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Findings from nearly two decades of research focused on the Columbia River littoral cell (CRLC), a set of rapidly prograding coastal barriers and strand-plains in the U.S. Pacific Northwest, are synthesized to investigate the morphodynamics associated with prograding beaches. Due to a large sediment supply from the Columbia River, the CRLC is the only extensive stretch of shoreline on the U.S. west coast to have advanced significantly seaward during the late Holocene. Since the last Cascadia Subduction Zone (CSZ) earthquake in 1700, with associated co-seismic subsidence and tsunami, much of the CRLC has prograded hundreds of meters. However, the rates of progradation, and the processes most responsible for sediment accumulation, vary depending on time scale and the morphological unit in question. Remarkably, the 20th and early 21st century shoreline change rates were more than double the late prehistoric rates that include recovery from the last major CSZ event, most likely due to an increase in sediment supply resulting from inlet jetty construction. In some locations detailed beach morphology monitoring reveals that at interannual- to decadal-scale the upper shoreface aggraded about 2 cm/yr, subtidal sandbars migrated offshore and decayed while intertidal bars migrated onshore and welded to the shoreline, the shoreline prograded about 4 m/yr, and 1 to 2 new foredune ridges were generated. A detailed meso-scale sediment budget analysis in one location within the littoral cell shows that approximately 100 m3/m/yr accumulated between − 12 m (seaward limit of data) and + 9 m (crest of landward-most foredune). Gradients in alongshore sediment transport, net onshore-directed cross-shore sediment transport within the surf zone, and cross-shore feeding from a shoreface out of equilibrium with forcing conditions are each partially responsible for the significant rates of sediment supplied to the beaches and dunes of the CRLC during the observational period. Direct observations of beach progradation at seasonal- to decadal-scale are put in context of measured or inferred changes over time scales of decades to centuries.

This paper details the historical coastal evolution of the Columbia River littoral cell in the Pacific Northwest of the United States. Geological data from A.D. 1700 and records leading up to the late 1800s provide insights to the natural system dynamics prior to significant human intervention, most notably jetty construction between 1885 and 1917. All reliable surveys, charts, and aerial photos are used to quantify decadal-scale changes at the three estuary entrances and four sub-cells of the littoral cell. Shoreline, bathymetric, and topographic change over three historical intervals—1870s–1920s, 1920s–1950s, and 1950s–1990s—are integrated to provide an understanding of sediment-sharing relationships among the littoral cell components. Regional morphological change data are developed for alongshore segments of approximately 5 km, enabling comparisons of shoreline change to upper-shoreface and barrier volume change within common compartments. The construction of entrance jetties at the Columbia River (1885–1917) and Grays Harbor (1898–1916) has profoundly affected the evolution of the littoral cell, and has accentuated the morphological coupling between the inlets, ebb-tidal deltas, shorefaces, and barriers. The jetties induced erosion of the inlets and offshore migration of ebb-tidal deltas. The change in boundary conditions at the entrances enabled waves to rework the flanks of ebb-tidal deltas and supply enormous quantities of sand to the adjacent coasts. Over several decades the initial sand pulses have been dispersed alongshore up to tens of kilometers from the estuary entrances. Winter waves and coastal currents produce net northward sediment transport across the shoreface while summer conditions tend to induce onshore sediment transport and accumulation of the upper shoreface and barriers at relatively high rates. Historical shoreline progradation rates since jetty construction are approximately double the late prehistoric rates between 1700 and the 1870s. Erosion rates of the mid- to lower shoreface to the south of the jettied estuary entrances have typically been greater than the accumulation rates of the upper shoreface and barrier, suggesting that the lower shoreface has been an important source of littoral sediments over decadal and longer time scales. Until recent decades, sediment supply from the ebb-tidal delta flanks and lower shoreface has largely masked the decline in Columbia River sediment supply resulting from flow regulation and dredging disposal practices. With the contemporary onset and expansion of coastal erosion adjacent to the jettied estuary entrances, proper management of dredged sediment is imperative to mitigate the effects of a declining sediment budget.

In this study, monthly beach elevation time series (between 1981 and 2003) at Duck, North Carolina are analysed using fractal methods. This work extends a fractal analysis carried out by Southgate and Moller [Southgate, H.N., Moller, I., 2000. Fractal properties of coastal profile evolution at Duck, North Carolina. J. Geophys. Res. 105 (C5), 11489–11507] using twice the amount of data (22.3 yr) with the aim of investigating the fractal properties at different profile locations over a larger range of timescales. Differences in fractal properties between the periods 1981–1992 and 1992–2003 are also examined. The results of this analysis are used to distinguish between the timescales on which the beach elevation responses at various cross-shore and alongshore locations are related (or unrelated) to external forcing. Two fractal analysis approaches, based on the calculation of global and local Hurst exponents, are used. The local Hurst exponent method identifies local fractal properties in the data over ranges of timescales and also accounts for nonstationarity in relation to the data mean. Hence, it is considered to be a more appropriate technique for identifying the fractal properties in such dynamic natural time series. The analysis of the entire 22.3-year long data set shows fractal properties over more varied timescales and beach locations than previously observed by Southgate and Moller [Southgate, H.N., Moller, I., 2000. Fractal properties of coastal profile evolution at Duck, North Carolina. J. Geophys. Res. 105 (C5), 11489–11507]. For the dune and upper shoreface, fractal properties are estimated at timescales between 1 and 50 months, while the inner and outer bar zones exhibit fewer fractal properties over varied timescales between 10 and 90 months. Cross-shore locations corresponding to the typical positions of the nearshore sand bars at Duck exhibit non-fractal properties, reflecting the dominant influences of wave forcing in these areas. Alongshore differences in the fractal properties (which were not previously studied) are also identified between the pairs of profile lines located north and south of the FRF pier. These observations demonstrate the importance of studying both alongshore and cross-shore morphological variability. The differences in the spatio-temporal patterns of the fractal properties identified for the 1981–1992 and 1992–2003 periods illustrate the variation of the beach morphology with time. This demonstrates the need for re-evaluating beach behaviour using extended data. The present work shows that the timescales on which fractal properties are estimated are consistent with the timescales on which previous studies found the influences of the external forcing conditions at Duck to be relatively weak.

Ground-penetrating radar (GPR) profiles of Holocene beach deposits were documented from the Kujukuri strand plain, Pacific coast of Japan, to examine a marker of past sea level recognized in these profiles. The Kujukuri strand plain has been uplifted over the last 6000 years, with a total relative sea-level fall of about 5 m suggested by seaward lowering of the lithologic boundary between the foreshore and upper shoreface facies. A GPR survey was performed on a modern aeolian dune and beach ridges of the strand plain using a PulseEkko100 system with 100-MHz antennae. The profiles obtained contain five vertically stacked radar units (R1–R5) with characteristic reflections. Ground truthing using sediment cores and the morphology of the modern beach suggest that these radar units correspond to aeolian dune (R1), small-scale swale (R2), backshore and foreshore (R3), upper shoreface (R4), and lower shoreface (R5) deposits, in descending order. The backshore and foreshore radar unit shows a sequence of continuous reflections dipping seaward at an angle consistent with the modern beach, whereas the underlying upper shoreface radar unit represents complicated and less-continuous reflections. The boundary between these two units is a downlap surface of the foreshore reflections, and is thought to have formed at about 1 m below the mean sea level at the time of deposition. The lateral tracing of the boundary in radar profiles across the strand plain indicates a total fall in relative sea level of 5 m, which is consistent with the drill core results. Radar profiles of the foreshore and upper shoreface deposits in the Kujukuri strand plain thus provide a past sea-level indicator that is available without drilling sediment cores.

It has become increasingly recognized that the typically 'unexpected' behavior of the nearshore profile over a sequence of storm events is a response to strong feedback between the antecedent morphology and the incident wave field. This paper systematically examines the suspended sediment transport and morphodynamics within the surf zone of a lacustrine multiple-barred upper shoreface. A range of significant wave heights (Hs) and local relative wave heights (Hsh-1; h = water depth) are considered in order to describe and identify the limits to the feedback mechanisms that can dominate the nearshore response. Data from collocated concentration and velocity sensors indicate that the direction and magnitude of suspended sediment transport varies with the degree of local wave energy dissipation and the cross-shore variation in these relationships depends partly on the local bed slope. This dependence indicates the presence of a strong "self-organization" at the scale of the individual bar. Within the inner surf zone, these bar-scale relationships are constrained by the shoaling transformations, which occur over the outermost bar. For ranges of incident wave height defined locally (e.g. intermediate waves Hs = 0.4 to 0.9 m; storm waves = 0.9 to 1.4 m) the innermost and middle bars remain in a state of self-organized equilibrium. For intermediate range waves, this equilibrium is a consequence of wave height reduction over the outer bar through breaking and the generation of secondary (harmonic) waves. For the storm wave range, the equilibrium is maintained through a resonant amplification of discrete edge wave modes, with the bars forced to a position coincident with the surface elevation antinodes. These upper shoreface scale feedback mechanisms are weakened (particularly for intermediate wave heights) following threshold storms capable of moving the outermost bar offshore and lower on the profile. This allows the middle and inner bars to be forced directly by variations in the offshore incident waves. Thus, the bars respond in a cyclic manner, the bar cycle. © 2005 Elsevier B.V. All rights reserved.

Sedimentological and morphological changes on the upper and lower shoreface during relatively stable sea-level highstand conditions have been investigated in the Pomeranian Bight, southern Baltic Sea, at time scales ranging from storm events to millennia. In order to cover that variety of time scales, different methods have been applied. Seasonal variations in the morphology of the upper shoreface were measured accurately using the tracer stick method. The ratio of breaking waves and energy dissipation due to wave breaking are the main forces controlling redeposition on the upper shoreface with the depth of disturbance up to three times the net change. The impact of single storm events can be observed from sidescan sonar mosaics to remain on the decadal scale. Aerial photographs covering the upper shoreface show that the location of gates, channel-like systems where water masses move offshore created during storm events, also remain stable over decades. Sedimentological and geomorphological variations and changes on the lower shoreface are only measurable on the century to millennium scale because the main driving forces are longlasting processes like sea-level fluctuations or neotectonics. Data on these scales have much more uncertainty in their relationship to forcing functions than data at shorter time scales. Because the effects of coastal processes active on different time scales can interact, comprehensive understanding of large-scale coastal behavior requires investigations from short events to long-term processes. (C) 2002 Elsevier Science B.V. All rights reserved.

The US Army Corps of Engineers' Field Research Facility (FRF) at Duck, North Carolina, has collected approximately biweekly beach-nearshore profile data to 8-m depth and associated wave data since 1981. Sediment budget analysis was used to examine the medium-scale (years to a decade) variability of the beach-nearshore profile from 1981 to 1991. Significant changes occurred during four groups of energetic storm events during February/March of 1983, 1987, 1989 and December 1989. Each group was comprised of at least two storms within a period of less than 39 days both with Hmo > 4 m. During each storm group, offshore sediment movement caused a distinct outer bar to migrate offshore and grow in size resulting in an abrupt increase in the volume of sediment on the upper shoreface. The net profile changes were much larger than the changes due to single storms and the cumulative effect of the storms can be considered as one ‘event’. During these events, the first storm appears to have a destabilizing effect on the profile which has insufficient time to recover before the second (and subsequent) storm (s). As a result, several storms in quick succession are able to have a large impact on the morphology. The intervening periods between the groups of storm events (termed fairweather conditions) lasted up to 4 years. They are characterized by slow, but steady sediment redistribution (averaging 33 m3 m?1 year?1) from the upper shoreface (> 5 m depth) toward the shore, while the total sediment volume was effectively constant. The onshore feed of sediment was not significantly affected by individual storms during the fairweather conditions. These two processes of (1) morphologic change during groups of storm events and (2) the steady onshore feed of sediments from the shoreface during fairweather conditions appear to play an important role on medium- and long-term profile evolution at least at Duck.

Current knowledge of hydro-, sediment and morpho-dynamics in the shoreface environment is insufficient to undertake shoreface-profile evolution modelling on the basis of first physical principles. We propose a simple, panel-type model to map observed behaviour. The internal dynamics are determined by slope-dependent, wave-induced cross-shoreface transports, while the external driving factors are lateral sediment supply and sea-level rise. This model concept is tested with reasonable success against the observed behaviour of the Central Holland Coast, considering two hindcast periods, one covering the evolution over the last century, the other the Subboreal/Subatlantic evolution. A limitation of this model is that the cross-shoreface dynamics are solely steered by the variations of shoaling, short waves. Since a variety of other wave and current dynamics may be expected to be present in the coastal boundary layer, it may well be that the effects of the mechanisms and conditions which are not represented are hidden in the coefficients of the sediment-transport formula. This limits the accuracy of the coefficients as used, and our findings should be considered as an-order-of-magnitude estimate only. Indeed, behaviour-oriented modelling implies that generalization of results to arbitrary situations and conditions is not straightforward. Yet, we expect that some of the conclusions are more generally applicable. This concerns the substantiation of the assumption that the upper shoreface responds on a much smaller time scale than the lower shoreface, and the idea that the shoreface profile is not always and everywhere in equilibrium with its forcing. A worthwhile observation from the Holland Coast application is, that the bottom slope effect on the transport is only important at geological time scales. The profile evolution at the engineering time scales (say 10 to 100 years) is effectively quasi-static, in that there is no feedback between the long-term averaged transport and the state of the profile. This implies that at these smaller scales the profile changes can be predicted on the basis of a static sediment balance. This does not mean that the gravitational downslope transport is unimportant as a physical phenomenon in coastal profile evolution: It is only unimportant if a highly aggregated model like this is applied at relatively short time scales.

Holocene sediment lithofacies and dispersal systems on the east Coromandel shelf, New Zealand, are mainly characterised by an accommodation-dominated regime in which autochthonous siliciclastic sediments were reworked through erosional shoreface retreat during the post-glacial marine transgression (12.0–6.5 ka). Stabilisation of sea level at its present position ca. 6.5 ka initiated onshore reworking of the autochthonous deposits into fine-grained regressive barrier and shoreface sands, while coarser sands remained offshore to form an erosional-lag inner-shelf deposit. Modern episodes of shoreface erosion rework fine and coarse autochthonous sands offshore and northwards into very large (η = 0.5–2.5 m; λ = 250–1500 m) submarine dunes. The submarine dunes are similar in form to sand ridges on the North American Atlantic shelf, but with crests striking perpendicular to both the shoreline and generating flows. Allochthonous siliciclastic lithofacies are also important aspects of east Coromandel shelf sedimentation, and are transported offshore from infilled estuary systems to form very fine-grained upper shoreface and muddy mid-shelf sands. The regional geology has a strong influence on shelf lithofacies and dispersal systems off the east Coromandel coast. Southern shelf regions are associated with deep back-arc basins which have formed major late Cenozoic depocentres for sediments sourced from the Taupo Volcanic Zone. Further north, a shallow volcanic platform extends out across the shelf and forms a barrier to any large-scale along-shelf dispersal of sediments. Consequently, lithofacies in northern shelf regions tend to be highly variable and reflect local catchment lithologies.

Using the barred upper shoreface of Long Island, New York, as an example, this study provides a semi-quantitative demonstration of the concept that the distribution of grain sizes in a closed depositional system is the product of the reworking and redistribution by the physical process and the availability of the sediment source. In the particular case of Long Island, the physical process is represented by the agitation of sediment grain sizes by the shoaling waves under the average fair-weather wave conditions as a first-order approximation. A nearby subaerial morainal deposit represents the drowned glacial deposit on the shoreface as the sediment source. The probability of abundance of four representative sediment grain sizes across the upper shoreface of the study site was simulated. The shoaling wave field over a segment of the upper shoreface of Long Island was first simulated by a numerical wave and circulation model using deepwater incident waves under the conditions of the average fair-weather, remote ocean swells, and a local storm. The model results were then used to estimate sediment entrainment across the upper shoreface of the study site by using an empirical formulation developed for sediment movement under progressive waves. The probability of the occurrence of each grain size on the upper shoreface is characterized by a non-dimensional retention index. The results indicate that the fair-weather wave climate has the highest probability for sediment retention on the seabed. The cross-shore distribution of a grain size, which is represented by the probability of abundance (abundance index), can be simulated by multiplying the probability of occurrence (retention index) as a result of the differential wave agitation with the availability (grain-size frequency distribution) of the source sediment deposit. The grain sizes representing the fine sand group have the best fit between the observed and simulated distributions, suggesting a group of grain sizes that is in dynamic equilibrium with shoaling waves. For the rest of the grain sizes, the combined effects of shoaling waves and other secondary hydrodynamic processes are important in determining their cross-shore distributions.

The near-bed (0.10 m elevation), horizontal velocities were measured across a two-barred, lacustrine shoreface during a storm and reveal a spatially coherent but temporally variable pattern in the low-order moments of the velocity field. Large cross-shore velocity asymmetries indicated: 1. (1) Spatially extensive and temporally persistent offshore mean flows (up to 0.18 m s −1 across the landward slope of the linear outer bar) reflecting an undertow driven by a wave-induced setup. 2. (2) An onshore directed skewness opposing the mean flow, of wind wave origin and persistent under propagating bores in the inner bar system long after this asymmetry had disappeared from the outer bar. Extensive sediment reactivation with near-zero net sediment flux over the whole of the upper shoreface indicated a sediment prism in a steady state (volumetrically) over the storm cycle. Uniform depths of sediment reactivation with zero bed elevation change over the storm cycle revealed local slopes in a steady state in the outer linear bar. However, time integration of the near-bed velocity field at this location indicated an offshore net flux of water, while sedimentary structures indicated bedform migration (and thus at least bedload) almost uniformly onshore when ripples and megaripples were present. The sediment transport giving rise to the local equilibrium cannot be explained therefore on the basis of the mean properties of the near-bed velocity vector, but requires knowledge of the time-varying, instantaneous sediment transport vector. Onshore migration of the inner bar correlated well with the large and persistent onshore skewness of the velocity distribution in the inner surf zone associated with translatory surf bores throughout the storm decay period. Low-frequency oscillations were only significant close to the shoreline, but may have influenced the development of a sinuous three-dimensional inner bar form as it migrated onshore.

Distributions of seventeen grain sizes in the sand fraction of the shoreface sediments south of Long Island, New York, can be categorized into middle and lower shoreface species (very fine sand), upper shoreface species (fine sand), shoreface-depleted species (medium sand), and swash-zone species (coarse sand). The long-term fair-weather wave base of the study area at a depth of about 16 m is determined on the basis of the characteristic response of grain sizes to the average shoreface hydrodynamics. The crosshore deviations from the mean distribution for each grain size were examined by using empirical orthogonal function (EOF) analysis. These results show differential associations of grain-size deviations with various dynamic zones on the shoreface. The hydrodynamic processes of the modern shoreface are speculated to winnow out fine and very fine sands and transport them onshore, leaving behind on the lower shoreface and inner continental shelf a lag deposit of transgressive sand sheet composed mainly of medium sand.

Where the Atlantic coastal gradient is low and the substrate is unconsolidated, shoreface processes lead to an equilibrium shoreface surface, characterized by a straightened plan view and a concave-up profile. Maintenance of this surface during the post-glacial sea-level rise may lead to barrier formation by mainland beach detachment, where the outer oceanic shoreface is maintained by wave and current processes. Downwelling storm currents sweep sand from the shoreface of the middle Atlantic bight, transport it downcoast and seaward and deposit it on the adjacent inner shelf. Some of this sand is returned by the action of asymmetrical wave orbital currents during fair weather. However, there is a net loss in most areas. The loss is not made good by river sand input, since on the Atlantic Coast all river sand is trapped by estuaries. As a result the shoreface in these areas is undergoing erosional retreat. Mean horizontal retreat rates are on the order of 1–3 m yr−1 but most movement occurs in brief episodes with recurrence rates on the order of several events per century. Erosional shoreface retreat, coupled with aeolian overshoot, storm washover and the movement of sand through inlets into the lagoons, has lead to landward migration of the Atlantic barriers through the Holocene period of sea-level rise. The landward retreat of the barrier as a whole is as dependent on inlet formation as it is on erosional shoreface retreat. Repeated inlet breaching and the downdrift migration of inlets yields coalescing flood tidal deltas within the lagoon. The resulting surface forms a platform on which the subaerial barrier deposits can advance under the impetus of storm washover and aeolian action. The backbarrier deposits eventually re-emerge at the shoreface, where their upper beds are eroded and recycled. The barrier thus migrates over a pavement of its own flood tidal deltas and washover fans; sand is added to the system partly through the erosion of updrift headlands but mainly by means of scour in inlets, which reaches down to the underlying Pleistocene. The modern shelf sand sheet is the debris blanket resulting from the retreat process. The leading edge occurs as a thin veneer of rip-current fallout on the shoreface; this is periodically stripped off by winter storms to expose the underlying backbarrier strata. Further seaward, shelf sands eroded from the shoreface rest disconformably on backbarrier deposits; shoreface, beach and dune strata are always missing. Every grain of sand in this shelf sand sheet has occupied a position on the beach or upper shoreface within the recent past. However, the sheet as a whole has been reconstituted; its primary structures are those of the inner shelf floor. Backbarrier sand and mud deposits, characterized by channeling and landward-dipping reflectors, can be traced for over 100 km seaward across the middle Atlantic shelf, beneath the modern sand sheet. The backbarrier stratum together with the overlying shelf sand layer constitutes the record of barrier retreat across the Atlantic shelf surface during Holocene time. The sheet-like nature of this record indicates that, viewed at the appropriate time scale, barrier migration is a continuous process.

In part I of this paper, near-bottom fluid velocity and sediment concentration measurements from the shoreface of a middle Atlantic barrier (Long Island coast) are analyzed to provide insight into the dynamics of erosional shoreface retreat. In Part II ∗ , these data are combined with observations of coastal stratigraphy in order to construct a model for the evolution and behavior of middle Atlantic barriers. Wave motions on the Long Island shoreface tend to drive sediment onshore. Calculations of the onshore sediment flux driven by asymmetrical, shoaling waves show that for the wave states commonly encountered on the middle Atlantic shelf, values become strongly positive landward of approximately 10 m water depth (upper shoreface) but drop to very low values shortly seaward of that isobath. On the lower shoreface and inner shelf floor, fair-weather wave-current interaction tends to cause a landward creep of sediment, even though the wave-orbital component of the near-bottom velocity field is nearly symmetrical. This movement occurs because the wave approach direction generally lies within 90° of the direction (up-coast or down-coast) of the alongshore wind-driven current. Therefore, fluid shear stress acting on the sediments tends to be reinforced during the shoreward stroke of the wave orbital motion and partially cancelled during the seaward stroke. During major storms, the rate of sediment transport increases by at least an order of magnitude and the role of wind-driven currents becomes important. Much more sediment is resuspended by the wave orbital current component because storm waves are more powerful than fair-weather swells. But the wind-driven flow component is also much stronger and is now available for transporting the resuspended sediment. Storm flows over the shoreface occur in distinct dynamic zones (surf zone, friction-dominated zone, transition zone, geostrophic zone). The zones are defined by dynamical considerations and expand or contract with the intensity of the causative wind stress. During peak flow events, the characteristic length scales of the friction-dominated and geostrophic zones tend to correspond with the morphologic zones of the shoreface and inner shelf. The storm-intensified, wind-driven, alongshore flows of the lower shoreface are frequently jet-like in nature and may be upwelling or downwelling. Wind-driven coastal flows with a strong downwelling component occur during most storms on the Long Island coast and are particularly important to the coastal sand budget. During these events, sand is entrained by the storm-intensified upper shoreface circulation system of wave-driven alongshore currents and rip currents, and is fed into the main wind-driven coastal current. Because of the offshore component of bottom flow, sand is swept down the lower shoreface and onto the adjacent inner shelf. Fair weather processes may be unable to return storm-deposited sand to the beach from such an offshore position. The shoreface transport regime of the Long Island Barrier coast thus consists of long periods of time (months) during which sand moves slowly toward the beach, punctuated by short intense periods (hours or days) during which sand is transferred from the shoreface to the adjacent inner shelf. The long-term sense of movement of the shoreface, whether retreating (the Long Island case) or prograding, must depend on the loss or gain of sand by shoreface with respect to the inner shelf. The data shows that the coastal sand budget is controlled not only by the upper shoreface cycle (withdrawl of sand from the beach prism, storage in the breakpoint bar and its subsequent return to the beach), but by a cycle of larger spatial and temporal scale, in which sand is exchanged between the shoreface as a whole and the adjacent inner shelf.

The bathymetric components of a wave- and storm-dominated shoreface were examined as a key to understanding the controlling effects of hydrodynamic processes and geological factors that maintain the shoreface. Results of empirical orthogonal function analysis applied to bathymetric data from the upper shoreface of Long Island's south shore between Fire Island Inlet and Montauk Point show that this area can be divided morphologically into a headland section and a barrier island section. The headland section is characterized by well organized (well correlated) bathymetry in contrast to the barrier island section, which has more complex and less organized (less correlated) bathymetry. The first three spatial eigenfunctions (modes) account for nearly 90% of the variance among the headland shoreface bathymetry data, whereas the first three eigenfunctions of the barrier island section account for 82% of the variance among the data. The headland shoreface is steeper than the barrier island shoreface and is dominated by a primary nearshore bar mode, which accounts for 70% of the variance among the shoreface bathymetry data for this section. Secondary bathymetric components of the headland shoreface account for less than 20% of the remaining variance. The bathymetry of the barrier island shoreface is dominated by a terrace mode. This mode accounts for only 54% of the variance among the bathymetric data, however, and secondary bathymetric components account for more than 27% of the remaining variance. Underlying factors determining the differences in shoreface bathymetry between the barrier island and headland sections of the study area include topographic control by the outwash plain backing much of the headland section and proximity to sediment source. The factor directly responsible for differences in bathymetric components, however, is the relative difference in dissipative conditions between the two sections with respect to incident wave energy. Both sections have an outer dissipative domain and a more resonant inner domain. However, the barrier island section is twice as dissipative as the headland section.

The Santa Cruz coastal terrace fringes much of the northern Monterey Bay region, California. It consists mainly of a regressive sequence of high-energy, barred nearshore marine sediments deposited during the last (Sangamonian) highstand of sea level. This sequence can be sub-divided into several depth-dependent facies on the basis of paleo-current data and vertical sequence of sedimentary structures. These include a lower shoreface facies deposited in 10–16 m water depth, an upper shoreface facies (including both a storm-dominated assemblage and a surf zone assemblage) deposited in 0–10 m water depth, and a foreshore facies deposited in the swash zone, up to 3.5 m above high tide. The magnitudes of the storm events responsible for depositing these sediments were estimated by calculating paleo-wave heights using a variety of criteria (e.g., critical threshold equations, breaker depths, berm heights). In addition, the climate and paleogeography during the deposition of these sediments were essentially the same as today, allowing the use of present-day wave statistics to estimate the frequency of these storm events. The largest storms formed offshore-flowing currents (e.g., rip, wind-forced, and possibly storm-surge ebb currents) that resulted in the deposition of approximately 30% of the sediments seaward of the surf zone; however, the magnitude and frequency of these events are unknown. The remaining 70% of the sediment beyond the surf zone was deposited in response to smaller storm waves which were, on the average, at least 1.6 m high; such waves presently occur no more than 15% of the time. Sediments deposited during “fairweather” conditions (i.e., the remaining 85% of the time) have a low preservation potential, and are generally not preserved in this facies. In contrast, surf zone sediments were deposited by a variety of processes associated with waves whose maximum offshore heights were probably ≤ 2.2 m; such waves presently occur up to 92% of the time. Sediments within the swash zone were deposited by waves up to 3 m high, the largest of which presently occur approximately 2% of the time. Most of the sediments were deposited by storms of intermediate magnitude and frequency; different facies, however, appear to preferentially record events of different recurrence intervals. In particular, surf zone sediments were deposited under relatively small storm and post-storm conditions, whereas sediments deposited farther offshore record increasingly larger, less frequent storm events. Relatively rare events (e.g., the 100 or 1000 yr events) do not appear to have significantly affected sedimentation in these nearshore environments.

The depositional sedimentary structures and textures of a single-barred nearshore system on the Atlantic coast of eastern Long Island, New York, were studied along seven shore-normal transects. Data along these transects consisted of textural analysis of 160 sediment samples, temporal bedform observations, and 42 can cores for the analysis of sedimentary structures. Six sedimentary subenvironments were observed, based on distinct combinations of sediment color and texture, bedforms, physical, and biogenic sedimentary structures, and benthic infaunal communities. The shoreface environment is divided into the upper shoreface, the longshore trough, and the longshore bar. The divisions of the inner shelf environment are the shoreface-inner shelf transition, the offshore, and the coarse-grained deposit. The first five subenvironments are arranged in bands parallel to the shoreline, whereas the coarse-grained deposit occurs in patches across the inner shelf. The location of fair-weather wave base, coinciding with a reduction in slope (3.0–0.3°) from the shoreface to the inner shelf, is characterized by the cessation of debris surge in the troughs of ripples, the formation of a “rust layer” of microorganisms over the bedform surface, and a sediment color change caused by an increase in organic detritus. The sequence of bedforms and physical sedimentary structures observed in this system fits well with existing wave-generated (oscillatory) flow regime models. These models explain the observed sequences as a response to the degree of asymmetric flow created by shoaling waves. Distribution of biogenic structures and assemblages of infaunal organisms is influenced by the distance landward or seaward of fair-weather wave base. The overall relationships of this nearshore system can then be summarized as a hypothetical prograding stratigraphic sequence. The entire sequence is underlain by organic-rich, bioturbated, offshore deposits. Overlying the offshore is the planar-laminated sediments of the transition. Grading upward from the transition are the cleaner, planar-laminated, seaward slope deposits of the longshore bar. Above this, is a distinct erosional surface indicating the base of the massive to cross-laminated coarse sediments of the longshore trough. Capping the sequence are the cross- to planar-laminated, clean sands of the upper shoreface and foreshore.

An open ocean shoreface typical of long, wave-dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation. Sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents. Sand on the middle and lower shoreface, as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents. Storm events have been studied and modeled for the shoreface off Tiana Beach, Long Island. The dominant effect of coastal frontal storms is to cause significant shore-parallel bedload transport with important shore-normal secondary components. These storms tend to result in net offshore transport of sand removed from the beach and surf zone systems. The bedload transport during a storm is convergent on the shoreface leading to accretion. Most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf. Longer-term equilibrium can be maintained by slow return of sand up the shoreface during non-storm conditions. Annual and geologic time-scale budgets of shoreface sand transport and sedimentation yield equilibrium, net accretion or net deposition. The annual balance results from an integration of the event-scale bedload transport patterns and morphologic responses. These processes and responses have feedback mechanisms which stabilize the system over longer, but not geologic, time scales. Geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event-scale shoreface and transporting processes providing the mechanism to produce the changes in long-term morphology and sedimentation patterns. In the area of study, the long-term pattern is one of net shoreface erosion, and the permanent loss of sand to the shelf floor.