the 22nd Coastal Engineering Conference. ASCE, pp. 2471–2479. Van Thiel de Vries, J.S.M., van Gent, M.R.A., Walstra, D.J.R., Reniers, A.J.H.M., 2008. Analysis Overton, M.F., Pratikto, W.A., Lu, J.C., Fisher, J.S., 1994. Laboratory investigation of dune of dune erosion processes in large-scale flume experiments. Coast. Eng. 55 (12), erosion as a function of sand grain size and dune density. Coast. Eng. 23, 151–165. 1028–1040. Palmsten, M.L., Holman, R.A., 2012. Laboratory investigation of dune erosion using stereo Vousdoukas, M.I., 2012. Erosion/accretion patterns and multiple beach cusp systems on a video. Coast. Eng. 60, 123–135. meso-tidal, steeply-sloping beach. Geomorphology 141–142, 34–46. Payo, A., Kobayashi, N., Munoz-Pérez, J., Yamada, F., 2008. Scarping predictability of sandy Wiegel, R.L., 1964. Oceanographical engineering. Prentice-Hall, Englewood Cliffs, NJ, beaches in a multidirectional wave bassin. Cienc. Mar. 34 (1), 45–54. pp. 1–532. Pingree, R.D., Griffiths, D.K., 1979. Sand transport paths around the British isles resulting Wright, L.D., Short, A.D., 1983. Morphodynamics of beaches and surf zones in Australia. In: from M2 and M4 tidal interactions. J. Mar. Biol. Assoc. U. K. 59, 497–513. Komar, P.D. (Ed.), Handbook of coastal processes and erosion. CRC Press, Boca Raton, Rihouey, D., Blangy, A., Dugor, J., Dailloux, D., 2008. Technique vidéo appliquée à la FL, pp. 35–64. topographie de la plage intertidale. Xèmes Journées Nationales Génie Côtier - Génie Civilpp. 625–634.