Beach Berm Research Articles

Formation of beach‐ridge plains: an appreciation of the contribution by Jack L. Davies

AbstractA robust debate among coastal geomorphologists as to the processes by which beach‐ridge plains around Australia have formed was initiated by a former President of the Institute of Australian Geographers. This review gives special consideration to the work of Jack L. Davies, whose academic contributions to coastal geomorphology in Australia have not always been appropriately acknowledged when explaining how similar plains have evolved elsewhere in the world. Davies recognised that relatively steep storm waves caused erosion (cut) on beaches, whereas less steep long‐period swell waves returned sand (fill). He considered the beach berm to be the nucleus on which a beach ridge formed, which could subsequently develop into a foredune, in contrast to cobble ridges that were deposited during storms. Offshore conditions regulate supply of sand to the shoreline, partly through effects on wave refraction, with higher rates of supply where the nearshore is shallow. It was apparent to Davies that the elevation of successive ridges might, but not necessarily, provide evidence of past changes of sea level, despite adornment by variable amounts of windblown dune sand. Morphodynamic understanding of long‐term coastal evolution, based on radiocarbon dating chronologies, has demonstrated that Australian coastal plains formed over the past ~6,000 years when sea level has been close to its present level, in contrast to several documented locations in the northern hemisphere where the sea has been rising for the past few millennia. Particularly insightful were observations by Davies that ridge formation could be influenced by a range of factors including changes in sea level, storminess, or sediment supply. These factors acting singly or in combination seem likely to change in the future. Understanding such responses remains a high priority and can be addressed by new technologies, such as light detection and ranging, optically stimulated luminescence dating, ground‐penetrating radar, and computer simulation.

Constant wind regimes during the Last Glacial Maximum and early Holocene: evidence from Little Llangothlin Lagoon, New England Tablelands, eastern Australia

Abstract. Here we present the results of a multi-proxy investigation – integrating geomorphology, ground-penetrating radar, and luminescence dating – of a high-elevation lunette and beach berm in northern New South Wales, eastern Australia. The lunette occurs on the eastern shore of Little Llangothlin Lagoon and provides evidence for a lake high stand combined with persistent westerly winds at the Last Glacial Maximum (LGM – centring on 21.5 ka) and during the early Holocene (ca. 9 and 6 ka). The reconstructed atmospheric circulation is similar to the present-day conditions, and we infer no significant changes in circulation at those times, as compared to the present day. Our results suggest that the Southern Hemisphere westerlies were minimally displaced in this sector of Australasia during the latter part of the last ice age. Our observations also support evidence for a more positive water balance at the LGM and early Holocene in this part of the Australian sub-tropics.

Terrestrial Laser Scanning of Anthropogenic Beach Berm Erosion and Overtopping

ABSTRACT Schubert, J.E.; Gallien, T.W.; Majd, M.S., and Sanders, B.F., 2015. Terrestrial laser scanning of anthropogenic beach berm erosion and overtopping. Anthropogenic berms are widely deployed to manage coastal flooding. The dynamic erosion of scraped berms exposed to waves and a rising tide in southern California was monitored with a terrestrial laser scanner (TLS) on three occasions in February and March of 2012. An improved characterization of initial berm geometry and the dynamics of berm erosion was pursued to accurately predict the onset and impact of coastal flooding associated with berm erosion and overtopping. TLS is shown to yield a digital terrain model (DTM) with a vertical accuracy of ca. 3 cm, indicating it is an excellent source of data for initializing mechanistic and/or empirical models that could be used to predict the onset and rate of wave overtopping. Minimum scan point spacings required to achieve this level of accuracy are investigated and reported. Additionally, a dimensionless...

Dune Vegetation and Insect Communities Vary with Barrier Beach Geomorphic Setting on Sapelo Island, United States

Mallinger, R., 2014. Dune vegetation and insect communities vary with barrier beach geomorphic setting on Sapelo Island, USA. Journal of Coastal Research, 30(6), 1210–1217. Coconut Creek (Florida), ISSN 0749-0208. Coastal geomorphic processes, including shore disturbance events, shape coastal landforms and sand dune ecosystems. The magnitude and frequency of shore disturbance can affect dune vegetation diversity, community composition, and succession. Furthermore, these processes might impact higher trophic levels, such as insects, either directly or indirectly through changes in dune vegetation. The objective of this study was to characterize differences in vegetation and insect communities along sand dunes varying in geomorphic setting and exposure to shore disturbance. Vegetation and insects were sampled along Nannygoat Beach, Sapelo Island, Georgia, United States, in areas historically documented to differ in erosion rates and in exposure to storm surges and overwash. Dune height and beach berm width were measured to describe geomorphic setting. The north end of Nannygoat Beach had taller sand dunes and a shorter beach berm width, indicating less overwash but greater rates of erosion compared to the south end. Plant diversity was significantly greater on the north end of Nannygoat, while insect richness was significantly greater on the south end of Nannygoat beach. Both plant and insect community composition were significantly different between the north and south ends of the beach. Furthermore, the plant community composition was significantly related to the abiotic variables, while the insect community composition was significantly related to the plant community. These results suggest that vegetation communities of barrier islands are strongly influenced by geomorphic processes, while insect communities are, in turn, shaped by the vegetation communities.

OCEAN DRIVEN FLOODING OF A COASTAL LAKE

Analysis of Lake Conjola flooding in April 2006, provided in this paper, attributes it to waves pumping water over a 300 m long beach berm and into Lake Conjola. This overwash, generated by the medium wave height swell occurring during this flooding, was able to lift the lake levels near the entrance, persistently over several tidal cycles, to well above the ocean water levels. The wave pump model was used to model this flooding. Lake Conjola water storage and dynamics were modelled by using a two-node continuity based model that a change in storage in time is driven by the net inflow to a node and these nodes and the ocean are linked by log-law. The extents of these two nodes were established from previous water surface measurements. While the qualitative flood behavior was reproduced by this remarkably simple model, the peak flood level was not satisfactorily predicted when using literature values for model turning parameters. One reason for this mismatch was that the waves pumped against a head including critical flow on the beach berm. Based on recent images of Lake Conjola wave overwash events, it may be concluded that pumping against critical flow is too harsh. Removing this from the model has halved the gap between the measurements and predictions. However, more research is definitely required to establish what components should be included in the hydraulic head pumped against.

MODELLING BEACH MORPHODYNAMICS FOR SOUTHERN GOLD COAST BEACH NOURISHMENT PROJECT AT BILINGA BEACH

A new cross shore process model NSBEACH (New SBEACH) has been applied to the Southern Gold Coast Nourishment Project at Bilinga beach (Australia) where nearshore nourishment and bar movement with beach berm and dune building have been simulated. Following the extension of the Tweed River training walls in the late 1960s, the downdrift Southern Gold Coast beaches to the north suffered extensive and prolonged erosion. Between 1988 and 1996, 6.6 million m3 of sand was deposited in both onshore and nearshore locations along the beaches of the Southern Gold Coast. Extensive post-nourishment beach monitoring data shows the recovery of Bilinga beach with the nearshore nourished material transported onshore. There have been many unsuccessful attempts to numerically model the beach recovery processes following the nearshore nourishment on the Southern Gold Coast. Most coastal models have been developed for prediction of storm erosion and as such have limited abilities in simulating bar movement and onshore accretion with beach recovery over extended periods of time. NSBEACH (New SBEACH) has been developed with the ability to simulate short term storm erosion and the longer duration recovery processes under natural or nourished conditions. NSBEACH has been successfully applied at Bilinga beach over an extended simulation period of 8 months with both erosion and accretion responses of the beach successfully simulated.

Internal architecture of mixed sand-and-gravel beach ridges: Miquelon-Langlade Barrier, NW Atlantic

Abstract The internal architecture of a beach-ridge system can provide clues into the processes involved in its formation. Detailed investigation of the mixed sand-and-gravel beach-ridge plain on the Miquelon-Langlade Barrier (northwest Atlantic Ocean, south of Newfoundland) provides a better understanding of such sedimentary systems in terms of internal architecture, depositional processes and driving mechanisms. Investigations of this regressive paraglacial barrier included the topographic (RTK-GPS) and ground-penetrating radar (100 to 500 MHz antennae) data collection, orthophotographs and optically stimulated luminescence (OSL) dating. The Miquelon-Langlade beach-ridge plain is composed of two opposing progradational systems, reflecting contrasting eastward and westward hydrodynamic exposures. Four ridge sets, each with concave planform shapes, define the 500–1400-m wide eastward prograding plain along the sheltered eastern coast. Two ridge-sets with linear and fan-shaped planforms define the 200–500-m wide south-westward prograding plain along the energetic western coast. Beach-ridge units overlay a basal sedimentary unit that disrupted incoming wave energy and altered the planform morphology of the prograding plain. The internal architecture pattern of individual beach ridges are characterized by sigmoidal configurations with seaward-dipping beds (2.3–4.7° true dip-angles). It is proposed that these wave-built facies are deposited as beach berms, likely by fair-weather waves. The elevations of these facies are determined by the sea level elevation and the swash height of constructive waves during their formation. Beach ridges are overlain by either peat resulting from the flooding of topographically low-lying areas, or by aeolian sand deposits of varying heights and morphologies (relict foredunes). Despite the differences in wave exposure along each coast, the sedimentary composition and internal architecture of the two progradational systems are broadly similar; bed dip angles of the individual beach ridges differ by only 1–2°, steeper along the exposed westward-facing coast. Overall, the Miquelon-Langlade beach-ridge plain highlights the primary influences of wave exposure, inherited topography, and proximal sediment sources (from erosion of moraines) on coastal progradational patterns.

Modelling gravel beach dynamics with XBeach

Numerical cross-shore profile evolution models have been good at predicting beach erosion during storm conditions, but have difficulty in predicting the accretion of the beach during calm periods. This paper describes the progress made in modifying and applying the public domain XBeach code to the prediction and explanation of the observed behaviour of coarse-grained beaches in the laboratory and the field under accretive conditions. The paper outlines in details the changes made to the original code (version 12), including the introduction of a new morphological module based upon Soulsby's sediment transport equation for waves and currents, and the incorporation of Packwood's infiltration approach in the unsaturated area of the swash region. The competence of this modified model during calm conditions for describing the steepening of the profile, and the growth of the beach berm is demonstrated. Preliminary results on the behaviour of the beach subject to both waves and tides are presented. Good agreement is found between the model simulations and large-scale laboratory measurements, as well as field observations from a composite beach in the UK. The reasons for the model's capabilities are discussed.

Predictions of barrier island berm evolution in a time‐varying storm climatology

AbstractLow‐lying barrier islands are ubiquitous features of the world's coastlines, and the processes responsible for their formation, maintenance, and destruction are related to the evolution of smaller, superimposed features including sand dunes, beach berms, and sandbars. The barrier island and its superimposed features interact with oceanographic forces (e.g., overwash) and exchange sediment with each other and other parts of the barrier island system. These interactions are modulated by changes in storminess. An opportunity to study these interactions resulted from the placement and subsequent evolution of a 2 m high sand berm constructed along the northern Chandeleur Islands, LA. We show that observed berm length evolution is well predicted by a model that was fit to the observations by estimating two parameters describing the rate of berm length change. The model evaluates the probability and duration of berm overwash to predict episodic berm erosion. A constant berm length change rate is also predicted that persists even when there is no overwash. The analysis is extended to a 16 year time series that includes both intraannual and interannual variability of overwash events. This analysis predicts that as many as 10 or as few as 1 day of overwash conditions would be expected each year. And an increase in berm elevation from 2 m to 3.5 m above mean sea level would reduce the expected frequency of overwash events from 4 to just 0.5 event‐days per year. This approach can be applied to understanding barrier island and berm evolution at other locations using past and future storm climatologies.

Formation of Beach Profile with the Design Criteria of Seawalls

When wave energy builds up, beach berm and even dunes are quickly eroded with this material being removed offshore to form a bar parallel to the beach. It proceeds seawards during the course of the storm to reach some ultimate location prior to being dismantled and moved back to the beach by subsequent swell. There is difficulty in defining the steepness associated with storm, although it has commonly been accepted that steeper waves often produce a bar or a barred beach bar position and its crest height for a given storm condition. Therefore, criteria for the formation of bar and berm profiles respectively, need to be clarified.. In this paper, the available experimental data of large wave tank (LWT) from U.S. Army Crops of Engineering and Japanese Central Research Institute of Electric Power Industry are used to construct a new relationship. Finally, criteria for bar and berm formation and seawalls design are found, and new criteria form are quite simple and widely applicable.

Confronting coastal morphodynamics with counter-erosion engineering: the emblematic case of Wissant Bay, Dover Strait

Wissant Bay is a picturesque and highly frequented French coastal resort comprising beaches, dunes, marshes, and bold capes facing the Dover Strait. Situated at the southern approaches to the North Sea, the 8 km-long bay has, arguably, the most rapidly eroding shoreline in metropolitan France. Retreat has largely affected much of the bay shoreline west of Wissant town, with parts of this sector having lost up to 250 m in the last 50 years, whereas a much smaller sector east of the town is a zone of accretion. Various dune, beach and nearshore morphodynamic studies conducted over the last decade have identified chronic sand bleeding from the western sector and longshore transport to the east, within a framework of what appears to be an ongoing shoreline rotation process within a dominant longshore sediment transport cell between the headland of Cape Gris Nez to the west and the bold chalk cliffs of Cape Blanc Nez to the east. Retreat of the narrowing beach-dune barrier poses a threat in the coming years, as there is a likelihood of it being breached by storms. The seawall protecting Wissant town has also been repeatedly damaged since 2000 due to the chronic sand deficit. These changes involve interactions between a nearshore sand bank, a complex macrotidal beach comprising multiple subtidal to intertidal bars and troughs subject to strong longshore sand transport especially during storms, and aeolian dunes. The nearshore bank acts as a dissipater of incident storm wave energy and as a sand source for the multi-barred beaches and dunes, and has been strongly impacted by past massive aggregate extraction. The bank is, in turn, part of a larger system of mobile banks reworked by storms and tidal currents within the framework of a sand circulation system between the eastern English Channel and the southern North Sea. The aim of this work is to confront knowledge acquired on the morphodynamics of the bay with an engineering plan proposed to counter erosion and reestablish shoreline stability. The plan is based essentially on the creation of an ‘equilibrium’ beach profile, capable of withstanding storms, comprising an enlarged upper beach berm, and constructed through beach nourishment from a nearshore source located 20 km east of Wissant Bay. The plan has not been implemented because of cost. Even if it were to be implemented, its efficiency seems very doubtful because the beach profile simulations on which it is based neglect the complex multi-barred morphology and the overwhelming dominant longshore transport over bars during storms. The plan is also geared towards resolving a local problem of erosion that is embedded in the larger and rather complex spatiotemporal morphodynamics and sediment transport mechanisms evoked above. Wissant Bay is emblematic of the problems of erosion facing many communes in France, and elsewhere. The fight against shoreline erosion generally starts with the commonly insurmountable hurdle of fund-raising for costly engineering proposals that are not always based on a clear grasp of the embedded scales of change affecting the coast.

A hydrologic and geomorphic model of estuary breaching and closure

To better understand how the hydrology of bar-built estuaries affects breaching and closing patterns, a model is developed that incorporates an estuary hydrologic budget with a geomorphic model of the inlet system. Erosion of the inlet is caused by inlet flow, whereas the only morphologic effect of waves is the deposition of sand into the inlet. When calibrated, the model is able to reproduce the initial seasonal breaching, seasonal closure, intermittent closures and breaches, and the low-streamflow (closed state) estuary hydrology of the Carmel Lagoon, located in Central California. Model performance was tested against three separate years of water-level observations. When open during these years, the inlet was visually observed to drain directly across the beach berm, in accordance with model assumptions. The calibrated model predicts the observed 48-h estuary stage amplitude with root mean square errors of 0.45m, 0.39m and 0.42m for the three separate years. For the calibrated model, the probability that the estuary inlet is closed decreases exponentially with increasing inflow (streamflow plus wave overtopping), decreasing 10-fold in probability as mean daily inflow increases from 0.2 to 1.0m3/s. Seasonal patterns of inlet state reflect the seasonal pattern of streamflow, though wave overtopping may become the main hydrologic flux during low streamflow conditions, infrequently causing short-lived breaches. In a series of sensitivity analyses it is seen that the status of the inlet and storage of water are sensitive to factors that control the storage, transmission, and inflow of water. By varying individual components of the berm system and estuary storage, the amount of the time the estuary is open may increase by 57%, or decrease by 44%, compared to the amount of time the estuary is open during calibrated model conditions for the 18.2-year model period. The individual components tested are: berm height, width, length, and hydraulic conductivity; estuary hypsometry (storage to stage relationship); two factors that control wave-swash sedimentation of the inlet; and sea level rise. The elevation of the berm determines the volume of water that must enter the estuary in order to breach, and it modulates the wave-overtopping flux and frequency. By increasing estuary storage capacity, the estuary will breach less frequently (−27% change in time open for modeled excavation scenario) and store water up to 3months later into the summer. Altering beach aquifer hydraulic conductivity affects inlet state, and patterns of breaching and water storage. As a result of sea-level rise of 1.67m by 2100, and a beach berm that remains in its current location and accretes vertically, the amount of time the estuary remains open may decrease by 44%. Such a change is an end-member of likely scenarios given that the berm will translate landwards. Model results indicate that the amount of time the estuary is open is more sensitive to changes in wave run-up than the amount of sand deposited in the inlet per each overtopping wave.

Relationship Between Cross-Shore Active Profile and One-Line Shoreline Evolution Models Performance

Coelho, C., Lima, M. and Veloso-Gomes, F., 2013. Relationship Between Cross-Shore Active Profile and One-Line Shoreline Evolution Models PerformanceOne-line shoreline evolution models, such as GENESIS and LTC, are commonly used to predict coastal configuration changes, where the alongshore sediment transport is controlled by waves, water level, sediments' sources and sinks and sediments' properties. Nevertheless, these models' performance is also affected by considerations related to the definition of cross-shore active profile width, where both models present some differences. In GENESIS, the onshore limit of active profile is defined by the beach berm height, while in LTC, this limit is defined by the wave runup. In what regards the offshore boundary, depth of closure defines the limit in both models. However, GENESIS considers an average value, representing all the waves and all the extension of the modelled stretch whereas LTC allows considering a fixed value, similar to GENESIS, or a variable value depending on each wave height along the time. These considerations have impacts on the definition of the active width of the cross-shore profiles and, consequently, on the shoreline development along time. Thus, in this paper, cross-shore profiles tests are performed, ranging the depths of closure and onshore limits of cross-shore active profiles, in order to evaluate their influence in the shoreline evolution.

Assessing Coastal Landscape Change for Archaeological Purposes: Integrating Shallow Geophysics, Historical Archives and Geomorphology at Port Angeles, Washington, USA

ABSTRACTTo mitigate saltwater flooding, the waterfront and downtown areas of Port Angeles, Washington were built‐up with up to 8 m of anthropogenic fill beginning in 1913. Shoreline modification continued into the present as this important natural deep‐water harbour along the Strait of Juan de Fuca was developed for maritime industries. This and other historical activities obscured at least two historically occupied villages and burial sites of the indigenous Coast Salish Klallam people. Since these archaeological sites remain buried beneath the modern Port Angeles waterfront knowledge of the distribution of buried landforms, coastal zone processes, and estimates of site preservation and modern disturbance potential is needed for archaeological identification and preservation efforts. We created a model of the fill thickness by combining data from: (i) field observations, where the thickness of the fill could be observed directly in the landscape; (ii) topographic differences between pre‐fill sounding maps and present‐day LIDAR‐determined elevations; and (iii) ground‐penetrating radar (GPR) surveys. The GPR surveys also helped to reconstruct the now buried palaeoenvironment by identifying tidal lagoons, beach berms and stream channel features beneath the fill layer. The history of post‐glacial sea‐level change, here impacted by global eustasy, glacio‐isostatic and tectonic factors is the first control on the development of quasi‐stable coastal landforms suitable for long‐term human occupation. Knowledge of past landscapes is a critical component in the development of future archaeological site catchment ‘predictive’ models based upon the spatial distribution and stability of landforms and resource accessibility prior to the Euro‐American historic period of intensive shoreline modification. The geophysical and geomorphic identification and spatial reconstruction of buried landforms also provides needed insight into the geology of the subsurface and its control on the flow of groundwater and contaminants across the nearshore environment. Copyright © 2012 John Wiley & Sons, Ltd.

Liquefaction as an important source of the A.D. 2011 Tohoku-oki tsunami deposits at Sendai Plain, Japan

This paper describes the topographic change and the recovery process, as well as the sediment sources, for tsunami deposits based on field surveys and analysis of digital elevation model data before and after the A.D. 2011 Tohoku-oki tsunami at the Sendai Plain, Japan. We found that the amount of sediment deposited on land was approximately four times greater than the eroded volume of sediment at the beach. Large amounts of the sediments deposited at the studied transect probably originated from liquefaction. This result suggests that the vented sediments might have been an important source of the tsunami deposits if liquefaction is generated by the strong ground motion of a near-field earthquake. In contrast, minor erosion was observed at the beach, and the beach berm was rebuilt within three months after the tsunami. Moreover, the erosional channel that had cut into the beach had been filled by sand within 13 days after the tsunami. Therefore, it is not expected that a sedimentary record of the tsunami will be preserved in the nearshore zone along the Sendai coast, although remnants of small scours on land might remain long after the tsunami.

Sedimentological and morphological characteristics of gypseous coastal nabkhas on Bubiyan Island, Kuwait, Arabian Gulf

Gypseous nabkhas of peculiar morphology occur on the beach berm and backshore slope along the southern coast of Bubiyan Island in northeast Kuwait. Their sediments are muddy sands and are mainly composed of gypsum with small amounts of shells, shell fragments, quartz and feldspars. Two types of gypsum are recognised: detrital grains and authigenic crystals. The authigenesis of gypsum within the nabkha detrital sediments is responsible for the significant increase in the volume of the nabkhas as well as considerable change in their morphology from a standard aerodynamic form to a whaleback shape. The genesis and diagenesis of the nabkha sediments are discussed, and future studies are recommended. The study concluded that mineral authigenesis within aeolian nabkha sediments should be seriously considered during the interpretation of their granulometrical characteristics and morphometric parameters.

Long-Term Evolution of a Long-Term Evolution Model

This paper reviews the 25-plus year history of significant developments of the GENESIS shoreline response model. Topics discussed are line sources and sinks of sand, representation of shore-normal structures including natural sand bypassing, wave transmission by and shoreline response to shore-parallel structures, seawalls, migrating longshore sand waves, seasonal variation by cross-shore sand transport, sand transport due to tidal and wind-generated currents, preservation of the regional shape of the shoreline, and the interaction between the beach berm and the dunes behind it. Such developments have been done in a consistent way, based on thorough literature reviews, beta testing, comparison to beach behavior, and quality control. The challenges have been not only to represent the features themselves, but to be consistent to the basic assumptions of shoreline modeling theory. Through these added capabilities, GENESIS has evolved to meet the challenges of modern, multi-scale, long-term coastal engineering applications.

ON MODELLING BEACH PROFILE EVOLUTION

Behaviour-oriented beach evolution models are normally applied in a prognostic fashion, with model parameters and boundary conditions estimated from previous experience, other forecasts or from historic measurements. Here, we use observations of beach profiles to solve a cross-shore beach profile evolution equation in an inverse manner to determine key model parameters, cross-shore sediment diffusion coefficient and a time-varying source function. The data used to demonstrate the method are from Christchurch Bay in Dorset, United Kingdom. It was found that there is a significant contribution from diffusive processes to the morphodynamic variability of the beach profiles and that the development and disappearance of cross-shore coastal features such as upper beach berms and inter- and sub-tidal bars are well captured by the time-varying source function in the governing equation.

Elastic source model of the North Mono eruption (1325–1368 A.D.) based on shoreline deformation

Topographic data from the Shuttle Radar Topography Mission (SRTM) captures the permanent deformation of a prominent highstand of Mono Lake, California USA. Deformation of the Dechambeau Ranch highstand shoreline was measured using the elevation of the beach berm—shoreline bluff break-in-slope. Point source models and a boundary element dike model were used to approximate the source of deformation underneath the northern end of the Mono Craters. The point source model could not adequately explain the observed deformation. The dike model yielded the best results for a NW trending dike dipping 60° NE and inflated to widths greater than 60 m. The results suggest that the geometry of the source is more complex than a simple vertical dike and that the deformation is better explained with a dipping dike following a normal fault, or an elongated cryptodome.

Short-term morphodynamics of non-storm overwash

Overwash is an important process in barrier island evolution and its effects on the barrier morphology and sedimentology have been widely studied. However, the short-term sediment dynamics of overwash processes are not well known due to the lack of specific field studies. This paper presents field data that clarify the sedimentary dynamics of overwash processes on different washover morphologies, and determine the factors leading to non-storm overwash occurrence. Two fieldwork campaigns were undertaken during overwash events: GO.1 (winter of 2001), and GO.3 (winter of 2003), on western Barreta Island (Algarve, Portugal). The fieldwork included measurements of oceanographic conditions, overwash flows, morphology variations, mixing depth and sediment transport paths using tracers. The sediment dynamics induced by overwash varied according to the washover morphology (washover plain versus washover lobe). The sediment transport inside the washover plain was different for the two fieldwork campaigns (average mixing depth of 13 cm for GO.1 and 6 cm for GO.3); however it had similar main stages: Stage 1 — crest accretion, Stage 2 — onshore transport, and Stage 3 — dynamic equilibrium. The sediment transport inside the washover lobe can be characterised by one onshore flow stage, with erosion of the mouth and channel, and accretion on the washover fan. The main factors governing the occurrence of non-storm overwash in the study area were the combined occurrence of: (1) typical winter waves, (2) spring high tides, (3) washover crest below the high-tide level + 2 m, and (4) absence of prominent beach berm. This study proved that when the proper conditions are generated, non-storm overwash has sediment transport comparable to storm overwash and therefore may be significant for barrier evolution. Further field studies of overwash are needed, principally for more detailed overwash flow velocity measurements, high-frequency morphologic surveys, and barrier groundwater measurements.