Beach Recovery Research Articles

Morphological variability of sandy beaches due to variable oceanographic conditions: a study case of oceanic beaches of Rio de Janeiro city (Brazil)

Due to their overall east-west orientation, the Rio de Janeiro oceanic urban beaches are exposed to high energy meteoceanographic events, exhibiting large spatial and temporal morphodynamic variability that affect their use and functionality. The main goals of this study are to describe the morphology of these sandy beaches and to evaluate their response to different oceanographic conditions. Between 2016 and 2018 quasi-monthly monitoring surveys, comprising topographic and sedimentological sampling, were carried out at 21 sites distributed along Macumba, Recreio-Barra da Tijuca, Sao Conrado, Leblon-Ipanema-Arpoador and Copacabana-Leme beaches. During this period, 29 storm events were recorded by an oceanographic buoy near the study area (~20 m depth). The most energetic event occurred between 11 and 14 August 2017 and caused widespread morphological changes, as the 45 m retreat at the Recreio-Barra beach eastern sector. Overall, mean grain size decreases from west to east varying from coarse to medium sand. The topographic record shows decreasing slope and increasing width from west to east, except in the Leblon-Ipanema-Arpoador beaches, where beach rotation was documented. The main findings were the interannual variability trends to beach morphometric records, the period each beach needs to recover its mean width after erosional events and how severe are storm impacts. Besides contributing to the morphodynamic understanding of the studied beaches, new understandings of the impacts of storm events and the subsequent recovery of sandy beaches are presented.

RECOVERY OF SANDY BEACH AFTER TYPHOON WAVES - CASE STUDY ON CHIGASAKI COAST

Beach topography quickly changes in response to the action of storm waves, resulting in erosion of the foreshore with accretion under a calm wave condition after a storm. These seasonal beach changes may occur on beaches with protective measures or artificial beaches produced by beach nourishment. On these beaches, the shore protection function of a sandy beach is reduced when a trough is formed immediately offshore of the shoreline and the foreshore slope increases, indicating the importance of the study on topographic changes. Moreover, the time required for a beach recovery in response to wave conditions has not been sufficiently studied, along with the 3-D topographic changes associated with beach cycles. In this study, we aim to investigate these issues using the Narrow Multi-Beam survey data, wave data, and seabed materials data, taking the Chigasaki coast as an example. It was found that a seabed shallower than 2 and 3 m depths was eroded by rapid offshore sand transport during a storm event with the deposition of sand in a zone between 3 and 5 m depths, and then the beach recovered within 1-2 years after the storm. It was also confirmed that a bar and trough disappeared in 1-2 months under the conditions of HE = 0.5 m, TE = 8 s, and H/L = 0.005 when the crown depth of the bar was smaller than approximately 2 m. Thus, the topography after the storm waves recovers within several months or 1-2 years depending on wave conditions and the crown depth of the bar.Recorded Presentation from the vICCE (YouTube Link): https://youtu.be/W_P_3p_xd8U

INVENTARIO DE CARBONO EN LA RECUPERACIÓN DE PLAYAS CUBANAS

The objective of this study is to construct an inventory of carbon for the nourishment of Cuban sand beaches. It uses data of a beach nourishment project executed in 2016 in the archipelago of Jardines del Rey in Ciego de Avila, Cuba, according to an algorithm of carbon inventory for the recovery of beaches. The carbon budget was 62531.04 Mg, of which 952.36 were contained in consumed fossil fuels, 2338.95 were retained in the protected or rehabilitated vegetation, and 59239.73 Mg were retained in carbonate sands. The mole ratio in carbon compounds was used to transform the inventory into a net capture of 5084.16 Mg of carbon dioxide and the net depositions of calcium carbonate at 493652.11 Mg. These amounts were valued at 127 104.06 and 30 413 906.67 Cuban pesos, respectively. The total amounts were compared with the cost of investment. A positive net present value was deducted, representing a profitable investment in terms of carbon capture and increased carbonate sand surfaces on the studied beaches. We recommend to continue the study of sand beaches, in other to complete the inventory by our further research on carbon emission due to changes produced in the vegetation of the submarine zone.

SEDIMENTOLOGY OF BEACHES IN NORTHERN PALM BEACH COUNTY, FLORIDA, USA

Beach nourishment is a common strategy for erosion mitigation that also increases coastal resilience to storm impacts, provides habitat, and supports the economy. Regulations often require that placed sediment closely match the native grain size distribution and composition, however characteristics can vary based on the borrow site. Certain sediment properties will also influence beach slope and other critical beach functions. This study evaluates the 3-dimensional sediment properties and beach morphology of nourished and non-nourished barrier island beaches in northern Palm Beach County, Florida, USA. Surveyed beach profiles were compared with predicted slope based on median grain size. The inlet-adjacent beach managed with annual placement of beneficial use of dredged materials consisted of poorly sorted coarse sand and the steepest measured slope. Sediment was progressively finer and better sorted downdrift with decreasing foreshore slopes. Although sediment near the shoreline is typically the coarsest, clasts were finer than the mid-beach location suggesting that the sampling period coincided with beach recovery and onshore sediment transport of finer material. Sediment at the surface differed from sediment at depth, likely due to the frequent introduction of sediment from various borrow areas compared to the dominance of weathered coquina at depth. The non-carbonate, siliciclastic fraction was primary quartz with few other minerals. The estimated beach slope at the location with the coarsest sediment matched the measured slope. A lower beach slope was predicted for the other locations with finer grain sizes at the shoreline that was attributed to slightly steeper slopes associated with beach accretion. Therefore, complicated spatio-temporal morphodynamics of beaches should be considered when using median grain size from only one sampling event.

Analysis of Two Contrasting Seasonal Recovery Periods of an Open Sandy Beach, using High Frequency DGPS Surveys

Biausque, M. and Senechal, N., 2020. Analysis of two contrasting seasonal recovery periods of an open sandy beach, using high frequency DGPS surveys. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 377-381. Coconut Creek (Florida), ISSN 0749-0208.High frequency DGPS surveys were undertaken for 2.5 years (November 2015 until April 2018) on an open sandy double barred beach in the SW of France (Biscarrosse Beach) covering three winter and two summer periods. On those latitudes, summers are usually described as seasonal recovery periods. The morphological response of the beach during two consecutive summer periods (2016 and 2017) has been analyzed to identify processes involved in seasonal recovery. Analysis of alongshore mean profiles indicates that the summer 2016 is marked by a progressive berm reconstruction, manly driven by cross-shore sediment transport. The beach recovery in 2016 can be characterized as complete with a stable berm through the summer season associated with steady beach cusps, and a seaward dune foot migration. During this summer the variations in volume of each section of the beach (intertidal/supratidal beach and dune) show sediment transport firstly orientated from the intertidal beach toward the supratidal one, and, later, driven from the supratidal beach to the dune. This cycle is coherent with recent observations described by Philips (2017). In contrast, the summer 2017 is characterized by an incomplete recovery, an unstable berm and so, a much more complex dynamic: the berm, rapidly rebuild (by the end of June), started to erode in July. Six sequences of cross-shore sediment exchanges are measurable along the season between the intertidal and the supratidal beach, inducing successive erosion/ accretion of both sections of the beach. Thus, according to those results summers 2016 and 2017 present variable spatial and temporal dynamics. Moreover, analysis of hydrodynamic and environmental factors indicate that recovery periods not only depend on hydrodynamic conditions, such as wave energy and tide, but also on winter/summer morphological coupling, and sandbar/beach coupling.

Storm Response and Recovery Process after Nourishment of Dongsha Beach, Zhujiajian Island, Zhejiang Province

Jiang, Z.; Shi, L.; Guo, J., and Zhang, M., 2020. Storm response and recovery process after nourishment of Dongsha Beach, Zhujiajian Island, Zhejiang Province. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 231-236. Coconut Creek (Florida), ISSN 0749-0208.Effective beach nourishment can reduce storm-related erosion and promote beach recovery after storms. Herein the Dongsha Beach Nourishment Project is presented as an example. Topographic survey data and sediment samples were obtained immediately before and after the landing of Typhoon Talim (tropical storm No. 1718) in 2017 and again one, two, and six months later. The digital elevation model (DEM), beach profiles, and sediment particle sizes were used to analyze the initial response of Dongsha Beach and its recovery process. The project was compared to 16 other beach nourishment projects in China to assess its effectiveness. Talim eroded the beach as a whole, although erosion was most severe in the lower headland sheltered section and the straight section. The upper headland sheltered section suffered the least erosion and recovered most during the recovery period, followed by the straight section. The lower headland sheltered section showed the least recovery. Talim coarsened grains in the straight and upper headland sheltered sections. Grains in the high tide zone in the lower headland sheltered section appeared coarsened, while grains in the middle and low tide zones were refined. Sedimentary grains in the upper headland sheltered and straight sections returned to their pre-typhoon states within the first and second months of the recovery period, respectively. The lower headland sheltered section had not recovered after six months. The fastest recovery o ccurred within the low tide zone. Recovery in the mid-tide zone followed, while the high tide zone recovered most slowly. When Dongsha Beach was compared to 16 other beaches in China, the 2017 nourishment project appeared to be inefficient. However, high stability and good natural conditions will enable better results to be achieved at Dongsha Beach with scientific planning.

Lidar Observations of the Swash Zone of a Low-Tide Terraced Tropical Beach under Variable Wave Conditions: The Nha Trang (Vietnam) COASTVAR Experiment

A field experiment was conducted at a tropical microtidal intermediate sandy beach with a low tide terrace (Nha Trang, Vietnam) to investigate the short-term swash-zone hydrodynamics and morphodynamics under variable wave conditions. Continuous 2D Lidar scanner observations of wave height at the lower foreshore, subsequent run-up and swash-induced topographic changes were obtained. These data were complemented by detailed real-time kinematic GPS topographic surveys. Variable wave and tide conditions were experienced during the field experiment with relatively large swell waves (offshore significant wave height, Hs = 0.9 m to 1.3 m; peak wave period, Tp = 8 to 12 s) concomitant with spring tides at the beginning of the period, followed by mild wind waves (offshore Hs under 0.5 m and Tp 5 s) and neap tides. This resulted in the following morphological sequence: berm erosion followed by rapid neap berm reformation and beach recovery within a few days. New insights into the link between intra-tidal swash dynamics and daily beach profile evolution were found using the Lidar dataset. While waves directly cause morphology changes on a wave-by-wave basis, tidal levels were found to be a key factor in determining the morphological wave-effect (accretive or erosive) due to modulated interaction between surf and swash hydro-morphodynamics.

Design and Performance of Permeable Groins on a Low-Energy Natural Beach

Beach erosion, ubiquitous of sandy coasts around the world, can be exacerbated or mitigated with the use of hard engineering solutions including groins. The use of groins has been discouraged in many countries despite its capability to reduce sand losses. This study aims to design a 15 m permeable groin that allows sediment bypassing. Field experiments were conducted on a low-energy, sea-breeze dominated micro-tidal beach at the northern Yucatan peninsula during both mean and extreme wave conditions. Firstly, a short-term experiment consisted in monitoring the structure performance for 24 h during typical sea breeze conditions and the subsequent beach recovery after the structure removal. Secondly, a multi-day (60 days) experiment was conducted to investigate the performance of a single- and double-groin system during both mean and local storm conditions. Beach surveys were conducted to evaluate the beach response. Shoreline variability shows sediment accretion on the east side of the structure during sea breezes, whereas during NNW storm events, the accretion occurred on the west side. Importantly, on a scale of days, sediment bypassing occurs, and hence a net accretion was measured at both sides of the structure. During this time, a second structure was deployed 30 m apart to test the performance of a double-groin system, finding a net shoreline advance at all beach transects. Thus, low-crested short-length permeable groins are found to be a suitable emergency mitigation measure against beach erosion in micro-tidal environments causing moderate shoreline change.

Post-storm recovery assessment of urbanized versus natural sandy macro-tidal beaches and their geomorphic variability

After an erosive event induced by storms, beach recovery occurs under fair weather conditions. The geomorphic nature and rapidity of beach recovery following such high-energy events are, however, rather poorly documented. Storm Dieter hit the Belgian coast on 14–15th January 2017 causing widespread and severe damage to the coastal environment and infrastructures. This study focuses on two representative sandy macro-tidal beaches, one characterized by environmental settings with a natural dune-beach system composed of multiple intertidal bars at Groenendijk, and another by a nourished beach with devoid of bars and backed by an urbanized coastline at Mariakerke. Airborne LiDAR survey-based morphological changes were analyzed pre, post- and 4.5 months after the storm complemented by monthly topographic profiles to investigate and compare the beach response and recovery at the study sites. Despite site-specific environmental settings, sediment was removed from the backshore in both sites at a relatively similar net rate of −0.03 m3/m2/month equivalent to −0.001 m3/m2/day, and erosion also dominated in the intertidal zone during the storm. Deposition and erosion alternated on both the backshore and intertidal zones in the 4.5 month following the storm. However, the initiation of beach rebuilding was evident from 1.1 month after the storm. The beaches were largely recovered over the 4.5 months after the storm at a rate 2 to 3 times lower than that induced by the storm. The results showed a coherence in the accretional trend in the two sites, and especially the urbanized beach retained some natural ability to rebuild without recourse to post-storm artificial nourishment. The fast return to re-equilibrium in this macro-tidal environment may be partly explained by the fact that the eroded sediment caused by the storm was still locally present in the system and returned to the beach under low-moderate onshore-wave conditions during the post-storm period. A number of distinct morphological features such as the intertidal bars, embryo dunes and a backshore berm appeared in the course of net accretion. They participated in rapid beach recovery through efficient sediment redistribution with relatively low magnitude elevation changes occurring within, and across the backshore as well as the intertidal zone.

Set of indices to assess dune development and dune restoration potential in beach-dune systems on Mediterranean developed coasts

The purpose of this paper is to contribute with a tool to guide decision makers with some level of understanding of coastal dynamics as to the most appropriate management measures to adopt. A set of indices for assessing beach-dune systems and their potential for dune restoration are presented. The systems analysed are described using variables related to physical and anthropic factors, and the sites are classified according to the intervention actions required. Fifty beach-dune systems representing the range of types of beaches, the degree of urbanisation, and the dune morphologies found on the Catalan coastline (NE Iberian Peninsula) are sampled. The results show that beaches with the most developed dunes usually have high scores for management and low scores for urbanisation, while the less developed dunes are found on beaches with very low scores for management. Regarding the potential for dune restoration, the beaches are classified into four groups according to the management measures recommended: dune conservation, dune restoration, dune recovery, and renaturalisation of beaches where only incipient dunes can be developed.

Wave Period and Grain Size Controls on Short‐Wave Suspended Sediment Transport Under Shoaling and Breaking Waves

AbstractBeach recovery is key to the continued existence of sandy beaches and is typically driven by the onshore‐directed transport of sediment by short waves during low‐moderate energy conditions. The physical processes governing beach recovery are not well understood, but the theoretically developed dimensionless fall velocity, Ω = H/wsT, was suggested to be important for separating onshore/offshore sediment motion (Dean, 1973). In this paper, the effect of wave period and sediment grain size on short‐wave suspended sediment flux was investigated based on field measurements obtained beneath shoaling and breaking waves at Durras and Vejers beaches. The efficiency of the breaking waves in transporting suspended sediment onshore was roughly the same for the two beaches, despite the wave periods being larger and the mean sediment grain size coarser at Durras beach. The flux efficiencies were, however, shown to be degraded by wave‐current interactions and long/short‐wave interactions at Durras beach, especially. Excluding time series of strong undertow velocities (< −0.1 m/s) and infragravity wave‐energy (>5 m2/s3) resulted in significantly larger flux efficiencies beneath breaking waves at Durras beach compared to Vejers beach. These results indicate that wave‐current interactions and long/short‐wave interactions should be taken into consideration along with the wave period and mean grain size when estimating short‐wave suspended sediment fluxes. The results also showed that plunging breakers were more efficient in suspending sediment and transporting it onshore compared to spilling breakers/surf bores. This finding suggests that wave breaker type also is an important parameter to incorporate when modeling beach recovery.

Succession of microbial populations and nitrogen-fixation associated with the biodegradation of sediment-oil-agglomerates buried in a Florida sandy beach

The Deepwater Horizon (DWH) oil spill contaminated coastlines from Louisiana to Florida, burying oil up to 70 cm depth in sandy beaches, posing a potential threat to environmental and human health. The dry and nutrient-poor beach sand presents a taxing environment for microbial growth, raising the question how the biodegradation of the buried oil would proceed. Here we report the results of an in-situ experiment that (i) characterized the dominant microbial communities contained in sediment oil agglomerates (SOAs) of DWH oil buried in a North Florida sandy beach, (ii) elucidated the long-term succession of the microbial populations that developed in the SOAs, and (iii) revealed the coupling of SOA degradation to nitrogen fixation. Orders of magnitude higher bacterial abundances in SOAs compared to surrounding sands distinguished SOAs as hotspots of microbial growth. Blooms of bacterial taxa with a demonstrated potential for hydrocarbon degradation (Gammaproteobacteria, Alphaproteobacteria, Actinobacteria) developed in the SOAs, initiating a succession of microbial populations that mirrored the evolution of the petroleum hydrocarbons. Growth of nitrogen-fixing prokaryotes or diazotrophs (Rhizobiales and Frankiales), reflected in increased abundances of nitrogenase genes (nifH), catalyzed biodegradation of the nitrogen-poor petroleum hydrocarbons, emphasizing nitrogen fixation as a central mechanism facilitating the recovery of sandy beaches after oil contamination.

Multiannual Shore Morphodynamics of a Cuspate Foreland: Maspalomas (Gran Canaria, Canary Islands)

On a cuspate sandy foreland, the cycle of beach erosion and recovery is driven by the bi-directional approaches of wave climates, which also determine its specific shape. This work describes the seasonal morphodynamics of the Maspalomas natural cuspate foreland over a period of six years. This area, located in the south of Gran Canaria Island, consists of two beaches with different shoreline orientation, Maspalomas Beach and El Inglés Beach, converging to La Bajeta Tip at the head of the foreland. Shoreline variability and three-dimensional beach changes were measured and coupled to wave energy and longshore currents. From wave analysis, 112 storm events were identified over the period in focus. These events most frequently came from the northeast and in summer, which is consistent with the strong northeasterly trade winds between April and September. However, the strongest storms from the southwest were found to be the main cause of intense shoreline retreats, of up to 100 and 200 m, at Maspalomas Beach and La Bajeta Tip, respectively. The Maspalomas Beach sector showed interannual variability, with a general trend of erosion, whereas La Bajeta Tip demonstrated faster beach recovery. In contrast, El Inglés Beach sector presented a stable shoreline, in spite of the occurrence of wave storms approaching from northeast or southwest. Consequently, results indicate that energetic waves play a significant role in shoreline dynamics and Maspalomas landform shape. Post-storm sand recovery processes do not only occur during calm periods, but also during energetic events. The findings of this study have improved the understanding of seasonal and multiannual cuspate foreland morphodynamics, setting the groundwork for a potential long-term evolution model of Maspalomas coast.

Pluriannual beach-dune evolutions at regional scale: Erosion and recovery sequences analysis along the aquitaine coast based on airborne LiDAR data

Abstract: With apparent uniformity, the 230 km of the Aquitanian sandy coast presents many differences in geomorphological characteristics and evolutions at the event, seasonal, annual and pluriannual time scales. This contribution highlights work based on extensive airborne LiDAR coverage campaigns realized in 2011, 2014, 2016 and 2017. Geomorphological evolutions are studied at the scale of the sedimentary cells and subcells of the Aquitanian sandy coast, specifically through the automatic detection of dune erosion scarps and incipient foredunes, planimetric indicators analysis, and the sediment budget of the beach-dune interface. Analyses were performed for two periods: 2011–2014 (including the erosional impact of the 2013–2014 winter) and 2014–2017, presenting continuous and extensive beach recovery at the beach-dune interface. Dune erosion scarps and incipient foredune characteristics are analyzed. A classification based on the alongshore length of the erosion scarp shows great diversity of erosional dynamics, which are directly linked to the geomorphologic characteristics of the beach sediment availability and the nearshore bar system. This diversity includes homogeneously large erosional bands above a 1 km alongshore length, periodic Mega cusp embayments from 200 to 800 m, and a local erosion mark less than 200 m long. Analysis for the following period shows a prompt and massive recovery at the upper beach and dune foot proxies on the majority of the coast. However, the recovery process as well as erosion is strongly marked by a North–South gradient. The dune front was massively impacted in Gironde, with a retreat exceeding 25 m that was poorly prograded since 2014, whereas in Landes a progradation of the front dune is observed compared to 2011. During the first period (including the 2013–2014 winter), more than 15 500 × 103 m3 of sediment was eroded from the beach-dune interface, which represents on average a loss of 66 m3 per linear meter. The gains during the following period (2014–2017) are also massive, above 13 500 × 103 m3, with an average gain of 57 m3 per linear meter. Given the budget between the two periods, 86.5% of the sand eroded in 2014 had moved back in 2017 at the beach-dune interface but 90 % of the sand stocks are localised between the upper beach and the dune foot. The progressive recovery tendency at the beach-dune interface is massive but fragile because the sediments are potentially removable by storm marine processes in case of energetic events. At the pluriannaual, decadal and pluridecadal scales, the different sections of the coast follow various trends concerning erosion as well as recovery processes resulting in a contrasted long term coastline evolution from the north to the south of the coast.

Morphodynamics of sandy beaches under the influence of storm sequences: Current research status and future needs

This paper reviews and discusses the current research status, trends, and future needs in the field of beach morphodynamics under the influence of storm sequences. The paper reviews how the three main research methods, field investigations, numerical modelling, and physical modelling, have been used to study beach morphodynamics during storm sequences. Available quantitative definitions of storm sequences at different sites are presented and discussed. It is shown that the definition of storm sequences is site-specific and requires knowledge of the storm climate, beach characteristics, and the temporal scale of beach recovery. Subsequently, the paper brings together currently available approaches aimed at describing the effect of storm sequences on beach erosion in a general way. The importance of storm chronology and the effects of an extreme storm within a sequence of storms are highlighted. Following that, the more poorly studied aspect of beach recovery in between storms within a sequence is discussed. Three indicators for defining beach recovery, namely the shoreline location, sediment volumes, and the beach state, are identified and compared. Finally, important research needs, including the need for detailed physical modelling, are identified.

Accelerating Beach Recovery by Plowing the Intertidal Bar: A Field Experiment along the Northern Spanish Coast

ABSTRACT Gainza, J.; Garnier, R.; Nunez, P.; Jaramillo, C.; Gonzalez, E.M.; Medina, R.; Liria, P.; Epelde, I.; Uriarte, A., and Monge-Ganuzas, M., 2019. Accelerating beach recovery by plowing the i...

Video Sensing of Nearshore Bathymetry Evolution with Error Estimate

Although coastal morphology results essentially from underwater sediment transports, the evolution of underwater beach profiles along the diverse coastlines of the world is still poorly documented. Bathymetry inversion from shore-based video cameras set forth a more systematic evaluation and is becoming more commonly used. However, there are limitations to this profiling method that are insufficiently assessed, undermining confidence in operational applications. In this paper, we investigate the daily evolution of a low tide terrace (LTT) in Nha Trang beach, Vietnam, under strong seasonal forcing: from weak wind waves during summer monsoon to moderate waves during winter monsoon. A new error estimation for depth inversion is presented based on tidal evaluation. The method compares video-based estimate and direct measurement of tidal amplitudes to provide a quality criterion. It reveals three types of errors, the main one being a deep water error associated with physical limits—loss of celerity-bathymetry relationship in deep water. This error is dependent on wave period and thus has a strong seasonal pattern in Vietnam. It is generally detrimental to depth inversion where wind waves are dominant (in summer here). On the contrary, the second error type is larger for larger waves and is located at breakpoint, altering wave detection. The last error type is due to nonlinear effects and wave setup in shallow water. After removing the faulty data, we finally present the first reliable three-year time-series of a beach profile in Nha Trang, Vietnam. A main result is the overall stability demonstrated for the LTT beach, with rapid exchange of sediment between the terrace and the upper beach during typhoons, monsoon events or seasonal cycles. These tropical environments may provide faster beach recovery compared with mid-latitude configurations.

Morphological recovery of beach severely damaged by the 2011 great east Japan tsunami

The Great East Japan tsunami, which occurred on 11 March 2011 (the 2011 tsunami), caused significant changes to the coastal and estuarine morphology along the Sendai coast, Miyagi prefecture, Japan. The recovery process, which took place subsequently after the tsunami, is investigated using aerial photographs, bathymetry data, and Empirical Orthogonal Function (EOF) method. Results from the aerial photograph analysis indicate that the shoreline was in the dynamic equilibrium condition in the period before the tsunami (Period 1). The recovery of the shoreline was very fast in the period of two years post event (Period 2). However, it was more stable for the period of the next 4.5 years (Period 3). The analysis on the bathymetry data indicates that, besides the sediment supply from adjacent coasts, eroded sediment of the offshore seabed was transported onshore and led to a mass recovery of the shoreline at the lagoon areas. The littoral system of the Sendai coast also changed significantly between the periods before and after the tsunami, as well as between Periods 2 and 3. The sediment deposited inland and in the lagoon areas is perceived as the main reason that caused the retreat inwardly of about 70 m–80 m of the shoreline after the tsunami. Regarding the EOF analysis, the reflected coastal processes of the first three dominant components from the EOF analysis for two shoreline data sets after the tsunami can be explained. In Period 2, the morphological recovery at severely damaged areas (lagoons) was the most dominant process, whilst the second one was the cross-shore variety of shoreline which was the most dominant process preceding tsunami. The contribution rate of the first and second components in Period 2 is about 4 times different. In the period of the next 4.5 years (Period 3), the cross-shore variety of shoreline which was induced by high waves came back to be the most dominant process, whilst the second component reflects the longshore sediment transport. These two dominant components are similar to the ones before the tsunami. The contribution rates of the first two components before and after the tsunami are relatively close as well. That confirms that the coastal processes have returned back to the conditions before the tsunami. This is an important finding which is deduced from this study because a strong tsunami such as the 2011 tsunami could have been a major disturbance, tipping the “normal” cross-, long-shore variability of shoreface water interface towards a different regime.

Field observations of intra-wave sediment suspension and transport in the intertidal and shallow subtidal zones

Sandy beaches are highly dynamic due to the transport of sediment by waves and currents. While beach erosion is mainly driven by cross-shore currents, beach recovery is driven by the onshore-directed transport of sediment by incoming short waves. This latter process is complex and often inaccurately predicted by morphodynamic models. This is partly because of the omission of the effects of bed form-induced and surface-generated turbulence on sediment pick-up in these models. In this paper, the phase relationship between the oscillatory flow, turbulence and suspended sediment concentration was investigated based on field measurements obtained beneath shoaling waves, spilling breakers and surf bores. Wave-averaged and intra-wave variability in turbulence and suspended sediment concentration were analysed on a wave-by-wave basis, where individual waves were extracted and then grouped according to relative wave height. Beneath shoaling waves, small but steep wave ripples were shown to affect the phasing of suspended sediment concentration and to cause an offshore-directed short-wave suspended sediment flux. Beneath spilling breakers and surf bores, sediment was mainly stirred under the wave crest and the short-wave suspended sediment flux was onshore-directed. Based on the analysed data, several mechanisms were suggested to cause sediment stirring: friction between the wave orbital motion and the seabed, penetration of surface-generated turbulence towards the seabed, increased bed shear stress at the wave front due to acceleration skewness, and during conditions with strong undertow, wave-current interactions.

Modes of Berm and Beachface Recovery Following Storm Reset: Observations Using a Continuously Scanning Lidar

AbstractFollowing the rapid and destructive impacts of storm erosion, beach recovery is a key natural process of restoration, returning eroded sediment to the subaerial beach and rebuilding coastal morphology. While the effects of storm erosion have commonly been investigated, detailed studies into poststorm recovery are currently lacking. This study investigates wave‐driven recovery processes of the berm and beachface on a microtidal, swash‐aligned sandy beach. Following complete removal of the berm by a significant storm event, the entire 76‐day rebuilding of a swash berm is analyzed at the timescale of every semidiurnal tidal cycle, utilizing high‐resolution (5 Hz) swash and subaerial beach profile measurements from a continuously scanning fixed lidar. Tide‐by‐tide rates of subaerial volume change during berm recovery were most frequently observed between 1 and 2 m3/m/day, including losses and gains an order of magnitude larger than the more gradual rate of net gain (0.7 m3/m/day) observed for the entire recovery period. Patterns of berm crest formation and vertical growth were found to be primarily governed by the neap‐spring tide variations in total water levels. Tide‐by‐tide beachface and berm volume changes were used to classify four principal behavioral modes of subaerial profile variability during recovery. Using decision tree classification, modes were differentiated according to nearshore dimensionless fall velocity, swash exceedance of the berm crest, and ocean water levels. The findings provide novel behavioral and parametric insight into the tide‐by‐tide rebuilding of the beachface and berm by swash throughout a complete poststorm recovery period.