Beach Accretion Research Articles

MODELLING DUNE EROSION OF THE SEFTON COAST, LIVERPOOL BAY, UK

Dune erosion at sandy coastal systems poses significant threat to the hinterland areas due to flooding and subsequent damage to life and property. The Sefton Coast (Fig.1), bounded by Mersey (South) and Ribble (North) estuaries in the Liverpool Bay, represents about 20% of the UK’s dune system, has a high recreational value, form an effective coastal flood defense and consists of a significant number of conservation areas of national and international interest. This area is however susceptible to erosion during storm events where landward retreat occurs leading to dune breach and coastal flooding. Present study focused on an area around the Formby Point of the Sefton Coast (dashed-line polygon in Fig.1), which is a highly dynamic sedimentary system. The dune system at Formby Point beach showed continuous accretion (max ~4.7 m/year) during the last century but has become an eroding beach since early twentieth century (max. ~6.2 m/year). However, beach accretion can still be seen in far south and north of Fomby Point. The Sefton Coast experiences a semi-diurnal macrotidal regime with a mean spring tidal range reaching 8.22 m (Esteves et al., 2012). Mean annual significant wave height (Hs) is about 0.53 m while extremes exceed 5 m (Brown et al., 2010). The aim of this study is to investigate the response of the Formby Point dune system to extreme storm conditions based on the March 2010 storm event (max. Hs>3.5 m, see Brown, 2010). We use the 2DH process-based morphological model XBeach, which has been developed to investigate dune erosion under extreme conditions (Roelvink et al., 2009), in combination with the SWAN spectral wave model (Booij et al., 1999). The model set-up consists of a coarse-grid model (Sefton) and a fine-grid model (Formby Point) which encloses the area of interest. The Sefton model is driven by the Liverpool Bay WaveNet buoy wave data (Esteves et al., 2012). The outputs of the Sefton model provide wave and water level boundary conditions to the Formby Point morphodynamic model to investigate the beach response to the selected storm event. The model setup described above is then used to simulate nearshore hydrodynamics and morphodynamics. Fig. 1shows a snapshot of simulated Hs corresponding to the storm event occurred in the Liverpool Bay during 30 March and 02 April 2010, at the mean tidal level. Offshore waves are significantly attenuated when travelled from offshore to nearshore. Fig. 2 shows the model simulated exposure of the dune system and the beach during Low Water (LW) (a) and High Water (HW) (b). At LW, the beach exposes up to about 3 km while at HW, the entire beach drowns, exposing the dune system to incoming waves. Therefore, a storm event combined with HW may lead to damage the dune system and hence flooding of the hinterland of the River Alte area, due to the low dune height in this area. Relatively high morphological changes are observed around the Crosby channel area (see location in Fig. 1). The storm driven dune erosion occurred during the HW. Large storm waves propagate along the Crosby channel towards the River Alte area. The River Alte area is susceptible to coastal flooding during storms, as a result of the low dune crest in this area. Work is currently in progress to predict the dune evolution and flooding under the future climate change and sea level rise scenarios.

Reply to J.J. Muñoz-Perez et al. Comments on “Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain” by E. Poizot et al. (2013) Geo-Marine Letters 33(4)

In a novel finding for a beach environment, Poizot et al. (2013) identified an FB+ trend (sediments becoming finer, better sorted and more positively skewed upshore) on a well-developed swash bar on the upper foreshore of the Camposoto beach of Cadiz in SW Spain. In their Discussion of that paper, Munoz-Perez et al. (2014) provide some supporting arguments and also report grain-size, beach profile and other data from nearby beaches which differ from those of Poizot and colleagues for Camposoto beach, pointing out that a trend observed on one beach may not apply to a neighbouring beach. However, even though the absolute values differ, the overall trends actually do show the same general behaviour. In our Reply to their comments, we also address some difficulties in comparing granulometric datasets generated by different analytical techniques.

Comments on “Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain” by E. Poizot et al. (2013) Geo-Marine Letters 33(4)

This Discussion provides comments on the application of grain-size trend analysis to Camposoto beach (SW Spain) reported by Poizot et al. (2013) in Geo-Marine Letters 33(4):263–272. Some of their results are updated or complemented by existing data from other studies carried out on Camposoto and other nearby beaches. For example, a detailed breakdown of beach nourishment volumes and costs is presented, and the influence of a horizontal reef flat on the tilting of the beach profile around the mean or the low water level is highlighted. Moreover, data from the displacement of dyed samples are used to evaluate the relationship between sediment transport speed (va) and current speed (V), the corresponding ratio being consistent with the range of values reported by several other authors. Finally, some minor, although still significant, differences are detected in some granulometric parameters as well as in the profile shape. Determining the reason for these discrepancies could enhance our current knowledge about the factors controlling short-term beach profile responses.

Remote sensing, planform, and facies analysis of the Plain of Tineh, Egypt for the remains of the defunct Pelusiac River

The Pelusiac Branch was a distributary river in the Nile Delta that splits off from the main trunk of the Nile River as it flowed toward the Mediterranean. At approximately 25 A.D., it was chocked by sand and silt deposits from prograding beach accretion processes. The lower course of the river and its bifurcation point from the trunk of the Nile have been hypothesized based on ancient texts and maps, as well as previous research, but results have been inconsistent. Previous studies partly mapped the lower course of the Pelusiac River in the Plain of Tineh, east of the Suez Canal, but rapid urbanization related to the inauguration of the Peace Canal mega-irrigation project has covered any trace of the linear feature reported by these previous studies.The present study used multispectral remote sensing data of GeoEYE-1 and Landsat-TM to locate and accurately map the course of the defunct Pelusiac River within the Plain of Tineh. Remote sensing analysis identified a linear feature that is 135m wide at its maximum and approximately 13km long. It extends from the Pelusium ruins to the Suez Canal, just north of the Peace Canal. This remotely located linear feature corresponds to the path of the Pelusiac River during Roman times. Planform geomorphology was applied to determine the hydrological regime and paleodischarge of the river prior to becoming defunct. Planform analysis derived a bankfull paleodischarge value of ~5700m3s−1 and an average discharge of 650m3s−1, using the reach average for the interpreted Pelusiac River. The derived values show a river distributary similar in discharge to the modern dammed Damietta river. Field work completed in April of 2012 derived four sedimentary lithofacies of the upper formation on the plain that included pro-delta, delta-front and delta-plain depositional environments. Diatom and fossil mollusk samples were also identified that support coastal beach and lagoonal environments of deposition. Measured section columns and a shoreline parallel transect were also constructed to portray the paleogeography of the Mediterranean coastline in the Plain of Tineh at ~25 A.D. and indicate that the sampled study area is the downdrift margin of an asymmetric delta with barrier lagoon systems.

Using diamond-mined sediment discharges to test the paradigms of sandy-beach ecology

The prevailing view of sandy-shore ecosystems is that they are controlled largely by physical conditions, particularly particle size, slope and wave regime, but it is rarely possible to test this view by experimentally manipulating these attributes. We report a unique opportunity to accomplish this because large-scale alteration of these properties has taken place on the Namibian coast, associated with diamond mining. Elizabeth Bay diamond mine, near Lüderitz, started modern operations in 1991. Since then, 30.8 million tonnes of sediment with a particle size (<1.4 mm) coarser than the native beach sand have been discharged as slurry onto the beach as part of the treatment process. The physical and biological effects of this were monitored on seven occasions between 1993 and 2012, spanning three phases: (1) an initial pre-upgrade phase (1994–2004) with discharges of moderate intensity; (2) doubling of discharges during upgrade of the mine (2005–2008); (3) temporary cessation of mining (2009–2011). These vicissitudes resulted in both spatial and temporal physical changes, including massive beach accretion (350–620 m), overall increases in mean sand particle size and slope and decreases in Dean's Parameter, east-to-west gradients in beach slope, wave height and erosion, and changes in the beach state from dissipative towards reflective conditions. Alteration of physical conditions led to significant macrofaunal changes, with the community structure in the centre of the bay opposite the discharge points shifting from a state dominated by sand mussels to one dominated by peracarid crustaceans, accompanied by reductions in diversity, biomass and abundance. Grossebucht, which lies nearby and is not mined, provided comparative reference samples: physical conditions there changed little, and biotic communities were constant, significantly more diverse and had greater abundances and biomasses than at Elizabeth Bay. The changes in physical conditions and ensuing biological responses confirmed the prevailing paradigm that sandy beaches are physically driven, with diversity, abundance and biomass all declining at places and times where sediment particle size and beach slope increased due to sediment inputs.

Confirmation of beach accretion by grain-size trend analysis: Camposoto beach, Cádiz, SW Spain

An application of the grain size trend analysis (GSTA) is used in an exploratory approach to characterize sediment transport on Camposoto beach (Cadiz, SW Spain). In May 2009 the mesotidal beach showed a well-developed swash bar on the upper foreshore, which was associated with fair-weather conditions prevailing just before and during the field survey. The results were tested by means of an autocorrelation statistical test (index I of Moran). Two sedimentological trends were recognized, i.e. development towards finer, better sorted and more negatively skewed sediment (FB–), and towards finer, better sorted and less negatively or more positively skewed sediment (FB+). Both vector fields were compared with results obtained from more classical approaches (sand tracers, microtopography and current measurements). This revealed that both trends can be considered as realistic, the FB+ trend being identified for the first time in a beach environment. The data demonstrate that, on the well-developed swash bar, sediment transported onshore becomes both finer and better sorted towards the coast. On the lower foreshore, which exhibits a steeper slope produced by breaking waves, the higher-energy processes winnow out finer particles and thereby produce negatively skewed grain-size distributions. The upper foreshore, which has a flatter and smoother slope, is controlled by lower-energy swash-backwash and overwash processes. As a result, the skewness of the grain-size distributions evolves towards less negative or more positive values. The skewness parameter appears to be distributed as a function of the beach slope and, thus, reflects variations in hydrodynamic energy. This has novel implications for coastal management.

A 34 year record of foredune evolution, Dark Point, NSW, Australia

Hesp, P.A., 2013. A 34 year record of foredune morphodynamics at Dark Point, NSW, Australia In: Conley, D.C., Masselink, G., Russell, P.E. and O'Hare, T.J. (eds.)Incipient foredunes are formed by æolian deposition in plants on the backshore. They commonly evolve into established foredunes, and are present on many of the world's coasts, yet there are very few medium to long term studies on how they evolve and change over time. An incipient foredune suite has been monitored at Dark Point, NSW, Australia since 1978, providing a 34 year record of dune evolution and dynamics, and therefore representing one of the very few medium term foredune monitoring sites in the world.The foredune was initiated by the growth of a zone of discrete pioneer plant species (principally Spinifex) on the backshore following the destructive 1974–75 storms. Over a period of 24 years, 5 separate incipient foredunes developed as sediment was gradually returned to the surfzone and beach, and the beach prograded 70m. Sometime after 1998, storms cut back the seawardmost foredune and former foredunes were reactivated landwards of the 1998 foredune. This study demonstrates (i) how incipient foredunes form by both discrete seedling development, and seawards rhizome extension over time, (ii) how ramp and terrace morphologies eventually evolve into ridges, (iii) rates of beach accretion following storm erosion and backshore response, (iv) how wave erosion drives morphological changes and evolutionary sequences on foredunes, (v) the relationships between backshore height, foredune development and sea levels, and (vi) indications for the initiation and evolution of so-called ‘beach ridges'.

The coast between Cabo de Santa Maria (Portugal) and Rabat (Morocco): a mega-size headland-bay shoreline under control of the North Atlantic swell?

Equilibrium headland-bay beach systems have been mathematically described by logarithmic, parabolic and hyperbolic curve functions. The largest system of this type reported to date has a shoreline length of about 62 km. In the present study, an apparent headland-bay system is presented which has a shoreline length of about 500 km. It was discovered on satellite images, and is located between Cabo de Santa Maria in Portugal and the coastal city of Rabat in Morocco. It appears to be controlled by long-period North Atlantic swells diffracting around Cabo Sao Vicente at the south-western tip of Portugal, in combination with SW–SE wind wave climates impinging on the northern shoreline of Cadiz Bay. The coast shows two marked departures from the equilibrium shoreline along its central section north and south of the Strait of Gibraltar, which are easily explained. Thus, the promontories to the north of the strait still exist because there has not been sufficient time to erode these back to the equilibrium shoreline since postglacial sea-level recovery. The coastal indentation to the south is explained by an insufficient sediment supply from terrestrial sources to facilitate the required beach accretion. Perfectly adjusted planimetric headland-bay shoreline shapes represent situations where wave orthogonals approach the coast at right angles everywhere, i.e. there is no longer any alongshore sediment transport. Equilibrium shorelines form independently of the grain size of the beach sediment, whereas morphodynamic beach states are indirectly affected by the shoreline shapes because the latter are modulated by wave period and breaker height which also control the morphodynamic response of the beach in combination with the local grain size.

Sea-Level Rise and Subsidence/Uplift Processes in the Mexican South Pacific Coast

Abstract Buenfil-Lopez, L.A.; Rebollar-Plata, M.; Munoz-Sevilla, N.P., and Juarez-Leon, B., 2012. Sea-level rise and subsidence uplift processes in the Mexican South Pacific coast. Along the Mexican South Pacific coast, seismic activity can generate a relative and instantaneous fall in sea-level with differential recovery times along the coast that, considering the occurrence of new coseismic coastal uplifts, can induce recurrent hydrodynamic behaviors. These behaviors could be important for coastal processes, such as tide inlet stability or beach erosion and accretion rates. To obtain a first approximation of this phenomenon, four tide gauge records were analyzed. Results showed a relative fall in sea-level at two tide gauge stations: Acapulco (25.3 cm) and Puerto Angel (14.6 cm). By applying derived sea-level trends, it was observed that the needed time to recover the mean sea level before the events occurred was 25.1 y for Acapulco and 82.9 y for Puerto Angel. If the apparent increment of global sea-le...

철재형 이안제의 설계외력 산정기법 검증을 위한 실해역 시험

철재형 이안제는 구조형식이 단조롭고 설계가 용이하며 퇴적파랑을 통과시키는 등 장점이 많아 기존의 중력식 방파제의 대안으로서 기대된다. 철재형 이안제의 설계기법은 권혁민 등(2011), 권오균 등(2011), 이정렬 등(2011)이 보고한 바 있다. 권혁민 등(2011)은 철재형 이안제의 설계외력을 산정함에 있어서 유의파고에 상당하는 규칙파를 사용하고 말뚝의 심도설계를 위한 연직상향력은 수평판의 지점별 최대압력분포로부터 산정할 것을 제안하였다. 본 연구는 제안된 외력산정기법의 실해역 검증을 위하여 수행되었다. 또한 본 연구에서는 설계상 가능한 구조물에 대하여 실해역 실험을 통하여 축조 과정 기술 확보, 파괴 여부 판정, 철거 가능성을 검증하고자 한다. 철재형 이안제에 사용된 소파판은 <TEX>$9m{\times}12m$</TEX>(길이<TEX>${\times}$</TEX>폭)의 크기이고, 강관말뚝은 직경 711 mm, 두께 12 mm, 길이 23.2 m이다. 실해역 실험 결과, 본 구조물의 축조는 기존의 장비로 약 8시간 만에 1셀의 시공이 가능하고, 유의파고 5.83 m의 외력에 대하여 말뚝의 수평 및 수직 상호변위는 매우 작게 발생하였으며, 철거는 양호한 기후조건에서 2일이 소요되었다. 본 실해역 시험을 통하여 권혁민 등(2011)의 철재형 이안제에 작용하는 외력산정기법이 유용하며 말뚝의 인발력에 대한 마찰 안전율이 약 2.0에 상당하다는 것을 알았다. 또한 철재형 이안제는 설계, 시공, 철거가 간단하며, 소파판의 착탈식 운영방식으로 해안의 사정에 따라 모래포집량 조절이 가능할 수 있다는 기대를 높이게 되었다. The steel-type breakwater has the merits of structural simplicity and passing the long period wave for beach accretion. So, it has been expected to be a key tool for the strategic beach protection technology. The design methodology of the steel-type breakwater was published by Kweon et al.(2011), Kwon et al.(2011), Lee et al.(2011). For the analysis of the resistant friction load acting on the pile, Kweon et al. proposed the estimation method of the design up lift force acting on the dual horizontal plate. With a train of regular wave corresponding to the significant one, they integrated the distribution of the biggest pressure at each point. For the verification of the estimation method of the load on the pile, the study is carried out the experiment in a real sea state. Moreover, the construction procedure, the displacement, joint checking and removal possibility of the steel-type breakwater are discussed. The constructed breakwater has the horizontal wave energy dissipator of <TEX>$9m{\times}12m$</TEX>(<TEX>$length{\times}width$</TEX>) and pile diameter of 711 mm, thickness of 12 mm, length of 23.2 m. The construction took about 8 hours for 1 cell composed of 9 piles and 1 horizontal dual plate. There is a little vertical and horizontal displacement of pile attacked by the maximum wave height of 5.83 m. The removal of 1 cell took about 2 days. This study shows the merits of the easier design, faster construction and simpler removal of the steel-type breakwater. The structure could be estimated as a stable one because it has the horizontal dissipator on which acting a little compression and a little uplift force due to the perforated holes. Moreover, the easier removal could make it possible to manage the coastal line as depending on the conditions of erosion or accretion sand volume.

Large-scale laboratory investigation into the effect of varying back-barrier lagoon water levels on gravel beach morphology and swash zone sediment transport

It is generally accepted that the effect on beach morphology of the interactions between swash motion and the beach groundwater table depends on the elevation of the latter relative to that of the sea. Specifically, a low beach groundwater table is considered to enhance onshore sediment transport and beach accretion, while the reverse is thought to hold for a high beach groundwater table. Here, we use the results of a carefully designed series of tests conducted in the Delta Flume, the Netherlands, as part of the Barrier Dynamics Experiment (BARDEX), to unequivocally demonstrate the validity of this assertion. During the experiment, a 4-m high and 50-m long gravel barrier (D50=11mm) was constructed within the central region of the 250-m long and 7-m deep wave flume, enabling a back-barrier ‘lagoon’ to be located at its landward side. The groundwater table in the beach was manipulated by lowering and raising the lagoon level, and the gravel beach was subjected to variable wave conditions and sea/lagoon levels. Using as the initial beach profile the morphology resulting from 90min of wave forcing with the sea and lagoon at the same level, the identical wave forcing with a low lagoon level consistently resulted in onshore sediment transport in the swash zone and beach accretion, whereas the identical wave forcing with a high lagoon level consistently caused offshore sediment transport in the swash zone and beach erosion. The divergent beach morphological responses for the low and high lagoon levels could not be attributed to changes in the ‘bulk’ swash hydrodynamics (i.e., based on single-point velocity measurements) arising from a difference in the amount of swash infiltration into the unsaturated beach. Instead, application of a sediment transport model that accounts for the effects of in/exfiltration suggested that the onshore sediment transport and beach accretion for the low lagoon tests mainly resulted from enhanced bed shear stresses during the wave uprush due to infiltration into the saturated part of the beachface. Due to the large hydraulic conductivity of gravel (K=O(0.1ms−1)), the effect of altered shear stresses due to in/exfiltration may be an important factor in sediment transport in the swash zone of gravel beaches.

Quantifying Anthropogenically Driven Morphologic Changes on a Barrier Island: Fire Island National Seashore, New York

KRATZMANN, M.G. and HAPKE, C.J., 2012. Quantifying anthropogenically driven morphologic changes on a barrier island: Fire Island National Seashore, New York.Beach scraping, beach replenishment, and the presence of moderate development have altered the morphology of the dune–beach system at Fire Island National Seashore, located on a barrier island on the south coast of Long Island, New York. Seventeen communities are interspersed with sections of natural, nonmodified land within the park boundary. Beach width, dune elevation change, volume change, and shoreline change were calculated from light detection and ranging (LIDAR), real-time kinematic global positioning system (RTK GPS), and beach profile data sets at two ∼4 km long study sites. Each site contains both modified (developed, replenished, and/or scraped) and nonmodified (natural) areas. The analysis spans 9 years, from 1998 to 2007, which encompasses both scraping and replenishment events at Fire Island. The objectives of this study were to quantify and compare morphological changes in modified and nonmodified zones, and to identify erosional areas within the study sites.Areas of increased volume and shoreline accretion were observed at both sites and at the western site are consistent with sand replenishment activities. The results indicate that from 1998 to 2007 locations backed by development and that employed beach scraping and/or replenishment as erosion control measures experienced more loss of volume, width, and dune elevation as compared with adjacent nonmodified areas. A detailed analysis of one specific modification, beach scraping, shows distinct morphological differences in scraped areas relative to nonscraped areas of the beach. In general, scraped areas where there is development on the dunes showed decreases in all measured parameters and are more likely to experience overwash during storm events. Furthermore, the rapid mobilization of material from the anthropogenic (scraped) dune results in increased beach accretion downcoast.National park lands are immediately adjacent to developed areas on Fire Island, and even relatively small human-induced modifications can affect park resources and beach–dune response to storms. This study is the first to conduct a systematic analysis on how anthropogenic modifications affect resources at Fire Island National Seashore and provides essential information for effective management and preservation of coastal resources within the park.

Geomorphic Approach for Mitigating Impact of Harbor Construction on Sandy Beaches

Some harbors constructed on sandy shore have interrupted littoral drift, resulting in updrift beach accretion, siltation in navigation channel, or downdrift erosion. Conventional harbor design procedures have focused on water tranquility in the basin and prevention of sediment into the harbor, using scaled hydraulic experiments or numerical modeling which could not precisely determine the effect of breakwater orientation and its tip on adjacent beaches. After having discussed a wide range of field cases of harbors in Japan, Korea, and Taiwan, this paper then demonstrates the potential of a quantitative approach based on the static bay beach concept for mitigating the impact of harbors on sandy beaches. With this alternative, the most preferred location of a breakwater tip to minimize the adverse effect on adjacent shorelines can be readily devised with a freeware MEPBAY on a computer screen. This approach could benefit the work of experimentalists and numerical modelers on planning a new harbor or improving an existing one in many countries.

Beach and nearshore morphodynamic changes of the Tabarka coast, Northwest of Tunisia

Aerial photographs taken in the 1963 and 2001 and bathymetric charts, in conjunction with coastal processes are analyzed to assess changes in rate of shoreline position, seabed level, and seabed grain sizes along the Tabarka–Berkoukech beach at the north-western Tunisian coastline. The littoral cell of this beach, 12-km-long, is bounded by pronounced embayments and rocky headlands separated by sandy stretches. Although not yet very much undeveloped, this littoral is still experienced degradation and modification, especially along its shoreline, with significant coastal erosion at some places. Results obtained from analysis of shoreline position indicate that El Morjene Beach is experienced a landward retreat of more than −62 m, at a maximum rate of −1.64 m/year, whereas the El corniche beach is advanced about 16–144 m, at an average rate of 0.42 m–3.78 m/year. This beach accretion has been formed on the updrift side of the Tabarka port constructed between 1966 and 1970. Comparison of bottom contours deduced from bathymetric charts surveyed in 1881 and 1996 off the coastline between Tabarka Port and El Morjene Beach identifies erosional areas (sediment source) and accretionary zones (sediment sink). Erosion (0.87–4.35 cm/year) occurs between El kebir River Mouth and El Morjene beach, whereas accretion exists in the zone down wind of the port ranges between 0.87 and 5.21 cm/year. Morphological analyses of the shoreline and the seabed of the study nearshore area indicate that shoreline retreat corresponds to areas of seabed scour (sediment source) while shoreline accretion is associated with areas of seabed deposition (sediment sink). Furthermore, simulation of wave propagation using STWAVE model combined with grain size distributions of the seabed shows that fine sands are much dominated in depositional areas with low wave energy, whereas coarser sands in erosive zones with high wave energy. The results obtained suggest that the change of seabed morphology, wave height pattern and grain size sediment have a great influence on the modification of shoreline morphology and dynamics.

An integrated approach to coastal erosion problems in northern Tuscany (Italy): Littoral morphological evolution and cell distribution

Occupation of the coast has significantly increased in recent decades, mostly due to a greater demand for recreation and tourism. Today, erosion threatens many human-made structures and activities, requiring an integrated approach for the understanding of coastal dynamics and identification of alternatives to associated problems. This study investigates a 64km-long coastal physiographic unit in the northern microtidal littoral of Tuscany (Italy). Vertical aerial photographs and direct field surveys were used to retrieve changes in shoreline position over 1938–1997 and 1997–2005 time intervals. Significant beach accretion was observed during the first period updrift of Carrara (84m) and Viareggio (280m) harbours and at Marina di Pietrasanta (100m), whereas severe erosion occurred downcoast of Carrara harbour (−130m, at Marina dei Ronchi) and on the northern side of Arno river mouth (−400m). Similar trends were observed between 1997 and 2005; beach slope between the 1997 shoreline position and the closure depth correlated well with the distribution of erosion/accretion patterns from the 1938–1997 period (slopes were lower in eroded areas than at sites under accretion). Longshore distribution of erosion/accretion patterns was controlled by coastal compartmentalisation. Three of the main littoral cells were mostly formed by natural limits (i.e., Punta Bianca promontory, Marina di Pietrasanta, the Arno river mouth and the port of Livorno). Several sub-cells were created within these cells due to the introduction of human-made structures (such as Carrara and Viareggio harbours), which formed artificial fixed limits that allowed the transport of sediments (exclusively fines) in one direction only. Results will help improve the understanding of coastal processes and manage littoral sediment transport in a sustainable manner. This will reduce the need for structural interventions, such as breakwaters and groynes, which in the past decades prevented coastal retreat at local scale but shifted erosion downdrift, leading to degradation of the investigated area and requiring continuous maintenance.

LONG-TERM MONITORING ON THE SAND SPIT MORPHODYNAMICS AT THE TENRYU RIVER MOUTH

In this study, long-term monitoring on the sand spit morphodynamics at the Tenryu River mouth was carried out based on the time series of sand spit profiles extracted from the field camera recorded images between Apr 2007 and Dec 2009. Time stack images were applied to qualitatively characterize the variation of sand spit morphology at the representative longshore location. Primarily analyses were conducted by focusing on the bulk statistical properties of the recorded sand spit profile data. Detailed insight into the evolution process of the sand spit shoreline location was estimated through the Empirical Orthogonal Function (EOF) analysis. Sand spit riverside morphodynamics presents a short-term, but intensive variation pattern and is found to be closely related to the overtopping or flood events. Modification on the sand spit shoreline location shows an asymmetric nearshore process. In the first two years, slow beach accretion accompanying with the eastward longshore sand movement prevailed; whereas, rapid shoreline erosion, together with the westward longshore sand movement, became predominant in the following half year.

Cross-shore sediment transport and morphological response on a macrotidal beach with intertidal bar morphology, Truc Vert, France

A 3-week field investigation was conducted on a macrotidal beach with intertidal bar morphology with the aim of quantifying cross-shore sediment transport rates and beach response. Cross-shore transport rates were estimated in four different ways: (1) net transport from bed-level changes; (2) measured suspended sediment fluxes; (3) sediment fluxes associated with migrating wave ripples; and (4) total load transport predicted using the Bailard [Bailard, J.A. 1981. An energetics total load sediment transport model for a plane sloping beach. Journal of Geophysical Research, 86, 10938–10954.] model. Excellent qualitative agreement was found between the different measures under all recorded wave conditions, with onshore (offshore) sediment transport and beach accretion (erosion) observed under low-to- moderate (high) wave conditions. The agreement is due to the strong correspondence between the direction of mean cross-shore flows across the intertidal bar surface and that of the sediment transport. Significant onshore mean flows ( u = 0.1–0.2 m s − 1 ) were persistently observed under low wave conditions, and these were strongest in shallow water depths ( h < 1 m). These flows are attributed to the (weak) three-dimensional water circulation in the surf zone associated with the intertidal bar-rip morphology and caused onshore bar migration. Under high wave conditions, on the other hand, strong mean cross-shore flows ( u = 0.2–0.4 m s − 1 ), due to the bed return flow, were consistently directed offshore and resulted in bar destruction. Under low wave conditions, vertically-integrated suspended fluxes, ripple transport rates and predicted total transport fluxes were remarkably similar, but when the fluxes are integrated over a complete tidal cycle, they are considerably smaller than that derived from bed-level changes based on low tide surveys.

Open Coast Monsoonal Beach Dynamics

Abstract On the coast of Kerala, southwest India, oceanographic measurements were made at the beach, in the surf zone region, and on the inner shelf and then were combined with mechanism-focussed numerical modelling. The goal was to investigate the sedimentary dynamics of an open coast monsoonal beach. A closed sedimentary circulatory system (here described as a “step-ladder”) was identified. Strong annual cycles were observed in waves, winds, and currents. Regional-scale dynamic sediment equilibrium is maintained by an annual net northerly sediment flux in the near-shore, driven by wave-induced currents. This is balanced by a net southerly flux on the inner shelf, but driven instead by wind-induced currents that transport the wave-induced suspended sediment. The two counterdirectional sedimentary pathways are linked by cross-shore bridging transport. A clear association between the annual beach erosion and accretion patterns and the cross-shore direction of the near-bed bridging currents on the inner she...

Seasonal accretion and erosion patterns of a microtidal sandy beach

Monthly elevation surveys of a 1.5 km stretch of coast at Noordwijk, the Netherlands, were made (1) to quantify seasonal variability in the cross-shore position of high-, mean- and low-tide contours, beach width and beach volume, and (2) to examine the dependence of the variability on the offshore wave characteristics. Additionally, daily cross-shore positions of contours obtained from video images were used to examine daily beach response to wave characteristics between successive surveys. The more intense and frequent storm events in winter than in summer resulted in a seasonal change from a wide beach with a small volume at the end of winter to a narrow, large-volume beach in summer. The seasonal pattern in beach width resulted from the cross-shore sediment exchange between the supratidal and lower-intertidal part of the beach. In contrast to the coupling between beach behaviour and wave characteristics on a seasonal scale, beach variability between successive surveys was unrelated to day- to week-averages of the preceding offshore wave conditions partly due to the precise timing of a storm relative to the two survey moments. Moreover, daily variability determined from the video images showed that differing antecedent morphology to storms and alongshore variations in beach morphology contributed to spatially and temporally variable beach response.

Erosion and Accretion of Beach and Spit Systems in Northwest Spain: A Response to Human Activity

Abstract Three beach and spit systems have been studied in northern Galicia, along the northwest coast of Spain, within the regional context of sea level rise and coastal erosion. Each system forms part of an estuary's mouth complex within the inner part of the Ortigueira, Barqueiro, and Viveiro rias. Erosive processes along the coast have been characterised and been found to affect cliffs, beaches, and archaeological sites. To compare both long-term (decadal) and short-term (annual) erosion and accretion trends among estuaries, we analysed the morphodynamic characteristics, the degree of human occupancy, and the historical evolution of each system and monitored two profiles at each beach. Dynamic parameters—dimensionless fall velocity and relative tidal range—were calculated for the characterisation of beaches, and maritime climate data—significant wave height (Hs), peak period (Tp), wave fetch direction, and wave period were obtained, and wave height reduction was estimated for all estuaries. Detailed a...