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The Saffir–Simpson scale is useful for evaluating maximum sustained hurricane winds and storm surge over open water in the prelandfall window, but it fails to accurately account for the observed impacts over land. A new postland-fall hurricane classification system (HCS) is proposed that redistributes the categorization of hurricanes into types according to six variables: open water storm surge, rainfall, duration of hurricane force winds, maximum sustained winds, gust score, and minimum central pressure. Hurricanes are assigned values for each variable and summed for a numerical 0–100 grade. Principal component analysis and hierarchical cluster analysis are also performed on the six variables to categorize U.S. land-falling hurricanes into storm types. A total of 41 land-falling hurricanes in the United States since 1960 have been analyzed. The summation scores show many hurricanes that are of strength similar to their Saffir–Simpson classifications, with several notable exceptions. The cluster analysis identifies five different hurricane types. These types can be arranged to identify hurricane strength and structure more effectively than the Saffir–Simpson scale. In focusing on the observed storm intensity over land and the resulting human experience, the HCS allows a way to compare hurricane impacts across different periods.
The potential biological effects of elevated suspended sediment concentrations caused by beach nourishment activities are a commonly cited environmental concern; however, the spatial scope and magnitude of increases in total suspended sediment (TSS) levels are infrequently monitored. In this study, suspended sediment conditions were monitored for two nourishment events on the northern coast of New Jersey in 1997 and 1998. Samples were taken in the swash, surf, and nearshore zones near the discharge pipe and at reference areas both north and south of the fill sites. Sampling was also conducted after two major storms passed through the area in September 1999 (the remnants of Hurricanes Dennis and Floyd). For both nourishment events, swash zone suspended sediment concentrations were significantly higher at sites of active discharge and recently nourished stations than at unnourished stations; however, no differences in TSS concentrations were detected between nourished and unnourished stations in the surf zone and nearshore habitats during either nourishment event. Maximum bottom surf zone and nearshore TSS concentrations related to nourishment activities were 64 mg/L and 34 mg/L, respectively, compared with respective maximum bottom concentrations of 81 mg/L and 425 mg/L after storms. Background maximum bottom TSS concentrations in the surf and nearshore zones on unnourished portions of the beach were less than 20 mg/L. Elevated TSS concentrations associated with the active beach nourishment site were limited to within 400 m of the discharge pipe in the swash zone. More direct monitoring of TSS concentrations is needed to better understand the potential biological effects of beach nourishment activities.
Sediment grain size and total organic carbon (TOC) content in sediments, coupled with image processing analysis, were investigated to assess natural vs. anthropogenic distribution patterns of Posidonia oceanica seagrass meadow, in the proximity of a river mouth and a port embankment in the Gulf of Oristano (Sardinia, Italy). Two unvegetated areas (∼9 km2 each) were detected by meadow mapping: (i) in front of the river mouth, and (ii) close to the port.
Both unvegetated areas were characterised by a high silt clay content in the bottom sediments, allowing us to identify the deposition of fine sediments as a factor limiting P. oceanica distribution. A marked variation within the depth of sediment grain size was recorded close to the port, where a 5-cm layer with silt clay >50% overlapped a sediment with silt clay <20%, suggesting a recent change in depositional processes.
Grain-size fractionation was analysed using the silt : clay ratio, which indicated high-energy conditions in the area close to the port. Differently high TOC concentrations were found in front of the river mouth. These data allowed us to identify two different types of sedimentary process impacts on P. oceanica distribution: (i) a “natural” limitation because of the river inflow and (ii) an anthropogenic impact due to fine-sediment deposition following the dredging and building of the port.
Accelerator mass spectrometry (AMS) radiocarbon dating of basal high-marsh sediments from Romney Marsh, Revere, Massachusetts, provides a revised reconstruction of the late Holocene relative sea-level history of the region. After correction for changes in tidal amplitude, the sea-level change envelope reconstructed from five AMS radiocarbon dates of basal marsh sediments at Romney Marsh in Revere, Massachusetts, indicates a rise in mean sea level (MSL) of close to 2.6 m in the past 3300 years. The data indicate a possible decrease in the average rate of rise from 0.80 ± 0.25 mm/y between 3300 to 1000 YBP to a rate of 0.52 ± 0.62 mm/y between 1000 YBP and the past 150 to 500 years. An increase in the rate of sea-level rise is evident over the past few hundred years. A slowing of the rate of sea-level rise between 1000 YBP and historic times and the increase in the rate of rise to modern values is also evident in other sea-level records from Maine and Connecticut. The coherence between these sea-level records and concomitant climate changes in and around the North Atlantic indicates that regional-scale sea-level fluctuations in the region may be driven by climate forcing. However, earlier sea-level fluctuations correlated to sea-surface temperature variability are not well-resolved by this record or other records in the region and may indicate that changes in sea level are not tightly coupled with sea-surface temperature changes.
Hydrodynamic measurements and analysis of suspended sediments were conducted in the coastal area to reveal the source and dispersal processes of muds accumulating in Jinhae Bay, one of the largest bays in the Korea Strait. A number of hydrographic stations in the bay were occupied in order to obtain time series of suspended sediment concentrations, currents, water level, temperature, and salinity for one or two tidal cycles. The results, measured in May through October, suggest that a slight net influx of suspended sediments into the bay occurs consistently under low-wave, microtidal conditions. They also show a passageway of suspended sediments selectively through an entrance facing the open sea. The hydrodynamic measurements, together with tidal current pattern and landsat image of the suspended plume in the Korea Strait, indicate that the mud in Jinhae Bay has been fed largely by the adjacent Nakdong River, rather than by offshore sources.
Tamandaré, Pernambuco State, Brazil, has 9 kilometers of beaches that form three bays protected by coastal reefs. Until July 2001, these beaches were frequently covered by solid wastes, mainly plastics. Solid wastes carried by the wind and tides reached the native vegetation, where it remained imprisoned and accumulated in large amounts, making the beach aesthetically objectionable. The origin of the largest part of this solid waste was the local rivers. These rivers drain many municipalities but have their mouths next to Tamandaré. Beach users and locals were equally responsible for the accumulated residue. From August 2001, the municipal administration started a beach cleaning service, aiming to minimize the negative aesthetic effects caused by the accumulation of solid wastes. Sampling of plastic items accumulated on the beach within four transects of 2500 square meters each was carried out for 4 months before the cleaning service began and resulted in a total of 9289 plastic items. The dry and rainy season accumulations were significantly different. After the start of the service, in the same sampling area, plastic items were 1712 in total. In this case, the seasons were no longer significantly different. There were aesthetic, sanitary, and environmental benefits from the cleaning services. However, those were just a palliative and inefficient to definitely solve the problem. Municipalities will have to implement solid waste collection at their municipal sources and provide adequate disposal to solve the problem at the beaches of Tamandaré. Controlling the source of solid wastes from beach users through environmental education actions is also urgently needed.
Changes in shoreline positions along the Rio Grande do Sul coast, southern Brazil, are analyzed to determine the spatial and temporal variability of shoreline movements at a regional scale. Using a kinematic Differential Global Positioning System (DGPS) survey method, the 618-km long shoreline of Rio Grande do Sul has been mapped on five occasions between November 1997 and April 2002. These data show that the coastline responds differently to hydrodynamic and meteorological forcing along the three major coastal sectors. The observed differences occur especially in the magnitude of changes, in the time interval in which the shoreline returns to a previous position, and in the length scale of dominant shoreline changes. Here changes in shoreline position are examined with respect to grain size, shoreline orientation, storms, El Nino–Southern Oscillation (ENSO) events, and gradients of longshore sediment transport. Data analyses and modeling indicate that the alongshore variability in the patterns of shoreline change through time is closely related to shoreline orientation and the associated gradients of longshore sediment transport. Results indicate also that variability in wave energy and storminess influence seasonal changes, whereas ENSO events influence interannual changes. This study demonstrates the importance of understanding the drivers of shoreline change at a regional scale and has applications in studies concerned with coastal engineering and shoreline response to climate change.
In the Dutch coastal dunes, several projects have started in which aeolian activity is stimulated to enhance landscape rejuvenation by increasing aeolian erosion and deposition. The aim of these projects is to reverse vegetation succession and create opportunities for pioneer stages. In 1995, a drinking water extraction canal in the Amsterdam Water Supply Dunes was closed and the original landscape was restored. Since then, the development of the area was left to natural processes. This resulted in large-scale deflation structures and the development of sand drift areas. By means of air photographs, the changes in the landscape were studied. Initially, the sand drift area expanded, up to a maximum of 11 ha in 1999. In the following years, stabilisation of the surface by vegetation became more and more important. After 8 years of undisturbed development, half of the bare surface was still bare, and the active area was still 2.5 times larger than the stabilised area. But bare spots were scattered over the area, and the average size per spot decreased from 10 ha in 1995 to <1 ha in 2003. The percentage of surface covered by pioneer species was large (5 ha in 2003) and might result in increased stabilisation rates in future. Part of the stabilisation could be explained by meteorological conditions during the studied period. Part could be explained because the system is supply limited. Scale might be an important issue in the final success of remobilisation, as indicated by preliminary comparison to larger-scaled projects. Further comparisons are needed.
After eight years, it is still too early to say whether large-scale destabilisation measures in the case of artificially fixed coastal dunes result in durable aeolian activity and landscape rejuvenation. However, even if the area will be stabilised within the next years, the landscape has many impulses for new ecological development. For the next decade, we need to continue our monitoring programs; meanwhile, experimentation with methods of reactivation should be conducted.
This paper addresses the possibilities of the combined use of airborne hyperspectral data and airborne laserscanning data to study sand dynamics on the Belgian backshore and foreshore. In August 2000, August 2001, and October 2002, airborne hyperspectral imagery was acquired with a CASI-2 sensor from the entire Belgian beach at low tide. Hyperspectral images contain a reflectance spectrum for each pixel. The characteristics of this spectrum are influenced by the state, the composition, and the structure of the topsoil of the beach. After radiometric, geometric, and atmospheric correction of the images, a normalization of the spectral signatures was necessary to allow comparison of wet and dry pixels. Consequently, the first derivative of the normalized spectra was taken, followed by a spectral angle mapper algorithm that was used to perform a supervised classification. The beach was classified into eight sand classes. Almost simultaneous with the first two CASI campaigns (in September 2000 and September 2001), a laserscan survey was performed to generate digital terrain models with a mean vertical accuracy of 5 cm. By differencing both digital terrain models, a map with sedimentation and erosion zones could be extracted. The combined interpretation of the erosion/sedimentation map with the classified hyperspectral data yields an appropriate method for studying the processes of sand transport along the Belgian coastline. The method was tried out with success on the Belgian east coast.
Coconut groves have been described as important, historic resources of Ghanaian coastal agro-ecological zones. Although some recent surveys have revealed serious declines in coconut groves because of disease, woodcutting, settlement expansion, and coastal erosion, few studies document the situation of coconut groves within the larger socioenvironmental context of the Ghanaian coastal and inland agro-ecosystem. This paper uses an integrated methodology based on time series aerial photographs, ecological and GIS analysis, and age- and gender-based social surveys, to document the cultural biogeography of coconut groves in a case study of coastal Ghana. Although there is evidence of deforestation, moderate coconut conservation was also documented. It is concluded that long-term assessments, including forecasting, are possible if based on an integrated framework. This provides an effective complement for informed policy.
Contemporary three-dimensional numerical sediment transport models are often computationally expensive because of their complexity and thus a compromise must be struck between accurately modeling sediment transport and the number of effective sediment grain (particle) size classes to represent in such a model. The Environmental Fluid Dynamics Code (EFDC) was used to simulate the experimental results of previous researchers who investigated sediment erosion and gradation around a 180° bend subject to transient flow. The EFDC model was first calibrated using the eight distinct particle size classes reported in the physical experiment to find the best erosion formulations to use. Once the best erosion formulations and parameters were ascertained, numerical simulations were carried out for each experimental run using a single effective particle size. Four techniques for evaluating the effective particle size were investigated. Each procedure yields comparable effective particle sizes within a factor of 1.5 of the others. Model results indicate that particle size as determined by the weighted critical shear velocity most faithfully reproduced the experimental results for erosion and deposition depths. Subsequently, model runs were conducted with different numbers of effective particle size classes to determine the optimal number that yields an accurate estimate for noncohesive sediment transport. Optimal, herein, means that numerical model results are reasonably representative of the experimental data with the fewest effective particle size classes used, thereby maximizing computational efficiency. Although modeling with more size classes can be equally accurate, results from this study indicate that using three effective particle size classes to estimate the distribution of sediment sizes is optimum.
This study examines the habitat preference of the US federally threatened northeastern beach tiger beetle, Cicindela dorsalis dorsalis, and the effect of beach nourishment on existing habitats along two western Chesapeake Bay beaches. Winter Harbor Beach and Smith Point Beach, located approximately 100 km to the north, historically have supported large populations of C. d. dorsalis. Grain size distributions, sediment compaction at two depths, temperature, moisture, and beach width habitat parameters were analyzed by analysis of variance and Tukey's honestly significant difference multiple comparison test and related to the distribution and abundance of C. d. dorsalis. The results from this study indicate that this species prefers beaches at least 6 m wide, with moderately well–sorted sands having a mean grain size of 0.5 to 0.6 mm, and relatively compacted sediment with averages of 69 psi and 110 psi at depths of 10 and 15 cm, respectively. In addition, the two nourishment projects had a positive short-term effect on the beetle habitat despite differences in deposition location. At Smith Point Beach, deposition occurred on top of the subaerial beach with a minimal increase in beach width. At Winter Harbor Beach, nearshore deposition caused a 50-m increase on average in beach width. Within weeks of deposition, adults of C. d. dorsalis rapidly moved onto the nourished sections of both beaches and produced large numbers of larvae. Winter Harbor Beach experienced the greatest increase in beetle numbers, most likely because of the additional habitat created by nearshore deposition. However, continued erosion from natural and anthropogenic sources could produce a chronic threat to productive habitats. These findings will assist coastal engineers and developers in determining effective measures designed to aid both economic and ecologic interests.
A study of the changes in natural phytodiversity that can be linked to recreational activities on tertiary dunes (grey dunes) is presented. Ten neighboring areas on the Islands of Wolin (Poland) and Usedom (Germany), representing all major disturbance factors (holiday resorts, campgrounds, parking), were chosen with two appropriate reference areas from Usedom and Wolin Island (Poland) that are situated in remote parts of the coast and showed no permanent signs of human disturbance. The results of recreational activities, especially trampling, eutrophication, and the neighboring effects of nearby gardens, parks, or fallow land, were assumed to be the main factors influencing natural dunal phytodiversity. Mechanical stress from trampling could result in a decrease in phytodiversity, whereas rising nutrient levels (e.g., fecal deposits), as well as neighboring effects from urban development and a growing species pool, could lead to an increase in diversity, including the occurrence of generalist or ruderal species not typical of unmodified dunes. Hence, changes within natural dunal phytodiversity depend on character and intensity of recreational activities. Results show that the location of the beach largely influences visitor numbers and hence the level of disturbance. At holiday resorts, damage to dunes can be low, even though tourist numbers on the beach are very high, if the dunes can be overlooked from the main promenade. Visitors are reluctant to trespass onto the dunes if they are being watched by many people. Nevertheless, areas without major signs of human disturbance were mostly found on remote dunes that were only accessible by foot or bicycle. Application of established phytodiversity indices (e.g., H′) showed drawbacks in detecting the different types of disturbance; however, sensitivity is improved by a modified index (H′dune).
The Sixteen Mile Beach Complex is one of numerous active dune accumulations along the West Coast of southern Africa. The beach complex is composed of a sandy beach, coast-parallel dunes, and a dune cordon. Grain size analyses, calcium carbonate content, sand texture and composition, and radiocarbon ages were determined to understand the Holocene evolution of the Sixteen Mile Beach Complex. Changes in sand grain size and dune morphology allow the complex to be divided into three parts. The beach and the dune cordon at the southern end are composed of fine sand. The central beach has a rapid decrease in the fine sand fraction that coincides with the transition from the dune cordon to a single large coast-parallel dune ridge. The northern beach is composed of medium sand and consists of a series of prograded, vegetated coast-parallel dune ridges. The formation of these distinct regimes is a reflection of the different amounts of wave energy received by the complex from the predominant southwest swell.
The radiocarbon analyses of bulk sand samples show a progressive younger age of the carbonate beach sand toward the north, which reflects an increase in grain size and recently broken shell. The mean age of the beach is 2.4 ka based on an accelerator mass spectrometry (AMS) date of picked pink-colored carbonate grains. The fresh bulk carbonate beach sand has a mean age of 7.4 ka and reflects the presence of reworked Pleistocene beach and dune sand. Corrected bulk sand radiocarbon ages indicate that the dune cordon has been active since 4.5 ka with a mean dune migration rate of 5.3 m/y. However, variations in sand supply, sea level, and climate indicate a complex and erratic evolution of the dune cordon.
Electrical resistivity surveying is a commonly used geophysical method in civil engineering, but few examples of this application exist in palaeoenvironmental reconstructions. Here, we provide an example of the application of the method to the two-dimensional distribution of lithofacies from coastal back-barrier sites of south-west England. The region is particularly important in coastal studies because of the current paucity of stratigraphic data and its position along the fastest subsiding coastline in Britain. Surveys were carried out at four sites along the south Devon coastline with the ABEM LUND Imaging System. Ranges of electrical resistivity of subsurface sediments were interpreted by ground-truthing from boreholes placed along the survey runs. Electrical resistivity surveys carried out at coastal locations can be affected by a range of phenomena—in particular, saltwater intrusion from rising tides and storm-induced overwash events. Conductive groundwater can cause temporal variations in the electrical profiles measured at the surface. This has not been witnessed to any significant degree at our sites. Despite anthropogenic and environmental noise (e.g., fences, tracks, drainage ditches, streams, and the possibility of salt water intrusion), the system has produced encouraging results and demonstrated that the technique has a future in coastal research. In particular, it readily identified the depth of gravel barriers and depth to basal strata. Given the speed and efficiency of data collection and interpretation available in the field, such systems should prove valuable in future research. Integration of the resistivity profiles with borehole information and radiocarbon dates of selected samples show that back-barrier basins began to fill with fine minerogenic sediments and shells ca. 9000 to 8000 Cal BP, and the majority of sites became terrestrialised by ca. 4500 Cal BP.
Aeolian sand transport on beaches and in dune environments shows a great spatial and temporal variability that has important implications for modeling and monitoring of coastal systems. Yet there have been few quantifications or statistical characteristics of transport variability in natural environments. Transport variability can result from bed surface control in the form of differentiation in grain size, surface moisture, and microtopography, or can be induced by fluid forcing in the form of gusts, burst-sweep events, and streamwise vortices. A field experiment was conducted on a coastal dune near Guadalupe, California, to quantify transport variability over spatial scales of 0.1–4.0 m and temporal scales of 1–120 seconds. Results show that spanwise (lateral) variability increases with spatial scale and decreases with temporal scale. Minimum transport variability over the smallest distances and longest time scales is on the order of 30%, providing error margins for transportrate measurements and model extrapolations. Variability reaches a maximum level at spatial scales larger than roughly half the boundary-layer height. In relation to shear velocity, greatest variability is found near the transport threshold and smallest variability occurs during periods of high shear velocities.
With beach nourishment widely used today to combat shoreline erosion, it is desirable to monitor the postnourishment shoreline to evaluate the projects' success. Implementing a monitoring program is difficult because of time and personnel requirements. Remotely sensed elevation data, in particular that derived from airborne light-detection and ranging (LIDAR) sensors, could be used because of its extensive coverage. In 1998, a beach-fill project was carried out at Wrightsville Beach, North Carolina, and coincidentally LIDAR data were collected annually in this location from 1997 to 2000. This project uses the LIDAR data to identify beach and dune zones and to compute volumetric changes for each zone. Spatial variations are analyzed by examining shoreline segments, in which beach and dune volumes are determined for the different surveys. Spatial and temporal changes in both the beach and dune zones are monitored following the initial fill project. The passage of hurricanes Bonnie and Floyd in the fall of 1998 and 1999, respectively, provided an opportunity to evaluate how the nourishment project was affected by major storms. About two thirds of the initial fill material was removed from the subaerial part of the beach in the first year, probably mostly as a result of the hurricanes. The highest rates of beach sediment loss occurred in the nourishment zones. There was some recovery in the following years. The dune system also changed, both losing and adding sediment in different time periods. The influence of human manipulation of the dune is evident in the cross-shore profiles and the volumetric data. There is little evidence that the fill material moved alongshore to nourish subaerial areas adjacent to nourished zone. Although the nourished beach undoubtedly provided a buffer against the storm waves, poststorm beach recovery was not evident 2 years after the storms, making the long-term success of this project questionable.
Wave-ripple cross-lamination formed in a sandy lacustrine shoreface in the Canadian Great Lakes is characterized by (i) small, randomly superimposed sets of angle-of-repose cross lamination, with strongly bimodal dips; (ii) small, superimposed sets of angle-of-repose cross-lamination, where the thickest and most prevalent sets have onshore dips, and the thinner, subsidiary sets dip offshore. (iii) small, superimposed sets of angle-of-repose cross-lamination, with near unimodal landward dips; (iv) supercritical, sinusoidal lamination indicative of high rates of ripple climb. Preserved surface ripples frequently reveal form discordant internal structures with a set of landward-dipping cross-lamination superimposed on a lakeward-dipping unit, both within a near-symmetrical ripple form. The origin of this internal lamination is discussed in the context of the second-order theory proposed for mass transport in turbulent wave boundary layers. The characteristic increase and subsequent decrease in wave period generated during storms in this fetch-restricted environment leads to an offshore mass transport in the wave boundary layer at the height of the storm and an onshore flow as the storm decays. This would lead to a reversal in ripple migration and the possibility of generating the discordant formsets.
A series of partially drowned drumlins forms the backbone of the inner islands within Boston Harbor. The shoreline of these rounded glacial deposits is composed of actively retreating bluffs formed by continual wave attack. Comparisons of bluffs reveal variability in their height and lateral extent, as well as in the dominant mechanism causing their retreat. Two processes are responsible for bluff erosion and yield distinct bluff morphologies: (1) wave attack undercuts the bluff and causes episodic slumping, yielding planar bluff slopes, and (2) subaerial processes such as rainfall create irregular slopes characterized by rills and gullies.
We propose a model of drumlin bluff evolution that is based on processes of erosion and physical characteristics such as bluff height, slope morphology, and the orientation of the bluff with respect to the long axis of the drumlin and its topographic crest. The four phases of drumlin bluff evolution consist of (1) initial formation of bluff, with retreat dominated by wave notching and slumping processes; (2) rill and gully development as bluff heights exceed 10 m and slumped sediment at bluff base inhibits wave attack; (3) return of wave notching and slumping as bluff heights decrease; and (4) final development of boulder retreat lag as last remnants of drumlin are eroded by wave action. These phases capture the important physical processes of drumlin evolution in Boston Harbor and could apply to other eroding coastal drumlin deposits.
Beach profile change in the swash zone on gravel beaches is characterised by enhanced onshore sediment transport and berm formation, and infiltration loss in the swash zone is often given as the reason why gravel beaches are steeper than sand beaches. In this paper, we report on field measurements conducted on a gravel beach, Slapton Sands, Devon, UK, in April 2001. Collected data included surface pressures under uprush and backwash, subsurface pore water pressures, uprush and backwash velocities, and bed elevations. The field data were compared with predictions of the BeachWin model, which simulates interacting wave run-up/run-down, beach groundwater flow, swash sediment transport, and resulting beach profile changes. With a relatively large value of hydraulic conductivity, the model was able to predict the observed berm formation at the upper part of the beach. In contrast, the berm feature was absent in the simulation without swash infiltration effects included. The predicted erosion at the middle section of the beach, however, took place at a location landward of that of the measurements. Simulations were carried out to investigate the sensitivity of the model to changes in the hydraulic conductivity, friction factor, and coefficient ratio of uprush/backwash sediment transport. All parameters were shown to affect the simulation results—in particular, the formation and extent of the berm.
Grain-bed collision is a key component of saltation, but substantial uncertainty remains regarding many aspects of this process. Previous empirical work is used to develop a conceptual model of this process that accounts for the partitioning of impact energy between rebounding grains and the bed. The model envisions two distinct collision regimes: (i) a quasi-elastic regime at low impact speeds and (ii) an inelastic regime at high impact speeds. In the quasi-elastic regime, colliding grains retain a constant proportion of their kinetic energy, and thus rebound at speeds that are proportional to the impact speed and shear velocity. In the inelastic regime, colliding grains retain a fixed and limited amount of kinetic energy, transferring any excess above this limit to the bed. Rebound speeds are thus constant and independent of both impact speed and shear velocity. Impact energy transferred to the bed is expended in “deformation” (i.e., ejection, rearrangement, etc. of bed grains). These two collision regimes are separated by a critical impact speed/kinetic energy level that is controlled by bed texture (more directly, by the inertia or resistance to motion of the bed grains). Field measurements under near-threshold conditions are found to correspond to the higher speed inelastic regime, suggesting that inelastic collisions predominate in aeolian saltation on loose, unconsolidated sand beds. The quasi-elastic regime might therefore only be pertinent for reptating grains, or in situations in which interparticle bonding (from crusts, surface moisture, etc.) increases the “effective” inertia of bed grains and thus the critical impact speed separating the two regimes. It is also shown that rebound speed in the inelastic regime varies in inverse proportion to grain size (mass), so that particles rebound with an approximately constant level of kinetic energy regardless of size. Thus, larger grains will rebound at smaller speeds and follow lower, shorter trajectories, providing a mechanism that accounts for the commonly observed size sorting of grains subjected to aeolian saltation.
Sediment transport across a foredune and beach at Ocean City, New Jersey, was examined to identify the effect of houses, dune topography, sand fences, vegetation, and wrack lines during an offshore wind. Houses are as close as 18 m from the crest of the 2- to 3-m-high foredune and are up to 9.0 m high and 12.8 m wide and spaced 4.0 to 5.0 m apart. Data were gathered during a 1-day study on 3 March 2003 with the use of 15 vertical sand traps, 13 erosion pins, and eight sets of anemometers placed 0.3, 0.6, and 0.9 m above the ground surface. Wind speeds 0.9 m above the ground ranged from 1.61 to 3.75 m/s. Trapping rates were negligible on the vegetated dune crest and up to 2.03 kg m−1 h−1 near mid foreshore. The highest rate of trapping was 2.4 kg m−1 h−1 at a <10-m-wide unvegetated area in the dune.
Houses shelter the dune from offshore winds and might contribute to dune stability. Increases in wind speed in the offshore direction cause greater rates of transport on the seaward side of the dune where vegetation has not had time to become established. Dune vegetation, remnant sand fences, wrack lines, and the sheltered area in the lee of the seaward dune ridge can trap sediment moving offshore during relatively low wind speeds. Sediment deposited at these obstacles could contribute to deflation of the backshore, which is the primary source of sediment moved to the inter-tidal foreshore. Losses of sediment from unvegetated portions of the dune to the beach can be overcome by replacing sand fences and suspending beach raking until the calmer summer months.
Previous research has demonstrated that reconnection of impounded wetlands to the Indian River Lagoon benefits estuarine fisheries and emergent ecosystems. However, no effort has yet been made to quantify the effects of managed surface water flow on patterns of sedimentation. Sedimentation patterns strongly influence wetland evolution, including the distribution of open water and emergent landscapes. Thus, the enumeration of sedimentation rates provides a basis for reconstructing the processes responsible for historic landscape change. These data also provide a basis for predicting landscape change that can accompany hydrologic reconnection of impounded wetlands to the Indian River Lagoon.
In this investigation, conducted in the Merritt Island National Wildlife Refuge, Florida, we used cesium activity profiles to quantify rates of historic sediment accumulation at locations subject to managed (impounded) and unmanaged (natural) surface water hydrology. The data suggest impounded wetlands subject to historic submergence are now devoid of vegetation and experiencing substrate erosion in areas in which fetch is sufficient to induce wind-driven circulation. In unmanaged wetlands, surface elevations have kept pace with historic sea level rise solely through the in situ accumulation of organic matter.
These observations suggest that hydrologic reconnection of impounded wetlands subject to persistent flooding throughout historic time will result in rapid and widespread submergence to water depths in excess of 10 to 20 cm. At these depths, most wetland plant taxa will not successfully recruit via seedling exchange. Hence, attempts to restore wetland areas analogous to those investigated during this study (i.e., Impoundment D) cannot be achieved simply by removing management structures that obstruct natural surface water flow. The wetland surface must either be (1) incrementally flooded to estuarine water level elevations slowly over time or (2) raised to the appropriate hydroperiod elevation before reconnection with suitable fill material. One possible source of fill is the Intracoastal Waterway, located within 2 km of the Merritt Island National Wildlife Refuge and intermittently dredged to maintain safe navigation.
High-frequency measurements of airflow from ultrasonic anemometers and time-averaged cup anemometer profiles were taken during an oblique alongshore sand-transporting event (6.7 m/s) over a vegetated foredune in May 2002 as part of a larger study on the sedimentary dynamics of a beach-dune complex in Greenwich Dunes, Prince Edward Island National Park, Canada. Local flow and sand transport pathways deviated significantly from the regional wind because of topographic steering of oblique alongshore airflow on the beach back toward the foredune in the backshore. Flow decelerated on the lower seaward slope of the foredune because of flow stagnation and vegetation-induced roughness effects. On the upper seaward slope, flow veered crest-parallel because of secondary flow effects, including potential flow reversal, acceleration, and interaction with faster regional flow. An inflection point in velocity profiles indicates a momentum sink at plant canopy height, and above this height exists a distinct shear layer. Flow acceleration occurs only on the upper slope above the plant canopy as the shear layer intensifies. Flow steadiness, as indicated by the coefficient of variation in horizontal (U) and vertical (W) velocity, also declines up the seaward slope, in contrast to measurements of flow over unvegetated dunes, perhaps because of increasing vegetation-induced drag and turbulence. Gusting and vertical bursting was evident as honami motion in the beachgrass and was responsible for maintaining intermittent saltation into the foredune. Temporal correlations exist between U, W, and flow angle. As flow shifted onshore, both U and W increased because of enhanced topographic forcing and increased vertical lift on the lower seaward slope, whereas when flow shifted alongshore, U and W declined because of reduced forcing and acceleration effects because the dune is effectively less steep to flow.
Although these dunes align well with the vector of the regional resultant sediment drift potential, sand transport pathways followed local flow vectors of varying magnitude and direction. Offshore to oblique alongshore winds are typical of the summer wind regime, and, although frequently incompetent, they contribute to dune maintenance by cycling sand to the backshore for incipient foredune growth, scarp infilling, or both. To date, the role of secondary flows under alongshore winds in foredune morphodynamics has not been well documented.
Most second-half-of-the-twentieth-century oceanographic ships remain in a discreet anonymity, but a very few have grabbed the news headlines. The minisubmarine Alvin came into the public eye, but its image and fame never matched that of Jacques-Yves Cousteau's Calypso. The Calypso is surrounded by myths and stories about which her wily boss seldom commented. It remains gainsaid that the ship has had a scientific and adventurous career, numerous episodes of which unfolded on millions of television screens. That does not detract from the value of her expeditions and her scientific worth. The lives of the ship and Cousteau are intertwined. If ever an “oceanographic” ship was involved in controversies, the Calypso places among the ones on top of the list. This is the case for her scientific campaigns, for her cinematographic presentations, and now for her legal imbroglios. The authors have covered some of the Calypso's odysseys in previous papers; the present one briefly unfolds more of the Calypso's fascinating “life” and deplores her far from glorious end amidst tedious legal wrangles.
Average fractal dimensions (D) are calculated for Maine's four coastal compartments using a GIS approach and digitized U.S. Geological Survey 7.5-minute series topographic quadrangle maps. The D values indicate relatively little complexity for the southwest coastal compartment (avg. D = 1.11), higher complexity for the south-central compartment (avg. D = 1.35), and intermediate complexity for the north-central compartment (avg. D = 1.23). Our analysis suggests that the northeastern compartment should be further divided into two subcompartments (Cobscook Bay and non-Cobscook Bay), which have average D values of 1.37 and 1.18 respectively. Subdivision of the northeast coastal compartment is also supported by the geologic makeup of the region. Statistical tests show that all of the geologically different coastal compartments can be discriminated in terms of D at the 95% confidence level, whereas the geologically similar compartments (south-central compartment and Cobscook Bay subcompartment) cannot be statistically distinguished. Further research along previously glaciated shorelines should be carried out to build upon our results.
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