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The hurricane hit the Mississippi coast head on. Orrin Pilkey immediately rushed to Waveland to bail out his parents whose house was 4 blocks back from the Gulf of Mexico. Their house had been flooded up to the 5-foot level and a half dozen trees had crashed through the roof. Some neighboring houses were now piles of broken boards and glass. But the houses closer to the beach disappeared completely, leaving behind empty concrete pads as evidence of their former existence. The wood, the sinks, the refrigerators, the cars, and all the family treasures from the destroyed houses had piled up in a sort of dike or ridge well inland of the coast. Reopening of roads through the debris dikes resulted in large road cuts stratified with the layers of a human disaster. A railroad embankment on the back side of town halted the storm surge and marked the line between devastated homes and damaged homes. For once, it paid to have lived on the wrong side of the tracks. American flags flew from trees and house fragments and the prevailing attitude among survivors was one of patriotism and confidence that no mater what the odds, we shall return.
High-resolution seismic reflection profiles and bottom sediment samples indicate that the seafloor south of Province-town Hook, Massachusetts, at a water depth of 3 to 20 meters, is formed of relict shoreline features. Much of this morphology was constructed during the late Wisconsin regression 13,500 years ago and the Holocene transgression that began less than 13,500 years ago and reached a depth of 8 meters 4500 years ago, 6 meters 4000 years ago, 2 meters 1500 years ago, and near its present level less than 1000 years ago. The morphology of the seafloor reflecting modern-day processes is restricted to a narrow inner zone, where depths are less than 3 meters, and the center of Cape Cod Bay, where depths are greater than about 20 meters. The shallow inner zone is a high-energy environment that is in constant change, particularly during storms from the west. These storms affect not only the inner zone but also the beaches and the bluffs backing the beaches. The center of Cape Cod Bay is a region of low energy where fine-grained sediments from the north come to rest. The relict terrain between these two environments, however, is not free of recent sediment. Some of the detritus from the inner zone is transported westward to the relict terrain. The silt and clay fraction of these sediments also may be transported even farther westward and incorporated with the silt-clay facies in the center of Cape Cod Bay.
The present paper, “Eb- en vloedschaarsystemen in de Nederlandse getijwateren” (Ebb- and Flood-Channel Systems in the Dutch Tidal Waters), which was published in 1950, should be considered as Van Veen's most important publication since his thesis. It summarizes the results of 20 years of intensive study of estuarine and tidal-basin mor-phodynamics in The Netherlands. Unfortunately, Van Veen's paper was published in Dutch, with only a brief summary in English. Luckily, the figure captions were given in both Dutch and English, allowing international researchers coming across the paper to read it as a kind of “cartoon.” Understandably though, the paper has received very limited recognition in the international literature. We have seized this occasion to publish an English version of Van Veen's paper. The paper is testimony to Van Veen's keen observational and artistic skills. His approach is nearly “Da Vincian,” in the sense that he is not only a fascinated observer of nature, but a sharp one as well, and he tries to capture the essentials of the dynamic behavior of complex coastal systems in apparently simple sketches. Many of the natural systems that Van Veen studied have been regulated since; thus, this paper contains a set of irreplaceable, high-quality observations on the natural dynamics of tidal systems. It forms an excellent introduction to the study of channel dynamics in estuaries, tidal inlets, and tidal basins.
Dune migration response to regional inter-annual climate variability in Ceará, Northeastern Brazil was investigated. Dunes along the study area are mainly barchans and sand-sheets and they migrate at an averaged rate of 17 m/yr although this value depends on dune dimensions, the larger the dune the lower the migration. This is explained by the existence of a representative regional aeolian transport rate that is almost constant along the region inducing different dune response depending on dune size, which is a common feature of barchans fields. Estimated yearly transport rates from dune migration were compared to the values obtained by using the calibrated aeolian transport formula when fed by regional wind climate data. The results obtained differ by about 20% (100 m3/m/yr) from actual aeolian transport measurements (80 m3/m/yr) from dune evolution, which can be considered as a good agreement between both approaches. We show a relationship between dune displacement and strength of the dry season in the region. With larger displacements occurring in drier years, coincident with a more northern position of the Intertropical Convergence Zone (ITCZ), which occurred during strong El Niño periods. This relationship serves to link the dune migration in Northeastern Brazil with El Niño events. As El Niño Southern Oscillation (ENSO) supposes a major climatic perturbation, its effects will be transferred to all the dynamical processes controlled in a direct or indirect manner by the regional climate. These findings should be incorporated into Integrated Coastal Zone Management (ICZM) strategies for the region.
Surf information is imperative for safety, coastal planning, and engineering applications. Daily surf observations made primarily by lifeguards along the north shore of Oahu, Hawaii, have been digitized for the 35-year period from 1968 to 2002. The subjective nature of observations introduces uncertainty. This study analyzes the temporal consistency and estimates the accuracy of the observations. Comparisons are made to breaker heights derived from significant wave height and dominant wave period as measured by the nearest environmental buoys, one of which has a series length of 22 years. The comparison pairs are picked from the high-surf season of October through March for days dominated by long-period swell. The analysis shows the surf observations are consistent in time. The uncertainty is between 10% and 15% of the reported height, and the magnitude of the error increases with surf height. Given the large range in breaker heights on the north shore of Oahu, this error is small. Although the visual observations have low precision and only represent daylight hours, the time series are longer and more continuous than other breaker height data for this region. Thus, these observations represent the best available resource for understanding regional surf climatology, which is described in this study.
In SW Spain, numerous tourist beaches have been nourished over recent years to counteract coastal retreat. Nourishment projects have not produced great endurance, mainly because of the lack of basic information on coastal dynamics and longshore sediment transport paths. In order to cover these aspects in a sandy coastal sector south of the Guadalquivir River mouth, a beach monitoring program was carried out between 1996 and 1998, with a secondary program between 2000 and 2002. Four main beach types were identified, each one with different volumetric trends during the monitoring periods. Most beaches recorded accretion because of the prevalence of fair weather conditions, which emphasized differences among beaches. In a broad sense, beaches located on intertidal rock platforms recorded erosion or no change. Those located updrift of rock platforms or human-made constructions (groins) recorded accretion. These structures divide the coast into several littoral cells, which control longshore sediment transport between beaches. All this information is very useful for planning replenishment projects on eroding beaches. The distribution of cells, the sediment transport paths associated with them, and the volumetric trends obtained for every beach type were used for evaluating nourishment procedures, sand volume needs, and expected life time of the resulting artificial beaches.
Benthic maps provide the spatial framework for many science and management activities in coastal areas such as identification and protection of fish distributions and associated habitat as well as for monitoring changes in benthos and fish communities. To meet this need at Gray's Reef National Marine Sanctuary off the Georgia, U.S.A., coast, we created fine-scale benthic maps by visual interpretation of sonar imagery within a geographic information system. The major bottom types in the sanctuary—flat sand, rippled sand, hard bottom that is sparsely colonized with sessile invertebrates, and densely colonized hard bottom—were delineated through combined analysis of backscatter from side-scan sonar, bathymetry from multibeam sonar, scuba surveys, and video transects. Maps showed that unconsolidated sediments cover 75% of the bottom of this region; 8% occurs as flat sand plains with obvious burrowing and reworking of surface material by mobile benthic invertebrates, whereas 67% occurs as rippled sand without such fauna. The rest of the sanctuary consists of limestone bottom in two types of formations; either flat, sparsely colonized regions (25% of the sanctuary's total area) or as vertical ledges that are densely colonized with a diverse fauna of sessile invertebrates (<1%). Despite their limited area, these 0.5–2-m-tall ledge features harbor the majority of the sanctuary's biodiversity and biomass of both sessile invertebrates as well as ichthyofauna. A modified accuracy assessment procedure was used to account for spatial autocorrelation in the validation data and to separate thematic from positional accuracy. Overall thematic accuracy of maps is 95% for those areas of the map in which thematic accuracy and positional accuracy could be separated (87% of the mapped area). This fine-scale characterization provides a benthic inventory for a marine sanctuary and novel methods for mapping using sonar and accuracy assessment using transects.
Over the past 40 years, consideration of the potential effect of sea level rise on sandy coasts has been dominated by the conceptual model proposed in the Bruun Rule, which is used to predict the horizontal translation of the shoreline associated with a given rise in sea level. A review of the hypotheses that form the basis for this two-dimensional model suggests that the assumption of net sand transfer to the nearshore profile and deposition of a thickness of sediment equal to the rise in sea level is probably incorrect. Moreover, the model omits consideration of a significant component of the coastal sediment budget, namely the dune sediment budget, and the processes associated with beach-dune interaction. An alternative conceptual model is developed on the basis of a two-dimensional equilibrium profile similar to that which forms the basis for the Bruun Model. The proposed model incorporates consideration of the dune sediment budget and foredune dynamics. In contrast to the Bruun Model, it predicts no net transfer of sediment to the nearshore profile and preservation of the foredune through landward migration. It is argued that the model proposed here offers a better starting point for developing more realistic models of shoreline response to sea level rise that incorporate consideration of alongshore sediment transfers and more complex coastal morphology and sediment characteristics. Testing of the validity of the model and its potential use for integrated coastal zone management will require consideration of the volume changes associated with sea level rise on a decadal scale.
Factors controlling the distribution of shelf sand as a resource, a component of reef ecosystems, and a dynamic substrate are poorly understood. An initial step in understanding sand accumulation in each of these roles is to identify its areal extent and change through time. Digitized aerial photographs and digital images provide common, inexpensive data sets that are generally underutilized for the purpose of marine substrate classification. Here we use only two bands, blue and green (470 and 550 nm), to demonstrate the utility of simple aerial photography in classifying marine substrate. Although these two are acquired from a hyperspectral data set, they represent blue and green in an RGB image such as commonly available in digitized aerial photographs. We add as a third band the second eigenchannel of a principal components analysis of these bands. Using an artificial neural network classification model, we identify submarine and subaerial sandy substrate in a digital image of a detached reef island in the Red Sea, Gezirat Siyul, Egypt. With careful selection of training and test groups, using small percentages of the total classified image, we create an efficient and accurate classification model. The model, trained to identify two classes, “sand” and “other than sand,” produces a classified image that provides sand locations and approximate areal coverage. Confusion matrices for both training and testing groups have user's accuracies in the 90 percentiles, indicating accurate pixel classification.
Airborne laser bathymetry (ALB) is a new laser bathymetric survey tool that has applicability in clear coastal (Case II) waters to depths of −70 m. The new sounding technique features rapid acquisition of large, high-quality data sets via variable swath widths that are independent of water depth. This advanced ALB system was deployed along the continental shelf of southeast Florida (Palm Beach, Broward, and Miami-Dade Counties), providing a contiguous data set for 160 km of coast from onshore to 6 km offshore. Image enhancement of the ALB digital data facilitates recognition of numerous seafloor features and bathymetric patterns. Bathymetric analysis of the 600-km2 survey area on the continental shelf shows inherited lithologic features that are partly covered by surficial sediments. Primary parabathic (shore-parallel) provinces include: (1) nearshore rocky zones dominated by the Anastasia Formation, (2) coral-algal reef systems (Florida Reef Tract [FRT]), and (3) marine platforms (terraces). Sedimentary subprovinces include shoreface sands, interreefal sedimentary infills (coral rubble in basal sequences and near reef gaps), and finer-grained materials seaward of coral reefs. Tertiary topographic features include: (1) longshore bar and trough systems, shoals, sand sheets (flats), and diabathic (cross-shore) channels; (2) reef crests and ledges, forereef spur-and-groove topography, sediment ramps in large reef gaps, and incised paleo-river channels; and (3) drowned karst topography. Hierarchical organization (classification and mapping) of these bathymetric features is now possible for the first time because of the increased accuracy and density of ALB data. These data and related maps allow, for the first time, assessment of links between the influence of seabed morphology on wave transformation patterns and beach morphodynamics in southeast Florida.
The 15 km-long bedrock promontory of Cayenne, French Guiana, comprises several headland-bound fringing sandy beaches and numerous, more or less highly embayed, short pocket beaches that are affected by mud banks migrating alongshore from the Amazon to Venezuela. The influence of mud banks on this coast may be considered within a four-phased cycle characterised by a “mud bank” phase that leads to extensive wave energy dissipation, an “inter-bank” phase of relative mud scarcity and enhanced wave activity, and the two transitional phases between these two phases. Three profiles from two short (< 400 m long) pocket beaches were variably surveyed between November 2001 and November 2004, a period characterised by the last stages of a bank phase, a short transition, and an inter-bank phase. The profiles comprise an upper sandy segment linked to a relatively flat muddy lower beach that extends offshore, the sand-mud contact and elevation of this muddy lower profile depending on exposure to wave energy. Profile changes were basically cross-shore, with little or no evidence of longshore sand transfers, because of the poor propensity for development of longshore gradients in wave energy in these short embayed beaches. Differences in the intensity of profile change were due to variations in the degree of exposure to waves which strongly depended on the presence, inshore, of wave-dissipating mud. These pocket beaches differ from the more open and longer beaches of Cayenne, which show periodic alternations in longshore drift that lead to rare forms of beach rotation induced by wave interactions with the mud banks.
Field measurements of dissolved oxygen distribution in the vicinity of a small fishing harbor in Attica, Greece, are presented, and the positive effect on water quality of rubble mound structures are evaluated. Surveys conducted during the spring and summer periods of 1998, 2000, and 2002 included dissolved oxygen (DO) concentration and temperature measurements in 30 sampling stations inside and outside the harbor basin and in the neighboring beaches. Regular measurements of both wind direction and force in Beaufort scale, as well as some measurements of wave and current were also made.
Dissolved oxygen concentrations in the harbor basin and in the beaches were lower than those measured outside the harbor in the vicinity of the rubble mound breakwater on the order of 1–2 mg/L. Dissolved oxygen concentration was found to increase in the zone of wave breaking. The increase was steeper with increasing wave heights. It is thus concluded that the rubble mound breakwater improves water quality in the surrounding area.
The field measurements agree qualitatively with laboratory measurements performed at National Technical University of Athens of wave breaking on permeable breakwater structures. Further study on the influence of harbor structures on air-sea oxygen transfer is needed before quantitative conclusions can be drawn.
The possible influence on swash-zone sediment transport of hydraulic jumps is investigated using field measurements from two natural beaches in high-energy (Hs = 1.5 to 3.7 meters) dissipative conditions. Results from measurements of cross-shore velocity using electromagnetic current meters at z = 3 centimeters, water depth using pressure transducers at z = 0, and cross-shore bore displacement using video time stacks suggest that hydraulic jumps may occur in approximately one-third of infragravity backwashes. Results from sediment load measurements using traps suggest that backwashes containing jumps can advect approximately 2.5 times as much sediment offshore than a backwash not containing a hydraulic jump. The overall effect of hydraulic jumps appears to be to enhance offshore transport, especially in high-energy conditions, when infragravity backwashes are more common.
Satellite measurements of suspended sediment, temperature, and chlorophyll α are used in combination with surface current measurements to investigate surface circulation and structure of the Mississippi River plume. River discharge changes affect frontal locations, areal extent, and suspended sediment loads of the plume. During high river discharge (>20,000 m3 s−1) in spring, the sediment plume extends 23 km southwestward, covers 2700 km2, with maximum concentrations of 360 mg L−1. Plume temperatures vary seasonally from 10° to 28°C, with maximum surface fronts of 3.3°C km−1 in winter.
East winds, prevalent in autumn, winter, and spring, drive a westward flow of river waters around the delta, linking two isolated shelf regions and increasing river discharge onto the Louisiana/Texas shelf. During peak river flow, this westward current exhibits velocities of 40–90 cm s−1, is 20 km wide, and transports 140,000–165,000 m3 s−1 of river and shelf water. It usually turns toward the coast between 89.5° W and 90° W, feeding a clockwise gyre in the Louisiana Bight and a westward coastal current. The prevalent east winds trap river water and associated nutrients on the shelf where hypoxia later develops in late spring/summer.
During autumn and winter, short-term wind reversals from frontal passages rapidly reverse plume direction, initiate off-shelf transport, and reduce residence times for river waters and associated sediments, nutrients, phytoplankton, and carbon. During summer, persistent southwest and south winds force river water eastward, where cross-margin transport is likely due to the relatively narrow shelf. Slope eddies and the Loop Current control river water after leaving the shelf.
The origin of the radial sand ridges (RSR) in the southern Yellow Sea has been a controversial problem since they were discovered. The key to solving this problem is to answer whether the radial tidal current field existed prior to the formation of the RSR. With a two-dimensional tide model over the Bohai Sea, the Yellow Sea, and most of the East China Sea, the M2 tides and tidal currents at around 7000 years BP, 6000 years BP, 3800 years BP, the 8th and 11th centuries AD are simulated. The model results show that, from 7000 years BP to 3800 years BP, tidal currents north of the major longitudinal axis of the Paleo-Yangtze River Estuary (PYRE) converged toward and diverged from the mouth of this river and the distribution pattern of the tidal current field was largely similar to that of the tidal current field over the southern Yellow Sea. Toward the 8th century AD, the PYRE became a delta. The Yangtze River mouth migrated southeastward considerably until the 11th century AD, and the shorelines of the Yangtze River mouth and northern Jiangsu were generally similar in geometry to the present ones. At these two stages (the 8th and the 11th centuries AD), the radial tidal current fields with a focal point in Dongtai area were evident, and the distribution patterns of tidal current fields were much similar than at present. After the 11th century AD, the northern Jiangsu shoreline evolved gradually to the present position under the influence of the shifting Yellow River mouth and the present radial tidal current field, with its focal point in the Qianggang area, was formed eventually over the southern Yellow Sea. In short, the radial tidal current field off the PYRE and northern Jiangsu coast has existed and its distribution pattern has been quite stable since around 7000 years BP, despite the shoreline evolution of the PYRE and northern Jiangsu coast. However, the convergent location of the tidal currents has shifted from the mouth of the PYRE to the Dongtai area and then to the present Qianggang area. This suggests that the radial tidal current field in the RSR area existed before the formation of these sand ridges, and the RSR in the southern Yellow Sea were formed and are maintained by radial tidal current fields with sufficient sediment supply.
A morphodynamical model for coastal areas has been developed by simultaneously simulating the dynamics of waves, coastal currents, and sediment transport rates. The sediment transport rates are calculated on a staggered two-dimensional grid, and then the sediment budget is used to predict the coastal morphology changes. The model can simulate short-term and long-term morphological changes around coastal structures. A case study along the Nile Delta coast in Egypt is used to demonstrate the effectiveness of the present model by calibrating and verifying the model results with field measurements. The model can be applied to coastal domains with similar characteristics with appropriate parameter calibration.
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