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Predicting the future behavior of beach and nearshore systems requires an accurate delineation and understanding of coastal cell boundaries, sediment transport pathways, and sediment sources and sinks. Unfortunately, there is a paucity of field datasets on beach and nearshore morphological change that extend fully from the top of the dunes to beyond the depth of closure to enable quantification of the sediment budget. Here, for the first time, we employ a total sediment budget approach, examining a sandy and embayed beach located in the north coast of SW England, to investigate inter- and multi-annual embayment scale sediment dynamics over a 10-year period that includes extreme storm erosion and post-storm recovery. We demonstrate that, despite the deeply embayed nature of the beach, the shoreline orientation roughly parallel to the dominant wave direction and the overwhelmingly cross-shore forcing of the inter-tidal beach volume, the system is neither closed, nor balanced. The very significant net changes in the recorded sediment volume from dune top to depth of closure (−14.5 m ODN), representing a loss of c. 100 m3 m−1 during the extreme storm period and a gain of c. 200 m3 m−1 during the recovery period, indicate that significant sediment transport occurs seaward of the base of the terminating headlands and beyond the morphological depth of closure. The results further indicate that the inter-tidal region is partly uncoupled from the sub-tidal region, with the former region dominated by cross-shore sediment fluxes, whereas the subtidal region is also significantly affected by longshore sediment fluxes. A conceptual model is presented that balances the observed volume changes with inferred fluxes, forced by variations in total and alongshore wave power. This study contradicts the general assumption that when sediment exits the inter-tidal, it rests undisturbed in the sub-tidal, waiting for a period of low-moderate energy to bring it onshore. The large sediment volumetric variations across the lower shoreface (depth of 5–20 m), which are of the same order of magnitude as, but uncorrelated with, those occurring in the inter-tidal region, are suggestive of an energetic longshore transport system across this deeper region. It is possible that this transport system extends along the whole north coast of SW England and this finding may lead to a shift in understanding of sediment budgets along exposed and macrotidal embayments globally. Unlabelled Image • Full sediment budget was produced along an exposed macrotidal embayment and linked to wave forcing. • Inter- and sub-tidal volumes are not inversely correlated, indicating decoupling. • Sediment budget suggests significant exchange around headlands and/or across depth of closure. • Beaches on this coast type can be considered part of an extended coastal cell. [ABSTRACT FROM AUTHOR]

This paper describes the development, behaviour, and application of a mesoscale numerical geomorphological model of eroding soft rock and beach shores. The model, SCAPE (Soft-Cliff and Platform Erosion), describes coastal processes and engineering interventions and is a suitable tool for testing management strategies. The mesoscale capability of SCAPE arises because it includes a broad system: its principal modules describe wave transformation, platform erosion, and a (one-line) beach. Feedback within and between the modules regulates their behaviour, brings long-term (dynamic) stability, and allows quantified representation of qualitatively different shore behaviours. SCAPE is demonstrated through the construction of a model of more than 30 km of the North Norfolk coast. A precalibration initialisation phase is required to allow dynamic equilibrium to emerge. Once initialised, calibrated, and validated against an 87-year record, the model is used to explore the development of the North Norfolk coast from 2003 to 2053 under six management scenarios. The model is also used to demonstrate the losses and benefits of erosion under these scenarios and to reveal two qualitatively different modes of behaviour, termed rock strength limited erosion and sediment transport limited erosion. Some generic implications of these different modes are discussed. [ABSTRACT FROM AUTHOR]

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: Minor bedforms within the mudstone-dominated Early Jurassic Hettangian Saltford Shale Member (Liasicus up to Angulata Chronozone) of the Blue Lias Formation in central England, indicate weak seafloor erosion in a mid to outer ramp setting. Distal storm flows below maximum storm wave base are proposed as the most likely generative mechanism for silty scour and gutter casts that enclose concentrations of well-preserved schlotheimiid ammonites and arthropod trace fossils. Within the upper part of the Saltford Shale (probably Angulata Chronozone), a discrete layer of reworked and bioencrusted limestone nodules signifies an episode of more persistent seafloor erosion. The immediately overlying strata, transitional to the Hettangian–Sinemurian Rugby Limestone Member, are relatively bioturbated and feature fossils of macrobenthos, as well as shell concentrations resembling relatively proximal storm beds. This suggests that the reworked nodule horizon marks sea-level fall, rather than stratigraphic condensation associated with sediment starvation. The biostratigraphic evidence raises the possibility that this erosional episode correlates with a mid-Angulata Chronozone hiatus documented from the Wessex Basin, southwest England. Equally however, it could be linked to contemporaneous movement on one or more nearby faults, affecting the southern part of the English East Midlands Shelf. [Copyright &y& Elsevier]

Beach profile change in the swash zone on gravel beaches is characterised by enhanced onshore sediment transport and berm formation, and infiltration loss in the swash zone is often given as the reason why gravel beaches are steeper than sand beaches. In this paper, we report on field measurements conducted on a gravel beach, Slapton Sands, Devon, UK, in April 2001. Collected data included surface pressures under uprush and backwash, subsurface pore water pressures, uprush and backwash velocities, and bed elevations. The field data were compared with predictions of the BeachWin model, which simulates interacting wave run-up/run-down, beach groundwater flow, swash sediment transport, and resulting beach profile changes. With a relatively large value of hydraulic conductivity, the model was able to predict the observed berm formation at the upper part of the beach. In contrast, the berm feature was absent in the simulation without swash infiltration effects included. The predicted erosion at the middle section of the beach, however, took place at a location landward of that of the measurements. Simulations were carried out to investigate the sensitivity of the model to changes in the hydraulic conductivity, friction factor, and coefficient ratio of uprush/backwash sediment transport. All parameters were shown to affect the simulation results—in particular, the formation and extent of the berm. [ABSTRACT FROM AUTHOR]

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]

Beach nourishment is increasingly seen as an appropriate management solution in areas which are experiencing beach erosion. Such a scheme has been implemented along the Lincolnshire coast between Skegness and Mablethorpe, on the east coast of England, since 1994. Poorly sorted, gravelly sandy sediment has been placed on the beaches in a gently sloping seaward profile to raise beach levels and protect the hard defences from wave attack. Grain size analysis of beach sediments, topographic profiling and remote sensing have been used to monitor the beach response. After nourishment, wave reworking caused a rapid redistribution of sediment over the beach profile during the succeeding weeks. Coarse sediment has remained on the beach berm, while finer sediment has migrated to the lower beach and sub-tidal zone. The berm face has correspondingly become steeper, producing more wave reflectance, and further scour and erosion of lower beach sediment, although there appears to have been little alongshore sediment transport. The most severe sediment loss has occurred around promontories and on the central portion of the convex-shaped coast which experiences greatest wave exposure. While the nourishment scheme has improved the standard of defence, further sediment losses could be reduced by nourishing the beach with a more natural size grading, promoting a flatter beach profile and increasing the dissipation of wave energy. Unless stabilization of the beach profile can be achieved, further periodic renourishment will be required to maintain relatively high beach levels. [ABSTRACT FROM AUTHOR]

The effects of four offshore breakwaters built between 1993 and 1995 at Sea Palling, Norfolk, UK, on beach morphology are discussed. The structures were built during the first phase of a multi-phase construction programme and are expected to provide long-term protection for Sea Palling and 6000 ha of low-lying land against tidal inundation through the provision of a wide beach in front of the existing seawall and dunes. The results presented here span all stages of breakwater construction during Phase 1. Beach level changes were monitored during the period from 1995 to 1999. A Geographical Information System (GIS) was used to calculate differential surfaces between surveys in order to investigate local patterns of accretion and erosion and to determine volume changes between consecutive surveys. Additional data collected by the Environment Agency since 1991 were analysed to investigate beach and bathymetry changes prior to the construction of the breakwaters. In association with periodic nourishment programmes the scheme has been locally successful in retaining recharged sediment on the beach but the extent of the salients prevents to a great extent the south-eastward littoral drift. As a result, effects on the beaches, both down- and up-drift of the breakwaters, have been considerable. The continuing increase in beach volume indicated that by January 1999 equilibrium had not been reached. [Copyright &y& Elsevier]

Embayed beaches constitute a large proportion of the world's rocky coastlines, but there is a paucity of studies focusing on the longshore sediment exchange between embayed beaches separated by rocky stretches of coast. Here, we investigate the nearshore sediment transport dynamics along a 15-km stretch of the embayed coastline of north Cornwall, SW England, using Delft3D. Numerical simulations (coupled wave and tide) are conducted to compute major circulation modes and sediment fluxes, including order of magnitude for sediment bypassing between bays, for a wide range of modal and extreme wave conditions. Results indicate that extreme events cause (i) multi-embayment circulation and mega-rip formation where an alongshore current is deflected offshore (0.7 m s−1 at >20 m depth) in the down-wave sectors, (ii) large bypassing rates (103–104 m3 day−1 bypassing) and (iii) exchanges extending to depths that exceed the base of the headlands. Accretionary phases over moderate-high swell periods were associated with clockwise intra-embayment circulation with simulated currents inducing redistribution towards the south in the long embayments (>103 m3 day−1 longshore). This circulation mode is combined with significant bypassing rates around the shallower and wider headlands (102–103 m3 day−1). Predictions of sediment fluxes along the lower shoreface are based on the correlation between the modelled sediment fluxes and offshore wave-conditions (r > 0.92), providing insights into the potential sediment budget over multi-annual timescales. Hindcasted yearly bypassing rates around the headlands range between 103 and 105 m3 y−1 under an assumption of unlimited sediment supply, with the bulk of the transport occurring mainly during high energy events. Hence, the magnitude of the computed potential sediment fluxes presented here has implications for coastal evolution at longer timescales (>10 years), especially along sediment-starved coastlines. • Delft3D was used to investigate nearshore sediment transport dynamics • Full picture of sediment bypassing rates and paths along an embayed coastline is provided • Sediment budgets and headland bypassing rates over multi-annual timescales are predicted • Hindcasted bypassing (103 – 105 m3 y-1) will affect coastal evolution over the decadal scale • Magnitude of sub-tidal bypassing indicates substantial interconnectivity between cells previously thought limited to cross-shore oscillations [ABSTRACT FROM AUTHOR]

Blowouts are acknowledged as highly effective transport pathways. Their morphological form is indicative of aeolian transport and the propensity of their topography to modify airflow sufficiently to support transport has been extensively researched. As the evolution of sandy coastlines is governed by sediment exchanges between sub-units of the cross shore profile, blowouts located at the beach-dune interface may play a significant role in evolution through enhancing the landward transfer of sediment into the dune field. Although there is a growing number of studies detailing blowout transport, those which encompass synchronous measurement of flow and sediment exchange from the beach into the dune field remain extremely rare.This study, conducted at Sefton dunes, northwest England, details airflow and sediment transport dynamics at the beach-dune interface of a trough blowout. A dense array of 3D sonic anemometers, co-located with transport sensors were deployed during an oblique onshore wind event. Instantaneous flow and transport dynamics were measured on the back beach, the adjacent upwind foredune and within the throat of the blowout. Additionally, the morphological response was captured via pre and post event TLS surveys.The importance of alongshore deflected airflow in delivering sediment to the blowout throat area was highlighted by a linear trend of high magnitude transport intensity across the upwind foredune. Within the throat, levels of transport intensity displayed extremely high spatial and temporal variability across a relatively confined area. Multiple topographically forced flow modifications were observed. Although incident wind speed remained relatively constant, a sharp 15° onshore directional shift during the experiment resulted in a step change in transport intensity within the blowout, providing insight into how sediment is first delivered to the throat area and then driven landwards. [ABSTRACT FROM AUTHOR]