Foredune Ridges Research Articles

The structure and development of foredunes on a locally prograding coast: insights from ground‐penetrating radar surveys, Norfolk, UK

The internal structure of coastal foredunes from three sites along the north Norfolk coast has been investigated using ground‐penetrating radar (GPR), which provides a unique insight into the internal structure of these dunes that cannot be achieved by any other non‐destructive or geophysical technique. Combining geomorphological and geophysical investigations into the structure and morphology of these coastal foredunes has enabled a more accurate determination of their development and evolution. The radar profiles show the internal structures, which include foreslope accretion, trough cut and fill, roll‐over and beach deposits. Foredune ridges contain large sets of low‐angle cross‐stratification from dune foreslope accretion with trough‐shaped structures from cut and fill on the crest and rearslope. Foreslope accretion indicates sand supply from the beach to the foreslope, while troughs on the dune crest and rearslope are attributed to reworking by offshore winds. Bounding surfaces between dunes are clearly resolved and reveal the relative chronology of dune emplacement. Radar sequence boundaries within dunes have been traced below the water‐table passing into beach erosion surfaces. These are believed to result from storm activity, which erodes the upper beach and dunes. In one example, at Brancaster, a dune scarp and erosion surface may be correlated with erosion in the 1950s, possibly the 1953 storm. Results suggest that dune ridge development is intimately linked to changes in the shoreline, with dune development associated with coastal progradation while dunes are eroded during storms and, where beaches are eroding, a stable coast provides more time for dune development, resulting in higher foredune ridges. A model for coastal dune evolution is presented, which illustrates stages of dune development in response to beach evolution and sand supply. In contrast to many other coastal dune fields where the prevailing wind is onshore, on the north Norfolk coast, the prevailing wind is directed along the coast and offshore, which reduces the landward migration of sand dunes.

Mesoscale temporal changes to foredunes at Inch Spit, south-west Ireland

The history of foredune development and loss is examined on a decadal-scale basis at Inch Spit at the head of Dingle Bay. Inch currently has a foreland area (2 km(2)) with four low foredune ridges fronting the southern section (2.5 km) of the barrier. Analysis of maps (1842 & 1898) airphotographs (1949, 1967 gr. 1973) and field surveys (1993/94) of the shoreline has supported an interpretation of two to three possible sequences of sudden erosion of the foredunes and subsequent redeposition and reworking of foredunes over periods of 30 to 50 years. The erosion and deposition of the foredunes have been analysed in terms of variation in the following; human activity, sea-level, storm activity and longterm (annual to decadal) atmospheric forcing changes, but none of these factors individually account for foredune changes. It is argued on circumstantial evidence that the role of extreme storms and associated surge is the most probable key to understanding sudden foredune disappearance. Wave refraction modelling of extreme events has helped to specify the principal control on foredune loss. The result of specific microscale triggers (days) leading to mesoscale changes (decadal) is examined.

Formation of Ephemeral Bedform Turrets in Coastal Foredunes.

Rare, erosional turret bedforms are described in a coastal foredune environment. These ephemeral structures are formed as a result of moist columns of sand being sculpted by aeolian action of saltating particles. Mature formation of these features appears to be facilitated by the action of an advancing foredune ridge, first preserving and then isolating the turrets for further enhanced erosion within a dune environment. It is envisaged that these structures may be preserved in dune stratigraphy.

No evidence for interspecific interactions between plants in the first stage of succession on coastal dunes in subarctic Quebec, Canada

Coastal dunes are very dynamic systems, particularly where the coast is rising as a result of isostatic rebound. In those environments, succession proceeds from plants highly tolerant to sand accumulation, salt spray, and low nutrient availability to less disturbance-tolerant and stress-tolerant, more nutrient-demanding, and supposedly more competitive species. In the subarctic, the regional climate exacerbates the stresses imposed by local abiotic conditions on the dunes. I hypothesized that facilitation would be particularly significant on the foredune of subarctic coastal dune systems because of intense stresses (local and regional) and frequent disturbance in the form of sand deposition. Belowground and aboveground plant biomass was sampled at three different periods during the 1990 growing season along transects perpendicular to the shoreline on a coastal dune system in subarctic Quebec (Canada). The three herbaceous perennials found on the foredune (Honckenya peploides, Elymus mollis, and Lathyrus japonicus) were segregated in time during the growing season and in space along the topographical gradient. The biomass of Honckenya, the first species encountered as one progresses from the upper part of the beach towards the foredune ridge, was not correlated to substrate physicochemistry. However, the biomass of Elymus and that of Lathyrus, the next two species to appear along the flank of the foredune, were related to pH, Mg, Na, and Cl (negatively), and to P and Ca (positively). These results suggest variable linkages between substrate physicochemistry and plant species along the foredune, possibly in relation to species-specific tolerance for abiotic conditions and requirements for substrate resources or to microscale influence of the plants themselves on substrate physicochemistry. Removal experiments carried out over 2 years revealed only one significant unidirectional interaction between these three species along the topographical gradient, and little plant control over abiotic variables (e.g., soil temperature, wind velocity, and photosynthetically active radiation). Early primary succession on subarctic coastal dunes (and elsewhere) appears to be under the control of strong limiting abiotic conditions. As plants slowly gain more control over the physical environment, interspecific interactions (positive and negative) may become more significant. Key words: Elymus mollis, facilitation, Honckenya peploides, inhibition, Lathyrus japonicus, removal experiment, succession, tolerance.

Thermoluminescence ages and palaeoclimate from the lake Malata-Lake Greenly Complex, Eyre Peninsula, South Australia

Strandlines of playas from the Lake Malata-Lake Greenly Complex on the Eyre Peninsula, South Australia, preserve a detailed record of major changes in lake level and palaeochmate spanning the period 320 ka to present. Thermoluminescence ages of quartz from a total of 13 carbonate lunettes, a pedogenic disconformity, a recent foredune, a sub-parabolic dune and a major foredune ridge have been obtained. The age of 319±72 ka for the foredune ridge is centred at the interglacial highstand of stage 9 and represents a unique high lake level in the complex. The formation of lunettes has long been linked to the aridity of the Last Glacial Maximum (ca. 18 ka). We are able to show that deflation of playa sediment into lunettes has been relatively common and has occurred intermittently throughout the period 130 ka to present. The deflation events have been synchronous with the global glacial inception (ca. 115 ka), cold intervals (ca. 85 and 75 ka) and cold stadials following the main glacial transition (ca. 54 and 43 ka). During the Last Glacial Maximum, deflation commenced as early as 26 ka and culminated in maximum deflation between 20 and 17 ka. The most recent phase of deflation has been dated at ca. 1.9 to 1.2 ka.

Les dunes côtières des régions froides : exemples canadiens

Little is known about cold-climate coastal dunes. Along the Canadian arctic and subarctic sandy shorelines, coastal dune development is common. Along the Tuktoyktuk Peninsula, located in the southern Canadian Beaufort Sea, coastal dunes are generally low incipient features, sparsely vegetated. In subarctic settings, as along the emerging eastern Hudson Bay coastline, well developed azonal foredune ridges are found at sandy river mouths. Niveo-aeolian deposition represents a major process contributing to their development.

Sedimentary structures of cold‐climate coastal dunes, Eastern Hudson Bay, Canada

ABSTRACTA study of sedimentary structures of cold‐climate coastal dunes along Eastern Hudson Bay, Canada, showed that in areas of very sparsely vegetated surfaces, tractional sedimentary processes are dominant while in partly and well vegetated areas, grainfall deposition is the dominant sedimentary process. Alternating fine and coarse sand strata are characteristic of the vegetated foredune ridge. Coarse strata are interpreted to be mainly related to niveo‐aeolian deposition. In poorly vegetated areas deformed strata associated with the melting of snow were preserved. A vaguely stratified strata interpreted as a dimpled surface as well as coarse lenses with irregular basal contact were found. Such distinctive sedimentary structures may represent good indicators of cold‐climate conditions and could serve as criteria to identify aeolianites that may have been deposited in similar cold‐climate environments in palaeoenvironmental reconstructions.

Les forêts littorales en milieu dunaire : l'exemple de la Réserve Biologique Domaniale de Merlimont (Pas-de-Calais)

Forests on coastal dunes : the example of the National Biological Reserve of Merlimont (Pas-de-Calais). The authors emphasize the special nature of the birchwood in the moist soils of coastal dunes of Merlimont (Pas-de-Calais). The birchwood is the last stage of a successional process which appears on a sequential air photos analysis between 1947 and 1989. A structural complexity of the coastal forest can be well defined only in the inner part of the central depression between the dune ridges. Dynamic processes can be described as dominant in the vegetation landscape as follow : -on the foredune ridge and on the western part of the inter-dune flat area, a linear succession of marram grass and shrubs, -on the eastern part of the inter-dune flat area and on the hollows of the reardune ridge, a cyclic fluctuation in small clearings and borders of the birchwood (inner and outer dynamics), -in the transition area a nuclear colonization with patches of wind-bowed trees.

Foredune development along a subarctic emerging coastline, eastern Hudson Bay, Canada

A study of sedimentary processes and evolution of subarctic foredunes along a rapidly emerging coastline in southeastern Hudson Bay showed that niveo-eolian sedimentation is a significant process contributing to the formation of these foredunes. The fall storm berm and the sand-laden ice foot are the prime sedimentary sources for the niveoeolian deposits, which are generally coarser grained than the eolian sand deposited during summer. The annual sedimentation in the backshore zone is less than in typical mid-latitude regions. The development of established foredunes in this subarctic environment seems to require a longer period of time than in other climatic zones. The short-term backshore evolution (1954–1990) shows that sediment supply appears to be a major factor controlling foredune morphology and dynamics. Phases of sediment surplus seem to correspond to rapid seaward progradation and formation of low foredune terraces or low foredune ridges with a beach ridge-like morphology.Conversely, high foredunes probably develop during periods of lower sediment supply and slower beach progradation. On a longer time scale, the relative sea-level fall controls coastline progradation and results in the formation of raised, coast-parallel, relict foredune ridges.

Late Holocene dune formation on the Sefton coast, northwest England

Abstract Coastal dunes fringe the coast between Southport and Liverpool in northwest England, forming a natural barrier which prevents marine flooding of low-lying agricultural land in West Lancashire and north Merseyside. The dunes are best developed at Formby Point, where they reach 25 m above sea-level and blown sand extends some 4 km inland. This paper presents the results of an initial programme of field drilling, sediment analysis and radiocarbon dating which suggest that the dune complex developed from a large offshore sandbank, which was in existence by 6800 years ago. Behind the bank lay a large area of intertidal mudflats and sandflats with fringing saltmarsh. Dunes may have first become established on the emergent sand bank around 6000 years ago, but the oldest dunes for which there is direct dating evidence formed between 5700 and 5800 years ago. A period of dune stability, possibly associated with seaward progradation of beach and foredune ridges, appears to have occurred between 2500 years ago and the early Middle Ages. During the earlier part of this period oak and alder woodland covered the dunes and the sands were deeply podsolized. Historical and documentary evidence indicates that extensive sandblowing occurred all along the coast during the early Middle Ages, which was a period of exceptional storminess and rapid coastal erosion. Several settlements and farms were lost to the sea or were overwhelmed by blown sand as the coast eroded. Active sand tongues extended across the full width of the barrier and buried the backbarrier peats and silts along the western margin of Downholland Moss. Dune instability has continued intermittently until the present, although on a smaller scale, and consequently most of the present dune forms are relatively recent. Sand stabilization and foreshore reclamation measures undertaken in the second half of the nineteenth century were highly effective and contributed to a net seaward progradation of the entire Formby coastline between 1850 and 1900. Abandonment of these measures around the time of the First World War contributed to, but did not ultimately cause, a return to shoreline erosion and a new phase of frontal dune instability which is still in progress.

Changes since the Nineteenth Century to the Estuary-Barrier Complexes of North County Dublin

Over the past 150 years, two estuary-barrier complexes on the north Dublin coastline have undergone considerable morphological changes. These include a reduction in the size of the estuaries, and estuary mouths, and the accretion of beach sediments and foredune ridges around the distal or southern ends of the barriers. Increased estuarine reclamation, and the construction of the Dublin to Belfast Railway across one of the estuaries, has reduced the volume of the tidal prism and weakened the ebb and flood currents, requiring an adjustment in the dimensions of the tidal channels and estuary mouths. Disruption of the tidal regime has led to substantial hydrodynamic and morphological changes, the southward extension of the barriers representing an attempt to restore the hydraulic equilibrium of these estuary/barrier complexes by reducing the cross section of the estuary mouth. Subsequent adjustments to these changes, combined with increasing recreational pressure, have been responsible for recent degradation ...

Large-scale establishment of Ammophila arenaria and quantitative assessment by remote sensing : W. H. Van der Putten & E. H. Kloosterman, Journal of Coastal Research, 7(4), 1991, pp 1181–1194

New methods for the establishment of Ammophila arenaria (marram grass), i.e. sowing seeds and disk-harrowing rhizomes, were compared with the traditional method (planting bundles of culms). A large-scale experiment was undertaken on 120 ha of fortified foredune ridge and approximately 40 percent of this area was evaluated by airborne remote sensing (false colour photography). Above-ground biomass production and percentage cover of one- and two-year-old stands were determined by combining field data with colour density measurements on the images. A linear empirical relationship could be established between colour density ratio on the photographs and above-ground biomass, as well as percentage cover. This relationship depended on the age of the plantation. Planting method or relief did not influence this relationship. After the first growing season planted culms had produced less biomass and percentage cover than stands established via the new methods. In the second growing season the traditional method was the most productive. During the first growing season more than 90 percent of the total area had been stabilized successfully by the new vegetation. Therefore the alternative methods could be as effective for sand stabilization as the traditional method of planting. Effectiveness of the temporary sand stabilization after sowing and the origin of the culms and rhizomes used for planting affected productivity of the new stands more than the method of establishment. Therefore, if applied properly A. arenaria can be established at a practical level from seeds or rhizomes, instead of from culms, It is also shown that remote sensing could be used to assess above-ground biomass, percentage cover and heterogeneity of foredune vegetation.

The use of a GIS in assessing the impacts of sea level rise on nature conservation along the Dutch coast: 1990–2090

The Dutch coastline is expected to change considerably during the next 100 years. Erosion will prevail, although accretion will occur locally. To establish a new policy for coastal defence management an integrated policy analysis study was performed. Major dune functions (nature conservation, recreation, public drinking water supply, housing and industry) have been inventarized by using a Geographic Information System. This study reports on the part of the analysis which takes nature conservation interests into account. Evaluation of nature interests has been based on the criteria: rarity and diversity of plant species c.q. vegetation types, succession stage, and completeness. This results in a classification of nature into five classes, based on abiotic as well as biotic characteristics of the landscape. Losses of nature interests were studied due to: loss of land because of shoreline retreat, to remodelling of the foredune ridge, and to changes of the dune groundwater level. An evaluation is given of the methods used to assess ecological impacts. Ideas are presented for further research on the prediction of ecological impacts and on coastline management which combines traditional coastal defence with nature conservation.

Stratification models for vegetated coastal dunes in Atlantic Canada

SynopsisThe principal types of stratification and some characteristic sedimentary sequences found in vegetated coastal dunes in Atlantic Canada are described. Four examples are selected to show a range of dune types and depositional settings. In each case the documentation and interpretation of the internal structure and stratification has made an important contribution to understanding the evolution of the dunes. Stratification and depositional models are presented for:(1) a single, continuous, transgressive foredune ridge which maintains its form during transgression;(2) a discontinuous transgressive foredune ridge, interrupted by washover passages;(3) a “precipitation” dune, which buries an existing stable dune; and(4) complex dunes produced by two or more phases of aeolian activity characterised by different plant associations.

Restoration of coastal dunes breached by pipeline landfalls in north-east Scotland

SynopsisSix major oil and natural gas pipelines make landfalls on the coastline of north-east Scotland. Four land at St Fergus, one at Cruden Bay and one at Shandwick. The Cruden Bay line dates from 1973: at St Fergus landfalls were made in 1975, 1976 and 1984: and at Shandwick in 1979. With the exception of the Shandwick landfall, the pipelines cross relatively wide sandy beaches with associated dune ridges. All the pipelines were laid using a simple trenching technique whereby a beach trench was dug and a large V-shaped cut made through the main foredune ridge and interior backslope, inner dunes or slack environments. All these landforms were replaced quickly by backfilling. Thereafter, physical devices such as nets, brushwood, sand trapping fences and bitumen sprays ensured surface stability. Equally important was a replanting programme which had two main components: – hand-planted marram grass and agriculturally seeded grass mixtures. Topsoil was added, fertiliser was applied and other cultivation practices were used.Since 1973, several surveys of the progress and success of these restoration procedures have been made. On the whole, landform stability has been very satisfactory. Re-vegetation has met with mixed success, especially with regard to those changes which could be described as the gradual re-invasion of natural or local plant associations to replace the artificially planted species. Various lengths of time have ensued, and in some examples the rate and pattern of re-vegetation have been examined by means of periodic sampling. This has made possible reasonable assessments of the influence of local environment factors on the ability of sown species to establish and create a sward, the extent to which they persist over a period of years, and the ability of native species from the neighbouring dune system to re-invade and compete successfully in the developing turf. Standard methods have been used for planting marram grass to stabilise the steeper seaward sand slopes, but these are reviewed in the light of results of recent experimental studies of various planting techniques. The possibilities for exploiting these findings in the rehabilitation of any future pipeline crossings of dunes are considered. Since slightly different re-vegetation procedures were adopted in the several dune crossings under review, it is also possible to comment on the optimum solutions to restoration problems of this kind which are associated with mature coastal sand dunes.

The South Australia Coast and Holocene Sea-Level Transgression

Along the South Australia coast sea level has been relatively stable since 6.5 ka B.P. Tides are generally <1 m, and sediments are predominantly shelf- and shoreface-derived carbonate detritus. Deepwater wave height is persistently moderate to high, although breaker-wave height is highly variable along the coast. Shoreface barriers range from low-energy prograding tidal flats, cheniers, and beach and foredune ridges through moderate-to-high-energy prograding-to-recessive systems of foredune-ridge pro- gradation to high-energy barriers, consisting of massive mobile dunes. Breaker-wave regime dominates location, nature, and evolution of shoreface type by influencing sediment supply and morphodynamics. ing and since the postglacial marine transgression (PMT) to provide sediment for the formation of substantial barrier-dune systems along most of the -2,000-km open coast. Because of the semiarid climate, rivers and sediments derived from them are minimal. On the high-energy open coast, shorefaces have evolved in response to sediment supply, large waves, and strong on- shore winds. At the same time protection from ocean waves in Spencer Gulf and Gulf Saint Vincent, as well as local wave attenuation and coastal con- figuration, affords a range of moderate- and low-energy sandy shoreface types. Because the entire length of the South Australia coast has essentially the same sea-level history, the area provides an ideal natural laboratory in which to examine the response of this high-energy, extremely variable coast to the PMT and the subsequent stillstand. The purpose of this article is to present seven types of sandy shoreface-barrier evolution that are representative of the low-, moderate-, and high-wave-energy sections of the coast and to discuss the implications for Holocene shoreline evolution. The Quaternary sea-level history of southern Australia is well preserved by the gentle volcanic-induced upwarp in southeastern South Australia. This uplift has resulted in the preservation of a series of more than twenty cal-

Stimulation of vegetation growth on raised coastal fore-dune ridges.

In experiments to reduce the establishment time of Ammophila arenaria on sand dunes, bundles of 6 ramets placed so that the rhizomes were horizontal and the sprouts upwards produced significantly more (241) tillers/msuperscript 2 than the traditional method (vertical planting, 80 tillers/msuperscript 2). In sowing trials, disc harrowing 5 t straw/ha to stabilize the sand allowed 160 seedlings/msuperscript 2 to germinate after winter, while other methods of stabilizing the sand were unsatisfactory. Scattering rhizomes with dormant buds at 60/msuperscript 2 followed by disc harrowing to 10-15 cm and addition of slow-release NPK gave 43-67 tillers/msuperscript 2 within 1 year, but the surface needed stabilizing until emergence. Slow-release NPK at 90 + 20 + 20 kg/ha gave 1.7 times more tillers than did 45 + 10 + 10 kg/ha. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Regional Variability of Washover Deposits on South Texas Coast: ABSTRACT

Overwash processes play an important role in determining the stratigraphy of microtidal barrier islands. Along the microtidal coast of south Texas, regional variability in barrier island geometry produces a spectrum of washover types. South Padre Island is a low profile, transgressive feature with a discontinuous to nonexistent foredune ridge. It displays sheet overwash, coalescing washover terraces, and washover fans fed by large hurricane channels. North Padre and Mustang Islands are high-profile barrier islands with continuous foredune ridges, and thus only small, discrete interdune washovers occur. The relict tidal inlets between Mustang and Padre Islands are the sites of the largest washovers in the system, termed reactivated tidal deltas. This last type, although re atively rare in modern washover deposits, is probably similar in mode of origin to the large lobate back barrier features found on many high profile barriers on the Texas coast. Internal structures of the washovers were studied by trenching, box coring, and vibracoring. The dominant stratification type is plane beds with extensive heavy mineral laminae. Washover margins display some landward dipping foreset bedding. Hurricane channels show cut and fill structures with shell lags, plane beds, and some trough cross-beds. Directional features indicate that the washovers are formed by storm surge flood, and modified by surge ebb. This is supported by the existence of separate flanking ebb channels on some washovers, as well as current velocity simulations for the storm surge of Hurricane Allen, which show that flood currents are both stronger and longer lived than the ebb. In the ancient record, low profile barriers should be relatively thin deposits consisting of numerous coalescing washovers. Thicker sand bodies corresponding to high profile barriers should be found along strike. Since back-barrier facies have a higher preservation potential than other barrier environments, such a deposit might be dominated by reactivated tidal deltas. End_of_Article - Last_Page 1473------------

1980 Student Professional Paper: The Impact of Active Sedimentary Processes on Land-Use Planning Along a South Texas Barrier Island

Land-use planners rarely consider geologic problems arising from human alteration of natural systems. Development of South Padre Island, Texas has disregarded active coastal processes, creating a dangerous situation for residents and tourists: residential zones have been built in wash-over channels and portions of the foredune ridge have been removed for hotel construction. Shoreline erosion and the island9s susceptibility to the destructive forces of hurricanes are the two major problems identified in this study. To maximize protection from storm surge erosion and scour, it is recommended that high-cost commercial buildings be placed just behind the foredune ridge and residential zones be restricted to back-island areas not exposed to washover channels. With low cost and little effort, geologic input can be incorporated into any land-use plan.

Applications of Crab-Burrow Orientation to Environmental Analysis: ABSTRACT

Burrows of the ghost crab Ocypode quadrata (Fabricius) are widespread in beaches of Texas and Georgia. The orientation of these burrows and the factors that influence it are potentially useful in recognizing and interpreting ancient beach environments, shoreline position and orientation, and direction of dominant winds. O. quadrata burrows generally slope downward away from the shoreline with branches being landward of the main shaft. This preferred orientation is controlled by the direction of onshore winds. During the short excavation period (several minutes), individual crabs burrow 45° to either side of the local downwind direction. The mean orientation of all ghost crab burrows over days or larger periods of time, however, corresponds to the mean onshore wind direction. Other factors that influence burrow orientation include temperature and local landforms. When air temperatures drop below 15.5°C, ghost crabs generally stay in their burrows and reduce their activity. In Texas and Georgia, winter winds of these temperatures are generally offshore winds and consequently have little effect on burrow orientation. Where fore-dune ridges exist, burrows are randomly oriented in the interdune flats owing to wind shadows. In other places, mean burrow orientation is parallel with geomorphic features such as swales which tend to funnel the wind in specific directions. A model of ghost crab-burrow orientation was developed from laboratory experiments that can be combined with wind data to predict field observations in modern beach environments. End_of_Article - Last_Page 466------------