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Tourism is the basic industry in Fuerteventura Island (Canary Islands, Spain), mostly due to the sunny conditions and excellent beaches. Probably the best well-known beaches are those located in the southeastern part of Jandía Peninsula, locally named Sotavento Beaches. These beaches are the largest and widest in the whole archipelago, and are up to 15 km long and 800 m wide in some points. Interest has focussed on these beaches not only from the tourism point of view, but also from a geomorphological perspective. Based on beach profile data and aerial photographs from 1963 until 1996 from the central part of these beaches, landward migration of the coastline has been identified. The width reduction of these beaches –to the point that in some areas the beach has completely disappeared- is a consequence of the reduction of sediment supply to the coast from inland sedimentary deposits. This reduction in sediment supply and consequent beach erosion is due to the development of tourism resorts and associated activities, such as road widening, sand mining and gardening along the roads.
Few of the world's coasts are devoid of wave action, such that waves are considered as the dominant agent of coastal change at short (hours to weeks) to medium (months to years) time scales, and can act as triggers via extreme events at the meso-scale (decades). Coasts where waves are absent or where wave energy is so important as to obliterate the tidal signal are the extremes recognised as tide- and wave-dominated coasts. The rest are inevitably mixed wave-and-tide-dominated (WTD) coasts that constitute a considerable proportion of the world's coasts. This is not a new idea, but recent advances in the understanding of such mixed-influence coasts impose a reconsideration in terms of a perspective that involves process signatures, sediment transport patterns and coastal morphologies. While tides show a regular predictable temporal cycle, wave conditions generally exhibit large temporal variability expressed by irregular, but short-term/seasonal variations in energy and period. As a result, the WTD spectrum is not constant in power level and is probably very irregular, characterised by a few key spikes. Examples include the well documented moderate wave-energy micro- to meso-tidal sand barriers with frequent tidal inlets such as those of the southeastern coast of the United States, and the much less well known macro- to mega-tidal beaches and their associated nearshore storm and tide-controlled ridges and banks, such as those of the eastern English Channel.
Propagation of waves from Deep Ocean to a shoreline has been numerically modeled. Model equations govern combined effects of shoaling, refraction, diffraction and breaking. Linear, harmonic, and irrotational waves are considered, and the effects of currents and reflection on the wave propagation are assumed to be negligible. To describe the wave motion, mild slope equation has been decomposed into three equations that are solved in terms of wave height, wave approach angle and wave phase function. It is assumed that energy propagates along the wave crests, however, the wave phase function changes to handle any horizontal variation in the wave height. Model does not have the limitation that one coordinate should follow the dominant wave direction. Different wave approach angles can be investigated on the same computational grid. Finite difference approximations have been applied in the solution of governing equations. Model predictions are compared with the results of semicircular shoal tests performed by WHALIN (1971) and with the measurements of elliptic shoal experiment conducted by BERKOFF et al. (1982). Utility of the model to real coastal areas is shown by application to Obaköy on the Mediterranean Sea of Turkey.
The role of statutory designations to regulate activities is an important element in coastal zone management in Europe. In this paper we assess the utility of one such designation the “Area of Outstanding Natural Beauty” as a tool for coastal management in Northern Ireland. The designation is based on landscape quality and offers the potential for an integrated approach. However a variety of weaknesses reduce their effectiveness. Several suggestions are offered to improve the utility of this designation.
Tavira Island, the largest barrier island on Portugal's Algarve coast, exhibits a broad backbarrier area that probably consists of relict flood tidal deltas that were incorporated when associated tidal inlets closed. The tidal deltas are preserved as lobate landforms extending into the marsh, and are bordered by linear, partially infilled depressions that resemble flood channels on modern tidal deltas in the region. The origin and evolution of the incorporated deltas and the location of former inlets were investigated using a dataset of 6.7 km of ground-penetrating radar (GPR) profiles and more than 30 cores. The data reveal a complex stratigraphic framework including a series of lateral facies changes that are interpreted relative to the incorporated tidal delta model and sedimentary environments as seen in the modern barrier chain.
The Gulf of Maine (northeast US coast) records shelf evolution since deglaciation ca. 15 ka. Glacial erosion of bedrock left a complex coastline of bays, peninsulas and islands. Till and outwash provided coarse sediment for reworking in littoral systems throughout the Holocene transgression. Glaciomarine mud, the Presumpscot Formation, was an abundant source of fine sediments that were reworked in estuaries, embayments and back-barrier systems. Relative sea-level change was driven by both isostatic and eustatic components. Initial submergence to 70–130 m above present sea level was contemporaneous with marine-based ice-sheet retreat at 15-13 ka. Rapid emergence followed to 60 m below present, during continuing isostatic rebound at 13-11 ka. Finally, submergence and transgression occurred 10.8 ka to present as isostatic rebound was overtaken by eustatic sea-level rise. Reworking during emergence and lowstand brought sand and gravel to the present coast and inner shelf, building paleodeltas at the mouths of the Merrimack River and Kennebec River. Other rivers, such as the Penobscot, drained landscapes with fewer coarse-grained sources, and have primarily mud-filled estuaries, such as Penobscot Bay.
Detailed seismic reflection profiling and sidescan sonar mapping provide data for a model of inner-shelf evolution based on principles of sequence stratigraphy. The lower sequence boundary is the unconformity created on top of the Presumpscot Fm. and other glacial sediments during emergence. Lowstand systems tracts are best recognized in paleodeltas. Transgressive systems tracts are thin, but interrupted by parasequences of prograding deltaic and estuarine facies in some estuaries. Significant examples such as the newly discovered Penobscot Paleodelta (8–9 ka, 30 m below present sea-level) may relate to a slowing of relative sea-level rise. Highstand systems tracts formed in the late Holocene as the rate of sea-level rise slowed and the rate of sediment supply allowed stabilization and progradation of barriers and tidal deltas. Preservation potential of these features is controlled by the open coast ravinement unconformity, and by the tidal ravinement unconformity and bluff ravinement unconformity in embayments. Variability in preservation potential results both from paleotopography and differing energy of modern processes.
This work deals with the estimation of beach susceptibility to storminess in the Bay of Cadiz (SW Spain), and the concomitant environmental implications. For this purpose a comparison was made between the natural behaviour of beaches and the type and amount of coastal damage made by energetic waves in every beach type. Knowledge on the morphodynamic behaviour of beaches was obtained from a monthly topographic monitoring of 32 beach transepts normal to the coastline, performed during 30 consecutive months. Widely used morphodynamic parameters, like the Surf Similarity and the Surf Scaling parameters, were applied to the data, resulting in a general morphodynamic characterization of beaches, represented in a map of beach type distribution. Maximum coastal damage by storms was estimated by visual observations. Clear relationships between morphodynamic beach trends and amount of coastal damage have been obtained, and are presented in the form of a Beach Susceptibility Matrix. The matrix permits predictions of expected coastal damage associated with storms in other nearby beaches by means of a simple beach monitoring programme.
New data published in BLUM et al. (2001) suggest that middle Holocene sea level along the Texas Gulf of Mexico coast was at −9 m at ca. 7.8 ka, then rose rapidly to 2 m or more by ca. 6.8 ka. This view contrasts with the traditional, widely accepted interpretations of continual submergence until ca. 2–3 ka. or later. A middle Holocene sea level higher than present should have left a significant imprint on the coastal landscape, yet coastal landforms and deposits of middle Holocene age have not been identified in previous studies. Our recent research has now identified extensive Holocene beach-ridge plains on the mainland central Texas coast, landward of Holocene barriers, that may represent the geomorphic manifestation of this highstand. Long considered to be part of the isotope stage 5 interglacial period shoreline, these Holocene beach-ridge plains attain elevations of 2.5–3 m, extend for 10's of km along the mainland shore, and can be 1–3 km in width, roughly the same scale as the Holocene barriers. To further test the concept of a middle Holocene highstand, we have also investigated previously mapped Holocene shorelines along the Alabama coast. A series of optical luminescence ages suggest that some of the shorelines are middle Holocene in age, whereas others represent the earlier part of the late Holocene, prior to ca. 2–3 ka. In aggregate, these data suggest that relative sea level was at, or very close to, present elevations throughout the middle to late Holocene along the Gulf of Mexico shoreline, both to the west and east of the subsiding Mississippi depocenter, and the model of continual submergence until 3-2 ka. or later needs reevaluation.
The research highlights the consequence of an imbalance between “basin management scale” and “coastal management areas” and investigates the relationship between coastline erosion and natural evolution of the inland system at the short-medium timescale while taking account of local climatic changes and sea level rise.
The study was undertaken in the Bradano and Basento catchment basins, on the Ionian coast of Basilicata Region (Southern Italy) through an institutional agreement between ENEA (the National Agency for New Technologies) and the Italian Ministry of Environment. In this area previous studies highlighted an important erosional coastline trend that began about 1950. No previous study has considered the role of the coastal river catchment area in this erosion.
With this aim, contemporary data for coastal and inland evolution were gathered and compared, implementing existing knowledge with land use analysis in the Bradano and Basento basins using multitemporal Landsat TM Images. For the coastal zone, the analysis was carried out at a more detailed scale using different cartographic sources mainly at 1:10.000 scale spanning the past 45 years.
The hydrographic network data was analysed to consider fluvial solid transport, dams, locks, and historical precipitation data series. The land use changes analysis has focused on inland features related to the desertification process, rainfall intensity and climatic changes. These features have been analysed mainly in relation to their contribution to soil erosion and subsequent sediment supply availability. Analysis of the coastline focused on changes in beaches, dunes and backshore areas.
Coastal dunes are relatively rare features in the Azores islands and contribute to less then 1% to the total length of the archipelago's littoral zone, circa 844 km. Localised indications of aeolian activity, contemporaneous to the arrival of the first colonists in the 15th century have been found, but at present most of the coastal dunes are vegetated and stabilised. Dune sand has been exploited during the 20th century for industrial use, leading to severe damage or complete removal of a significant proportion of these features. In the 1950's the Santa Barbara area contained a rare and well-preserved example of an undisturbed active beach-foredune system, free of anthropogenic activities. It displayed a well-nourished beach profile margined by a coastal foredune and a climbing dune, which covered the adjacent bluff and extended landwards through an aeolian sand-sheet. Persistent sand mining between the early sixties and the late eighties, lead to volumetric depletion of the dune cover, lowering of the surface of the berm and triggering cliff erosion. In total, some 950,000 m3 of sand has been removed, the dunes making up half of this figure. Although this activity was stopped in 1995 by legal enforcement, the erosive process still currently persists indicating a surpassing of the natural resilience and maximum vulnerability of the coastal dune system. At present the bluff retreats at very high rates (0.6 m/yr), the dune features were totally obliterated and the sandy beach has been reduced in width to a single swash ramp which floods during half of the tidal cycle.
This study aims to provide a statistical description of wave conditions on the French Atlantic coast. The large scale spatial variability of sea states at the French Atlantic coast is assessed using wave rider time series at Biscarosse (in 26m depth) and l'ile d'Yeu (in 33m depth), about 300 km apart. The major differences between the two locations obtained from 3D histograms of significant wave heights, periods and directions indicate that (i) higher wave heights are encountered at l'Ile d'Yeu and (ii) larger range of wave directions and age at Biscarosse, mainly due to atmospheric forcing. The temporal variability at the two wave rider locations is shown by seasonal statistics, with two main seasons: October to March and April to September. Three types of data classifications are compared; 12 classes allow the main encountered situations to be described.
Geological controls on the origin and preservation of organic-rich facies in Holocene barrier sequences of northern New England are documented using sedimentological and geophysical databases. In addition to backbarrier marsh interfingering with washover/aeolian deposits, several distinct modes of organic accumulation are recognized in association with clastic barrier facies. These include: 1) basal lake gyttja or wetland peats (thickness: 0.1–2.5 m); 2) intra-barrier saltwater/freshwater horizons (0.01–1.2 m); and 3) foreshore peat exposures (up to 1.2 m). Freshwater peat and gyttja underlying barrier lithosomes below contemporaneous Mid-Holocene sea level suggest extensive backbarrier lake and wetlands, possibly due to a wetter climate. Present freshwater organics accumulate up to several meters below lake level, which is controlled by the elevation of groundwater table and, over the long term, sea level trends. In some areas, the saltwater-freshwater peat transition is attributed to cessation of long-term saltwater input into the backbarrier, commonly as a result of tidal inlet closure, rather than relative sea-level fall. The association of well-preserved tree stumps and saltmarsh peat exposed on the foreshore suggests drowning of the upland fringe by rising sea level around 2.5–3.0 ka BP and subsequent barrier rollover.
Whereas basal ages of high-marsh peats are conventionally used for sea-level reconstruction, radiocarbon dates of the top portions of in-situ organic units may provide near-maximum ages of burial by barrier sediments. This information is independent of compaction and type of dated material and may be used to estimate the timing of barrier emplacement at or near its present position. Age estimates are less constrained when dating allochtonous organic material, but may still provide upper age limits for overlying clastic sequences. Similar to other mid- to high-latitude coastal settings, parts of maritime bogs and ponds in mid-coastal Maine have been buried episodically by storm overwash or dune migration over the past 5,000 years. The chronology of these events varies over a short distance along the coast as a function of barrier exposure and morphology, antecedent geology, and changes in sediment supply and vegetation cover.
In shallow highly productive coastal environments intense biogeochemical activity is concentrated in the upper sediment layers. However, pore water composition of permeable inter-tidal sediments change as water flows over the areas during ebb and flood tides. In order to examine metal post-mobilisation, inter-tidal sediment cores of 4 cm length and particles settled in sediment-traps over several periods during 10 months were collected in Ria Formosa (SW Iberian Peninsula). Concentrations of Al, Fe, Mn, Cu and Cd, loss on ignition and the proportion of fine fraction were determined in sediment layers of 0.5 cm thickness and in sediment-trap material. Levels of Mn in sediments were similar to those in sediment-trap material, although enrichment in the topmost sediment layer (0.1 mm) was observed as MnO2 is formed. Although Fe in sediments and sediment-trap material ranged within similar intervals, two relationships with Al were found showing that sediment-trap material are impoverished in Fe in comparison to sediments. This suggests that Fe is mainly cycled inside the sediment. Copper and Cd exhibited different patterns. Levels in sediment-trap material were not correlated to Al or LOI, probably due to local contamination or uptake by plankton. These values were lower than levels in the topmost sediment layer, suggesting that Cu and Cd that reach the sediment surface are rapidly released to the water column. Concentrations in sediments, including the topmost layer, exhibited two relationships to Al, for both Cu and Cd. One corresponding to background values and the other found in stations closer to the anthropogenic sources. In these cases Cu and Cd are incorporated into the sediments that is facilitated by AVS values close to the sediment surface.
This paper attempts to reconstruct the evolution of the Salpi lagoon during the Holocene. The authors examined archaeological evidence and historical documents supplemented by field data. The research highlights the role of climatic variations and human interference in evolution of the lagoon. The data collected show that:
At the beginning of the Holocene the sea level rise caused the development of a sandy barrier between Gargano Headland and Murge. This barrier enclosed a wide coastal lagoon, called “Laguna di Salpi”.
Favourable environmental conditions permitted human occupation on the inner side of the lagoon during the early Neolithic by populations coming from the eastern coasts of the Adriatic Sea.
At the end of the Neolithic the lagoon evolved into a sabkha and the whole area was abandoned until end of the 3rd millennium B.C.
Between the III and I millennium B.C. the lagoon, communicating by several entrances with the sea, was deep enough for navigation.
Between the II and I century B.C. the Tavoliere coastal area was affected by malaria and the lagoon settlements were abandoned.
During the Middle Ages the Tavoliere coastal plain was almost depopulated, whereas the area around the lagoon was densely inhabited.
Despite many attempts at reclamation during the Modern Age the whole Tavoliere was a malarial area.
The lagoon then turned into a large coastal swamp which survived up to the 1930s when, after the “Serpieri - Iandolo” law, radical reclamation activities began.
Two areas of the ancient Holocene lagoon still survive: the first is a swamp called Palude Frattarolo, the second is an area dedicated to salt production, called Saline di Margherita di Savoia.
Wetland loss in many estuaries around the world, has been attributed mainly to undermining and collapse of channel banks. This study aims to quantify bank erosion and vertical erosion/accretion rates on intertidal sediments in the Odiel tidal marshes (SW Spain). Bi-monthly erosion/accretion measurements were taken on eight channels over a four year period, using markers (iron stakes) located on intertidal areas and on eroding banks. The intensity of erosion divides the Odiel marshes into two zones. The northern zone has low erosion rates (horizontal erosion c. −20 cm year−1 and vertical erosion / accretion between 0 and −1 cm year−1), and coincides with low levels of human activities. The southern zone has higher erosion rates (horizontal erosion c. −25 cm year−1 and vertical erosion / accretion between 0 and −5 cm year−1) and exhibits higher levels of anthropogenic pressure. The highest horizontal and vertical erosion rates (c. −80 cm year−1) were recorded on navigation channels. Horizontal and vertical erosion showed a positive linear relationship (r2 = 0.66; P< 0.01), indicating that sediments mobilized by bank erosion are not deposited on adjacent intertidal areas. Erosion led to mature marsh habitat loss of c. 17000 m2 year−1 and a sediment mobilization of c. 16500 m3 year−1.
Particular atmospheric conditions produce frequent storm surges in the Lagoon of Venice, locally called “acqua alta”: the highest event of this kind was registered in 1966. The process became of some importance in the last 100 years, when man-made subsidence caused a gradual sinking of the town and lagoon's bed.
Four cores were collected in a range of intertidal environments of the Northern lagoon to undertake radionuclide studies using profiles of natural 210Pb (using the Constant Rate of Supply and Constant Initial Concentration models) and anthropogenic 137Cs. The best agreement between the three dating methods was found at San Giacomo, an eroding saltmarsh at the edge of a navigation channel, with a sedimentation rate ranging from 0.22 to 0.29 cm yr−1. This site recorded the flood of 1966 as a characteristic break in the 210Pbex profile, as dated by the CRS model. For the Cona tidal flat, both the CRS model and the position of the Cs peak-marker gave similar accretion rates, 0.16 and 0.18 cm yr−1. However, two different CIC accumulation rates were calculated, 0.29 cm yr−1 for the deepest section of the core and 0.17 cm yr−1 for the uppermost part. The break in the 210Pbex profile, again corresponds to the flood of 1966. The effects of subsidence were recorded as an increase in accumulation rate between 1910 and 1931, when there were up to 15 floods per year (1926). Higher sedimentation took place during the period 1958–1973, when years with over than 50 flood events were frequent. The maximum deposition rate (0.43 cm yr−1) occurred again around 1967, consistent with the record of the exceptional flood, if the accuracy of the dating is taken into account. The sedimentation rates calculated for the two other mudflats, Rosa and Saline, were more problematic to interpret because of downcore mixing and/or the occurrence of reducing conditions.
Although beach nourishment is considered the only viable option for maintaining oceanfront beaches, the prohibition of large-scale mining of mainland sites and estuarine channels has made it difficult for communities with severe erosion problems to plan mitigation. Figure Eight Island, North Carolina, is an example of a community where erosion during the past decade has increased dramatically due to the combined effects of the bordering inlets and the impacts of recent hurricanes. The chronic erosion has prompted a system wide investigation aimed at inventorying the offshore sand resources for long-term management of the oceanfront beach. The contrasting behavior patterns of Rich and Masons Inlets, which form the island's northern and southern boundaries respectively, have influenced historic shoreline change patterns. Although Rich Inlet has been relatively stable, the ebb channel has shifted repeatedly; and as a consequence, reconfiguration of the expansive ebb delta has led to severe erosion along a 2 km reach downdrift of the inlet. Mason Inlet is a small migrating system whose soundside channels have shoaled since the mid 1990's, resulting in a dramatically reduced tidal prism and increased migration rates that exceeded 140m y−1. Migration and consequent realignment of the trailing barrier resulted in oceanfront erosion that extended for 3 km updrift. Relocation of the inlet is planned for early 2002. Less than 10% of the 4.0 million m3 needed for nourishment will be available as a result of the relocation efforts.
Although the shoreface has been viewed as a potential borrow source, data indicate it has a low potential for providing significant volumes of quality sand. The lack of shoreface sand resources and the minor amount available from future dredging activities at Mason Inlet strengthens the need for developing a sound sand management strategy for Rich Inlet for long-term maintenance of the oceanfront.
Two barrier island systems from southern Mozambique (Inhaca and Bazaruto) are described. Both systems comprise a composite barrier island or barrier island chain that developed on a steep continental margin as a result of initial (Pleistocene) spit progradation. Continuing aeolian dune deposition against this initial core during subsequent sea-level highstands and lowstands has given rise to the highest dunes (120m) of any known barrier island. Wave reworking of the composite barrier island sediment during the past 6000 years of the Holocene sea-level highstand has resulted in the formation of spits, barriers, barrier islands and bluffs on the downdrift and bay side sections of the barrier island systems. The relative stability in position of the barrier systems at contemporary sea level is attributed to their large sediment volume and the development of equilibrium shoreline forms under swell waves. Beachrock and aeolianite outcrops provide anchor points for the development of contemporary shoreline forms.
The prediction of coastal evolution is difficult due to the variety of spatial and temporal scales over which coastal changes occur, and the inter-dependence between different geomorphic features as components of the natural system. Despite these difficulties, it remains necessary to attempt to identify coastal geomorphic issues that are relevant over decades to centuries.
This paper describes the development of geomorphic tools to assist in gaining an improved understanding of coastal behaviour, based upon key controls, influences and linkages within the coastal system. These geomorphic tools are then applied to the coastline of central southern England in order to demonstrate their applicability.
Data on cross-shore sand transport were obtained during two tidal cycles on a dissipative macrotidal pocket beach in the outer Gironde Estuary (SW France). Sediment samples were collected, using streamer traps, at different elevations above the bed across the surf zone whilst measuring nearshore waves and cross-shore currents on the beach. During the experiment the tidal range reached 3.8 m and the current speeds on the beach were up to 0.5 m s−1. Wave activity was characterised by a variable significant height, ranging from 0.3 m at low to 0.94 m at high tide, due to the sheltering effect of a nearshore sand bank.
The study found that the median grain size of the transported sediment ranged from 0.207 mm to 0.333 mm, decreasing slightly away from the bed, with less than 0.056 mm variation throughout the water column. This vertical distribution was assumed to be related to a near uniform mixing by saturation of turbulence and to large scale vertical eddies under breaking and/or broken waves.
The fluxes calculated using the sediment captured in the streamer traps increased exponentially or linearly towards the bottom, whilst some curves had an S-shaped profile. These results confirm the general theory of a decrease in sediment transport rate away from the bed. However, the S-shaped profile may be due to coherent vortex structures which led to strongly irregular patterns. Finally, the sediment fluxes appeared to be higher during the ebb than during the flood tide, indicating a tidal influence on sediment transport.
Beaches are highly valuable tourist resources; therefore determining their carrying capacity is an essential factor for their sensible use and management. The study synthetically presented in this paper is focused on the SW coast of Portugal, during the summer of 1998 and 1999. It explores the concepts of physical carrying capacity (number of individuals a beach can physically accommodate) and social carrying capacity (concentration of individuals above which beach users become uncomfortable – crowding perception).
Two distinct methods of data collection were used. Measurements on georeferenced digitised aerial photography were used for the physical carrying capacity evaluation. For the social carrying capacity, several user counts, video images and more than 200 interviews were conducted at five different beaches, exploring landscape perception, landscape evaluation and behaviour.
The results achieved enable the understanding of fundamental differences between the two carrying capacity types and how to link and integrate them within management plans. The results also illustrate the difficulties in producing a universal carrying capacity formula, which can be applied in any beach indiscriminately. Nevertheless, the limitations encountered do not question the validity of these studies, as they are evidently of great importance for beach management and thus should be used in a flexible way, fully adapted to the existing specific site conditions.
A field experiment was carried out over a period of five weeks on an intertidal ridge and runnel system on the Northumberland Strait coast of Nova Scotia, Canada. The area is microtidal with a spring tidal range of just under 2 m. The main purpose of the research was to examine the effects of changing water depth and bar emergence on the morphodynamics of the system and to determine the controls on the stability of the ridges during non-storm conditions. The system is developed on a gently sloping platform over 300 m wide at spring low tide with an average gradient of 0.004. It is characterised by the presence of 5 or 6 ridges in the intertidal zone and 2 bars in the subaqueous zone. The ridges are 0.35–0.50 m in height, 50–60 m in wave length, and the continuity of the ridges alongshore is broken by drainage channels. The system at Linden Beach is similar to others that have developed in a number of areas along this coast on platforms resulting from recession of relatively weak sandstone cliffs. Topographic surveys were carried out along 10 profiles spaced 25 m apart using a total station and the position of the ridge crests and troughs was also mapped using a GPS system. Measurements of wave transformation, water motion and suspended sediment concentration over individual tidal cycles were carried out along a profile across the second ridge and associated troughs using electromagnetic current meters, resistance wave staffs and OBS nephelometers. There were no major storms during the monitoring period but there were a number of days with significant wave heights >0.4 m and the measurements spanned the full range from neap to spring tides. During the five week period the ridge crests exhibited a high degree of stability with maximum movement <5 m. The effects of tidal currents were isolated through measurements made during calm conditions with light winds. Measurements indicate that wave shoaling and breaking across the ridge crest at mid to high tide have the potential to transport large quantities of sediment landward and thus to induce landward migration under non-storm conditions. The stability of the bars appears to be controlled by a combination of offshore flows across the bar crests due to undertow and tidal currents near high tide, and through the transport of sediment alongshore in the troughs and offshore in the drainage channels on the ebb tide. The dynamics of the system more closely resembles that of sub-tidal multiple parallel bars than that of intertidal swash bars.
Early February 2001, the Richmond River, Northern NSWAustralia, suffered an immense fish kill, affecting over 35 kilometres of riverine and estuarine habitat, and the surrounding coastal ecosystem. A flood, combined with summer heat, pasture grasses, drainage channels, and sediment, triggered a chain reaction that left the coastal river devoid of oxygen and life.
The Richmond River has many forms of agriculture within its catchment, as well as commercial and recreational fishing and a high tourism industry. Much of the floodplain has been cleared for crops or grazing, with a marked increase in drainage channels being developed to take floodwaters back off the land and into the river. Erosion from cleared lands and developing areas caused large quantities of sediment to smother in-river habitats of the river system. Towns, such as Lismore and Ballina, are built on the riverbanks, causing strain on where floodwaters can go. These factors have caused massive losses in habitat for fish and other aquatic species, as well as terrestrial species that are crucial to the balance of the coastal riverine ecosystem.
The decision was made to allow the river to regenerate on its own accord. Early monitoring over six to eight months, suggests rapid recovery of the river habitat. The general community and Governments need to help reduce the probability of this event occurring again by re-vegetating river banks and floodplains, and implementing better drainage and land management solutions. To help ensure that this scale of event does not happen again in the future within other coastal catchments, improved management of land, river and coasts need to occur.
Morphological analysis of ridge and runnel systems is carried out for a 1.6 km long straight shoreline at the Truc Vert Beach (French Atlantic Coast). Foreshore has been investigated through high-resolution shoreline cartography and topographic surveys recorded during summers, from 1999 to 2001. Hydrodynamic data are from the VAG-ATLAwave model and a TRIAXYS wave buoy.
1999 shoreline maps show three rhythmical ridge and runnel systems with an average wavelength of 480 m. The SSW-NNE trend bars were about one meter high. Runnels were SW-NE oriented. The crosshore profiles of 1999 point out the shoreward sediment's transfer of both berm and bar. During summer 2000, bars and channels are disrupted, whereas 2001 surveys show an irregular and double system of nearshore and foreshore bars.
The shoreline map analysis underlines a conceptual model of ridge and runnel systems described by four phases: from the nearshore bar formation to the bar welding to the foreshore and system organization. These rythmical systems migrate longshore to the south.
The Barqueiro Ria, located on the north coast of the Iberian Peninsula, is one of the Galician “Rías Altas”, which includes Arealonga Beach, the longest beach in the Ria, located in the inner portion. During the 1990s strong erosion has been registered on the beach and associated dunes, while a wide intertidal spit has grown westward. This behaviour is related to the hydrodynamic and sedimentary characteristics of the Ría and Sor Estuary. Tide and wave influence are evaluated using numerical simulations for storm events. Seasonal topographic monitoring of beach and dune profiles and surface sediment samples allow to describe the variations in sedimentary volume and map sediment units. Furthermore, grain size parameters trends are used to determine the sediment transport patterns. Three different zones have been defined along beach and foredune according to their sedimentary dynamics behaviour: i) Eastern zone, with a clear erosive tendency generating the backshore and foredune destruction ii) Middle zone, with dune erosion but sediment accumulation in the intertidal zone, and iii) Western zone, where the beach presents an accumulative profile, with a well developed supratidal area and active dunes.
A topographic survey of the north bank shoreline of the Authie estuary, in northern France, was carried out between 1997 and 1999 in order to determine the short-term morphological organisation, within the estuary, of sand eroded from this chronically retreating north bank. The data complement meso-scale analyses of aerial photographs that highlighted a recycling of this sand, eroded from coastal dunes lining the estuary, into the intertidal inner estuarine sink. The beach at the foot of these dunes serves as an important temporary storage zone for this sand and may show substantial short-term accretion. Much of this sand is, however, transported into the inner estuary by the westerly winds that build up longitudinal dune ridges over a shallow intertidal inner estuarine sand platform that forms the long-term sand sink on this northern shoreline. Sand transported from these ridges ends up as diffuse sand sheets that impinge on muddy sediments derived from upland. Over the longer-term, these dune ridges are recycled into this inner estuarine sediment sink by winds, wave erosion and changes in the position of the Authie channel. In this highly accreted estuary, where minor transport of sand towards the inner estuary by weak flood currents is balanced by seaward evacuation of sand in the main channel, this beach and dune sand transport pathway constitutes the major infill pathway of the estuary. The accretion of sand in the intertidal estuarine sink engendered through this transport pathway is also important in encouraging fine-grained deposition and salt marsh development by providing a shallow substrate. This example shows that accelerated silting of a sandy wave-exposed estuary may occur without the intervention of meso-scale changes in tidal transport.
In situ abrasion of shingle beach material is a neglected area of study in coastal geomorphology, with reduction in beach volumes normally attributed to longshore and offshore drift. Results from field abrasion experiments conducted on flint shingle beaches on the East Sussex coast, southern England, show that in situ reductions in volume of beach material may be more significant than has been thought. Two beaches composed almost entirely of flint shingle were seeded with hard quartzite from a Devon beach and less resistant limestone from a South Wales beach that are readily distinguishable from the flint.
The seeding commenced in January 2001. The pebbles, similar in size and shape to the natural flint shingle, were left in the surf zone at two sites. Prior to exposure the pebbles were engraved with a code number and weighed. At regular intervals those that could be re-found were re-weighed and returned to the beach. Abrasion rates were calculated for each pebble as percentage weight loss per tide. By the end of October 2001, more than 700 measurements of abrasion rates had been made from a total of 431 pebbles.
Average limestone abrasion rates (0.0266% loss of weight per tide) were three times greater than those of quartzite (0.0082% per tide). Measurable abrasion rates were recorded over just a few tidal cycles, not only in severe wave conditions but also in much calmer weather. The maximum abrasion rates recorded exceeded 1% per tide for limestone.
Erosion of unprotected levee banks decreases their structural integrity and increases the likelihood of failure. Several types of restoration structures for levee protection and stabilization have been used in the Sacramento–San Joaquin River Delta, California, to reduce erosion. The purpose of this paper is to describe the results of a field experiment designed to measure the effectiveness of organic restoration structures (brush bundles) in altering the hydrodynamic regime in the vicinity of levees, with specific focus on changes in boat wake energy. Two simple hypotheses were tested: 1) restoration structures reduce boat wake energy, and 2) energy reduction is dependent on water depth. Field work was conducted August 29–31, 2000 on Georgiana Slough, which is a tidally influenced (spring tidal range of 2 meters) distributary of the Sacramento River. Pressure sensors were deployed offshore and landward of the restoration structures. Data collection occurred with the bundles in place and with them removed. Boat wakes were generated during rising and falling tides to capture the effects of fluctuating water levels. Wakes were characterized by index wave height, period and energy. Comparing sample means of normalized energy with the bundles removed and with the bundles in place revealed a 60% reduction of energy by the bundles. It was also determined that energy reduction was tidally, or depth dependent. The reduction of energy by the structures indicates that they are an effective method to protect against boat-wake induced, levee erosion.
In the reliability-based risk assessment, the second order reliability index (βII) method and the Conditional Expectation Monte Carlo (CEMC) simulation were utilised in order to analyse the safety levels of Haydarpasa Port main breakwater, Sea of Marmara, Turkey. The failure probability was forecasted in the βII method by approximating the Hudson performance surface with a second-degree polynomial having an equal curvature at the design point where the design and structural parameters were taken into consideration. In the past, applications of reliability-based risk assessment methodology in Turkey for design conditions, only wave characteristics, tidal range, storm surge, wave set-up and the structural system parameters were included. Tsunami risk was not considered a major design parameter and was not included in the computations.
In this study, a structural stability criterion in coastal engineering is suggested to achieve a common definition of reliability including the tsunami risk. The model introduced in this study is a practical technique for reliability-based risk assessment of breakwaters subject to tsunami risk. In order to determine the occurrence probability under design conditions, which is a function of storm waves, tidal range, storm surge and tsunami height, the CEMC simulation was interrelated with the βII method. From the reliability-based risk assessment model applied to Haydarpasa port as a pilot study in Turkey it was found that, inclusion of the tsunami risk increases the failure risk of the structure, and as lifetime of the structure increases, the impact of tsunami risk on the failure mechanism is more important. For Haydarpasa port main breakwater, tsunami was not the key design parameter when compared to storm wave, however, in places with great seismic activity, tsunami risk may be very significant depending on the occurrence probability and the magnitude of the tsunami.
Rio Grande do Sul is the southernmost state in Brazil. Open sandy beaches dominate the 630-km long shoreline that is 76% still undeveloped. Less than 5% of the state's population (totalling 9.7 million people) live in coastal cities. However, the coastal population is growing faster than the state's average since 1990. Although intense erosion is widely accepted along the beaches of Conceição lighthouse and Hermenegildo, the extent of erosion along the Rio Grande do Sul shoreline is still a controversial issue. Discussions arise from the contrasting results presented by studies addressing coastal erosion in Rio Grande do Sul. Recent DGPS monitoring indicates that about 80% of the Rio Grande do Sul shoreline is eroding; wave refraction studies indicate that it is mainly stable, and long-term coastal evolution modelling reveals a predominantly prograding shore for the last 5 ka. This work critically evaluates published data on long- and short-term causes of coastal erosion in Rio Grande do Sul, in an attempt to highlight the unanswered questions that could minimize the debate. The analysis includes sea-level rise, concentration of wave energy due to large-scale coastal topography, sand deficit as the long-term causes of erosion, storm surges, concentration of wave energy due to small-scale submerged features, interference in the longshore sediment transport, and human activities as the short-term causes. Discrepancies in shoreline change results are a matter of the temporal scale in question and what are the causes that play a significant role in it. For coastal management purposes short-time events represent a far greater hazard than long-term trends. It is therefore reasonable to state that in order to support decision-making mechanisms in Rio Grande do Sul a better understanding of the relationship of storms, sand budget, and beach erosion is necessary.
The harbour of Fortaleza (Ceará - Brazil) is facing infilling processes by sand and fine-grained sediments. The influx of sand into the harbour resulted in the generation and growth of an internal beach (Praia Mansa), located on the sheltered side of the main jetty (Titan). Two tracer studies were performed in the harbour vicinity in order to understand sand transport patterns around the jetty and inside the harbour. For this purpose 1,410 kg (experiment FORT I), and 420 kg (experiment FORT II) of dyed sand were released from a boat at depths between 3.5–5 and 6–11 m below mean sea level, respectively. For FORT I a series of 23 surveys were carried out over a period of two months, including the collection of about 1,000 samples. Detailed maps of sand transport and dispersion were obtained for each survey. During the FORT II experiment only 45 samples were collected at different surveying days, giving an idea of the broad sediment dispersion patterns.
The general tracer dispersion and transport pattern observed at FORT II proved that the sediment arriving to the main jetty arrives by littoral drift from the Futuro beach, after bypassing the Titanzinho groin. The analysis of FORT I maps showed that the sand moved along the external part of the Titan jetty at rates about 30 m/day. Subsequently, due to wave refraction and diffraction around the jetty tip, the tracer started to be transported towards the internal part of the harbour. The computed average displacement rate of the tracer head was about 5 m/day. The last survey, 58 days after the tracer release, shows the existence of dyed sand inside the harbour, at the nearshore portion of Praia Mansa beach. This confirms that Praia Mansa is still slowly but continuously accreting, by addition of sediment transported around the jetty. The results also demonstrate the durability and the effectiveness of dyed sands for the study of sediment transport and harbour infilling.
Nauset Spit was breached during a moderate northeast storm on 2 January 1987, forming New Inlet. Factors leading to the breach included a long-term narrowing of the barrier; a 0.5-m storm surge superimposed on near perigean, perihelion, and spring tide conditions; restricted flow through existing inlets, and large differences in tidal range and tidal phase between the ocean and Pleasant Bay. Ultimately, destruction of the foredune ridge and a large hydraulic slope across the barrier (> 1.2 m) facilitated the development of an overwash channel, which led to tidal exchange and inlet formation. As the channel captured an increasingly larger portion of the bay tidal prism, the inlet grew in size from 0.5 km after two months to almost 2.0 km wide by early 1988. Opening of New Inlet increased the tidal range from 1.2 to 1.5 m, which drastically changed the hydraulic character and sediment transport patterns in Pleasant Bay.
The opening of New Inlet washed much of the sand from the eroding barrier into the bay. As the dimensions of the inlet increased, the ebb-tidal delta grew in volume reducing the amount of sediment bypassing the inlet. Sand continues to enter the backbarrier building sand shoals and bedforms. The decrease in sand supply to the downdrift barrier caused 100 m to 300 m of shoreline recession immediately south of the inlet from 1990 to 2000. During the past six years the rate of erosion has decreased slightly due to more active transport of sediment past the inlet. The major mechanism of inlet sediment bypassing is accomplished through the breaching of hydraulically more efficient channels through the outer portion of the ebb delta. This process results in the formation of swash bars along the downdrift portion of the delta. These bars are 100 m to 300 m long and attach to the landward beach every 1 to 3 years. Permanent breaching of the spit platform has not occurred at New Inlet due to rapid accretion of Nauset Spit and backbarrier shoals directing ebb flow away from the spit platform.
An important area of uncertainty in swash sediment transport modelling is the impact that swash lens hydrodynamics, including flow velocity and local swash depth, may have on the direction and magnitude of net sediment transport over time, and hence the morphological evolution of the beachface. Swash, as manifested in the instantaneous shape of the lens, may be categorised as uprush, ‘flow reversal’or backwash, each phase having a characteristic hydrodynamic regime. However, the exact character of each phase, including the appearance of hydraulic jumps or retrogressive bores as well as the depth and flow velocity of the lens, are determined by a complex interaction between antecedent beachface conditions, beach groundwater dynamics and initial hydrodynamic inputs. Measurement of swash processes using conventional fixed instruments does not provide the temporal or spatial resolution necessary to adequately quantify or even identify the relationship between these factors.
Video imaging of the two-dimensional, cross-shore water surface and beachface provides a means of acquiring high-resolution data of the water surface and beachface morphology. Previous experiments have used analogue camcorder technology and associated image processing and geographical information systems (GIS) technology to capture water surface information. Due to image degradation from the analogue interleaving process, manual digitisation of the water surface was found to be the most practical data capture technique.
The aim of this research was to capture two-dimensional images of the swash lens in a laboratory flume using a digital video camera recording direct to PC hard drive and to compare to water depth data captured using a capacitance probe. Digital video capture has a number of potential advantages over conventional analogue video, including:
- the removal of the post-capture analogue to digital conversion stage (frame-grabbing) and
- improved geometric and radiometric image quality, both resulting in higher spatial resolution.
The results of this comparison suggest that the data captured by the digital video system are comparable in resolution to that collected by the wave gauge. Suggestions as to the future use of IEEE1394 video technology for swash measurement and possible improvements to the data capture mechanism are made.
Aeolian sand transport estimation is extremely important to calculate for sediment budgets in beach/dune systems. However, the number and location of high frequency sampling (> 1Hz) devices deployed on the beach/dune systems still have some limitations, related basically to equipment budget and its integrity during high energy events.
Field experiments took place in Portugal, mainly along the SW and S coasts, over long periods (weeks to almost 2 years) on medium energy, non-dissipative beaches with 0.3 mm to 0.5 mm and moderate to well sorted quartz sand. Data provided by all monitoring devices was used to feed a well-tested flow model and shear velocity was calculated at every node of the monitored beach surfaces.
Although longshore wind events were affected little by beach morphology, cross-shore wind events on the other hand resulted in well-defined, heterogeneous shear velocity zones along the beach profile. Relative shear velocity values varied from a minimum on the berm to maximum on the beach-face to berm transition, with values of up to 500% of berm data. Model application to beach face, embryo dune and foredune zones consistently resulted in 150% to 200% of berm shear velocity values. Using the width of representative beach zones to calculate potential aeolian sand transport dramatically reduces its values to about 1% if monitoring equipment is located over the berm crest and to about 60% when sensors are positioned on the embryo dune zone. These values were consistent with actual/estimated rates obtained using different sand trapping devices. Low wind speed events activate the surface sporadically, reflecting micro-topography, with saltation inertia producing complex sand transport patterns, as is usually observed in situ. As wind speed increases, shear velocity relations over the whole surface are amplified, eventually resulting in narrow beach areas intensively activated while others rarely contribute as sediment source areas to aeolian transport
Extensive Spanish dune areas were totally altered and destroyed in the course of massive tourist urbanization and road construction projects during the 1960's–1970's. Littoral drift interruption by harbour and marinas as well as sand mining for construction and agriculture purposes also contributed to accelerated dune erosion. Furthermore, human trampling, refuse dumping, excessive dune recreational pressure, use of all-terrain vehicles and cropping, are amongst the main causes contributing and accelerating physical and ecological degradation of most Spanish dune systems.
Before 1988, Spanish coastal dunes were totally unprotected. The 1988 Spanish Shore Act (“Ley de Costas”) arose with the aim of regulating the coastal activities and preventing littoral destruction. The Spanish Shore Act protects all coastal dunes precludes their destruction by sand mining and any other form of development, . However, this law still does not prevent some of the above negative activities occuring. Furthermore, the complexity of existing boundaries of the different authorities involved in coastal zone management policy makes integrated dune management a difficult task.
The National Spanish Coastal Authority, Ministry of Environment, have been aware of this problem and undertook a strong policy on dune restoration which has been incremented yearly. In this paper the main dune problems found along the Spanish coastline are outlined, paying particular attention to the analysis of certain case studies and an overview of the different dune restoration techniques used is given. Seven representative examples in which the authors were involved are discussed.
The Black Ledges, a series of islands, shoals, and ledges in East Penobscot Bay, Maine, was mapped with digital sidescan sonar and shallow marine seismic reflection equipmentA total of 38 km2 of sidescan and 600 km of seismic data was collected during four cruises in 2000–2001. The sidescan sonar reveals a surficial geology dominated by muddy sediments with frequent, patchy outcrops of gravel and minor amounts of bedrock. There are seven large concentrations of pockmarks with populations totaling over 3500 in the areas of muddy sediments. Generally circular, pockmarks range in size from five to 75 meters in diameter and up to eight meters deep. Calculations show over 2 × 106 m3 of muddy sediment and pore water were removed from the system during pockmark formation. Seismic data reveal a simple stratigraphy of modern mud overlying late Pleistocene glaciomarine sediment, till and Paleozoic bedrock. Seismic data indicate areas of gas-rich sediments and gas-enhanced reflectors in close association with pockmarks, suggesting methane seepage as a cause of pockmark formation. Pockmarks are alsorecognized in areas lacking evidence of subsurface methane accumulations adding further validity to the late stage of development for the field. Elliptical pockmarks, found in nearly 40 m of water, show modification by currents and degradation of the pockmark form. This suggests depletion of methane and a late stage of development. A more intensive investigation of the area, including coring and high-resolution geophysics is currently in progress.
Small tidal creek estuaries provide important ecological habitats that are increasingly under pressure from urban expansion. In south-eastern North Carolina these coastal counties are among the fastest growing counties in the state. In New Hanover County alone, urbanized land use has increased by 100% between 1976 and 1999. This urbanization has led to an encroachment and loss of these valuable resources. To study the impacts of urbanization, five tidal creeks were analyzed for land use characteristics and phosphorus compounds in sediments. The goals of this study were: a) identify the land use characteristics of the five tidal creek watersheds within New Hanover County; b) compare and contrast these watershed land use characteristics with concentrations of phosphorus measured from sediment samples taken at various locations within these watersheds; and c) perform a spatial sensitivity analysis of the contributing area to these sample locations to determine the relationships between land use and concentrations of inorganic phosphorus. The tidal influences and minimal topographic relief within these watersheds made it impossible to accurately map the drainage area for each sampling site and therefore a spatial sensitivity analysis method was developed to analyze the land use adjacent to each sampling site. The land use potentially contributing to each sampling site was calculated using three radius measurements (0.25, 0.5, and 0.75 mile). Results indicate that the there is no significant statistical relationship between the various types of land use development (e.g. commercial, industrial, transportation, etc.) and the percentage of inorganic phosphorus in the tidal creeks. In comparing simply developed versus undeveloped land, there is a nonlinear relationship between the percentage of developed land and the percentage of inorganic phosphorus. In comparing the buffer sizes, the level of geographic analysis is most closely related to the percent inorganic phosphorus at the 0.25 and 0.5 mile radii and less at 0.75 mile radius. Results from this study illustrate the usefulness for careful geographic scrutiny and robust spatial analysis.
Spartina anglica is an invasive alien plant species whose spread threatens the biodiversity of Irish estuarine mudflats, sandflats and saltmarshes. Models have been developed to predict its distribution to facilitate population control and conservation management, but a more precise definition of the wave-related model parameters is required. This study investigates the distribution of established Spartina anglica in Strangford Lough, Northern Ireland, in relation to wave-related hydrodynamic parameters, generated using a numerical computer model for wave generation and propagation in shallow water.
The distribution of S. anglica was statistically associated with shorter waves. Longer waves are indicative of deeper water, affect a larger and deeper volume of water and travel at faster speeds than shorter waves. They are, therefore, more likely to disrupt Lough sediment surfaces and uproot S. anglica seedlings, thus limiting establishment. Other simulated wave-related hydrodynamic parameters showed little variation between sites with and without S. anglica.
Although input wave parameters were taken for storm conditions, the simulated wave parameters generated by the study did not pass recognised thresholds for initiating sediment transport. To further investigate the linkages between wave-related hydrodynamic parameters and S. anglica establishment, therefore, it may be necessary to re-assimilate the wave model using higher input waves (i.e. exceptional storm waves). This study forms a preliminary basis for understanding interactions between wave-related hydrodynamics and S. anglica establishment and for developing a predictive model of S. anglica distribution patterns.
The nearshore zone of County Wexford, south-east Ireland, is characterised by a series of coast-parallel north-south trending linear sandbanks with intervening channels. These sandbanks are up to 30metres in elevation, and individual banks are up to 15km long and 3km wide. They appear to be temporally persistent and were noted on medieval charts. Several theories exist regarding the processes responsible for the formation and maintenance of these sandbanks. This study documents historical patterns and rates of bathymetric and morphological change on the sandbanks at a meso-timescale (decades to centuries), identifying possible sources, sinks and transport corridors for sediment from 1840 onwards. The results indicate progressive northward extension and steepening of the landward margin of the sandbanks over a 135 year period.
There is abundant landscape evidence for extensive land reclamation conducted within the Shannon estuary wetlands. To date, little published research is available which identifies how much reclamation has occurred, its timing and the likely environmental implications. This paper addresses these questions on the basis of available cartographic and documentary data on land reclamation in this area. Identification of reclaimed land was based on the 2nd Edition Ordnance Survey of Ireland Map Series of 1924. These maps represent landscape features relating to reclamation, such as embankments, artificial arterial drainage channels and sluices. Using such indicators for the purpose of demarcation, the extent of the lands reclaimed has been mapped. Documentary information on reclamation schemes was acquired from the National Archives files on the Irish Quit Rent Office, including letters, memoranda, draft bills and Government Acts, legal documents and statements of account, and these support and supplement cartographic data.
In total, approximately 6,500ha of the Shannon estuary lowlands were reclaimed for agriculture and other purposes. This has significantly altered the morphometric characteristics of the estuary, as embankments and revetments for flood protection have reduced the potential energy dissipation area and the water storage capacity of the estuarine wetlands. Reclamation has resulted in modification of the estuarine physical environment and its hydrodynamics, and altered the character of the wetland habitat in the estuary environs.
Maine's tourist beaches have experienced chronic erosion for a long time. Efforts by scientists and government planners to regulate development have run into conflict with property owners. To reconcile the two groups, a beach profiling project was begun to better understand the behavior of beaches as well as to bring the regulators and regulated together. Early results have demonstrated that southwest storms lead to beach accretion; northeast storms lead to erosion. A web site and an annual meeting where the data are presented have each proven very popular. This program of involving volunteers to gather otherwise-hard-to-collect data has been very successful and would work in many other locations.
There has been considerable research into the science of global climate change, however, there is presently little guidance for coastal authorities on accounting for the physical impacts of ongoing climate change in future land use planning and coastal defence policy.
For the central south coast of England, this paper briefly identifies ‘coastal climate change scenarios’for the next 80 years. A qualitative geomorphological appraisal of the potential impacts of these changes on coastal landforms and processes is presented, based upon generic ‘coastal behaviour systems’ that take account of the various sensitivities to change of the natural and managed coastline. Functions such as the sensitivity of coastal slopes to increasing effective rainfall, and barrier beaches to increased water levels, are considered. The likely future ‘behaviour’ of these systems, and in particular the potential for climate-induced changes, are identified.
The likely response of the coastal systems then provides an objective framework for evaluating hazard and risk. The levels of risk are strongly linked to the historic pattern of land use and development, which in many cases will not accommodate natural adjustment of coastal features. Without effective management, hazards will increase and coastal communities will be vulnerable and at risk under future climate change.
Recommendations are made regarding improving the risk management framework in the face of climate change impacts. Recommendations include issues such as compensation, the planning framework, coastal defence provision, nature conservation, data collection and education.
Although the results are specific to the study area, the methodology developed is transferable, offering a valuable model for other coastal managers.
Methodological aspects of GPS (Global Positioning System) and Total Station (Electronic Distance Measurement) surveying techniques were examined as part of a beach monitoring programme which was used to assess morphological variation of a high-energy beach system at Runkerry, Co.Antrim, Northern Ireland. The accuracy of the instruments as well as data processing methods concerning data conversion in different plane coordinates systems is discussed. GPS with Real Time Kinematics (RTK) provides high-resolution control on topographical surveying within limits on the order of centimeter-level accuracy in the horizontal and 2 cm in vertical dimension. Total station (EDM) also demonstrated high accuracy during its use in the monitoring programme. The model of EDM used in this work had a 5 to 6 degrees offset angle for the orientation due to the inherent characteristics of the instrument. A threshold-narrowed point selecting treatment was used to form a beach profile point set for the profile plot and any further processing. This work demonstrates that a two-dimensional translation and rotation for horizontal dimension data conversion is preferable over linear regression method; while the linear regression method for the vertical dimension data is still acceptable. It is suggested therefore that when a conversion of beach surveying data from one plane coordinate system to another is required, then this combined approach should be adopted in the analysis.
The morphology of river mouths can be completely changed by dramatic flow changes caused by climate changes in catchment basins. Agricultural activities that overexploit water produce changes in sediment discharge that are reflected in sedimentation rates in dams. The basic aim of this study is to assess the causes and effects of rapid delta formation in Gomec (an important tourism centre on the Aegean Sea coast of Turkey), as a result of river catchment changes between 1998 and 2001. The rapidly developing delta covers an area of approximately 2 km length and 100 m width and was studied using numerical simulation and field studies. Bathymetric measurement, flow velocity and oceanographic parameters were measured. Bottom sediment samples were taken from the river and adjacent sea and sources were determined by mineral analysis. River flows and wave properties (determined from hindcast wind data) were used in the numerical model studies. The development of the delta was predicted for different scenarios. It is concluded that unless remedial action is taken, the delta will continue to develop rapidly and will produce both morphological and ecological impacts.
The calculation of the degree of sediment disturbance through wave action in the surf and swash zone has been examined at various levels in recent years using a number of empirical techniques. Quantifying ‘depth of disturbance’(also know as sediment mixing depth) enables a better understanding of nearshore processes, where interaction between sediment and surf zone wave action is complex. Better understanding of how sediment responds to given surf and swash zone parameters is paramount in examining a number of phenomena such as natural beach evolution, sediment movement around engineering structures, the design and planning of beach renourishment schemes, and the monitoring of pollution behaviour. Previous empirical studies have concentrated their efforts in various methodologies such as the use of sediment tracers to mark the sediment, depth of disturbance rods deployed over a tidal cycle and the use of plug-holes filled with marked sediment.
All efforts at estimating sediment disturbance in the field to date have resolved their measurements only after a complete tidal cycle and have been unable to measure processes during the actual perturbations caused by wave action within the tidal event, an essential period of activity to understand bed elevation patterns. This paper seeks to address the present shortfall in methodology with the design and construction of a new, high resolution, vertical measurement system. The new instrument, a Sediment Activity Meter (SAM), characterises surface elevation changes in the sediment bed of the surf zone at a given deployment location at approximately 2 minute sampling intervals. This technique will, for the first time, enable realistic comparisons to be made between bed change and the main forcing variables of the system during a tidal cycle.
The paper mainly outlines the basic design of the new field instrument and describes, for the first time, surf zone seabed elevation changes (at a single point) measured at approximately 2-minute intervals alongside corresponding wave parameters and water depths within the surf zone. The field trials took place on a high-energy beach system in Northern Ireland.
This review of research on estuarine beaches in the USAexamines the linkages between geomorphology and biota and impacts of shore protection strategies. The effects of timing and frequency of storms, wave processes, and tidal range on morphologic response, sediment activation, infiltration and exfiltration of water through the foreshore, and litter distribution on the surface are evaluated along with the impacts of human adjustments, including bulkhead construction and beach nourishment. The effects of these factors on faunal activity are illustrated by evaluating the suitability of beaches as spawning areas for horseshoe crab egg production and the resulting effect on migratory shorebirds. Future research is recommended to: 1) time biological sampling to episodic storm events to evaluate impacts of habitat modification; 2) identify spatial differences in the dimensions of the low tide terrace that control the dynamics and biological functions on the foreshore above it; 3) design biological sampling plans according to geomorphic process regimes rather than static morphologic features on the beach; 4) standardize sampling locations to facilitate comparison among different sites; 5) conduct simultaneous studies of sediment activation by waves and by fauna; 6) determine the role of litter on faunal community structure and function; 7) conduct detailed physical and biological studies at bulkheads to determine the significance of position on the intertidal profile; and 8) determine the significance of nourishing a beach with fill material significantly different from native materials.
Shoreline salients are low triangular landforms, which project seaward as promontories. The term tombolo is applied when this landform is joined to an island or obstacle. This work presents a literature review of salients and tombolos, with a classification of singular landforms, and discusses the relationships between morphological parameters. It also analyses the planform of these features (sigmoid model and parabolic model) on the coast of the State of Santa Catarina in the south of Brazil. Interpretation of aerial photographs and topographical maps enabled the identification of 15 tombolos and 10 salients. The observed proportions and the symmetry of these landforms are directly related to the geological conditions and predominant wave direction. For salience data, regressions between X/B and B/S presented an R2 of 0.79. Regressions between the obstacle depth (d) and the average length of incident waves were obtained, and the results (B*d / (L2) ~ S*d / (L2)) exhibited high R2 values (0.83 and 0.80) for salients and tombolos for data in the literature. The parabolic model was found to be suitable in the analysis of the planform shape of the feature as this model incorporates geometric and dynamic (wave direction) variables.
Wind-abraded rocks (ventifacts) are common coastal features associated geomorphically with beaches, estuary mouths and sand dunes. This paper compares evidence for ventifaction from similar coastal settings in Donegal (Ireland) and Oregon (USA) and considers their implications for coastal sediment dynamics. Ventifacts on a bedrock platform at Gweebarra Bay, Donegal, show pit and groove ventifact styles and are estimated to have formed over some < 2500 years. Ventifacts on a boulder jetty (built 1892–1901) on the Oregon coast, USA, show similar grooves and pits. Winds above the threshold for sand transport and possible abrasion are present for 28–30% of the time at both locations. Based on depth of rock loss, wind abrasion rates on the Oregon coast are 0.24–0.95 mm yr−1, two orders of magnitude greater than in Donegal. Coastal sediment fluxes on these coasts since the late Pleistocene have responded to sea-level fluctuations and changes in onshore sediment supply. Sediment systems are presently less dynamic than in the past, and some coastal geomorphic features may be largely relict.
Gravity currents are important phenomena that play a critical role in the advection of fluids in natural and man made environments. Boat locks, which are a common feature on many coastal waterways, are one type of system that can generate gravity currents. These locks usually have a set of vertically hinged gates at each end which, when opened, permit water from within the lock to exchange with the outside water in the form of gravity currents. By using the results from a series of laboratory experiments the properties of these gravity currents were examined when the lock water was heavier than the outside water. It was found that the swinging action of a lock gate had a significant influence on the rate at which the water initially leaves the lock as a slumping gravity current, with the initial speed of the flow being dependent upon the gate's opening speed. However, the final velocity achieved by the gravity current was independent of the gate opening speed; indicating that the total amount of entrainment of water into the flow was independent of opening speed.
Flow dynamics on the vegetated surfaces of coastal wetlands may impact a wide range of processes including geochemical exchanges at the sediment water interface, larval recruitment and dispersion, and sediment deposition and retention. Nevertheless, little field data exist which describe flow behavior through emergent vegetated wetlands and its control over sediment transport and deposition. The goal of this paper is to describe canopy flow dynamics and suspended particulate transport for a variety of marshes that differ with respect to vegetation type and tidal regime. In situ measurements of tidal currents were collected in micro-, meso-, and macrotidal marshes of the Pacific, Gulf of Mexico and Atlantic coasts of the US and in a UK marsh on the North Sea. Mean flow speeds, vertical velocity profiles, and turbulence intensities were evaluated as were canopy characteristics and total suspended solid (TSS) levels. Broad scale flow characteristics exhibited little variation among sites. Mean flow speeds were almost always less than 10 cm s−1 regardless of tidal regime. The presence of vegetation (regardless of type) significantly reduced both flow speed and turbulence intensity relative to adjacent open water areas. Variations in canopy morphology and the physical structure of individual plants control fine scale hydrodynamics, and influence particle advection, and particle settling. Flow speed magnitude and the importance of creek channel processes, however, appear to be most strongly influenced by the tidal regime in each of the marsh types examined.
This paper examines some of the Spanish coastal management policies that have relevance for the small business enterprises located on the sea-front. Physical protection of the coast through erosion control programmes and urban planning policies are considered, with special emphasis on the 1988 Shores Act that attempts to treat coastal planning more holistically than has historically been the case. Business awareness and response to the coastal actions are investigated through a survey of 150 small businesses in four localities on the Costa del Sol. Results indicate a lack of universal understanding and approval of management policies and objectives, although significant geographical variations exist in views expressed. Forced relocation of businesses has influenced attitudes, as have perceptions that money has not been effectively spent. However, there is clearly much misunderstanding of work that has been effected, and much might be gained through improved dissemination of information by both local authorities, regional and central government to a business community whose livelihood is very much dependent upon an attractive and well-managed coastal environment.
The River Bann, Northern Ireland, discharges onto the high-wave energy, swell-dominated North Atlantic coast. The funnel-shaped estuary, buttressed by Tertiary basalt outcrops, is partially barred by dunes developed on a mid-Holocene gravel barrier. The meso-scale evolution of the estuary and nearshore zone therefore demonstrates the interaction of fluvial, marine and coastal processes. Echo sounder, side-scan sonar and Chirp sub-bottom profiler were used to map bathymetry, surficial sediments and sediment stratigraphy respectively. Side-scan sonar data, ground-truthed by surficial sediment sampling, yielded 3 distinct acoustic facies, interpreted as sand (90% of study area) bedrock (9%) and gravel (1%). Oblique nearshore sandwaves, (wavelength 20 - 60m, height 0.8 - 2.4m) are replaced 1.5km offshore by planar sands (20m water depth). Adjacent to the bedrock headland of Portstewart Point lies a relict shore platform (at −30m OD Belfast), likely formed during a late-Pleistocene lowstand. Individual boulders up to 1m diameter are imaged on the bedrock surface. The surface is partially overlain by active, shore parallel gravel wedges surfaced by ripple beds (wavelength 1.5m, height 1.0m) which are partially overlapped by planar sand. Repeat seasonal surveys show general onshore surface bedform migration during winter and offshore re-distribution of sediment in summer. These changes suggest that west to east tidal currents re-circulating sediment between the offshore and nearshore zones are modified seasonally by changes in wave regime and river discharge. Chirp surveys revealed two main seismic stratigraphic units, termed inshore and offshore, overlying the acoustic basement, the inshore unit being more internally complex. Four major controls on Holocene nearshore sedimentation on the north coast of Northern Ireland are suggested: (1) antecedent geological constraints, (2) sediment supply, (3) wave climate and (4) tidal current regime. Apart from antecedent geology, these controls have been, and continue to be, modified by RSL fluctuations and storm events.
Most previously developed coastal vulnerability/sensitivity indices acknowledge that the addition of socio-economic variables would assist in defining vulnerable areas. This study investigated the incorporation of socio-economic variables into a GIS based coastal vulnerability index for wave-induced erosion in Northern Ireland.
In this application, a socio-economic sub-index was developed to contribute potentially one third of the overall index score; the other components consisted of coastal forcing and coastal characteristic sub-indices. All variables were ranked on an arbitrary 1–5 scale with 5 being most vulnerable. The variables were merged within sub-indices and then the sub-indices were combined to produce the overall index.
Several problems were encountered in assessing socio-economic vulnerability indicators. These relate to the inherent difficulties involved in ranking socio-economic data on an interval scale. Temporal aspects also caused difficulties as socio-economic variables vary over time as coastal populations and policies change. There were also problems in relation to the size of the unit used to display the data and how this affected the vulnerability of certain areas. Larger, more fundamental, problems in relation to human perceptions of vulnerability were also investigated. The final results of the combined index were tested against field and desk-top studies and although they correlated well with expected outcomes, the results did suggest an under representation of the socio-economic index. Suggestions are put forward to alleviate this problem in any future developments.
Despite decades of rigorous investigation reliable prediction of aeolian sediment transport rates continues to prove impossible. Transport rate formulae are based on the governing principal of steady state equilibrium, such that wind velocity produces a linear response in sediment flux. Field experiments however demonstrate a highly non-linear response and considerable deviation between observed and predicted transport rates. The limited predictive ability of the transport rate equations is largely attributed to crude measurement techniques that characterise wind velocity and sediment flux using time averaged values on the order of minutes effectively concealing a time scale on the order of seconds on which the equilibrium condition is established. Attempts however to resolve a characteristic time scale, continue to reveal only inextricable complexity. It is becoming clear from the study of multi-component systems that such non-linearity is a pervasive attribute of system dynamics.
Wind tunnel experiments were conducted to examine the nature of steady state sand transport under uniform forcing. Grains traversing a collimated region, illuminated by 500w halogen lighting, were acquired by video camera and transferred to computer at a rate of 10 frames per second. A suite of image analysis techniques was developed to quantify the volume of sand recorded in a sequence containing on the order of 104 images and a transport time series generated. Wind velocity measurements acquired using a Pitot tube / manometer combination and simultaneous with transport measurement, are recorded using a second video camera positioned normal to the manometer.
In contradiction to the steady state hypothesis, sand transport was observed to flux sporadically suggesting that the dynamics of aeolian transport are similar to avalanches observed in a sand pile. The number size distribution for transport events shows clear power-law scaling over about 2.5 orders of magnitude which is consistent with the dynamics of self-organised critical systems. Such systems are inherently unpredictable, a fact which may contribute to our understanding of the intractability of the aeolian transport problem.
To achieve sustainable coastal management and planning, the interaction between fine-grained - in particular, vegetated - intertidal environments and incoming waves needs to be better understood. Previous studies have established that wave attenuation over saltmarshes can be significantly greater than over unvegetated intertidal surfaces. However, detailed, quantitative information on the effect of marsh elevation in the tidal frame, marsh width, seaward marsh edge configuration (e.g. cliffed versus ramped marshes), seasonal changes in marsh surface roughness (e.g. creek density, vegetation composition) and incident wave conditions, however, has been lacking. Based on a 10-month-long wave/tide dataset from two sites on the Dengie marshes, eastern England, this study addresses the effect of (i) marsh edge topography; (ii) marsh width; (iii) inundation depths; and (iv) seasonal changes in marsh surface vegetation cover on wave height and wave energy dissipation. Directional waves and water levels were recorded at 21 locations across both shallow-sloping and cliffed (cliff height of ca. 1.5m) intertidal profiles. In addition, changes in marsh surface vegetation cover and composition were recorded on a seasonal basis.
Wave height attenuation over 310m of the shallow-sloping profile averaged 92 % over the monitoring period. Further analysis shows that the most rapid reduction in wave heights occurs over the most seaward 10 meters of permanent saltmarsh vegetation, where wave height attenuation averaged 2.1% and 1.1% per meter at the shallow-sloping and cliffed site respectively. Across the mudflat and the saltmarsh as a whole, wave height dissipation rates were significantly lower with an average of 0.1% and 0.5% per meter respectively. The presence of a saltmarsh cliff increased average wave heights by up to 0.5% per meter. Observed wave height attenuation showed a seasonal pattern at both sites (average wave energy attenuation near the marsh edge was highest in September – November and lowest in March – July) and appears to be linked to the cycle of seasonal vegetation growth.
The study provides criteria for the assessment of the wave dissipation potential of marshes characterised by different widths, edge configurations and slopes, variability of water depths, and seasonal variations in vegetation cover/density.
There will be increasing pressure on northern coastal and offshore regions for resource extraction as resources become scarce in more accessible regions. Marine navigation and transportation is likely to increase in response to economic development, and as ice cover reduces and the ice free season extends as a result of climatic changes. This article considers how economic development within northern coastal and marine regions may be reconciled with conservation. Integrated coastal management may be a useful process to reconcile economic development and conservation values.
Existing, developing and de facto approaches to integrated management for northern coastal and marine regions are examined in the context of scenarios for economic development and conservation. These scenarios include marine shipping and hydrocarbon exploration and production for coastal and offshore waters of Alaska, northern Canada, and the North Sea. These approaches to integrated management are one means of considering marine resources and their utilization with a sustainable development framework. These approaches may also be a means of reconciling marine protection and other sectors such as shipping, hydrocarbons and fisheries.
The article concludes that approaches to integrated management which reconcile economic and conservation values will be complex and consultative. The approaches will need to consider the interests of local peoples and communities, the needs of ecosystems and migratory communities, and environmental impacts and mitigation of development. The success of different approaches for reconciling economic development and conservation may be gauged by the range of issues and interests considered in these processes.
Intertidal flats are very sensitive coastal environments. They support large communities of highly specialised fauna and flora and are subject to physical processes that combine hydrodynamic and sedimentary processes that are highly sensitive to change. An added factor to the difficulty of studying and monitoring intertidal flats and their environment is that they may be situated near a human settlement that requires protection from flooding or inundation. Monitoring sensitive intertidal flat ecosystems to obtain precise and updated information on its geomorphological and biological state is a challenging task for coastal scientists, managers and engineers, who have to deal with both, the conservation of the environment and human demands.
This paper describes a monitoring programme designed to establish, for a sensitive intertidal flat, the state of a comprehensive number of environmental factors prior, during and after the construction of sea defences. The rigorous assessment of environmental impact has been the backbone of the design and implementation of this monitoring programme based in Newtownards, at the Northern end of Strangford Lough in Northern Ireland. The Lough is a major wildlife and scientific resource that is subject to several domestic conservation designations as well as being considered, under European Community Directives, as a site of importance for nature conservation. The individual components of the intervening forces and responses have been identified and studied on a high-resolution spatial basis whilst not interfering with the fragile ecosystem. Biological and geomorphological parameters were identified for monitoring. Surveys comprised plant ecology, spatial distribution of density and type of vertebrates and invertebrates, sedimentological analysis (both historical and contemporary), hydrodynamic controls and topographic evolution as well as salt marsh shoreline monitoring. A wide range of technologies have been implemented to achieve a monitoring programme that that can be fully integrated in a Geographic Information System minimising post-processing times for interpretation and data-base access. Some of the techniques include the use of an ATV mounted DGPS with sub-centimetre accuracy for topographical and biological surveys, colour infrared digital airborne image acquisition using the Kodak DCS460 and image analysis, as well as numerical wave modelling of wave propagation. A virtual monitoring centre is being created as the main outcome of this project. The participating institutions (research, management and the public) will be able to access the electronic libraries and maps via an integrated web-based database. This project has been approached as a research and development programme that serves as a model for integrated coastal zone management in sensitive tidal flat ecosystems.
In Ireland, coastal zone management has proceeded largely in an ad hoc manner and is based on sectoral legislation covering issues such as fishing, water quality, coastal protection, etc. Within this framework there exists a plethora of national and local institutions whose responsibility is divided between the marine and terrestrial sub-zones of the coastal zone. This paper presents results from a survey of local government approaches in 16 coastal local authorities to 2 aspects of coastal zone management, viz. coastal protection and application of the national legislation contained in the Foreshore Acts. The approaches of three local authorities are highlighted to illustrate that management, while based on the same legislative and administrative framework, varies considerably between local authorities. While changes in the administrative structure of local government are on-going it is important that the current problems of legal ambiguity and administrative uncertainty are clarified in order to provide a more consistent approach to coastal protection in Ireland.
The characterisation of the dynamics of Figueira da Foz beach, in the West coast of Portugal, is presented based on the analysis of previous studies and results obtained from the application of a numerical model. Advances on the understanding of the beach dynamics have been achieved by the quantification of the annual and seasonal longshore transport and several beach profile parameters. An evaluation of the contribution of the wave climate components on the longshore transport was also obtained. The results allow sustaining a prediction of the effect of a future change of the wave climate on the longshore transport. Figueira da Foz shoreline change was simulated based on different conceptual scenarios and the results, although not quantitatively conclusive, allow the understanding of the influence of the neighbouring beach hard rock outcrops on the recent evolution.
In northeastern Dorchester County, Maryland, 100 and 250 MHz ground penetrating radar surveys were used to define the east-west trending, linear Parsonsburg Sand deposit as a stranded estuarine shoreline complex, composed of three distinct highstand successions emplaced during climate-driven sea level cycles during the mid Pleistocene. These deposits form a broad ridge with 5 meters of relief, rising from their contact with the Kent Island Formation at 10 m MSLto ~ 14 m MSLalong the crest. The thin (<5 m) highstand deposits are cut into the underlying Pliocene Beaverdam and/or Miocene Pensauken Formations and overtop one another, attaining modern elevations of 12 m, 11 m, and 14 m MSL, in succession. Radar facies and lithologic data were used to identify transgressive and highstand components of these deposits, as well as backbarrier, shoreface, and nearshore facies and structures which can be traced into their equivalent bay bottom facies in the adjacent Kent Island Formation. These data correlate well with similar regional and global coastal deposits of marine oxygen isotope stage 11 age.
The methods used to determine or predict volumes of sand transported by longshore currents are briefly reviewed. We argue that the methods are flawed and that a fundamental re-examination of both field and theoretical approaches is in order. Net transport numbers obtained by any existing method should be considered order-of-magnitude values at best that are in no case sufficiently precise for coastal engineering purposes such as prediction of beach nourishment costs and environmental impacts.
A description is given of the response of phytoplankton composition to eutrophication caused by an increase in fresh water flux in four Empordà salt marsh basins. Cyanobacteria and mixotrophic phytoplankters (especially haptophytes and dinoflagellates) are the most abundant organisms in these basins. Under stable conditions, cyanobacteria take competitive advantage of the lack of inorganic nitrogen caused by confinement. Mixotrophs dominate coinciding with water inputs. The importance of the allochthonous supply probably favours mixotrophs, which may also take nitrogen heterotrophically. The phytoplankton-invertebrate biomass ratio (P/I) and the chlorophyll-phytoplankton biovolume ratio (Chl/BV) respond differently to stabilisation of freshwater input, depending on the degree of eutrophy of the basins. Thus, in more eutrophic basins flux regulation causes an increase in P/I and a decrease in Chl/BV, indicating higher density of mixotrophs and lesser density of invertebrates. Less eutrophic basins respond in the opposite fashion.
The Cresmina dune is a transgressive loose sand body of approximately 300m wide by 230m long, that is moving from NNW to SSE along the Guincho-Oitavos dunefield. This dunefield, located near Cascais, in the west coast of Portugal, can be classified as an headland bypass dunefield. The sand enters the system from two beaches at north, migrates on top of a marine abrasion platform, cut into cretaceous hard rocks, returning to the sea at south.
In order to determine the trend of evolution, the advance rate and the resultant sand drift that is occurring, a four year campaign (2000–2004) for monitoring the precipitation ridge of the transgressive dune and the contiguous area, is being carried out with one detailed topography survey per year.
Topography surveys are made using a Trimble DGPS with 1.5cm and 2.5cm of horizontal and vertical accuracy respectively. ArcView GIS is used to process the data and display the results. Because subtraction of 3D surfaces relative to different years is our goal, a very large effort is made to survey all the elevations on the studied area. Detail surveys of the 43,067m2 have been done with approximately 10m spaced measurements in flat smooth topography but 0.15m in rough topography.A 10cm grid is calculated using the measured points and the resultant Digital Elevation Models show elevations below 10cm.
The comparison between surfaces obtained from the 2000 and 2001 surveys clearly show the areas affected by deflation and accumulation. A volume of transported sand into the study area of 14,249m3, approximately 39.7m3year−1 per meter of dune section, and a variation of the precipitation ridge advance of 0.5m to 10m, depending on dune high and relative position were determined. Asymmetric evolution of the dune and influence of leeward relief in sand drift are clear.
Over 90% of the once vast tidal-freshwater wetlands of the Sacramento-San Joaquin Delta have been leveed and removed from tidal and floodwater inundation. Contemporary restoration efforts breach and/or remove the levees surrounding delta islands with the goal of regaining wetland habitat. However, experience so far with levee-breaches, both planned and unplanned, has shown that the transition from shallow open water to Tule marshes occurs slowly, if at all. Sedimentation rates in tidal marshes are an important control on this transition. This two-year study examined potential controlling factors on vertical accumulation including sediment type, and inorganic and organic soil components. Measured rates of surface accretion are in excess of 10 mm/yr. Gravimetric determinations show the main control on variations in soil accretion appears to be mineral sediment accumulation, with highest rates being close to inputs from the Sacramento River and lowest rates in interior marshes in the south-central delta. Rates of organic accumulation are remarkably similar among areas. However, measurements of marsh surface elevation change reflect the volumetric contributions of soil components and appear to be influenced by interannual changes in vegetation associated with minor variations in salinity. Marshes in breached-levee sites showed higher annual rates of marsh surface elevation change than reference marshes. This study demonstrates the importance of examining volumetric rather than gravimetric contributions to marsh soils in evaluating the factors controlling the vertical development of tidal marshes.
The morphology of three macrotidal ridge and runnel beaches in northern France was analysed from over 200 profiles in order to identify intertidal spatial and short-term (weeks) profile variability, at both the inter-site and intra-site levels. The beaches, essentially composed of medium to fine sand, are exposed to fetch-limited waves variably dissipated by nearshore sand banks. They have spring tidal ranges of 5.6 to 7.2 m, and sediment budgets ranging from equilibrium to deficient or surplus. The results show that spatial and temporal morphological variability is controlled by: (1) variations in exposure to wave action that depend on the proximity of nearshore sand banks, as well as on protection offered by artificial structures; and (2) by the state of the beach sediment budget. Where equilibrium sediment budget conditions prevail, as in the Dunkerque-Est sector, the beach exhibits a regular alternation of ridges and runnels that represent a cross-shore alternation of fluid-bed interaction domains involving surf/swash activity and channel flow conditions. Energy dissipation at the bed is spent in the construction and destruction of wave and tidal micro- and meso-scale bedforms, leaving little scope for macro-scale ridge migration or change in form, except under exceptionally high wave energy conditions. Chronic sediment losses, as in Wissant Bay, or gains, as in Calais-Hoverport, are recycled respectively alongshore and to embryo dunes and are not necessarily translated in terms of significant meso-scale (years) beach volumetric changes. The short-term beach sediment budget changes however favour active bed readjustments that explain distortion of the regular ridge and runnel form and marked profile mobility, even under low to moderate wave energy conditions.
This paper describes the development of a monitoring and management system for designated sea defences in Northern Ireland, which are managed by the Rivers Agency of the Department of Agriculture and Rural Development. The system developed was termed a “Management Response System” and includes a comprehensive monitoring regime combined with proposals for assessing the condition and performance of the sea defences.
The designated sea defences are at various locations in Lough Foyle, Belfast Lough, Strangford Lough, and at Killough, on the Irish Sea coastline. These defences protect extensive areas of low lying agricultural land, residential properties, and other various assets such as airports, the Belfast to Londonderry railway line and an army base. The study indicated that a breach of these sea defences would cause extensive flooding.
The long-term objective of Rivers Agency is to monitor, maintain, upgrade, and strengthen their sea defences. The development of this monitoring and management system aims to adopt “Best Practice” in terms of sea defence asset management.
Monitoring is often seen as an activity that is supplementary to managing sea defences. In fact, monitoring is a primary means of managing flood risk. In undertaking this study the aim was to ensure that the need for monitoring was based on an appreciation of flood risk. Moreover, monitored information should not just be collected but should be used to inform management decisions regarding flood risk. It is often this feedback loop that is missing when monitoring is considered in isolation to the overall management of sea defences.
The study assessed the flood risk associated with the sea defences and also defined how this risk is managed, the ‘Management Response’. This information was then used to define a comprehensive monitoring regime including visual inspections, structural surveys, site surveys, and environmental monitoring. The system recommends that an annual review report should be completed to summarise the results obtained and recommend further monitoring and remedial works for the following year's monitoring programme. This annual review will also inform management decisions on the need to upgrade the sea defences.
During the short period for which the system has been implemented to date, the conclusions drawn indicate that the management response system does provide an effective means of managing the designated sea defences within Northern Ireland. The monitoring has been targeted based on flood risk, and the monitoring results are used to assess the need for capital and maintenance works. Comparison of the system with published monitoring recommendations from agencies in the UK, Europe and the USA indicate that the system represents “Best Practice”.
The embankment of the Imboassica River formed the Imboassica Lagoon located to north of the State of Rio de Janeiro by the coastal sandbank, which separates it permanently from the sea. Formerly, the lagoon used to be connected to the sea naturally when waves broke the sandbar. Presently, connection is established artificially to prevent roads and houses from flooding. Such action increases the diversity of fish species living in the lagoon and therefore expands the fishing activity. This study investigated the effects of such openings on the structure of local fish community. Among the 26 species collected by gillnets, Hoplias malabaricus, Paralichythys brasiliensis, Gerres aprion, Genidens genidens, Strongylura timucu, Mugil curema, and Geophagus brasiliensis were the most abundant during the study. Lycengraulis grossidens, Archosargos probatocephalus, Tilapia rendalli, and Micropogonias furnieri were dominant before the canal was opened, whereas Anchovia clupeoides and Trachinotus carolinus were dominant in the period after the canal opening. Species diversity and evenness were practically constant during the months before the canal opening. Although both indices decreased substantially while the sea connection remained open, they returned to the same level as before when the canal was closed again. Cluster and detrended correspondence analyses showed similar patterns of two distinct groups of months before and after the canal opening supporting the idea that distinct fish assemblages occupied that environment before and after the event. Our results show that artificial canal opening is a factor that affects the structure and species composition of the fish community in the Imboassica Lagoon.
In the present contribution the presence of sand waves in the Messina Strait, Italy, is analysed, on the basis of unpublished data gathered during two different surveys carried out in 1991 and 1992. The study is carried out both from a sedimentological and morphological viewpoint, and in relation to the hydrodynamics in the Strait. Sand waves in two areas are examined: the first one lies just outside the northern part of the Strait, where the flow is rather complex, while the second one lies farther south in the Strait, where the tide characteristics force the flow essentially to oscillate along one direction. As a matter of fact, the dunes are made up with rather coarse sand; therefore, even where current direction varies significantly, only the highest currents are able to mobilise sediment. However, the differences in flow conditions play a significant role on the generation of smaller scale bed-forms (megaripples) in the first area, as obtained from a FFT analysis, and a likely sand bank in the second one.
A morphometric analysis showed that there is not a remarkable variability of these geometric characteristics at constant depth in the two areas. Steepness does not change much as well, and it appears always very low, thus suggesting a likely negligible effect of flow separation on these sand wave morphodynamics.
Time for the examined bed-forms to re-orient has been computed, on the basis of a defect dynamics theory, with the aim of partially investigating the risk for buried cables and pipelines to become exposed. Such time has been estimated as more than one century for both areas, thus implying that it does not play a significant role on problems concerning duct and cable cross design in the Messina Strait.
Low frequency waves, motions with typical frequencies of 0.001–0.05 Hz (also called infragravity or long waves) play an important role in many coastal sedimentary processes. So it is of considerable interest to improve our knowledge not only of their generation but also of their structure, in particular in very shallow water, where it has been shown that the wave energy spectrum can be dominated by long-period waves. Infragravity wave frequency structure on a transect crossing the surf zone of a fine grained, gently sloping double-barred beach was investigated using data from a 3-element coherent bottom-mounted pressure and current sensor line. In particular, it is shown that the infragravity wave frequency structure is largely controlled by the local bathymetry and appears to be unaffected (or at least not significantly) by water depth and wave breaking. In particular, the far infragravity band (< 0.01 Hz) is significant only at sensor situated landward of the ridge and runnel system and thus at all stages of the tide (water depth covering 0.6 m to 2.5 m) The nature of this far infragravity motion is not well understood. On the other hand, the 0.02–0.035 Hz band is linked to the difference nonlinear triad interaction associated with the two primary incident waves (peak frequencies centred around 0.06 Hz and 0.09 Hz).
The sediment budgets of most beaches in southern California are dominated by sand contributions from coastal streams. Extensive alteration of fluvial systems by the construction of dams and debris basins has reduced substantially the volume of sand reaching the shore. This is one factor in the chronic erosion of these beaches. The purpose of this research is to assess the magnitude of the impacts of coastal dams and debris basins on sand delivery using direct measurements of sediment impoundment rates within eight watersheds.
Sediment impoundment data were obtained for 28 dams and more than 150 debris basins in the watersheds of eight rivers: the Santa Ynez, Ventura, Santa Clara, Los Angeles, San Gabriel, Santa Ana, San Dieguito, and San Diego. The cumulative effect of these structures is the impoundment of more than 4,000,000 m3 yr−1 of sediment. This is equivalent to a potential deprivation of beach sand of roughly 3 m3 yr−1 per m of shoreline in the five southern California coastal counties.
The sedimentation records for individual watersheds are interpreted in the context of wet and dry climate episodes in the last century. The data are compared to estimates of sediment delivery derived from stream gauge records. In most watersheds, the majority of sedimentation occurs behind one dam, and the contributions of debris basin impoundment are secondary. The net effect is a substantial reduction of potential sand supply to the coast.
Accurate water surface topography data and its spatial and temporal variability provide information about the interaction of physical processes acting in coastal regions. At the inlet system in Teignmouth, UK, these data complement methods for the extraction of nearshore morphology using remotely sensed video techniques. The video methods normally assume that the water surface is horizontal over the region, an assumption that is often invalid in shallow water. The study area is a complex macro-tidal inlet system bounded by a rocky headland and a 2 km-long beach. In order to predict the water surface topography and its response to different tide, wave and river discharge conditions, a calibrated and validated numerical model (MIKE21 HD, NSW) was applied. The water surface topography at the inlet and adjacent coast exhibits high spatial and temporal variability, mainly related to the tidal phase. It is the interaction between the tidal phase and the sandbar morphology, defining the velocity field in the channels, which drives the water surface topography distribution across the region. Since a small, unaccounted, difference in water level may result in significant deviations of the horizontal shoreline position, this study highlights the importance of using numerical modelling in conjunction with the video image techniques for the extraction of nearshore morphology.
The study area covers 21 km of sandy coast between Porto Garibaldi and Porto Corsini (northern Adriatic Sea). The main problem in the area is beach erosion. This is due to the evolution of the delta of the Reno River, and to the effects of past anthropogenic impacts that modified the sediment transport dynamics of the beach. An important factor affecting the morphological evolution of the site is land subsidence. This caused an important modification of the relative elevation of the ground at sea level, increasing the beach erosion. Another phenomenon analysed in the study is the closure of the mouth of the Bellocchio channel, that links the Adriatic Sea with the existing lagoons (Ancone di Bellocchio and Valli di Comacchio). The mouth sanding process influences the water exchange and the hydraulic circulation within the lagoons and creates severe water quality problems. The study takes into account the most important physical and biological variables of the local environment and suggests some management interventions defined and verified with the use of numerical models. The solutions follow the basic principles of Integrated Coastal Zone Management established by the European Community take a wide ranging perspective, build on an understanding of specific conditions in the area of interest, work with natural processes, ensure that decisions taken today do not foreclose options for the future.
There are approximately 400 barrier islands on the world's deltaic plains, with a combined length of 4,100 kilometers. They make up 30% of the world's estimated barrier islands (by length). Deltaic barrier islands make up more than half of barrier islands in South America, Asia, and Africa, but only 5% in North America and Europe due to differing sea level rise history. Barrier islands are present on all types of deltas, including wave, tide, and river dominated deltas. The transgressive model of barrier island formation on the Mississippi Delta is well understood, but applies to relatively few deltaic barrier island chains. Spit formation, and to a lesser extent beach ridge accretion, on active lobes appear to be the most dominant processes of barrier island formation. A simple morphologic classification based on island length and inlet width is presented. Five island types (Nile, Mangoky, Niger, Gurupi, Mekong, and Mississippi) are described, relating island, inlet, and shoreface morphology to the relative roles of wave, tide, and fluvial processes. Human alterations to the sediment supply, extraction of hydrocarbons, and the projected near future acceleration of sea level rise poses a significant threat to many deltaic barrier island systems, many of which already display geoindicators of disintegration.
This paper presents a model study of the sediment transport processes of a shingle beach under the combined action of waves and tides. Parallel experiments were carried out with a constant water depth corresponding to the high water level of the tidal experiments, thus allowing a direct comparison between the two cases. It was found that the presence of the tide affected the beach behaviour differently depending on the wave climate. Under storm conditions, a rolling bar was clearly seen moving below the Mean Water Level (MWL) with both the flood and ebb tides. Under swell conditions on the flood, sediment was eroded once a critical depth had been reached but was moved onshore in the uprush to form the berm. The presence of the tide was shown to increase the size of the berm in a summer profile, and push the offshore bar further seaward in the winter profiles. The overall beach slope did not change when subjected to the wave attack without the tide but altered significantly under the combined action of the wave and the tide.
Beach litter found along the Bristol Channel and the coastline of mid-Wales, UK, together with litter obtained from Turkey, Malta, Spain, Tunisia and U.S.A. tourist beaches, and litter gathered from rural roads in Gloucestershire, England, UK, was analyzed by principal component analysis (PCA). PCA distinguished between riverine, sewage-related debris and shipping/fishing source items, but sourcing beach user litter was more problematic. This was attributed to a difference in litter transport mechanisms. PCA for the Bristol Channel distinguished between riverine and marine sources (inner vs. outer channel) and also a sewage sourced group. PCA indicated a land-based source for marine debris found on Mediterranean and USA beaches together with roadside litter from England. Three ‘litter markers’ introduced into the analyses, were comprised of different source groupings: ‘vessels’ (both fishing and other sea going vessels), ‘beach users’, and sewage-related debris (SRD). The former stood out from the latter two markers with beach user and SRD markers appearing to be indistinguishable. The item numbers in each group were six, five and three respectively and this could account for the findings.
It was shown that ignition loss (organic matter adhered to singing sand) could be new index related to reduction of sound quality in ‘singing sand’. Ignition loss for the Kotobiki Beach was found to be about 0.5%. To recover the quality of the sound producing property of singing sand, wave action, bottom profile and sediment renourishment were investigated. For optimum sound recovery of the beach, it was found that the ideal injection point was near the offshore bar under erosive wave action conditions.
The aeolian transport conditions on a macro-tidal ridge and runnel beach in northern France were monitored over two 30-minute experiments, representing respectively conditions of onshore and offshore to shore-parallel wind flow. Several anemometers, a portable weather station, acoustic grain impact counters (saltiphones), temperature and ground moisture probes, and aeolian sand traps were deployed in order to determine the effects of topographic, moisture and bedform variations on aeolian sand transport. The instruments were deployed across a ridge/runnel/ridge system on the mid- to upper beach, and on the upper beach terrace linking this ridge and runnel system to the dune front. The results show that the near-ground wind velocities are slowed by the pronounced ridge and runnel topography of the upper beach. The ridge and runnel system segments the fetch, whatever the wind direction. The experiment involving an onshore wind was associated with negligible rates of sand trapping in spite of suitable wind conditions. Significant trapping occurred during the offshore to shore-parallel wind experiment, but this was limited to the upper beach terrace and upper ridge and runnel, and there was little downwind transport below this upper ridge/runnel/ridge set. These preliminary experiments and the field observations suggest that the important degree of wave-tidal bedform development over the beach surface and the high moisture levels in the runnels and sometimes on the ridges, both common characteristics of ridge and runnel beaches, tend to limit sand mobilisation. It is tentatively suggested from this data set that this ridge and runnel beach is characterised by a moderate and balanced exchange of sand with the dune front.
Four natural inlets, existing in a multi-inlet, barrier island system, were studied for the period between the 1940s and 1996. Inlet width and position of the inlet channel were determined using a series of vertical aerial photos and charts. The objective of the work was to determine the association between inlet migration patterns and different hydrodynamic conditions, major storms and engineering interventions. Results indicate that natural inlet opening and evolution were mainly affected by three factors: (a) existence of sub-embayments (western and eastern) inside the system, (b) exposure to wave energy, and (c) inlet efficiency. Two distinctive eastward migration patterns were found by analysing the correlation coefficient (r) between inlet width evolution and inlet migration and by the comparison of the shape of the curves fitted to the inlet migration behaviour.Typical migration of the high-energy flank (on the west side of the system) is characterised by an initial stage of readjustment, with low migration rates, followed by a stage of high eastwards migration rates, up to a limiting position. Inlet width remains reasonably constant during the entire migration cycle, thus the correlation between inlet width and position is very low.Typical inlets on the low-energy flank (east side of the system) are formed by barrier breaching during major storms and produce initially very wide inlets. Eastward inlet migration on the low-energy flank follows a natural logarithmic curve where channel migration is accompanied by strong constructional processes on the updrift barrier. Due to subsequent inlet width reductions, the correlation between inlet width and position is significant.
Sediment transport patterns within coastal environments continue to be of strong concern to the coastal engineer, scientist and manager. A study was conducted on Saltwater Creek, Gold Coast, Australia, which is a small microtidal estuary/embayment system that has no continual inflow of freshwater with inflows only resulting from direct catchment rainfall. Use was made of an Acoustic Doppler Current Profiler (ADCP) and a profiling transmissometer to determine the likelihood of tidal flow induced resuspension. Results showed that the apparently simple system was actually highly complex in nature. It was susceptible to significant sediment loadings as the result of catchment runoff and biological activity. Resuspension activity within the main channel was qualified and found to play only a minor role in the observed suspended sediment loadings. The results obtained have permitted the development of a conceptual model, from which some future management strategies can be proposed. Importantly, the techniques used in this study can be applied elsewhere to investigate sediment transport (including resuspension) properties when equipment resources are limited.
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