Search

Coastal sediment grain size is an important factor in determining coastal morphodynamics. In this study, we explore a novel approach for retrieving the median sediment grain size (D50) of gravel-dominated beaches using Synthetic Aperture Radar (SAR) spaceborne imagery. We assessed this by using thirty-six Sentinel-1 (C-band SAR) satellite images acquired in May and June 2022 and 2023, and three NovaSAR (S-band SAR) satellite images acquired in May and June 2022, for three different training sites and one test site across England (the UK). The results from the Sentinel-1 C-band data show strong positive correlations (R2 ≥ 0.75 ) between the D50 and the backscatter coefficients for 15/18 of the resultant models. The models were subsequently used to derive predictions of D50 for the test site, with the models which exhibited the strongest correlations resulting in Mean Absolute Errors (MAEs) in the range 2.26–5.47 mm. No correlation (R2 = 0.04) was found between the backscatter coefficients from the S-band NovaSAR data and D50. These results highlight the potential to derive near-real time estimates of coastal sediment grain size for gravel beaches to better inform coastal erosion and monitoring programs. [ABSTRACT FROM AUTHOR]

Most empirical equations used for wave runup predictions have been developed from measurements at straight sandy beaches in unlimited fetch environments. While there are empirical equations to predict wave runup on gravel beaches, they have not been tested for prediction of wave runup on pocket gravel beaches, in limited-fetch environment, which can be found around Mediterranean. This paper addresses this lack of measurements on this type of beaches and examines the alongshore variability of wave runup. Wave runup measurements were made using video observations along 3 cross-sectional profiles on the pocket beach of Ploče, Croatia. The measurements have shown that the wave runup can vary for about 71% even around the centerline of the pocket beach. This variability is due to beach orientation and alignment of beach profiles to the prevailing wave direction, as well as difference in beach slope. Comparison of wave runup predictions from five well-known empirical equations and field measurements showed significant underprediction (up to NBIAS = −0.33) for energetic wave events, and overall high scatter (up to NRMSE = 0.38). The best performing wave runup equation was used for further refinement outside the original parameter space by including the Goda wave peakedness parameter (Qp). The newly developed empirical equation for wave runup reduced the NBIAS to 0 and the NRMSE by 31% compared to the original equation (developed equation metrics: R = 0.91, NBIAS = 0, NRMSE = 0.2, HH = 0.2 on the study site). This empirical equation can potentially be used for design of coastal structures and artificial beaches in similar environments, but further measurements are needed to test its applicability to a range of forcing and environmental conditions. [ABSTRACT FROM AUTHOR]

Finkl, C.W. and Makowski, C., 2022. Classification of coastal belts in the Argentine subpolar southeast coast of Tierra del Fuego using the BCCS (Biophysical Cross-shore Classification System). Journal of Coastal Research, 38(5), 908–924. Coconut Creek (Florida), ISSN 0749-0208. The Biophysical Cross-shore Classification System (BCCS) was experimentally applied to the southeast coast of Tierra del Fuego, Argentina, by compartmentalizing the coast into seven discrete coastal belts that retained a degree of homogeneity from 2 km offshore to about 5 km inland. By interpreting satellite imagery, coastal belts were subdivided into cross-shore transects with alongshore spread to produce codified concatenations that characterized specific eco-geomorphological sequences comprising domains. Different types of domains were identified by archetypes that specified a particular Dominant Catenary Sequence (DCS), which in turn was refined by the inclusion of subarchetypes to produce a Coastal Ecological Sequence (CES). The seven coastal belts comprising a 58.5 km stretch of shore contained 39 CES transects that averaged about 1.5 km of shore length, but ranged from 0.8 km to 3.3 km in alongshore stretch. Dominant offshore, inshore, and onshore classificatory units included Rock (R), Beach (Be), and Cliff (Cl) catenas, which were followed inland by Wetland (W), Lake (Lk), Channel (Ch), and Upland (U) archetypical sequences. Delta (De) and Beach Ridge (Br) archetypes were noted as minor features in some cross-shore transects. Common trisequent DCS transects included R-Be-Cl and Be-Cl-U, which subsequently incorporated landward variations with Lagoon (L), Lake (Lk), and Wetland (W) archetypes. Results of this experiment showed that the BCCS comprehended how subpolar periglacial and paraglacial coastal belts dominantly comprised by glacial outwash have ground surface manifestations that are recognizable in satellite imagery by recurring spectral patterns. This cold tundra coastal region is thus largely characterized by rocky offshores and gravelly beaches backed by cliffs (composed of unconsolidated materials) and channeled wetland (peatland) hinterlands with coastal marine lakes and forested uplands. In accordance with the BCCS, this classification can be concised to CES subarchetype code sequences such as Rrr-Besi-Clse-Wmr-Chmd-Lkcm-Ufo. This study demonstrates that codification of cross-shore eco-geomorphological transects using the BCCS provides a shorthand notation for classifying coastal belts in high-latitude regions. [ABSTRACT FROM AUTHOR]

Most empirical equations used for wave runup predictions have been developed from measurements at straight sandy beaches in unlimited fetch environments. While there are empirical equations to predict wave runup on gravel beaches, they have not been tested for prediction of wave runup on pocket gravel beaches, in limited-fetch environment, which can be found around Mediterranean. This paper addresses this lack of measurements on this type of beaches and examines the alongshore variability of wave runup. Wave runup measurements were made using video observations along 3 cross-sectional profiles on the pocket beach of Ploče, Croatia. The measurements have shown that the wave runup can vary for about 71% even around the centerline of the pocket beach. This variability is due to beach orientation and alignment of beach profiles to the prevailing wave direction, as well as difference in beach slope. Comparison of wave runup predictions from five well-known empirical equations and field measurements showed significant underprediction (up to NBIAS = −0.33) for energetic wave events, and overall high scatter (up to NRMSE = 0.38). The best performing wave runup equation was used for further refinement outside the original parameter space by including the Goda wave peakedness parameter (Qp). The newly developed empirical equation for wave runup reduced the NBIAS to 0 and the NRMSE by 31% compared to the original equation (developed equation metrics: R = 0.91, NBIAS = 0, NRMSE = 0.2, HH = 0.2 on the study site). This empirical equation can potentially be used for design of coastal structures and artificial beaches in similar environments, but further measurements are needed to test its applicability to a range of forcing and environmental conditions.

This paper presents an innovative multi-thematic map (1:2500) that integrates morpho-sedimentological data, hydrodynamic processes, seasonal morphodynamic transitions and the distribution of the benthic habitat of a Mediterranean microtidal, wave-dominated gravel beach system. It is part of a larger cartography of coastal areas, and is based on an interdisciplinary sea-land approach that is applicable worldwide and aims to facilitate coastal management practices and future scientific research. The applications to coastal management include: the facilitation of coastal vulnerability assessments; easy-to-access, up-to-date digital geospatial data; and baseline studies for the future assessment and monitoring of environmental changes. The main environmental features that control the marine processes of this gravel beach appear to be linked to geological and morphological contexts such as the presence of the river mouth, the outcropping of a beach-rock along the coastline, the deposition of gravelly sediment in the beachface and the seagrass cover.

This paper presents an innovative multi-thematic map (1:2500) that integrates morpho-sedimentological data, hydrodynamic processes, seasonal morphodynamic transitions and the distribution of the benthic habitat of a Mediterranean microtidal, wave-dominated gravel beach system. It is part of a larger cartography of coastal areas, and is based on an interdisciplinary sea-land approach that is applicable worldwide and aims to facilitate coastal management practices and future scientific research. The applications to coastal management include: the facilitation of coastal vulnerability assessments; easy-to-access, up-to-date digital geospatial data; and baseline studies for the future assessment and monitoring of environmental changes. The main environmental features that control the marine processes of this gravel beach appear to be linked to geological and morphological contexts such as the presence of the river mouth, the outcropping of a beach-rock along the coastline, the deposition of gravelly sediment in the beachface and the seagrass cover. [ABSTRACT FROM AUTHOR]

This paper presents the use of an Eulerian–Eulerian multi-phase model to examine sediment transport over a gravel beach under regular waves. A previously published full-scale experiment is reproduced numerically; the simulated wave deformation, flow velocity, pore pressure, and morphological evolution are consistent with measurements. The multi-phase model can produce berm formation for smaller waves and beach erosion for larger waves as observation in previous field studies. The sensitivity analysis suggests that the nonlinear component of drag has significant effect on the berm formation through infiltration and exfiltration. The two simulated forces applied on the sediment (drag and buoyancy) are examined. The drag is the main force directly for sediment transport; therefore the sediment transport rate has high correlation with depth-averaged flow velocity. The buoyancy that is caused by plunging flow impacting beach face can push the sediment landward in the bore front, where the flow acceleration has its peak. The flow acceleration is considered in some previous sediment transport models empirically for simulating morphological evolution of gravel beach under waves. The buoyancy links the flow acceleration and sediment transport rate in the bore front. • Sediment transport in a gravel beach is simulated using a multiphase model. • The drag is the main force directly for sediment transport. • The buoyancy links the flow acceleration and sediment transport rate in the bore front. • The nonlinear drag has the effect on berm formation. [ABSTRACT FROM AUTHOR]

Abstract This paper illustrates a novel coastal exposure assessment approach. The approach is based on the employment of the model chain WavewatchIII+XBeach , which is first used to draw a map showing the extent of the populated areas that are likely to be interested by flooding, and subsequently to establish the exposure of the area to specific events. The model chain is calibrated by comparing the simulated runup values of a storm with those obtained by processing on-field images recorded by a camera system. The approach herein presented allows to take into account the local coastal geomorphology features and hydrodynamics of the area so as to obtain locally accurate results. The information collected is usable by local beach managers in coastal management planning. The method is applied on Bonassola beach, which is a pocket beach located on the NW Mediterranean along the Eastern coast of Liguria, Italy. Weather and offshore waves data collected during the last 16 years were used. The application of this method has allowed to draw a map of the areas that are subject to flooding during storms and has correctly stated that three of the seven biggest storms in the last 16 years would eventually result into flooding of populated area. The study has also shown that the exposure of the study area to the storms is sensitive to the period and the direction of the waves. Highlights • Coastal exposure map allows to coastal managers to evaluate local risk level. • Local scale application supplies more accuracy of storm impact. • Model chain is operative tool to evaluate coastal hydrodynamic pattern. • Camera system supply accurate runup excursion values on investigated area. • Flooding risk is related to coastal geomorphology and grain size distribution. [ABSTRACT FROM AUTHOR]

This paper proposes a coastal erosion monitoring system for beach erosion management, which we demonstrate on natural and artificial pocket gravel beaches in Croatia. The approach uses low-cost Structure-from-Motion (SfM) photogrammetric imaging and multi-view stereo (MVS) to produce high-resolution 3D beach models for detecting morphological changes and erosion occurrence. Coastal state indicators, such as the shoreline position and subaerial beach volume, are derived from the 3D models and used to quantify changes between surveys. The method is illustrated through two case studies and, to our knowledge, these are the first repetitive measurements taken on the Croatian eastern Adriatic Coast (CEAC). In case of the natural Brseč beach, beach rotation was found to be a response to natural forcing from waves of various incident directions. For the artificial Dugi Rat beach, which loses sediment every winter and is subsequently re-nourished every spring, monitoring showed that beach nourishment is of limited durability. Both case studies showed that the SfM-MVS technique is suitable for the rapid and frequent acquisition of 3D survey data, from which quantitative coastal indicators can be derived to inform future coastal management interventions. Significantly, this low-cost data acquisition has a great potential for regular beach management survey. The introduction of beach monitoring in Croatia is timely because emerging Integrated Coastal Zone Management (ICZM) practices will require data-based approaches. Moreover, rare natural pocket beaches and the ever-increasing number of artificial beaches are extremely vulnerable to natural and man-made changes. Adaptive beach management, based on systematic monitoring data, should be included in the ICZM, and we detail how SfM-MVS-based monitoring can be used at different levels of the ICZM. Implementing robust ICZM monitoring will require broad considerations and consultation with all stakeholders, so we propose that SfM-MVS beach surveys should be initially integrated into the existing monitoring practices for CEAC sea water bathing quality. Extension of the existing database with rapidly-gathered low-cost 3D beach survey data, from a number of targeted beaches, could be used to provide a crucial baseline for the ICZM and strategic coastal monitoring of the CEAC. [ABSTRACT FROM AUTHOR]

Infragravity waves (frequency, f = 0.005–0.05 Hz) are known to dominate hydrodynamic and sediment transport processes close to the shoreline on low-sloping sandy beaches, especially when incident waves are large. However, in storm wave conditions, how their importance varies on different beach types, and with different mixes of swell and wind-waves is largely unknown. Here, a new dataset, comprising shoreline video observations from five contrasting sites (one low-sloping sandy beach, two steep gravel beaches, and two compound/mixed sand and gravel beaches), under storm wave conditions (deep water wave height, H0 up to 6.6 m, and peak period, Tp up to 18.2 s), was used to assess: how the importance and dominance of infragravity waves varies at the shoreline? In this previously unstudied combination of wave and morphological conditions, significant infragravity swash heights (Sig) at the shoreline in excess of 0.5 m were consistently observed on all five contrasting beaches. The largest infragravity swash heights were observed on a steep gravel beach, followed by the low-sloping sandy beach, and lowest on the compound/mixed sites. Due to contrasting short wave breaking and dissipation processes, infragravity frequencies were observed to be most dominant over gravity frequencies on the low-sloping sandy beach, occasionally dominant on the gravel beaches, and rarely dominant on the compound/mixed beaches. Existing empirical predictive relationships were shown to parameterize Sig skillfully on the sand and gravel beaches separately. Deep water wave power was found to accurately predict Sig on both the sand and gravel beaches, demonstrating that, under storm wave conditions, the wave heights and periods are the main drivers of infragravity oscillations at the shoreline, with the beach morphology playing a secondary role. The exception to this was the compound/mixed beach sites where shoreline infragravity energy remained low.

ABSTRACT Landward retreat (marine transgression) is a common response of coastal systems to rising relative sea level. However, given sufficient sediment supply, the coast may advance seaward. The latter response of gravel barriers has been recorded in parts of southeastern and northwestern Canada, where seaward-rising sets of beach ridges are observed in areas of Holocene RSL rise. Cape Charles Yorke, northern Baffin Island, is a 5 km long gravel foreland characterized by seaward-rising beach-ridge crest elevations. The prograded morphology of the Cape Charles Yorke foreland is a prime example of coastal response to a combination of rising RSL and abundant sediment supply, an unusual and little-documented pattern in the Canadian Arctic. The main gravel supply to Cape Charles Yorke is likely from eroding bedrock and raised marine deposits southwest of the foreland. Although not the dominant sediment source, the Cape Charles Yorke delta contributed to the formation of the foreland by sheltering it from easterly storm waves and providing an anchor point for the prograding ridges. The truncation of relict ridges by the modern shoreline suggests a recent regime shift from continuous deposition to predominant erosion. The cause and timing of this shift are unknown but could result from a recent dwindling in sediment supply, increased accommodation space, increased wave energy, and/or an accelerated rise of relative sea level. [ABSTRACT FROM AUTHOR]

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Early Oligocene (Late Rupelian) Alzey Formation (Mainz Basin, Upper Rhine Graben, Germany) records the development of a rocky coast depositional system during transgression. The formation unconformably overlies Permian bedrock across a composite transgressive ravinement surface. Exposure of the surface shows a succession of subplanar bedrock terraces, separated by near-vertical risers. Terraces show a broad staircase geometry and display wave-erosional features (notches, sea stacks, furrows). Detailed sedimentological and palaeoecological investigations reveal prograding beachface and shoreface depositional units that overlie terraces and are adjacent to risers. Terraces are interpreted as wave-cut platforms, backed by palaeocliffs. The staircase architecture records the episodic landward migration of palaeoshorelines onto palaeotopographic highs during the Early Oligocene. Stacking patterns of gravelly beach and shoreface associated units (facies tracts) indicate successive episodes of terrace cutting, beach development, drowning and shoreline backstepping during an overall relative sea-level rise. The exceptional preservation of the stair-cased rocky shore may be attributed to a highly jerky rising relative sea-level, as the result of the conjugated effects of rift-controlled tectonic subsidence and eustatic sea-level oscillations. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: 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 (D 50 =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. [Copyright &y& Elsevier]

Abstract: A prototype-scale laboratory study (BARDEX — Barrier Dynamics Experiment) was conducted within the 250-m long and 7-m deep Delta wave flume, The Netherlands. A 4-m high and 50-m long gravel barrier (D 50 =11mm) was constructed within the central region of the flume, enabling a back-barrier ‘lagoon’ to be located at its landward side. By the installation of a multi-stage pump system the water levels at the ‘sea’ and ‘lagoon’ sides of the barrier could be manipulated independently. A series of experiments were undertaken to examine the groundwater fluctuations and flow within the barrier system subject to varying lagoon levels and wave conditions. In accordance with previous sand experiments, the wave-induced watertable over-height at the beachface was confirmed to be independent of sediment characteristics. Varying back-barrier lagoon levels were observed to have significant effect on both the maximum watertable over-height within the barrier and shoreline set-up (vertical position of the point of intersection between mean water surface through the swash zone and beachface), as well as the direction and magnitude of though-barrier groundwater flux. The effective hydraulic conductivity of the D 50 =11mm gravel barrier was determined to be K =0.16ms−1. At higher Reynolds numbers (Re >~40) associated with local watertable gradients exceeding 0.025 and resulting turbulent losses, the transition from laminar to turbulent through-barrier flow was indicated by a reduction in local K. However, for the parameter range encountered this effect was modest only (<10%), and for many practical purposes it is proposed that the application of Darcy''s Law to estimate the exchange of ground-ocean water through coastal gravel barriers is well within the range to which the necessary field parameters can be realistically estimated. [Copyright &y& Elsevier]

This study assesses the stability of Arctic gravel coasts across a range of timescales, based on field and remote-sensing studies of three coastal sites near Resolute Bay, Nunavut. It considers shore-zone sensitivity to ice, wind, and wave forcing at storm-event and annual timescales within a longer-term context, including coastal emergence resulting from postglacial isostatic uplift partially counteracted by accelerating sea-level rise. Another long-term factor associated with climate change is the potential for increased seasonal depth of thaw in the beachface and nearshore. The coast in this area is ice bound on average for 10 months of the year, but the annual duration of ice cover has decreased over the past 30 years (1979-2009) by 0.95 d/y. A longer open-water season has implications for the number and timing of storm-wave events, with increased probability of storms impacting the coast later in the season when the seasonal thaw layer is approaching maximum thickness. Overall, shoreline progradation surpassed erosion in the Resolute area between 1958 and 2006, reflecting a combination of sediment supply and emergence. The coastal impacts of storms were found to be short lived and not necessarily indicative of longer-term trends. Gravel shorelines can be resilient in the face of intermittent storm impacts, but thresholds of stability in this high-latitude setting are poorly understood. If current trends of rising sea level, increasing open-water duration, and more frequent effective wave events continue, there is a heightened potential for more rapid coastal change in the region. [ABSTRACT FROM AUTHOR]

Abstract: Few large-scale field measurements of longshore sediment transport have been undertaken on beaches composed of coarse sediments, in part owing to difficulties associated with measurement in energetic swash zones in which large clasts are moving. Here we present results from a field experiment in which Passive Integrated Transponder tags were used to investigate patterns of cobble transport over 8months on a mixed sand and gravel beach on the east coast of New Zealand. The study objectives were to document rates of alongshore transport, and measure rates of cobble abrasion under field conditions. Cobble recovery rates were highly variable over the study period with 30–60% recovery at site 1 compared to much lower (0–20%) recovery rates at sites 2 and 3. Consistent uni-directional patterns of net alongshore sediment transport were observed. The median cobble transport rate was approximately 500m over 207days, indicating long-term net northward transport rates on the order of 2–2.5m/day. Results highlight a number of factors, in addition to longshore energy flux, that are important for understanding the observed patterns. In particular, across-shore sediment transport during storms may have been smaller at site 1 than the other sites owing to lesser wave exposure. This is partly responsible for higher cobble recovery rates at this site and also an increased amount of time during which cobbles were able to be transported alongshore on the lower beachface. Unique to this study, results demonstrate the use of PIT tags to provide direct measurement of cobble abrasion under natural processes. Repeat weight measurement on individually tracked cobbles show that after 207days the median loss was 11.3g, or 1.8% of total weight. There was a general trend of abrasion increasing with net transport distance, but longshore cobble movement was highly variable ranging from 130 to 2500m. [Copyright &y& Elsevier]

Abstract: The 4.5km-long gravel beach fronting the exclusive resort of the city of Nice, on the French Riviera, in southeastern France, was artificially nourished from 1976 to 2005 to the tune of 558,000m3, making this long-term operation one of the most significant for gravel beaches in the world. Nourishment has ranged from nil in certain years (1979, 1980, 1983–85, and 2001–2002) to a peak of over 97,000m3 in 2000. Analyses of 50 transects covering the beach highlight no significant change in net beach width over this 30-year period of massive gravel nourishment. A Principal Components Analysis and a Cluster Analysis used to detect patterns in the 87 beach-width measurement dataset show no clear spatial trends in transect groups that can be interpreted in terms of the morphology of the beach and the steep inner shoreface. Significant wave height off Nice shows no change over the period 1979–2005. Since there is no possibility for alongshore gravel leakage on the strongly embayed Nice beach, the relative stability in beach width clearly implies loss of recharged gravel offshore. Gravel loss following nourishment is favoured by: (1) the steep inner shoreface inherited from the geological context of Nice beach at the flanks of the southern Alps, and (2) the practise of artificial beach widening through flattening, in summer, of a narrow (5–15m-wide) mobile zone of the profile in order to enhance the ‘carrying’ capacity of this highly touristic beach. Beach widening and flattening following nourishment bring close to the very steep inner shoreface zone several cubic metres of gravel for each metre of beach that may be permanently lost downslope during autumn and winter storms. Recharged gravel is redistributed alongshore and offshore leakage is probably enhanced where small narrow submarine canyon heads impinge on the beach, resulting in a very narrow shoreface. Mean beach width shows an oscillating alongshore pattern that may be due to the influence of these canyons as pathways of gravel loss offshore. However, there is no correlation between mean beach width and distance to the 10-m isobath, used as a surrogate for inner shoreface width. Storms are associated with plunging waves that are particularly effective and concentrated, on this almost tideless shore, over the narrow mobile zone of the beach profile where a series of steep reflective berms are built during storms. The high dynamic pressures associated with this narrow zone of concentrated wave breaking, and energy reflection from the steepened profile, are deemed to contribute to the permanent downslope loss of gravel. This situation of long-term gravel loss is probably accepted by the beach management authority because of the low cost of obtaining nourishment material and the advantages derived from a temporarily wider beach in terms of recreational space. [Copyright &y& Elsevier]

A great many studies on wave breaking have been carried out, and much experimental and field data have been documented. Moreover, on the basis of various data sets, many empirical formulas based primarily on regression analysis have been proposed to quantitatively estimate wave breaking for engineering applications. However, wave breaking has an inherent variability, which suggests that a linear statistical approach such as regression analysis might be inadequate. This study presents an alternative nonlinear method using an artificial neural network (ANN), one of the soft computing methods, for predicting breaking-wave heights and water depths. Using data from laboratory experiments showing that wave breaking characteristics on a gravel beach are different from those on a sandy beach, we developed a three-layered feed-forward type of network to obtain the output of wave-breaking heights and water depths using deepwater heights, wave periods, and seabed conditions as inputs. In particular, the effects of the groundwater table on wave breaking on a gravel beach were considered. We then aggregated the laboratory data to train the ANN to predict the wave breaker index. The results predicted by fully-trained ANNs are more accurate than those obtained by existing empirical formulas, and they identified factors crucial for predicting wave breaking. These results show that ANNs are useful tools for both the prediction and mechanistic analysis of wave breaking. [ABSTRACT FROM AUTHOR]

Abstract: Continuous Argus video data and fortnightly measurements of subaerial morphology were obtained over a 3-year period from a steep macrotidal gravel beach on the southwest coast of the U.K. Concurrent wave and water-level data were also collected, enabling the correlation of the observed morphological changes to the hydrodynamic forcing. Wave conditions are generally low (H s ≈0.5–1m), but the beach is affected by frequent storm wave activity (c. 15 storms per year with H s ≈2–4m) with waves either approaching from the south (swell waves) or from the east (wind waves). An assessment of the three-dimensional morphological response of the beach to the two typical storm types was carried out by analysing the impact of 27 storms that occurred from April 2007 to April 2009. Southerly storms cause accretion of the supratidal zone and erosion of the intertidal zone, and a significant loss in overall beach volume. Easterly storms, on the other hand, induce supratidal erosion and intertidal accretion, and a significant gain in overall beach volume. During the intervening calm periods a small supratidal berm is constructed and a modest gain in overall beach volume occurs. Wave modelling indicated that opposing longshore energy fluxes occur for the different storm types with a northerly energy flux during southerly storms and a southerly flux during easterly storms. Weekly shorelines derived from the Argus images revealed that the northern end of the beach widened by c. 30m and the middle beach receded by c. 40m over a relatively brief period (a few months). The occurrence of this beach rotation event is attributed to a higher frequency of southerly storms and/or a lower frequency of easterly storms over this period. Thus, the development and stability of the beach on annual time scales depend on the relative contributions of the two storm types, and their sequencing. Longshore sediment transport (LST) rates derived from the data on beach morphological change were compared with several littoral drift formulae previously applied to gravel beaches. The CERC equation, with a proportionality factor k between littoral drift rate I l and longshore wave energy flux P l of k =0.054, yielded the best results. [Copyright &y& Elsevier]

Abstract: State-of-the-art morphodynamic field data were collected from Slapton Sands (UK), a fine-gravel beach (D 50 =2–10mm), over a 10-day period under a range of wave–tide conditions, comprising a mixture of southerly swell and easterly wind waves (H s =0.5–1m; T s =4–8s; tide range=3–4m). Over the field period, the upper beach experienced accretion and berm formation during tides with low steepness, swell-dominated wave conditions (H/L <0.01), and underwent erosion during tides dominated by high steepness wind waves (H/L >0.01). Surprisingly, the intertidal beach showed an opposite trend with sediment losses under swell conditions and an increase in sediment volume due to wind waves, and suggests that upper beach morphological change can be decoupled from the overall sediment budget. A submerged accretionary feature (the beach step) grew and migrated onshore on the rising tide, typically reaching a maximum relief of around 0.5m, then gradually decreased in prominence while migrating offshore as the tide fell, resulting in little net morphological change. The step was better developed during the falling tide than the rising tide and, through its control on the swash hydro- and sediment dynamics, the step had a significant effect on the development of the berm. Swash flow velocities under the conditions measured were often in excess of 2ms−1 for both the uprush and the backwash. Onshore mean flows occurred in the upper swash region (<40% inundation), while the lower swash region (>40% inundation) was characterised by offshore mean flows. Swash infiltration losses in the swash zone increased from 40% in the lower swash region to 100% in the upper swash region. The most energetic swash flows and the strongest offshore mean flows occurred at the transition between swash zone and surf zone (90–100% inundation). [Copyright &y& Elsevier]

Abstract: This paper describes the application of Canonical Correlation Analysis (CCA) to derive forcing–response relations between the wave climate and shoreline position on a macrotidal gravel barrier located in the southwest of the U.K., and to develop a tool to determine shoreline positions from wave records. The data sequences comprise wave climate recorded by a nearshore directional wave buoy and video-derived shorelines over a time span of one year and a half. The hydrodynamic conditions are used to determine the probability density function of wave heights and alongshore energy fluxes. These are then related to shoreline change through a CCA analysis. The CCA analysis identifies patterns of behaviour of the wave conditions and the shoreline position, and the relation between both patterns is found to provide useful information about the beach response to wave action. The analysis shows that the movement of sediment is greater at the southern end of the study area and that there is an immediate shoreline response to the wave action. In the case of coastal management it is more often the case that wave forecasts are available on a routine basis. The ability of the CCA to provide useful estimates of shorelines from wave conditions was tested by using measured waves to calculate the corresponding shoreline position from additional data at the end of the sequences. Shoreline positions determined with the CCA agreed well with the measured ones. Thus, the CCA is found to be a useful tool to determine unknown shoreline positions and support effective coastal management if good quality hydrodynamic and morphological data are available to input into the initial set-up of the technique. [Copyright &y& Elsevier]

Abstract: This paper presents an integrated investigation of physical processes generating impulsive pressures under the action of plunging breakers impinging on gravel beaches. This work is an extension of a recent investigation which suggested that wave impacts from plunging breakers acting on gravel beaches may be a key mechanism to enhance sediment mobilisation. In particular, comparisons of full scale laboratory measurements against model results from a well-validated phase/depth-resolving numerical model based on the Reynolds–Averaged Navier–Stokes (RANS) equations are presented. This represents the first attempt at comparison with such a tool against observed hydrodynamics on steep (slope~1/8) gravel beaches at prototype scale. In order to understand how impulsive pressures are generated under plunging waves, the numerical model is used to carry out a detailed investigation to examine the role of each of the acceleration terms in the momentum balance. Consistent with prior studies, numerical results show that under plunging breakers the local acceleration (∂u/∂t) alone cannot be used as a proxy for pressure gradients. However, the contribution of the third term (w∂u/∂z) of total acceleration is recognized for the first time and indicates that this term has an important role in both the induced pressure gradient and sediment mobilisation as induced by this particular type of breaking. Furthermore, results suggest that a parameterisation of the pressure gradient in terms of ∂u/∂t+u∂u/∂x, may not suffice when dealing with plunging breakers and hence there is a lack of a suitable parameterisation of this process in the present literature. Thus, for different types of breaking it may be necessary to consider a different characterisation of the pressure gradient toward the parameterisation of sediment transport inside the surf zone. [Copyright &y& Elsevier]

Mixed sand and gravel beaches form a wedge of protective sediment at the base of eroding cliffs. In profile these beaches are typically steep with a prominent storm berm. If the volume of beach sediment is insufficient, storms strip beach sediments seaward, exposing the cliff toe to wave attack. The beach volume is thus crucial to the protection of sea cliffs. In this article we describe a method of calculating alongshore variation in the volume of mixed sand and gravel beaches using ground penetrating radar (GPR). Eighteen sites were studied along 50 km of the east coast of South Island, New Zealand. The method was underpinned by an ability to map the boundary between beach sediments and underlying Pleistocene alluvial-fan sediments. This was achieved by studying the radar facies, particularly landward- dipping overwash deposits and seaward-dipping beach erosion surfaces. The method was ground-truthed in three ways: (1) a stream provided a clean section through one site that was imaged by radar; (2) a storm stripped beach sediment from three sites exposing the substrate, which was then surveyed and compared with radar profiles; (3) excavations in a previous study at nine sites were used to combine the stratigraphy with the radar images. GPR proved highly effective in this environment, revealing thin beaches in the south of the study area that thicken northward in the direction of alongshore sediment transport. Cliff height decreases northward such that there is a transition from beaches in front of cliffs, to beaches that overtop low cliffs, to barriers in front of a coastal lagoon. [ABSTRACT FROM AUTHOR]

The autocorrelation technique for estimating grain-size from digital images of sand beds has been extended and validated for use on coarse sand (0·7 mm) and gravel (up to ∼20 mm). A number of aspects of the technique have been explored and some potential improvements suggested. Autocorrelation is just one suitable statistical method sensitive to the grain-size of sediment in digital images; four additional techniques are presented and their relative merits discussed. A collective suite of techniques applicable to the general problem of grain-size estimation from digital images of sediment might broaden the applicability to more sedimentary environments, as well as improve its accuracy. These techniques are compared using a large data set from a gravel barrier beach in southern England. Based on over 180 samples, mean grain-size of sieved and imaged sediments correspond to within between 8% and 16%. Some theoretical aspects of the spatial arrangement of image intensity in digital images of natural sediments are addressed, including the fractal nature of sediments in images, which has potential implications for derivation of grain-size distributions from images of sand-sized material through segmentation and thresholding. The methods outlined in this contribution may also find application in further uncovering the geometric structure of sediment beds, as well as in the simulation of sedimentation processes. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents observations of pressure impulses from wave impacts of breaking waves on steep coarse-grained beaches. It builds upon recent investigations on gravel beaches which suggest the wave impact of a plunging breaker is an important process that shapes the morphology of these beaches and that is not taken into account under many modelling frameworks (Pedrozo-Acuña, A., Simmonds, D.J., Chadwick, A.J. and Silva, R., 2007. A numerical–empirical approach for evaluating morphodynamic processes on mixed and gravel beaches. Mar. Geol., 241(1–2): 1–18). Full scale laboratory measurements of induced pressures by plunging breakers acting on gravel beaches are reported showing that these are more significant than those reported for sandy beaches under the forcing of similar wave conditions. Additionally, four different types of pressure-curves are identified and classified in terms of the type of forcing behind its generation. It is shown that measured impact pressures within the gravel beach are a consequence of plunging breakers propagating over the beach profile, with maximum pressure values being up to 4.5 times the quasi-hydrostatic induced pressure for a given wave height. It is demonstrated that the largest measured impacts are not only related to larger values of wave height and vertical displacement of the free surface but also to the wave steepness of the incident wave. Results suggest that between two plunging breakers of the same height, the steeper will produce a stronger wave impact. The plunging of breakers onto a gravel beachface and the ensuing pressure gradients are suggested as a key mechanism for understanding sediment transport and the resulting morphology of gravel beaches. [Copyright &y& Elsevier]

Beach-nourishment operations designed to replace sediment lost through erosion change the identity and meaning of coastal landscapes. Seven beaches in Tuscany, nourished with marble-quarry waste, reveal how an industrial byproduct is naturalized by particle rounding and sorting and can become a positive symbol of human-altered nature. The marble was placed on formerly sandy beaches, resulting in different grain size and color of sediments, beach morphology, and value for human use. The abrasion rate of marble makes the nourished beaches unsatisfactory when viewed solely as protection structures, but the rapid particle rounding and aesthetic appeal of marble increase the acceptability of the beaches for recreation. [ABSTRACT FROM AUTHOR]

Abstract: The morpho-sedimentary evolution of a pure gravel beach step over a tidal cycle is examined during fairweather conditions using detailed measurements of nearshore hydrodynamics, morphological and sedimentary change, and nearshore sediment transport. The characteristics of the beach step are analysed with specific reference to the concurrent dynamics of the beachface, a departure from previous studies which have treated the step as a feature isolated from the nearshore region as a whole. The step and berm are both accretionary features strongly linked to tidal stage, yet their temporal evolution is independent, the relaxation time of the berm being linked to the spring–neap tidal cycle, and that of the more transient step linked to the semi-diurnal tide. Over this time-scale the beachface is a closed sedimentary unit, although the beach step may be differentiated from the beachface using sedimentary moments. Indeed, despite the location of the step in the region of wave breaking, it has relatively stable sedimentology, remaining characteristically coarser and more leptokurtic than the swash zone. Co-spectral analysis between nearshore bed motion and cross-shore current velocity reveals that significant nearshore sediment transport occurs at sub-incident frequencies in response to wave groups. Motion of the nearshore bed is not a linear function of velocity magnitude or direction, so it is likely that there is a role for the various mechanical properties of the bed. Therefore a better description of nearshore sediment transport in the region of the beach step would require instantaneous sediment size information, allowing the use of a time-variant friction factor. [Copyright &y& Elsevier]

Abstract: Pedrozo-Acuña et al. [Pedrozo-Acuña, A., Simmonds, D.J., Otta, A.K. and Chadwick, A.J., 2006. On the cross-shore profile change of gravel beaches. Coastal Engineering, 53(4): 335–347] presented a numerical–empirical investigation of the processes that control sediment transport in the swash zone on steep gravel beaches. This was based on a sensitivity analysis of a sediment transport/profile model driven by a highly non-linear Boussinesq model [Lynett, P., J., Wu, T.-R. and Liu, L.-F., P., 2002. Modelling wave run-up with depth-integrated equations. Coastal Engineering, 46: 89–107] which was compared to near full-scale measurements performed in the GWK flume in Hanover. In this paper we have extended our analysis to compare these earlier results with those relating to a mixed sediment (gravel and sand) beach. The parametric sensitivity analysis also incorporates a discussion of the effects of acceleration about which there is much debate. The sensitivity analysis suggests that fluid acceleration can contribute to the onshore movement of sediment that causes steepening of initially flat beach faces composed of coarse sediment. However acceleration alone cannot be the cause of the observed berm growth during the GWK tests. Instead, a complex balance of processes is responsible for the profile evolution of coarse-grained beaches with no single dominant process. [Copyright &y& Elsevier]

Abstract: Groundwater responses to swash motions were observed on a natural gravel beach at Slapton Sands, UK. Detailed hydrodynamic measurements of swash depth, flow velocity and groundwater elevation were made using a cross-shore array of pressure transducers and current metres. The groundwater-level remained closely linked to the tidal elevation throughout the flood and ebb stages of the tide and prevented the formation of an elevated seepage face. The swash and groundwater spectra were dominated by a broad band of incident-frequency energy, but both displayed an increasing contribution of low-frequency energy moving landwards. A behavioural divergence was identified across the swash zone as groundwater motions were observed when no swash is overhead on the beach face. Fourier analysis and cross-correlations assisted to identify the role of two distinct pathways in the transferral of fluid from the swash to the groundwater. One that causes instantaneous swash-frequency groundwater-level rises via an energy flux through the saturated lower beachface. A second pathway, lagged by up to 4s, was caused by vertical infiltration from large swashes across the unsaturated upper beachface. Infiltration across the upper-swash zone causes the backwash discharge to be weakened by 50% compared to the uprush discharge, severely limiting the ability of the backwash to transport sediment. The lack of tidal-scale groundwater-level asymmetry ensures that the upper beachface remains unsaturated throughout the whole tidal cycle and allows continued infiltration. It is concluded that this persistent infiltration has important consequences for the morphological changes commonly observed on gravel beaches by allowing accretion in the upper-swash at all stages of the tide. [Copyright &y& Elsevier]

Abstract: Observations of morphological change and swash sediment loads, concurrent with measurements of water level, waves and currents, were obtained during a spring-to-spring tidal cycle on a steep macrotidal gravel beach in southwest England. The wave conditions experienced during the field experiment were relatively calm and the significant inshore wave height and period averaged 0.4m and 6 s, respectively. Incident-frequency water motions dominated the hydrodynamics, and the phasing between water surface elevation and cross-shore and alongshore currents was inconsistent with standing edge wave motion. Morphological change was directly related to maxima in shoreline elevation and four modes of berm adjustment identified: regression and rollover in response to falling and rising water levels, respectively; and removal and reformation during and after storms, respectively. Swash processes transported substantial amounts of sediment at rates comparable to sand beaches and the net transport under modal wave conditions was estimated to be 1kg per swash onshore per unit metre beach width. Steep hydrodynamic gradients induced by the abrupt slope breaks of the step and berm are one of the main causes of the large morphological variability characteristic of gravel beaches. [Copyright &y& Elsevier]

Although sandy foreshore facies are generally characterized by parallel lamination, wavy lamination is predominant in the mixed sand and gravel foreshore facies of the Pleistocene Hosoya Sandstone, which crops out along the Pacific coast of the Atsumi Peninsula, Aichi, central Japan. The foreshore facies consists of three sedimentary subfacies; interbeds of gravel and parallel laminated sand of the lower foreshore facies, parallel laminated fine to medium sand beds containing scattered pebbles and cobbles of the middle foreshore facies, and wavy laminated fine to medium sand beds containing scattered pebbles and cobbles of the upper foreshore facies. A lack of erosional surfaces in the middle foreshore facies indicates the continuous accumulation of sand in flat beds under upper plane bed flow. The wavy laminated sands of the upper foreshore facies exhibit erosional surfaces indicative of repeated deposition and erosion. The erosional surfaces are undulatory, with depressions (10 cm wide and 3 cm deep) that contain scattered pebbles and cobbles. These depressions reflect backwash erosion of sand around and below the pebbles and cobbles. Sand draping over the undulating erosional surfaces forms the wavy lamination. The wavy laminated sand with scattered pebbles and cobbles is a key facies of an upper foreshore or swash zone, and is a good sea-level marker. [ABSTRACT FROM AUTHOR]