Abstract There are many user interests on coasts and in estuaries, including economic activities (ports, harbours, navigation, fishing, mineral extraction), recreation (bathing, walking, sailing, fishing, birdwatching), flood defence, water quality, nature conservation, and conservation of the historical and archaeological heritage. Often these interests are conflicting, and managers frequently have to attempt a compromise or make hard decisions based on a prioritized course of action which reflects economic, political and legal constraints (see, for example, Barrett 1992 ; Kay & Alder 1999 ; Flemming 2000 ). Often the decisions are taken on the basis of inadequate background information and a poor understanding of the functioning of the invariably complex coastal system under consideration. In a world of increasingly rapid technological and economic development, sea-level rise, and possible global climate change, central tasks facing the coastal and estuarine manager are to predict and manage change, undertaken against a background of constantly moving goalposts. There is an urgent need for a much better framework of background environmental data and more effective and reliable management tools, founded on sound scientific understanding, which can provide the necessary guidance and basis for policy formulation. Although, these needs have been recognized, and some progress has been made in the past few years, an adequate suite of such tools and frameworks for environmental monitoring are still some way off.

Abstract Estuarine fronts may develop in several locations, across the water body as transverse, halocline-related features, as overbank spills, or where tidal flats release waters into principal tidal channels. In many estuaries longitudinal fronts originate at headlands or are associated with major sandbanks (Bowman 1988 ). Commonly a front separates a near-shore water mass from that of the main flow of tidal waters. In the marginal waters flows are slower than in the main channels, and suspended sediments and pollutants released to these marginal zones do not mix freely with the principal tidal waters entering and leaving the estuary. These nearshore waters also often differ in temperature from the channel waters (Anderson et al. 1992 ). It is suggested that the linear convergent frontal systems provide the ideal sites for the accumulation of sediment, and exert some control on the distribution of longitudinal estuarine sand banks. Some, but not all of these are associated with headlands. The geomorphological evolution of the sand bank systems within the upper and middle reaches of the Tay Estuary, Scotland, are discussed in relation to present and past locations of longitudinal fronts. The Middle Bank, off Dundee, is seen to occur between the lines of longitudinal fronts formed during the flood and ebb phases of the tide. The Naughton Bank, off Balmerino is related to an ebb phase headland-induced flow separation. In the seaward reaches longitudinal fronts locate the outer margins of the tidal flats and become axially convergent in the Tayport-Broughty Ferry narrows.

Abstract Salt marsh and mud flat sedimentation in the Wadden Sea and in similar depositional regions is usually dependent on the net import of fine-grained sediments from adjacent marine environments. This net import takes place as a result of several processes such as settling lag and scour lag. This paper utilizes a database comprising time series of tidal velocity and turbidity in the Grådyb tidal area of western Denmark as the basis of a simple conceptual model which describes the transport, deposition and resuspension of fine-grained material in the area. The results demonstrate that: (a) grain sizes close to the sand/silt boundary are most sensitive to lag effects; (b) scour lag is much more important than settling lag; (c) raised temperatures enhance the net-lag effect for silt with increasing importance for finer grain sizes; (d) with increased suspended concentrations, the time it takes to resuspended the material deposited at slack water (the resuspension lag) is of increasing importance for the net-lag effect.

Abstract Near bottom current measurements have been compared with sonographs revealing a variety of subtidal dune geometries at eight stations in the middle reaches of the macrotidal Tay Estuary, Scotland. At six stations, dune asymmetries did not support the tidal dominance expressed in terms of maximum or average current speeds. Determination of bottom tidal current dominance according to the length of time during which a speed of 0.5 ms −1 was exceeded, as a proxy for the inequality of the total ebb and flood tide bedload sediment transports, provides a better, but not perfect, correlation with sonographs. Other controls on dune asymmetry and reversal are height, sediment discharge rate and bottom current velocity fluctuations. The study has shown that bedload transport processes and pathways in this relatively small (c. 8 km 2 ), dynamic part of the estuary are far more complex than previously inferred and near bed flows do not simply correspond with the surface water circulation pattern. Neither sonographs nor current data alone are adequate to gain an understanding of subtidal bedforms in such an environment.

Abstract A field study was conducted on a section of Allen Creek marsh in the Bay of Fundy to examine changes in suspended sediment circulation and deposition over single tidal cycles. Net flow velocity, suspended sediment concentration and sediment deposition were measured over 13 individual tidal cycles during the summer of 1998. A vertical array was deployed in the low marsh region, consisting of three pairs of electromagnetic current meters, OBS tm probes and one pressure transducer. Sediment deposition was measured using full-cycle sediment traps. The temporal distribution of sediment deposition was monitored using sequential sediment traps exposed at different tidal stages. The data suggest that sediment deposition on the marsh surface is primarily controlled by the interaction of water flow, marsh morphology and vegetation. The highest amounts of sediment are deposited during conditions of high suspended sediment concentration and low wave activity, particularly when the relative roughness of the vegetation is the highest. Loss of suspended sediment from the water column was shown to be correlated with the sediment trap data; however, predictions of sediment deposition based on the variation in suspended sediment concentration were found to be valid only for conditions with less than 0.15 m high waves. For higher wave conditions, the use of suspended sediment loss calculations should be used primarily for estimating the relative rather than absolute values of deposition on the marsh surface.

Abstract Measurements of velocity and suspended sediment concentration were carried out in a saltmarsh tidal creek network in the Cumberland Basin, Bay of Fundy, Canada. The study area was located on the NW shore of the basin in part of an undyked marsh that is about 200 m wide with a simple reticulate creek network. The area is macrotidal with spring tides greater than 12 m and suspended sediment concentrations in the basin characteristically range from 150–300 mg l -1 . The purpose of the study was to determine vertical and along channel variations in these two parameters over individual tidal cycles and to use these data to assess the role of the tidal creeks in the import and export of water and sediment from the marsh surface. Measurements using a vertical array of co-located electromagnetic current meters and OBS probes for measuring suspended sediment concentration were carried out over four spring tides at a cross section in the lower part of Middle Creek. Six sets of measurments were carried out at four locations along the length of the creek, a distance of about 200 m over six tides ranging from spring to neap. Maximum mean velocities measured over sampling times of eight minutes did not exceed 0.1 m sec −1 in Middle Creek and 0.15 m sec -1 in Main Creek. Transient high velocities associated with the overbank flows were weakly developed as a result of the absence of significant levees or embankments on the marsh surface. Suspended sediment concentrations in the creek generally decreased steadily over the period of inundation. Flow across the marsh margin occurred simultaneously with the achievement of bankful conditions and the creeks themselves appear to play a relatively minor role in the movement of water and sediment onto and out of the marsh. Despite the fact that the marsh surface is still low in the tidal frame and active sedimentation is still occurring, the low flow velocities and observations in the field suggest that the tidal creek network is unable to flush itself and that it is contracting.

Abstract One method of studying the functional morphology of estuaries and the potential implications of developments is presented. The approach makes use of a hybrid modelling approach to predict the state of the estuary relative to its present day target steady state. The technique has now been applied to a number of UK estuaries, which allows the variability between systems to be illustrated. For one of the estuaries a range of modifications has been examined to try and identify how the functional behaviour of the system might be affected (e.g. remove flood banks) and these are discussed. Experience to-date has shown that this approach helps to develop an understanding of gross system behaviour and how this might change in the future. It does not provide detailed predictions for specific locations within the estuary, although the role of particular components in the system is highlighted.

Abstract From the Somme estuary to Belgium, much of the French coast is characterized by aeolian dunes, sand-choked estuaries and nearshore sand banks. The lack of sand-bearing rivers in this area and the abundance of sand in the English Channel point to the latter as the source of this important sandy accumulation. A comparison of patterns of nearshore and coastal accumulation with results from studies of the hydrodynamics and marine sand transport pathways suggests long-term drift of sand towards the French coast and the North Sea in response to tidal flows and meteorological forcing. This has occurred through sand bank migration onshore, and sand transport alongshore in a pathway hugging the French coast. From this tide-driven ‘conveyor belt’, fine sand moved onshore to form aeolian dunes, while sand of all sizes has accumulated as thick estuarine fill. This mode of Holocene coastal development emphasizes the joint action of tidal currents, storm waves and wind activity, within an overall framework of tidal dominance in this macrotidal setting.

Abstract The comparison of aerial photographs of eroding coastal dunes located between Dunkerque (Northern France) and the Belgium border revealed that the retreat rate of the dune front increased between 1957 and 1988. Analyses of hourly water levels from the Dunkerque Harbour tide gauge showed an increase in the frequency of high water levels associated with storm surges during the same period. Significant wave heights that could be generated during these high water level events were computed according to a wave hindcast model and using wind data collected at Dunkerque. These analyses show an increase in storm magnitude and frcquency during the last two decades of the study period, and suggest a strong relationship between dune front erosion and frequency of storm surge conditions. Since relative sea-level is rising in the southern North Sea, coastal dunes will probably be more frequently reached by storm waves in the future. Consequently, more severe coastal dune erosion may take place during the next decades, increasing the risk of flooding of coastal lowlands.

Abstract The Authie is a rapidly infilling macrotidal (mean estuary-mouth spring tidal range = 8.5 m) estuary in Picardy, northern France, whose mouth is affected by strong tidal currents and wind waves generated in the English Channel. The estuary cuts across a major sand dune barrier and has been sourced by sand derived from offshore and alongshore, as well as from recycling of the aeolian dunes lining its north bank. Sand released by the severe erosion of these north bank dunes is temporarily stored on the beaches. A small fraction of the sand is back-cycled into the dunes via blowouts. The rest is transported towards the inner estuary where it forms longitudinal aeolian dune ridges and sand sheets that are ultimately recycled into sandy-muddy intertidal flats that develop into salt marshes. The erosion of the dunes lining the north bank of the estuary represents a morphodynamic adjustment to concentration of the tidal flux against this north bank by massive accretion and progradation of a south-bank sand platform. This erosion contributes in giving a funnel-shaped estuary mouth and probably in accommodating the tidal prism following large-scale reclamation of the inner estuary. The estuary-ward recycling of aeolian dune sand enhances overall accretion of the estuary whose ultimate fate is complete silting up in the decades to come.

Abstract The nature and environmental significance of variations in sedimentological parameters of a restricted-fetch lake coastal system (Milarrochy, Loch Lomond) are described in the context of climate change. Grain size characteristics of the beach, streams, cliffs and nearshore/offshore sedimentary environments are distinct, with variability being related to sediment supply, beach altitude and process conditions. Beach grain sizes range from silt to cobble, and are predominantly rounded discs and blades. There is an overall trend of offshore fining with increasing depth, beyond the mixed surf zone and clear limit of coarse sediment (coarser than -1 phi), resulting from dominant shore-normal process trends. Seasonal trends of water level fluctuation, sediment discharge and transfer from river to beach are important controls on local scale variability. The broader significance is that local physiography, sediment characteristics and supply strongly influence beach sedimentology and morphological response, even in the context of larger scale climate change. The record of sedimentological variability detailed here is significant for beach management projects and a better understanding of lake sedimentary facies within the Quaternary.

Abstract Acquisition of high resolution data regarding the stratigraphy and internal structure of coastal sedimentary sequences is becoming increasingly important in many sedimentological, geomorphological and geoarchaeological studies. Such information is usually obtained from the logging of field exposures, shallow trenches and cores. However, ground-penetrating radar (GPR), a relatively new and rapidly developing non-invasive geophysical technique, may also aid such investigations in certain coastal settings, providing additional, complimentary and often unique data sets. The technique is based on the transmission, reflection and reception of high frequency electromagnetic (radar) waves, with reflections occurring in the subsurface due to the varying electrical properties of the sediments. Such reflections can occur due the presence of primary sedimentary structures, lithological/material changes or water content changes. Examples presented from the UK indicate that the technique can accurately delineate the stratigraphy and internal sedimentary structure of coastal barriers, spits and strandplains, both above and below a fresh groundwater table. Sand and/or gravel-dominated beach-dune systems on moderate to high wave energy, macrotidal coasts appear to provide optimum settings for GPR deployment. In addition, the technique also has the potential to locate, map and provide stratigraphic context for a wide range of archaeological features that are commonly found in such coastal environments.

Abstract The coastal dune system of the Aquitaine region, SW France, is the largest in Europe. At the present time the dunes are mostly stabilized by forest vegetation which is largely the product of dune stabilization schemes undertaken since the late 18th century. Much of the shoreline is currently eroding at rates of 1–2 ma −2 , which are likely to increase if predictions of accelerated sea-level rise and increased storminess are correct. The sources of the beach and dune are poorly understood, and need to be identified in order to assess the sand budgets and likely dynamic response of the dune systems to changes in environmental forcing factors. This paper presents the results of an investigation to characterize the beach and aeolian sand in the region, and to identify its origin. The dune sands were found to be texturally and compositionally similar to the Quaternary Sable de Landes which occurs landward of, and partially beneath, the coastal dune belt. The results suggest that marine, aeolian and local fluvial reworking of the Sable de Landes has provided the main source of coastal dune sand, although marine erosion of Pleistocene deposits exposed in the coastal cliffs of the Medoc has made a secondary contribution.

Abstract The Engineering & Physical Sciences Research Council research site at Bothkennar is located on former intertidal mudflats adjacent to the Forth estuary, which were reclaimed for agricultural use around the year 1784. A desiccated surface crust has developed in the 200 years following the reclamation, largely in response to the introduction of artificial drainage. Its formation has involved both compaction and material translocation, due to effective stress changes and to infiltration and geochemical alteration respectively. At first, new deposits accumulated in an artificial tidal lagoon and underwent autocompaction under saturated conditions. The subsequent introduction of field drains and cultivation then induced suction stresses due to evapotranspiration, leading to overconsolidation by around 150–200 kPa. These processes have also been associated with the development of an immature soil profile to a depth of around 0.7 m. The infiltration of fresh water has caused both desalination and the eluviation of clay particles. There is also a general rise in pH and fall in Eh with depth, which is associated with leaching and the downward translocation of DCB (dithionate-citrate-bicarbonate) soluble iron compounds. We conclude that the physical development of the crust was rapid and is now largely completed, whereas the chemical development is not yet completed and thus the soil profile remains immature.

Abstract The Marine Pollution Control Unit of the Department of Transport are at present testing the suitability of burial and landfarming of oily residues in sandy coastal environments as an alternative to landfill sites. The tendency for oil related compounds to sorb to sediments (and hence to affect their cohesiveness) has been extensively investigated, but this has not involved or permitted the ‘observation’ or measurement of advection/diffusion processes or the breakdown of these residues within sediments. MRI, which is a multidimensional technique allowing the position of nuclei (most commonly protons) to be located within a known volume of substrate, for example sediment, provides a means of monitoring the change in position and the eventual breakdown of oil within sediments, thus offering a method of assessing the harming potential of oils in near-shore environments. Two dimensional (2D) and three dimensional (3D) MRI analysis of the movement of oil in estuarine sediments show that, using appropriate parameters, movement of the oil can be both observed and quantified. To aid quantification a sample holder fabricated from polyvinylsiloxane, an inert material visible in magnetic resonance images has been used as an internal intensity standard. The results show the great potential of MRI in studying protonated contaminants in these materials, notwithstanding the presence of paramagnetic species in estuarine sediments, which might distort the image. Sediments studied thus far have been collected from the Tay Estuary, NE Scotland.

Abstract The factors which influence the morphology, drainage characteristics and erosion resistance of saltmarshes are of major interest from the standpoint of flood defence and habitat recreation. Sedimentological characteristics, including grain size distribution, mineral composition and pore fluid chemistry arc all highly important. Of particular importance in muddy marshes is the nature of the clay mineral assemblage and dissolved cations present in the pore fluids. In marshes which are deficient in detrital calcium carbonate, such as those in Essex, UK, sodium ions dominate the exchange sites on clays, leading to the formation of thick water films around the clay particles and slow rates of sediment consolidation. This, in turn, causes low erosion resistance and a tendency for the development of highly dissected marsh morphology. Calcium and magnesium-rich marsh sediments, on the other hand, allow these ions to replace sodium in exchange sites, leading to more rapid dewatering and consolidation. Erosion resistance is thereby enhanced and such marshes tend to be characterized by low drainage densities and a low ratio of bare mud to vegetated surface area. The possibilty of engineering the erosion resistance and morphology of marshes through chemical treatments requires further investigation.

Abstract Simultaneous measurements of vertical accretion from marker horizons and marsh-elevation change from sedimentation-erosion tables (SET) were made in selected marshes along the East Anglian coast of the UK in order to address the following objectives: (1) to ascertain the validity of treating accretion measurements obtained within tidally dominated, minerogenic saltmarshes as equivalent to surface elevation changes; (2) to explore the implications, in terms of physical and biological processes, of discrepancies between separately measured vertical accretion and elevation change within contrasting marsh types. Data were collected from several marsh environments at Scolt Head Island and Stiffkey on the North Norfolk coast and at an experimental managed realignment project near Tollesbury, Essex. Scolt Head Island was selected for its long-term datasets of marsh accretion, Stiffkey for its contrasting open coast-back barrier settings, and Tollesbury for its experimental management, in order to illustrate the potential application of the SET method and evaluate the relationship between vertical accretion and elevation change in a variety of marsh settings. The relationship between vertical accretion and elevation change varied widely among marsh settings of different age and height (within the tidal frame) at Scolt Head Island and Stiffkey. Rates of vertical accretion and elevation change were similar in the older and mid-height settings on Scolt Head Island, indicating control of elevation change by surface accretionary processes (e.g. sediment deposition). However, subsurface processes controlled elevation at three of the marsh sites. Spartina Marsh, the youngest and lowest of the back barrier settings at Scolt Head Island, exhibited continuous shallow subsidence (vertical accretion greater than elevation change) over a 4-year period, implying that compaction controls elevation change. In the upper part of Hut Marsh and the interior of the Stiffkey marshes, elevation change exceeded vertical accretion suggesting that subsurface processes (e.g. organic accumulation) controlled elevation in these settings. Surface accretionary processes control elevation change in both the highly dynamic, outer marsh at Stiffkey and the low, restored marsh at Tollesbury. Despite the occurrence of shallow subsidence, all sites gained elevation at an annual rate comparable to that of sea-level rise. In summary, the SET provides the means to critically evaluate the influence of vertical accretion measures on elevation and represents an improved method by which to evaluate the vulnerability of a marsh to sea-level rise.

Abstract The continuous, progressive, irreversible and asympototic processes of sediment autocompaction play a significant but so far largely neglected role in determining the co-evolving character of Holocene landscapes and sedimentary sequences formed in coastal marshlands. Autocompaction ensures that actual total sediment deposition rates are always greater than the rate at which sea-level rise creates accommodation space. High rates of autocompaction help to foster resource-rich, mineralogenic tidal marshes that can be readily exploited by humans from neighbouring higher ground, for example, dryland areas, or locations within the marshland where peat formation had persisted sufficiently late that domai, raised bogs had not yet completely collapsed. Subsequent autocompaction may bring about a significant inversion of relief. The general effects of autocompaction are a high degree of vertical stratigraphic distortion and displacement amounting to as much as a few metres, depending on the depth to ‘basement’, the lithologies present, and their order of deposition. Autocompaction results in inaccurate sea-level curves when based on intercalated peats, inaccurate rates of sea-level change when calculated on a bed-averaged basis, and inconsistent age-altitude relationships among archaeological sites preserved in coastal deposits. The challenge is to predict/retrodict autocompaction in Holocene coastal lowlands, in order to better understand sequence development, the evolution of surface environments, topography and landscape, and the constraints placed upon (and opportunities presented to) human communities living in these contexts.

Abstract This paper presents the results of an investigation into the Holocene depositional history of Southampton Water, southern England. A three phase history of estuary development is proposed. Between c. 7500 and 5000 BP (8200 to 5700 cal. a BP), mean sea-level rose rapidly from c. –9 m to –4 m OD . During this interval thin basal peats which developed in present outer estuary locations were inundated and the area of intertidal and subtidal environments within the estuary expanded. Relative sea-level (RSL) rise began to slow between 5000 and 3000 BP (5700 and 3200 cal. a BP) and a phase of saltmarsh and freshwater peat accumulation occurred. In this interval freshwater peat-forming communities extended outwards and seawards across former saltmarsh and mudflat environments and caused a reduction in the extent of the intertidal area within the estuary. During the late Holocene there was a switch to renewed minerogenic sedimentation as most of the freshwater coastal wetlands of Southampton Water were inundated. This tripartite model is broadly applicable to the Thames and the Severn estuaries, suggesting that regional processes have controlled their macroscale evolution. RSL change and variations in sediment supply emerge as key controls during the first two phases of estuary development. The late Holocene demise of the estuary wetlands probably reflects a propensity for increased sediment reworking and unfavourable conditions for the accumulation and preservation of organogenic deposits due to reduced rates of long-term RSL and watertable rise.