Delta lobe degradation and hurricane impacts governing large-scale coastal behavior,South-central Louisiana,USA

A large deficit in the coastal sediment budget, high rates of relative sea-level rise (~0.9 cm/year), and storm-induced current and wave erosion are forcing barrier shoreface retreat along the periphery of the Mississippi River delta plain. Additionally, conversion of interior wetlands to open water has increased the bay tidal prism, resulting in degradation of barrier islands due to inlet widening, formation of new inlets, and sediment sequestration at ebb-tidal deltas. Single-beam bathymetric surveys along a 165-km stretch of south-central Louisiana barrier coast, from Raccoon Point in Terrebonne Parish to Sandy Point in Plaquemines Parish, were conducted in 2006. These data, combined with historical bathymetry from three time periods (dating to the 1880s), provide a series of digital elevation models that were used to calculate sediment volumetric changes and determine long-term erosional-depositional trends. Dominant patterns during the 125-year period include (1) erosion of ~1.6 × 10⁹ m³ from the shoreface, forcing up to 3 km of shoreface retreat, (2) sediment deposition in coastal bights and at ebb-tidal deltas, and (3) a combined increase in tidal inlet cross-sectional area from ~41,400 m² to ~139,500 m². Bathymetric and shoreline change datasets separated by shorter time periods (sub-annual) demonstrate that these long-term trends are driven by processes associated with major hurricane impacts, and that rates of shoreface erosion are an order of magnitude greater during active hurricane seasons compared to long-term trends.     

Regional stratigraphic framework linking continental shelf and coastal sedimentary deposits of west-central Florida

A regional study of the Holocene sequence onlapping the west-central Florida Platform was undertaken to merge our understanding of the barrier-island system with that of the depositional history of the adjacent inner continental shelf. Key objectives were to better understand the sedimentary processes, sediment accumulation patterns, and the history of coastal evolution during the post-glacial sea-level rise. In the subsurface, deformed limestone bedrock is attributed to mid-Cenozoic karstic processes. This stratigraphic interval is truncated by an erosional surface, commonly exposed, that regionally forms the base of the Holocene section. The Holocene section is thin and discontinuous and, north or south of the Tampa Bay area, is dominated by low-relief sand-ridge morphologies. Depositional geometries tend to be more sheet-like nearshore, and mounded or ridge-like offshore. Sand ridges exhibit 0.5–4 m of relief, with ridge widths on the order of 1 km and ridge spacing of a few kilometers. The central portion of the study area is dominated nearshore by a contiguous sand sheet associated with the Tampa Bay ebb-tidal delta. Sedimentary facies in this system consist mostly of redistributed siliciclastics, local carbonate production, and residual sediments derived from erosion of older strata. Hardground exposures are common throughout the study area. Regional trends in Holocene sediment thickness patterns are strongly correlated to antecedent topographic control. Both the present barrier-island system and thicker sediment accumulations offshore correlate with steeper slope gradients of the basal Holocene transgressive surface. Proposed models for coastal evolution during the Holocene transgression suggest a spatial and temporal combination of back-stepping barrier-island systems combined with open-marine, low-energy coastal environments. The present distribution of sand resources reflects the reworking of these earlier deposits by the late Holocene inner-shelf hydraulic regime.     

Facies architecture of the mixed carbonate/siliciclastic inner continental shelf of west-central Florida: implications for Holocene barrier development

Sediment vibracores and surface samples were collected from the mixed carbonate/siliciclastic inner shelf of west–central Florida in an effort to determine the three-dimensional facies architecture and Holocene geologic development of the coastal barrier-island and adjacent shallow marine environments. The unconsolidated sediment veneer is thin (generally <3 m), with a patchy distribution. Nine facies are identified representing Miocene platform deposits (limestone gravel and blue–green clay facies), Pleistocene restricted marine deposits (lime mud facies), and Holocene back-barrier (organic muddy sand, olive-gray mud, and muddy sand facies) and open marine (well-sorted quartz sand, shelly sand, and black sand facies) deposits. Holocene back-barrier facies are separated from overlying open marine facies by a ravinement surface formed during the late Holocene rise in sea level. Facies associations are naturally divided into four discrete types. The pattern of distribution and ages of facies suggest that barrier islands developed approximately 8200 yr BP and in excess of 20 km seaward of the present coastline in the north, and more recently and nearer to their present position in the south. No barrier-island development prior to approximately 8200 yr BP is indicated. Initiation of barrier-island development is most likely due to a slowing in the Holocene sea-level rise ca. 8000 yr BP, coupled with the intersection of the coast with quartz sand deposits formed during Pleistocene sea-level highstands. This study is an example of a mixed carbonate/siliciclastic shallow marine depositional system that is tightly constrained in both time and sea-level position. It provides a useful analog for the study of other, similar depositional systems in both the modern and ancient rock record.     

Late Holocene chronology,origin, and evolution of the St. Bernard Shoals,Northern Gulf of Mexico,USA

Several shore-parallel marine sand bodies lie on the Louisiana continental shelf. They are Trinity Shoal, Ship Shoal, Outer Shoal, and the St. Bernard Shoals. These shoals mark the submerged positions of ancient shorelines associated with abandoned deltas. Three of these shoals are single elongate deposits. The fourth shoal, the St. Bernard Shoals, consists of a group of discrete sand bodies ranging in size from 44 to 0.05 km², 25 km southeast of the Chandeleur Islands in 15–18 m of water. The St. Bernard Shoals are stratigraphically above the St. Bernard delta complex, which was active 2,500–1,800 years b.p. Understanding the evolution of the St. Bernard Shoals is necessary to reconstruct the Holocene chronology of the St. Bernard delta complex and the eastern Louisiana continental shelf. For this study, 47 vibracores and 400 km of shallow seismic reflection data collected in 1987 across the Louisiana shelf were analyzed. In June 2008, 384 km of higher-resolution seismic reflection data were acquired across the study area and appended to the preexisting datasets. Vibracores were integrated with seismic profiles to identify facies and their regional distribution. Our results demonstrate that the deltaic package stratigraphically below the St. Bernard Shoals is chronologically younger than the northern distributaries, but derived from the same trunk distributary channel (Bayou la Loutre). The river eventually bypassed the northern distributaries, and began to deposit sediment further onto the continental shelf. After abandonment, the overextended delta lobe was rapidly transgressed, creating a transgressive shoreline that eventually coalesced with earlier shorelines in the region to form the Chandeleur Islands. The St. Bernard Shoals formed by the reworking of the relict distributary deposits exposed on the inner to mid shelf during and subsequent to shoreface ravinement.     

Stratigraphic framework of sediment-starved sand ridges on a mixed siliciclastic/carbonate inner shelf; west-central Florida

Seismic reflection profiles and vibracores have revealed that an inner shelf, sand-ridge field has developed over the past few thousand years situated on an elevated, broad bedrock terrace. This terrace extends seaward of a major headland associated with the modern barrier-island coastline of west-central Florida. The overall geologic setting is a low-energy, sediment-starved, mixed siliciclastic/carbonate inner continental shelf supporting a thin sedimentary veneer. This veneer is arranged in a series of subparallel, shore-oblique, and to a minor extent, shore-parallel sand ridges. Seven major facies are present beneath the ridges, including a basal Neogene limestone gravel facies and a blue-green clay facies indicative of dominantly authigenic sedimentation. A major sequence boundary separates these older units from Holocene age, organic-rich mud facies (marsh), which grades upward into a muddy sand facies (lagoon or shallow open shelf/seagrass meadows). Cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies (ravinement or sudden termination of seagrass meadows). The shelly sand facies grades upward to a mixed siliciclastic/carbonate facies, which forms the sand ridges themselves. This mixed siliciclastic/carbonate facies differs from the sediment on the beach and shoreface, suggesting insignificant sediment exchange between the offshore ridges and the modern coastline. Additionally, the lack of early Holocene, pre-ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively. Radiocarbon dating has indicated that these sand ridges can form relatively quickly (1.3 ka) on relatively low-energy inner shelves once open-marine conditions are available, and that frequent, high-energy, storm-dominated conditions are not necessarily required. We suggest that the two inner shelf depositional models presented (open-shelf vs. migrating barrier-island) may have co-existed spatially and/or temporally to explain the distribution of facies and vertical facies contacts.     

Subaqueous deltaic formation on the Atchafalaya Shelf,Louisiana

The Atchafalaya River in Louisiana shares the third largest drainage basin in the world with the Mississippi River. Sediment cores and seismic profiles were used to examine the development and impact on land accretion of an early-stage subaqueous delta accumulating on the shallow (<25 m water depth) continental shelf seaward of the Atchafalaya River mouths in the period (∼100 years) since the Atchafalaya has captured a significant fraction of the overall Mississippi discharge. The subaqueous clinoform is muddy (70–100% finer than 63 μm) and extends approximately 21–26 km seaward of the shell reef (to 8 m water depth) across the mouth of the Atchafalaya Bay, with a discontinuous, and, in places, mobile modern mud layer <20 cm thick covering a relict deltaic shoal area further seaward. The sigmoidal clinoform has a topset surface that steepens from east to west (1:2500 to 1:1600), a foreset with maximum slopes of about 1:550, and a limited bottomset region (<0.5 km wide). ²¹⁰Pb and ¹³⁷Cs geochronology show maximum sediment accumulation rates (>3 cm/year) correspond to the foreset and bottomset region, with rates decreasing to as low as 0.9 cm/year on the shelf topset region and its extension inside Atchafalaya Bay. Seven sedimentary facies are observed in the subaqueous delta, with differences created by degree of biological destruction of physical stratification, which is inversely related to sediment accumulation rate, and by the proximity of an area to the riverine sand source. There is a marked alongshore sediment dispersal pattern observed by the progressive winnowing of sand and coarse silt to the west. There is also a significant increase in shell content in Atchafalaya Bay relative to shelf facies. The resulting sigmoidal clinoform deposit (<3 m thick) more closely resembles strata geometries of subaqueous mud deltas associated with energetic systems (e.g., Amazon, Ganges–Brahmaputra, Fly), than it does the mature Mississippi delta 180 km to the east, albeit on a smaller scale and in shallow water.     

Accelerated relative sea-level rise and rapid coastal erosion:: testing a causal relationship for the Louisiana barrier islands

The role of relative sea-level rise as a cause for the rapid erosion of Louisiana's barrier island coast is investigated through a numerical implementation of a modified Bruun rule that accounts for the low percentage of sand-sized sediment in the eroding Louisiana shoreface. Shore-normal profiles from 150 km of coastline west of the Mississippi delta are derived from bathymetric surveys conducted during the 1880s, 1930s and 1980s. An RMS difference criterion is employed to test whether an equilibrium profile form is maintained between survey years. Only about half the studied profiles meet the equilibrium criterion; this represents a significant limitation on the potential applicability of the Bruun rule. The profiles meeting the equilibrium criterion, along with measured rates of relative sea-level rise, are used to hindcast shoreline retreat rates at 37 locations within the study area. Modeled and observed shoreline retreat rates show no significant correlation. Thus, in terms of the Bruun approach, relative sea-level rise has no power for hindcasting (and presumably forecasting) rates of coastal erosion for the Louisiana barrier islands.     

Facies, internal structures and sequences of modern Gironde-derived muds on the Aquitaine inner shelf, France

Seventy cores from the Aquitaine continental shelf were examined using radiographic and grain-size techniques in order to describe the sedimentary structures of the muddy deposits, and to evaluate their depositional processes. Four lithofacies are identified in this fine-grained deposit: (a) homogeneous silty sand, (b) interbedded homogeneous mud and sand, (c) silty-clayey mud, and (d) mottled mud. They show a logical pattern in relationship to the water depth and the distance from the coast.

Primary structures are present particularly in the landward and central portion of the mud fields, where the sediment is organized into sequences with a sharp-based erosional contact, overlain by a fining-up succession (centimetre to decimetre scale). The beginning of each of these is characteristic of a high-energy storm event, which is common on this shelf. The settling of suspended fine sediment corresponds to the flood estuarine discharge during quiet periods. Primary sedimentary structures decrease in the distal area where the muddy sediment is frequently reworked by infauna. Finally, primary structures and their preservation depend on the relative magnitudes of surface waves, storms, infaunal mixing and fluvial sediment deposition rates (i.e. floods).     

海州湾岸线蚀淤演变及预测

基于2013—2021年间海州湾18期Lansat 8遥感影像,利用海岸线类型多样性指数、岸线变化率（EPR）和净海岸移动量（NSM）对海州湾各类型岸线蚀淤演变情况进行分析,并基于Prophet时间序列预测模型对2025年岸线进行定量预测。结果表明,9年间基岩岸线整体较稳定;琴岛栈桥到临洪河口淤泥质岸线不稳定,岸线明显向海淤积;砂质岸线整体较稳定,无明显蚀淤倾向。预测2025年海州湾淤泥质岸线呈向海延伸趋势,临洪河口附近岸线呈向海延伸趋势,其余岸线均无明显淤蚀变化,较为稳定。     

Sediment retention at the Changjiang sub-aqueous delta over a 57 year period,in response to catchment changes

The growth of a river delta system is controlled mainly by fluvial sediment discharge and sediment retention in the deltaic areas. In the present study, we attempt to define a sediment retention index, R, and its relation to the deposition rate of the delta. Based upon two assumptions that the amount of the sediment that escapes from the deltaic areas, Q_E, is stationary with minor fluctuations, and that there is a linear relationship between the deposition rate averaged over the sub-aqueous delta (D_av) and the deposition rate at accretion sites within the delta (D_R), the changes in the accretion/erosion patterns of the Changjiang sub-aqueous delta during the period of 1951–2007, in response to river sediment discharge changes, are analyzed. The results show that the sediment retention index can be related to the deposition rate of the sub-aqueous delta; the spatial-temporal distribution pattern of the deposition rate reveals the behaviour of sediment retention of a delta system. For the Changjiang sub-aqueous delta, fluvial sediment discharge data, together with Pb-210 based deposition rates, provide useful information on sediment retention. Changes in the sediment retention index and the accretion/erosion patterns of the sub-aqueous delta have taken place in response to river input changes. In order to improve our understanding of the processes associated with estuarine sediment retention, sediment cores with sufficient spatial coverage may be collected and analyzed to establish accurate Q_E–R and D_av–D_R relationships. In combination with numerical modeling of sediment transport, these relationships form a basis for the analysis of sediment retention mechanisms.     

Sequence stratigraphy and depositional architecture of the Pearl River Delta system,northern South China Sea: An interactive response to sea level,tectonics and paleoceanography

Using a combined dataset including 3D seismic volumes, 2D profiles and 127 industrial wells, this study systematically investigated sequence stratigraphy and depositional architecture of the Pearl River Delta system (PRDS) during the Middle Miocene. In total, six stratigraphic sequences (SQ1 to SQ6) were recognized for the Hanjiang Formation, each of which could be further subdivided into a transgressive systems tract (TST) and a regressive systems tract (RST) according to a T-R sequence stratigraphic model. Seismic geomorphologic approaches were then conducted to interpret and map the key depositional elements, including fluvial channel systems, river mouth bars, longshore bars, shelf sand ridges and shelf sand sheets. After a detailed construction of the paleogeography for each of the twelves systems tracts, it was found that the types, geometries and depositional regimes of PRDS significantly altered at ca. 13.8 Ma. Before ca. 13.8 Ma, the PRDS were dominated by well-developed fluvial systems and an overall lobate shape, indicating a fluvial-dominated process. However, after 13.8 Ma, the whole PRDS began to form enormous shoreline-parallel depositional elements such as longshore bars, shelf sand ridges and shelf sand sheets, indicating dominant shore-parallel regimes. Besides, the whole deltaic system displayed obvious southwest deflection in map view after 13.8 Ma.Detailed analysis showed that this sudden change in the evolution of the PRDS could be ascribed to an interactive response to several factors. At ca. 13.8 Ma, the sea level began to rapidly rise and caused the fluvial energy to decrease, which was likely to lead to the diversion of the fluvial systems. Besides, the gradual uplift of the Dongsha Rise resulted in the raised shelf topography in the east region, thus confining the fluvial channels to flow southwestward. What's more, a few key paleoceanographic events, including the reglaciation of the Antarctic ice-sheet and the shoaling of the Pacific-Indian Ocean Seaway, might have contributed to the intensification of the southwesterly flowing paleocurrent along the northern South China Sea, thus triggering the delta asymmetry and deflecton of the PRDS after 13.8 Ma.     

Shoreline changes and beach-sand sorting along the northern Sinai coast of Egypt

 Changing shoreline positions along the Sinai coast of Egypt were determined by comparing aerial photographs and historical charts with present-day conditions. The analyses identify longshore patterns wherein erosion along a protruding stretch of the coast gives way to accretion in an adjacent major embayment. This pattern defines two coastal subcells consisting of source/sink couplets. There is a general correspondence between the mineral variation, grain sizes of beach sand, and the patterns of shoreline changes. Associated with erosion/ accretion shoreline change is a selective transport of different minerals according to their densities and grain sizes. Two heavy-mineral groups were obtained by applying Q-mode factor analysis on the heavy-mineral data. These two groups are influenced by transport processes, including sediment provenance from different sources: eroded Nile delta west of Sinai, relict sediments from the former Nile distributaries, and sediment supply by land valleys and from wind-blown sand. Received: 2 June 1995 / Revision received: 29 May 1996     

Depositional history of the Lagniappe Delta,northern Gulf of Mexico

The northern Gulf of Mexico continental shelf is characterized by superimposing deltas. One such delta, informally named Lagniappe, extends east of the Mississippi Delta from mid-shelf to the continental slope. This late Wisconsinan delta is adjacent to, but not associated with the Mississippi Delta complex: the fluvial source was probably the ancient Pearl and/or Mobile Rivers. The fluvially dominated Lagniappe Delta is characterized by complex sigmoid-oblique seismic-reflection patterns, indicating delta switching of high-energy sand-prone facies to low-energy facies. The areal distribution and sediment thickness of the delta were partially controlled by two diapirs.     

Beach and shoreface response to sea-level rise: Ocean City, Maryland, U.S.A.

Sea-level is one of the principal determinants of shoreline position. Sea-level rise induces or accelerates on-going shore retreat since deeper water decreases wave refraction, thus increasing littoral drift, and also allowing waves to arrive closer to shore before breaking. Tidal records from the US East and Gulf coasts indicate a relative sea-level rise of approximately 0.3m has occurred during the past century. Concomitantly, erosion has been prevalent almost everywhere along these sandy shorelines. Ocean City, Maryland, was selected as a case study site to determine historical shoreline changes and to project future beach erosion based on accelerated rates of sea-level rise. During the past 130 years (1850–1980), this shore has retreated approximately 75m and many highrise buildings at Ocean City are now threatened during storm conditions. Accelerated sea-level rise is expected to increase the rate of retreat by a factor of 2 to 5 based on analysis of present trends. This significantly reduces the planning time available for mitigating the hazard and increases the vulnerability of this urbanised barrier through time.     

Geoacoustic character,sedimentology and chronology of a cross-shelf Holocene sediment deposit off Cabo Frio,Brazil (southwest Atlantic Ocean)

The Cabo Frio region in the state of Rio de Janeiro, southeast coast of Brazil, is characterized by a local coastal upwelling system and converging littoral sediment transport systems that are deflected offshore at Cabo Frio, as a consequence of which a thick cross-shelf sediment deposit has developed over time. To investigate the evolution of this muddy deposit, geophysical, sedimentological and geochemical data from four sediment cores (3.8–4.1 m in length) recovered in water depths between 88 and 141 m were analyzed. The high-resolution seismic data show variable sediment thicknesses ranging from 1 to 20 m, comprising two sedimentary units separated by a high-impedance layer at a depth of about 10 m below the seafloor at the coring sites. According to the available age datings, the upper sedimentary unit is late Pleistocene to Holocene in age, whereas the lower unit (not dated) must, by implication, be entirely Pleistocene in age. The boomer-seismic reflection signal can be divided into three echo-types, namely transparent (inner shelf), stratified (middle shelf) and reflective (outer shelf), each type seemingly related to the local sediment composition. The upper 4 m of the upper sedimentary unit is dominated by silty sediment on the middle shelf, and by upward-fining sediments (silty sand to sandy silt) on the inner and outer shelf. The downcore trends of P-wave velocity, gamma-ray density and acoustic impedance are largely similar, but generally reversed to those of water and organic carbon contents. Total organic carbon contents increase with decreasing mean grain size, periodic fluctuations suggesting temporal changes in the regional hydrodynamics and primary productivity fuelled by the local upwelling system. The reconstruction of sedimentation rates in the course of the Holocene is based on 35 AMS age datings of organic material recovered from variable downcore depths. These range from a maximum of 13.3 cm/decade near the base of the inner shelf core (7.73–7.70 ka BP) to generally very low values (<0.11 cm/century) over the last thousand years in all cores. Over the last 6 ka there appear to have been three distinct sedimentation peaks, one between 6 and 5 ka BP, another between 4 and 3 ka PB, and one around 1 ka BP. Due to different time intervals between dates, not every peak is equally well resolved in all four cores. Based on the similar sedimentology of the inner and outer shelf cores, an essentially identical sedimentation model is proposed to have been active in both cases, albeit at different times. Thus, already during the last glacial maximum, alongshore sediment transport was deflected offshore by a change in shoreline orientation caused by the Cabo Frio structural high. The source of terrigenous material was probably a barrier-island complex that was subsequently displaced landward in the course of sea-level rise until it stabilized some 6.5 ka BP along the modern coast.     

Marsh expansion at Calaveras Point Marsh, South San Francisco Bay, California

Studies of shoreline progradation along low-energy vegetated shorelines have been limited, as these environments are generally experiencing erosion rather than deposition, with extreme erosion rates frequently found. This study examined yearly changes along a vegetated shoreline at Calaveras Point Marsh, South San Francisco Bay, California, using aerial photography, to determine the roles of climatic, watershed, and coastal process in driving shoreline changes. In addition, sediment accumulation was monitored on a yearly basis at 48 locations across the marsh to determine the role of geomorphic factors in promoting accumulation. Calaveras Point Marsh was found to have expanded from 49.26 ± 5.2 to 165.7 ± 4.7 ha between 1975 and 2005. Although the rate of marsh expansion was not positively correlated with yearly variability in precipitation, local streamflow, delta outflow, water level observations, population growth, or ENSO indices, marsh growth was greater during years of higher than average temperatures. Warmer temperatures may have promoted the recruitment and growth of Spartina foliosa, a C₄ grass known to be highly responsive to temperature. Other factors, such as the formation of a coastal barrier, a recent change in the location of the mouth of the Guadalupe River, and channel readjustment in response to diking are credited with driving the bulk of the marsh expansion. Sediment accumulation was found to be high closest to channels and to the shoreline, at low elevations and in recently vegetated marsh. Globally, the pace of sea level rise exerts the primary control on wetland development and persistence. However, at local geographic scales, factors such as tectonic events, modifications to natural sediment transport pathways or land use changes may overwhelm the effects of regional sea level rise, and allow for wetlands to develop, expand and persist despite rapid sea level rise.     

辽河拗陷东部凹陷南部地区古近系沉积体系与储层评价

Detailed studies on a number of core sections,well logs and seismic date of the paleogene systems of the southern part of eastem sag in Liaohe Depression revealed theat six sedimentary systems,i,e.delta,lake,fan delta,braided river,delta,river and alluvial fan,were distinguished,The sedimentation in the studied area remarkably controlled reservoir and the variability of sedimentary facied caused the diversity of reservior sand bldies and the inhomogeneity of reservoir properties plane distribution;The best reservoir properties are the sand bodies of deltaic front and braided-river deltaic front;the better are the sand bodies of braided-river deltaic plain,deltaic front,braided river and meandering river;the medium reservoir properties are the sand bodies of delta plain,the fan-delta front,the alluvial-middle fan,beach-bar and turbidite fan;the wores are the sand bodies of upper fan and lower fan of alluvial fan,alluvial plain.The favorable sedimentary facies belt controlled the distribution of favorable reservoir and it was an important evidence for prediction favorable stratigraphiv reservoir.     

Sea-level, sediment supply and coastal changes: Examples from the coast of Ireland

Sediment supply and pre-existing shoreline morphology are crucial factors in controlling coastal changes due to sea-level rise. Using examples from both southeast and northeast Ireland, it can be shown that sea-level change may trigger a sequence of events which leads to both static and dynamic shoreline equilibrium. Cliff erosion and longshore sediment movement in east Co. Wexford has led to injection of sediment onto the shelf, and the growth, under both wave and tide regimes, of linear offshore shoals. These shoals now control the pattern of shoreline erosion and provide a template for possible stepwise evolution of the coast under any future sea-level rise. In contrast, the nearby coast of south Co. Wexford comprises a series of coarse clastic barriers moving monotonously onshore, via overwash processes. Here the behavior of the barrier is conditioned by the antecedent morphology of both the beach face and stream outlet bedforms. Finally, the rock platform coast of Co. Antrim presents a far more resistant shoreline to incident marine processes, yet even here there is strong evidence of present process control over so-called ‘raised’ platforms and embayments. It is concluded that coastal sediment supply and dynamics, together with coastal morphology and its interaction with waves, present a far more complex variety of sea-level indicators than is normally acknowledged.     

Reduction of sand demand for shore protection

Beach nourishment is an environmentally preferred method of shore protection, but the annual sand requirement may lead to substantial maintenance costs. The shoreline processes, involving the surf zone, beach and dune, are reviewed with the aim of reducing the annual sand requirement of eroding shorelines. It is shown that surf zones with equilibrium profiles, on which the wave energy conversion is evenly distributed across the surf zone, from experience for given conditions indicate least loss of sand. On steep, eroding shorelines it may be difficult to establish an equilibrium profile. For such cases, the use of perched surf zones is recommended, which are supported at the seaward limit by an underwater sill. For reduction of littoral transport, the use of pervious pile groynes is recommended. These are arguably more efficient than impervious groynes. The sand loss from a usually dry beach by raised water levels is shown to be a function of the beach slope and is least when the storm waves at raised water levels do not cut an erosion escarpment. The loss of sand from a dune by infrequent severe storm tides can be prevented with the aid of a built-in membrane. These sand losses are usually large and constitute an uneconomic use of this sand resource. The proposed concepts and measures are linked to existing knowledge, augmented by data from the large wave flume (LWF) in Germany and field data from the North and Baltic Sea coasts.