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Conventional aeolian sand transport models relate mass transport rate to wind speed or shear velocity, usually expressed and empirically tested on a 1-s time scale. Projections of total sand delivery over long time scales based on these models are highly sensitive to any small bias arising from statistical fitting on empirical data. We analysed time series of wind speed and sand transport rate collected at 14 independent measurement stations on a beach during a prior field experiment. The results show that relating total sand drift to cumulative above-threshold wind run yields models which are more statistically robust when fitted on empirical data, generating smaller prediction errors when projected to longer time scales. Testing of different power exponents indicates that a linear relationship between sand drift and above-threshold wind run yields the best results. These findings inspire a speculative novel phenomenological model relating the mass flow of air in the boundary layer to the mass transport of sand over the surface.

Airflow dynamics and potential sediment transport were measured and modelled across various barchan dune topographies and incident wind conditions. Modification of near surface flow was recorded simultaneously in three dimensions (3D) using dense arrays of high-resolution 3D ultrasonic anemometers. In situ measurements provided rigorous validation and calibration for computational fluid dynamics (CFD) modelling. Measured and modelled results show good agreement between flow velocity, directionality, and turbulence intensity. Modelling of characteristic airflow conditions and surface shear stress beyond the instrument locations, elucidated airflow dynamics across the entire landform surface at an unprecedented level of detail. Emergent turbulent airflow patterns were identified in the form of two counter-rotating vortices that converge at the dune centreline downwind of the dune crest. Integrating a sediment transport function with CFD surface airflow allows for the spatial mapping of flux patterns across the entirety of the dune and interdune surface. On the stoss slope and laterally along the outer barchan arms, there is strong potential sediment flux in response to increased streamwise stress. In lee-side locations, sediment transport remains at ‘above threshold’ conditions and is redirected in response to complex turbulent vortices identified in the overlying wake zone. The precision of the models allows for the identification of complex flow perturbations and associated surface stresses that prove difficult to measure in the field. CFD in combination with a sediment transport function is demonstrated to be a useful tool in investigating morphodynamics of mobile dune systems.

The distribution and geomorphology of aeolianite outcrop on the coast of KwaZulu-Natal, South Africa are described in the context of its preservation potential in the geological record. Aeolianite on the contemporary coast comprises discontinuous, widely spaced, outcrops less than 100 m in longshore extent and typically 50–60 m wide that reflects the combined action of subaerial weathering and physical abrasion in the coastal zone since the mid-Holocene (approximately 7000 yrs). The dominant morphological component is an intertidal erosional platform that slopes gently landward. It is fronted by a notch in the mid intertidal zone (0 m MSL) and contains active erosional potholes on its seaward margin. The platform surface is encrusted by a variety of marine organisms. Landward of and contiguous with the intertidal surface are small elevated outcrops of aeolianite in the supratidal zone. These comprise a 3 m-high seaward scarp with a basal notch in the high intertidal zone + 1 m MSL. Gullies in the scarp trap coarse clasts of eroded aeolianite as well as bedrock. The upper surface of the supratidal aeolianite is planar with large potholes within which accumulations of coarse clasts and oyster shells have been cemented. The upper surface is interpreted as a remnant of an intertidal platform formed at a higher mid-Holocene sea level. The supratidal outcrop is subject to weathering and disintegration. Major joints divide the outcrop into cuboid blocks with axes of 3–4 m. Eroded blocks on the seaward face that exceed 1 m diameter, remain in-situ and become locked in place by repeated shaking. Smaller blocks that collapse from the seaward face accumulate in small gullies or are dispersed. The facet most likely to be preserved in the geological record is the planar intertidal platform. The morphology of aeolianite on the contemporary coast is markedly different from submerged aeolianite ridges on the adjacent shelf which are of higher relief, wider and more laterally extensive. Preservation potential of aeolianite under subaerial conditions is low and the widespread high-relief aeolianite on the shelf is attributed to rapid inundation or burial during transgression.

This work is part of a Vice Chancellor's Research Scholarship funding for PhD studies at the Centre for Coastal and Marine Research, School of Environmental Sciences, University of Ulster.

The coast of southeast Africa is dominated by sandy beaches that tend to be confined within log-spiral or headland-bound embayments. Investigations using serendipitous air imagery data set have been previously undertaken and conclusions drawn about the stability of the coast. We show that conclusions drawn from this data, with respect to the high water mark (HWM) position are fraught with errors, which include tidal state, pressure regime, beach slope, high-swell erosion, seasonal and multi-annual changes. We highlight and discuss these sources of error, together with their magnitudes. The most significant of these are the high-swell, seasonal and multi-annual variations. From case studies we show that the seasonal beach rotation and long-term beach width variation are responsible for tens of metres of unaccounted HWM variation, 30 to 50 m is common, with maximums reaching 60 to 100 m. Overall the southeast African coastline appears to be in a state of long-term dynamic equilibrium. There is no evidence of any sea-level rise-forced transgression in the coastal sediment budget, despite sea-level rise (SLR). If such a signal is, in fact present, it is lost within the beach width variation. Some southeast African coastal reaches are suffering chronic erosion, but these are related to anthropogenic impacts. The extreme difficulty of placing a HWM, with any temporal validity on this coast precludes the routine use of the Bruun Rule. Although no transgressive signature is found, there is evidence of a decreasing coastal sand budget as a result of anthropogenic or natural climate change, or both. This decrease in the coastal sand volume is likely to result in increased future erosion. Copyright © 2016 John Wiley & Sons, Ltd.

Nearshore bars play a pivotal role in coastal behaviour, helping to protect and restore beach systems particularly in post-storm conditions. Examination of bar behaviour under various forcing conditions is important to help understand the short- to medium-term evolution of sandy beach systems. This study carried out over a nine-week period examines, the behaviour of three intertidal bars along a high energy sandy beach system in northwest Ireland using high-frequency topographic surveys and detailed nearshore hydrodynamic modelling. Results show that, in general, there was onshore migration for all the bars during the study period, despite the variability observed between bars, which was driven mostly by wave dominated processes. Under the prevailing conditions migration rates of up to 1.83 m day−1 and as low as 0.07 m day−1 were observed. During higher wave energy events the migration rates of the bars decelerated in their onshore route, however, under lower wave energy conditions, they quickly accelerated maintaining their shoreward migration direction. Tidal influence appears to be subordinate in these conditions, being restricted to moderating the localized wave energy at low tides and in maintaining runnel configurations providing accommodation space for advancing slip faces. The study highlights the intricate behavioural patterns of intertidal bar behaviour along a high energy sandy coastline and provides new insights into the relative importance of wave and tidal forcing on bar behaviour over a relatively short time period. Copyright © 2016 John Wiley & Sons, Ltd.

Pilkey, O.H. and Cooper, J.A.G. 2014. Are natural beaches facing extinction? In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa) Journal of Coastal Research, Special Issue, No. 70 pp. 431–436. ISSN 0749-0208. On a generational scale, on developed shorelines, the world's recreational beaches are doomed. This is largely because of the widespread assumption that preservation of buildings is a higher priority than preservation of beaches in response to sea level rise. Continuing beach degradation will be inevitable through active or passive processes. Active degradation means the actual removal of the beach, mostly as a result of shoreline engineering or mining. By far, the most important cause of beach loss in this category will be hard structures, especially seawalls. The incorrectly but widely perceived panacea of each replenishment will become economically impossible because of raised sea levels. Replenishment leads to intensified bea...

Loureiro, C., Ferreira, O., Cooper, J.A.G., 2014. Non-uniformity of storm impacts on three high-energy embayed beaches. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 326–331, ISSN 0749-0208. Coastal storms are highly significant and destructive events and important natural hazards that have major impacts upon the physical and human-cultural coastline environments. Exceptional coastal storms in the last decades have emphasized the urgent need to reinforce scientific knowledge regarding the frequency, impact and role of these extreme events. This is particularly relevant for embayed beaches, where geomorphological control promotes characteristic morphodynamic responses that are distinct from the better studied long-linear beaches. This paper analyses storm response from datasets of morphological change obtained from three embayments located in three distinct wave environments...

In spite of the worldwide abundance of beachrocks and their acknowledged utility as an indicator of former sea level position, some studies have expressed doubt as to their position of cementation on paleo shorelines. These criticisms are not, however, coupled with nuanced sedimentological studies of beachrocks. Instead, few beachrock studies acknowledge any facies and therefore disregard important signatures of the depositional environment and, consequently, utility as paleo sea level indicators. This study presents detailed sedimentological descriptions and interpretations from two beachrock localities along the subtropical, microtidal, wave-dominated eastern coastline near Durban, South Africa. The outcrops record the migration of a paleo inlet and deposition in sub, inter, and supra tidal environments. Understanding the inferred depositional environment, and observed stratigraphic relationships between various beachrock facies is critical to teasing out the local evolution of shoreline and relative sea level. The outcrops studied here record multiple episodes of Holocene sea level rise and fall.

This paper presents an analysis of decadal (mesoscale) geomorphic change on sandy barrier islands in thefetch-limited environment of Chesapeake Bay. Low energy barrier islands exist in two settings: on the fringe of marshes and in open water and this analysis shows the various types of barrier island to be genetically related.Barrier islands that face the dominant wind and wave direction (E or W) retreat via barrier translation, preserving the barrier island volume. Those that exist in re-entrants are dominated by longshore transport processes, are strongly affected by sediment supply and are subject to disintegration.Marsh fringe barrier islands are perched on or draped over the surface of the underlying marsh. They migrate landwards via barrier translation during periodic high water events accompanied by large waves (hurricanes and northeasters). The underlying marsh surface erodes under all water levels and the rate of retreat of the barrier island and underlying marsh may take place at different rates, leading to various configurations from perched barrier islands several metres landward of themarsh edge, to barrier islands that have a sandy shoreface extending into the subtidal zone. The coastal configuration during landward retreat of marsh fringe barrier islands is subject to strong local control exerted by the underyling marsh topography. As erosion ofmarsh promontories occurs and marsh creeks are intersected and bypassed, the configuration is subject to rapid change. Periodic sediment influxes cause spits to develop at re-entrants in themarsh. The spits are initiated as extensions of adjacentmarsh fringe barrier islands, but as the sediment volumeis finite, the initial drift-aligned spits become sediment-starved and begin to develop a series of swash-aligned cells as they strive formorphodynamic equilibrium.The individual cells are stretched until breaches form in the barrier islands, creating inlets with tidal deltas. At this stage the low energy barrier islands closely resemble open ocean barrier islands. Continued reworking leads towidening of the inletswith consequent loss of constriction of tidal flow. The tidal deltas are, thus, no longermaintained and ultimately the island systemdisintegrates through inlet widening and is transformed to subtidal shoals. Barrier islands at various stages in this evolutionary cycle can be observed around the bay. Mid-bay barrier islands are affected by wave processes from both sides. This helps maintain the barrier island form and enables barrier islands to persist as sediment is exchanged between both sides of the island.Rates of barrier island translation are extremely high (up to 30 m/year over a 12 year period). This is attributed to the lowvolume of sand, which facilitates complete rollover in short periods. Accelerated sea level rise is likely to hasten the translation rates ofmarsh fringe barrier islands. The rapid disintegration ofmost spits compared to the persistence of marsh fringe barrier islands points to a reliance on the marsh as a stabilising point. If the marshes are overstepped by rising sea level as appears to be happening, the complete disintegration of the barrier islands is highly likely.

Green, A.; Cooper, J.A.G., and LeVieux, A., 2013. Unusual barrier/inlet behaviour associated with active coastal progradation and river-dominated estuaries. The mesoscale behaviour of unusual barrier inlets on the east coast of South Africa is described. The inlets are associated with river-dominated estuaries and are consequently subject to periodic closure during low river flow. They are also located on a prograding barrier coast. Deflection of the estuary channel of a small river in the direction of longshore transport by 1230 m resulted in its capture by the estuarine channel of a larger river. The larger catchment river was not deflected by coastal progradation but maintained its position by periodic breaching of a channel through the barrier during floods. Flood breaches reseal by landward reworking of ephemeral deltas and may undergo limited migration. A tidal inlet at the northern end of the barrier is maintained by a small tidal prism and has a flood-tidal delta. It exhibits limited late...

Wind flow within blowouts is extremely complex as streamline compression, expansion and reversal may occur over and around a single landform. As a result high resolution temporal and spatial measurements are required during a range of incident wind conditions to resolve near surface airflow patterns and turbulent structures. This study examined three-dimensional airflow within a coastal dune trough–bowl blowout using 15 ultrasonic anemometers (UAs) and a high resolution computational fluid dynamics model. Measured total wind speed and vertical wind speed behaved consistently through 5 Beaufort wind scales ranging from ‘fresh breeze’ to ‘strong gale’, increasing relative to incident wind speed, whilst wind direction at each UA did not alter. Due to the agreement of modelled and measured data, ‘hurricane’ (37 m s −1 ) incident winds were also simulated and were consistent with modelled and measured wind direction at lower wind speeds. Modelled wind turbulence data was not compared with measured as only average conditions were simulated. However, the standard deviation of measured wind direction remained constant at each anemometer throughout the range of incident wind speeds, whilst the standard deviation of wind speed and turbulent kinetic energy increased relative to incident wind speed. This paper demonstrates that wind flow behaviour within blowouts throughout this range of wind speeds is governed by topography and is relative to, but does not change structurally with incident wind speed. As a result the extent of streamline compression, expansion, steering and reversal remain constant.

Blowouts are common landforms found within coastal dunes. Their dynamics are primarily driven by aeolian transport caused by surface wind stress, though patterns of deflation and deposition within blowouts are poorly understood as near surface wind flow is complex. Three‐dimensional wind flows around blowouts have yet to be properly quantified, especially within zones of separation, re-attachment and acceleration. This has been largely due to inadequate measurement of airflow and a lack of suitable airflow models. With this in mind, we present results from a study that has quantified alongshore and oblique onshore wind flow dynamics over a bowl blowout on the Belmullet Peninsula, Ireland. Using ultrasonic three-dimensional anemometry (measuring at 50 Hz) and three-dimensional computational fluid dynamic (CFD) modelling, we measure and model for the first time in 3D a detailed picture of the heterogeneity of wind flow over this type of terrain. During alongshore wind conditions, wind speeds within the deflation basin were retarded by 50% compared to the foredune zone and flow separation restricted to a small zone in lee of the windward rim. Wind was directed into the deflation basin through a gap in a western erosional wall, termed the blowout throat. In oblique onshore wind, airflow orientated with the blowout throat remained unchanged in direction and slowed by only 30% compared to wind speed on the foredune. In lee of the erosional wall adjacent to the blowout throat, small zones of flow separation occurred close to the erosional wall. In both cases, the highest variation in wind speed and direction occurred in zones of separation and attachment whilst flow increased in steadiness with height over the erosional walls. The results illustrate that wind is manipulated according to localised topography within the bowl blowout itself. Resulting zones of potential sediment transport (erosion and deposition) are spatially complex and alter with wind direction. The presence of a blowout throat has a significant influence on airflow patterns within a deflation basin. Modelled (CFD) and measured anemometer data demonstrated excellent comparisons for wind direction and speed, allowing much greater spatial measurement resolution than physical instrumentation. Simulated turbulence did not correlate well with measured data, highlighting the requirement for high frequency, three-dimensional anemometry in areas of complex flow.

Aeolian sediment transport under offshore winds is usually discounted from sediment budget considerations of coastal dunes. Results presented here indicate however, that depending on wind orientation and foredune morphology, positive contributions to the sediment budget can arise from offshore winds. Lee-side airflow patterns, seaward of the foredune crest, under offshore winds were studied at three sites of varying foredune geometry along Magilligan Strand, Northern Ireland. Ultrasonic anemometers recorded 1 Hz wind velocity data at 1° intervals. Descriptive statistics and wind rose diagrams were used in the analysis of these data. Under perpendicularly offshore winds each site exhibited a different type of lee-side airflow pattern. A tall (11·4 m), sharp-crested foredune produced flow separation with a recirculation cell. A lower (6·6 m), more rounded, foredune crest exhibited lee-side flow that remained attached but was deflected parallel to the crest, while flow over a low incipient foredune crest resulted in attached flow with no deflection in the lee. The morphology of the lee slopes best explained these airflow adjustments. More obliquely offshore winds were also found to affect the secondary airflow patterns, with a smooth transition from flow separation to flow attachment as the incident angle decreased. At higher wind velocities this smooth transition was replaced with a more abrupt switch between the secondary airflow types. This threshold was located at similar approach angles to those recorded for desert dunes (90° +/− 20°). These findings have significant implications for the post-storm recovery and long-term evolution of beach-dune systems where the predominant winds are offshore, and offer an explanation for the presence of many beach-dune systems in lee-coast locations. Copyright © 2010 John Wiley & Sons, Ltd.

There are more than 15,000 barrier islands in fetch-limited nearshore environments around the world. About half that number are actively evolving (eroding, accreting, migrating) in response to oceanographic processes and are the subject of this study. The remaining half consists of inactive islands protected by surrounding salt marsh or mangroves. Despite their global abundance these islands have not been previously systematically studied or even recognized as a major landform type. More than 70% of fetch-limited barrier islands are found on trailing edge coasts because conditions there are favorable for formation of sheltered waters. Fully 50% are found in the coastal zone of Australia, Mexico, and Russia. We identify eight different types of fetch-limited barrier islands based on genesis and mode of occurrence. Most of the active islands form in estuaries or bays (Spencer Gulf Australia), behind open ocean barrier islands (Pamlico Sound, North Carolina), or on flood tidal deltas of open ocean t...

Experiments carried out at Magilligan Strand on the north coast of Ireland suggest that topographic steering of offshore winds is an important facet of the aeolian sediment transport system at this location. A five-day study (18-22 June 2005) investigated the pattern of airflow over the foredune while simultaneously collecting data on sediment flux. A simple instrument setup was used to characterise the airflow: a sonic anemometer was placed at the dune crest, with another on the mid-beach. Horizontal traps, electronic and integrating, measured sediment flux on the supra-tidal beach. Results show that offshore wind flow deviated from its original direction in the lee of the dune (seaward of foredune). The change in direction was not a simple steering of flow to a singular new direction, but rather flow separation resulting in turbulent multidirectional flow - including reversal. Traps located at the foot of the dune scarp recorded sediment transport during events forced by offshore winds. Data from sediment traps, wind and observational evidence have been used to argue that sedimentation was occurring in this zone. When budgeting for sediment movement within beach-dune systems it is important to take into account the effect of secondary airflow patterns during offshore winds and their role in constructive processes of foredune formation, particularly in post-storm recovery. (C) 2008 Elsevier B.V. All rights reserved.

Unsuccessful attempts to use process-scale models to predict long-term aeolian sediment transport patterns have long been a feature of aeolian research. It has been proposed that one approach to overcome these problems is to identify micro-scale variables that are important at longer timescales. This paper assesses the contribution of two system variables (secondary airflow patterns and fetch distance) to medium-term (months to years) dune development. The micro-scale importance of these variables had been established during previous work at the site (Magilligan Strand, Northern Ireland). Three methods were employed. First, sand drift potentials were calculated using 2 years of regional wind data and a sediment transport model. Second, wind data and large trench traps (2 m length x 1 m width x 1.5 m depth) were used to assess the actual sediment transport patterns over a 2-month period. Third, a remote-sensing technique for the identification of fetch distance, a saltation impact sensor (Safire) and wind data were utilized to gauge, qualitatively, sediment transport patterns over a 1-month period. Secondary airflow effects were found to play a major role in the sediment flux patterns at these timescales, with measured and predicted rates matching closely during the trench trap study. The results suggest that fetch distance is an unimportant variable at this site. Copyright (C) 2007 John Wiley & Sons, Ltd.

Despite acknowledgement by scientists and modelers of the shortcomings of mathematical models of beach behaviour, they continue in widespread use for engineering design and environmental impact studies. In part, this is because of the assumed absence of a viable alternative approach to prediction. The objective of this paper is to suggest that a conceptual approach can succeed as an alternative to mathematical models for predictions with accuracy ranges useful for engineering and coastal management purposes. The most valuable information for prediction is past engineering experience on the beach in question or the experience on neighboring beaches. The next most useful may be the global experience on oceanographically similar beaches. Another approach is the use of geoindicators and field studies on the beach. The widely applied “predict nothing” approach to beach engineering may well work if fortified by common sense. Finally, a composite approach in which the assembled body of information on a ...

Two barrier island systems from southern Mozambique (Inhaca and Bazaruto) are described. Both systems comprise a composite barrier island or barrier island chain that developed on a steep continental margin as a result of initial (Pleistocene) spit progradation. Continuing aeolian dune deposition against this initial core during subsequent sea-level highstands and lowstands has given rise to the highest dunes (120m) of any known barrier island. Wave reworking of the composite barrier island sediment during the past 6000 years of the Holocene sea-level highstand has resulted in the formation of spits, barriers, barrier islands and bluffs on the downdrift and bay side sections of the barrier island systems. The relative stability in position of the barrier systems at contemporary sea level is attributed to their large sediment volume and the development of equilibrium shoreline forms under swell waves. Beachrock and aeolianite outcrops provide anchor points for the development of contemporary shore...

The role of statutory designations to regulate activities is an important element in coastal zone management in Europe. In this paper we assess the utility of one such designation the “Area of Outstanding Natural Beauty” as a tool for coastal management in Northern Ireland. The designation is based on landscape quality and offers the potential for an integrated approach. However a variety of weaknesses reduce their effectiveness. Several suggestions are offered to improve the utility of this designation.

The methods used to determine or predict volumes of sand transported by longshore currents are briefly reviewed. We argue that the methods are flawed and that a fundamental re-examination of both field and theoretical approaches is in order. Net transport numbers obtained by any existing method should be considered order-of-magnitude values at best that are in no case sufficiently precise for coastal engineering purposes such as prediction of beach nourishment costs and environmental impacts.

Methodological aspects of GPS (Global Positioning System) and Total Station (Electronic Distance Measurement) surveying techniques were examined as part of a beach monitoring programme which was used to assess morphological variation of a high-energy beach system at Runkerry, Co.Antrim, Northern Ireland. The accuracy of the instruments as well as data processing methods concerning data conversion in different plane coordinates systems is discussed. GPS with Real Time Kinematics (RTK) provides high-resolution control on topographical surveying within limits on the order of centimeter-level accuracy in the horizontal and 2 cm in vertical dimension. Total station (EDM) also demonstrated high accuracy during its use in the monitoring programme. The model of EDM used in this work had a 5 to 6 degrees offset angle for the orientation due to the inherent characteristics of the instrument. A threshold-narrowed point selecting treatment was used to form a beach profile point set for the profile plot and any further processing. This work demonstrates that a two-dimensional translation and rotation for horizontal dimension data conversion is preferable over linear regression method; while the linear regression method for the vertical dimension data is still acceptable. It is suggested therefore that when a conversion of beach surveying data from one plane coordinate system to another is required, then this combined approach should be adopted in the analysis.

A Late Quaternary sea-level curve for South Africa is presented on the basis of new and published data from a range of sea level indicators and a variety of locations. Available evidence suggests that sea level in South Africa broadly follows that described from the Caribbean but that deviations occur during sea-level highstands. During the last interglaciation (oxygen isotope stage 5) and the late Holocene, coastal emergence produced higher sea levels in South Africa than those identified in the Caribbean during the same time intervals. This is tentatively ascribed to predicted lithospheric deformation in continental margin settings.

The Mgeni Estuary is situated on the east coast of South Africa. Tidal salinity changes commonly extend 2.5 km upstream from the mouth. The subtropical climatic regime causes seasonal flooding, the geomorphological effects of which are increased by a steep river gradient. A 120-150 year flood event during September 1987, with an estimated peak discharge of 10800 cumecs, resulted in the erosion of 1.86 × 106 m3 of sediment from the estuary. The normal high tide volume of the estuary (0.35 × 106 m3) increased to 1.85 × 106 m3 after the flood. The post-flood intertidal volume (tidal prism) of the estuary was 0.43 × 106 m3 compared to 0.19 × 106 m3 before the event. The nature and extent of erosion in the estuary was controlled by the composition of the estuary banks and bed material. Gravel and sand substrates were preferentially eroded from the estuary bed before the cohesive bank materials were undercut in sections of the estuary. Mud and fine sand were deposited on overbank areas when the flood waned and a lag of coarse sand and gravel was produced on the estuary bed. Approximately 46 per cent of the bedload sediment supplied to the estuary since 1917 was retained in the estuary until the 1987 flood. The remainder was transported through the system and into the Indian Ocean. Results show that catastrophic floods play an important role in sedimentation in small estuaries.

HUANG, J.D.; JACKSON, D.W.T., and COOPER, J.A.G., 2010. Piecewise polynomial expression of beach profiles.

Megarips have long been recognised as an important, yet poorly documented, mechanism of beach erosion on high-energy embayed beaches. The persistence and cumulative effect of megarips during storm groups, are described from three embayed beaches (Arrifana, Mt. Clerigo and Amoreira) exposed to high-energy wave conditions in the mesotidal, bedrock-dominated southwestern coast of Portugal. Morphological changes, determined by topographic monitoring and supplemented by interpretation of digital imagery over two years, revealed the development of storm-induced megarips, which exerted a major influence on beach erosion. Differences in megarip influence within and between beaches are related to embayment geometry and orientation, which significantly influence the nearshore wave field. Rip location is topographically controlled, being determined by alongshore variations in breaking wave height and obliquity, along with interaction of wave-driven circulation patterns and embayment nearshore topography. Moderate beach sand loss during individual storms was linked to the development of megarips with associated rip-neck and feeder channels. Extreme erosion, however, occurred when megarips and feeder channels persisted during successive storms, promoting continued erosion and seaward sediment export. Observations show that once initiated, megarip channels persist for several months and continue to act as conduits for offshore sediment transport under non-storm conditions. The maintenance of such rip circulation systems, driven by morphodynamic feedback, reduces beach recovery ability until the rip-neck and feeder channels are infilled.