Showing papers in "Journal of Coastal Research in 2000"

Storm Impact Scale for Barrier Islands

Abstract: A new scale is proposed that categorizes impacts to natural barrier islands resulting from tropical and extra-tropical storms The proposed scale is fundamentally different than existing storm-related scales in that the coupling between forcing processes and the geometry of the coast is explicitly included Four regimes, representing different levels of impact, are defined Within each regime, patterns and relative magnitudes of net erosion and accretion are argued to be unique The borders between regimes represent thresholds defining where processes and magnitudes of impacts change dramatically Impact level 1 is the 'swash' regime describing a storm where runup is confined to the foreshore The foreshore typically erodes during the storm and recovers following the storm; hence, there is no net change Impact level 2 is the 'collision' regime describing a storm where the wave runup exceeds the threshold of the base of the foredune ridge Swash impacts the dune forcing net erosion Impact level 3 is the 'overwash' regime describing a storm where wave runup overtops the berm or, if present, the foredune ridge The associated net landward sand transport contributes to net migration of the barrier landward Impact level 4 is the 'inundation' regime describing a storm where the storm surge is sufficient to completely and continuously submerge the barrier island Sand undergoes net landward transport over the barrier island; limited evidence suggests the quantities and distance of transport are much greater than what occurs during the 'overwash' regime

Shoreline Mapping Techniques

Abstract: Numerous coastal mapping techniques have been developed over the last twenty-seven years (STAFFORD, 1971; DOLAN et al., 1978; FISHER and SIMPSON, 1979; LEATHERMAN, 1983; McBRIDE et al., 1991; THIELER and DANFORTH, 1994a, OVERTON et al., 1996). These techniques, used to measure shoreline erosion, barrier island migration, and dune erosion, vary in approach, accuracy, expense and training/time requirements. Some of the more recent coastal mapping techniques apply advances in cartography and photogrammetry providing high-resolution measurements with less error than manual methods that use a photographic comparator or stereo zoom transfer scope. However, such techniques are expensive, require extensive training, and may take longer than manual methods. While many coastal mapping studies would benefit from these advanced techniques, not all studies require the high resolution these more recent techniques offer. When beginning a coastal mapping project or choosing to upgrade laboratory facilities, researching established coastal mapping techniques before choosing from among them requires extensive literature review. To assist researchers, engineers and planners who wish to undertake a coastal mapping project, this paper provides an overview of the errors associated with shoreline mapping, and a discussion of factors to be considered when selecting a coastal mapping technique.

Long-term Shoreline Position Prediction and Error Propagation

Abstract: Beach erosion necessitates forecasting future shoreline positions for effective coastal management. Simple forecast methods, such as end-point rate and linear regression have been proposed in the coastal literature and are widely used. However, the matter of the error of forecasts has largely been neglected. If measurement errors and a linear trend of erosion were the only factors determining shoreline position, making predictions of future shoreline positions and their associated confidence intervals would be easy using linear regression. Unfortunately, real and sometimes enduring fluctuations of beach width occur that are much larger than the measurement uncertainty. Wintertime fluctuations of up to several 10's of meters are well-known; most investigators for this reason do not use winter shoreline positions to study long-term shoreline behavior. An individual great storm can cause beach erosion amounting to scores of meters requiring a decade or more for recovery. Using shoreline position data in linear regressions without considering storm-caused erosion and subsequent beach recovery may yield inaccurate predictions of future position resulting from the underlying erosion, and greatly inflated estimates of uncertainty (e.g., 95% confidence intervals). A case study of shoreline position change in Delaware is presented to show how consideration of knowledge other than shoreline positions alone can lead to useful results for shoreline position forecast errors. It is also demonstrated that modern, more accurate survey measurement techniques can be helpful in improving the quality of forecasts even if the inherent variability of shoreline position indicators remains at the level of many meters.

Impacts of Winter Storms on Circulation and Sediment Transport: Atchafalaya-Vermilion Bay Region, Louisiana, U.S.A.

Abstract: This study investigates the changes in circulation, sediment resuspension, sediment flux and salinity that accompany "winter storms" in the Atchafalaya Bay region, events that occur 20 to 30 times each year between October and April. NOAA-14 satellite reflectance imagery and time-series measurements of winds, water levels, current velocity and turbidity demonstrate that wind direction and speed are the major controlling factors for circulation, sediment transport and suspended sediment concentrations. East winds (occurring 62% of the time) induce a westward flow of sediment-laden Atchafalaya river water along the coast. West winds reverse the direction of plume movement and increase the size of the plume, partly as a result of Ekman processes. The strong north winds, characteristic of winter storms, cause rapid flushing from the shallow bays (30-50% of volume) and water level changes in excess of 1 meter. Seaward of these bays, a large sediment plume (180 km alongshore, 75 km offshore) is produced by the wind-wave resuspension of bottom sediments and the wind-forced seaward transport of bay and inner shelf waters. Water and sediment flux is primarily southeastward, temporarily disrupting the westward flow of river water along the coast. In the Vermilion-Cote Blanche Bay system, northwest winds maximize sediment resuspension and the seaward flux of sediment-laden river and bay water. The storm-related sediment resuspension and transport reduces the rapidity of delta development and deposition in these bays and re-distributes sediment along the inner shelf.

Short-Term Consequences of Nourishment and Bulldozing on the Dominant Large Invertebrates of a Sandy Beach

Abstract: Biological responses of the dominant beach macro-invertebrates to beach nourishment and bulldozing, two widely practiced structure-free methods of responding to shoreline erosion, were evaluated along Bogue Banks, North Carolina. Sediments taken from maintenance dredging of a channel in Bogue Sound and used for beach nourishment in a replicated design were substantially finer (3.67 vs 2.33 Φ) than those of untreated beaches and contained large concentrations of shell hash. In response to nourishment, densities of Emerita talpoida and Donax spp. were lower by 86-99% on nourished beaches in early-mid July, 5-10 weeks after cessation of the nourishment project. Beach bulldozing done to augment the primary dune reduced the width of the intertidal beach by about 7 m and replaced it with a wedge of coarser, shellier sand taken from the lower beach. In late July-early August about 3 months after termination of bulldozing, counts of active burrows of ghost crabs Ocypode quadrata were 55-65% lower on bulldozed beaches, with most of the reduction occurring on the 7 m of high beach occupied by the newly formed dune face. Despite no detectable difference in slope of the lower beach, Emerita talpoida densities were 35-37% lower on bulldozed beach segments of 0.5- and 3-km, and, while Donax spp. exhibited no consistent residual response to bulldozing, two of three contrasts showed increased abundances of >100% on bulldozed segments. Failure of Emerita and Donax to recover from nourishment by mid summer when they serve as a primary prey base for important surf fishes, ghost crabs, and some shorebirds may be a consequence of the poor match in grain size and high shell content of source sediments and/or extension of the project too far into the warm season. Effects of bulldozing on ghost crabs may conceivably be mitigated by measures to stabilize the dune face after bulldozing, but the effects on Emerita and Donax are not easily interpreted so potential mitigation measures for mole crabs and bean clams are unclear.

Influence of inner-continental shelf geologic framework on the evolution and behavior of the barrier-island system between Fire Island Inlet and Shinnecock Inlet, Long Island, New York

Abstract: High-resolution, sea-floor mapping techniques, including sidescan-sonar and subbottom profiling, were used to investigate how the geologic framework of the inner-continental shelf influenced the Holocene evolution and modern behavior of the Fire Island barrier-island system, Long Island, New York. The inner-continental shelf off Long Island is divided into two physiographic provinces by a broad outcrop of Cretaceous coastal-plain strata offshore of Watch Hill; this outcrop was part of a subaerial headland during the Holocene marine transgression. Erosion of the headland during transgression furnished sediment to the inner-continental shelf downdrift to the west. The sediment was, in turn, reworked by oceanographic processes into a series of shoreface-attached sand ridges. The oldest (~ 1200 yr BP) and most stable part of the barrier-island system is immediately landward of the outcropping coastal-plain strata and thickest sand ridges. East of Watch Hill, Pleistocene sediment either is exposed on the inner-continental shelf or is buried by a veneer of modern reworked sediment. Here the barrier-island system has migrated landward at a faster rate than the segment west of Watch Hill and has been breached by numerous historic inlets. Because the Pleistocene sedimentary deposit is generally of uniform thickness throughout the study area and unconformably overlies the Cretaceous coastal-plain strata, both the Holocene and historical evolution of the Fire Island barrier-island system are controlled by the physiography of this regional unconformity. In particular, the shoreface-connected sand ridges appear to be a significant source of sediment to the western portion of Fire Island. Previous attempts to develop a sediment budget for this coastal system have failed to explain volumetric discrepancies, primarily because poor assumptions were made about the nature of sediment transport in the system. A more realistic sediment budget must include a significantly larger spatial scale, including sediment input from the inner-continental shelf.

Influence of Antecedent Topography on Coastal Evolution as Tested by the Shoreface Translation-Barrier Model (STM)

Abstract: This paper demonstrates that antecedent topography played a very important role on the coastal evolution of Rio Grande do SuI (RS) in Brazil during the Holocene. By modeling the last 9 ka of sea level change using the general morphology of the present shelf as the substrate over which barriers have translated a successful reconstruction was obtained showing the position of the coastline at the time of the Post-Glacial Marine Transgression maximum (5 ka). Not only has the antecedent topography played an important role in the definition of the coastal shape of RS, it has also pre-determined the type of coastal barrier: prograded barriers along coastal reentrances, and receded and mainland beach barriers along coastal projections. Analysis of sediment budget indicated that more than half of sediments needed for progradation along coastal reentrances came from the shelf. The Shoreface Translation-Barrier Model (STM) was used to recreate Holocene coastal shorelines and to simulate sediment volumes.

Hydrodynamics and Cross-Shore Sediment Transport in the Swash-Zone of Natural Beaches: A Review

Abstract: The high velocities and suspended sediment concentrations in the swash-zone mean that the sediment transport processes in this zone are likely to be important contributors to shoreline erosion and accretion. However, studies of hydrodynamics and sediment transport in the swash-zone have been relatively few compared with those in the rest of the nearshore zone. Studies of swash-zone hydrodynamics have included run-up measurements using electrical resistance and capacitance devices, as well as cameras. Run-up has been modelled mostly using the non-linear shallow water equations. Sediment transport studies in the swash-zone require instrumentation which can unobtrusively obtain measurements close to the bed, therefore, very few data exist so far. Studies have been performed in incident –wave dominated relatively low energy conditions on steep reflective beaches, measuring individual swash events, and the sediment transport processes modelled with reasonable success on the uprush only. Studies made on high energy dissipative beaches have found the swash to be dominated by oscillations at infragravity frequencies, with suspended sediment concentrations being 3 to 9 times higher in the swash-zone than the inner surf-zone. The added complication of groundwater influx and outflux is also recognised as an essential area of study, whose processes should be included in any model of the swash-zone sediment transport.

The Use of Mathematical Models to Predict Beach Behavior for U.S. Coastal Engineering: A Critical Review

Abstract: A number of assumed empirical relationships (e.g., the Bruun Rule, the equilibrium shoreface profile, longshore transport rate equation, beach length: durability relationship, and the renourishment factor) and deterministic numerical models (e.g., GENESIS, SBEACH) have become important tools for investigating coastal processes and for coastal engineering design in the U.S. They are also used as the basis for making public policy decisions, such as the feasibility of nourishing recreational beaches. A review of the foundations of these relationships and models, however, suggests that they are inadequate for the tasks for which they are used. Many of the assumptions used in analytical and numerical models are not valid in the context of modern oceanographic and geologic principles. We believe the models are oversimplifications of complex systems that are poorly understood. There are several reasons for this, including: (1) poor assumptions and important omissions in model formulation; (2) the use of relationships of questionable validity to predict the morphologic response to physical forcing; (3) the lack of hindsighting and objective evaluation of beach behavior predictions for engineering projects; (4) the incorrect use of model calibration and verification as assertions of model veracity; and (5) the fundamental inability to predict coastal evolution quantitatively at the engineering and planning time and space scales our society assumes and demands. It is essential that coastal geologists, beach designers and coastal modelers understand these model limitations. Each important model assumption must be examined in isolation; incorporating them into a model does not improve their validity. It is our belief that the models reviewed here should not be relied on as a design tool until they have been substantially modified and proven in real-world situations. The "solution," however, is not to increase the complexity of a model by increasing the number of variables. What is needed is a thoughtful review of what beach behavior questions should or could be answered by modeling. Viable alternatives to the use of models do exist to predict the behavior of beaches. Three such alternatives to models are discussed for nourished beach design.

The Relationship Between Incident Wave Energy and Seacliff Erosion Rates: San Diego County, California

Abstract: The coastline of San Diego County, California, is characterized by steep seacliffs cut into 5 to 115 m high uplifted marine terraces. Over the past few decades, rapid population growth in the area has promoted a substantial increase in cliff-top development, despite a limited understanding of the long-term cliff erosion rates and their controlling factors. Wave erosion at the base of the seacliff is usually assumed to be a basic driving mechanism of coastal cliff retreat. We investigated the influence of waves on seacliff erosion by comparing high-resolution, long-term seacliff erosion rates to wave parameters (height, energy, and power or energy flux) in 10 m of water, the break-point, and at the cliff toe. Seacliff erosion rates range from 3.0 cm/yr in well-lithified Cretaceous sandstone to 43.0 cm/yr in unlithified Pleistocene sands. The wave parameters were calculated using the California Data Information Program (CDIP) Southern California Refraction-Diffraction Model (SCRDM), an empirical relationship for breaking wave height, and a new term we define as relative power at the cliff toe. Directional wave data from offshore South-Central California were used to initialize the model. The distribution of wave power in 10 m of water and at the breakpoint and cliff toe appears to be inversely related to historical seacliff erosion rates at our study sites. As a result, our findings suggest that waves, while an important mechanism of seacliff erosion, are secondary to material properties in the overall retreat of San Diego seacliffs. Along the San Diego coastline, material strength appears to largely determine seacliff stability and the rate and manner of retreat.

Benthic Foraminifera and Environmental Changes in Long Island Sound

Abstract: Benthic foraminiferal faunas in Long Island Sound (LIS) in the 1940s and 1960s were of low diversity, and dominated by species of the genus Elphidium , mainly Elphidium excavatum clavatum, with common Buccella frigida and Eggerella advena . The distribution of these species was dominantly correlated with depth, but it was not clear which depth related environmental variable was most important. Differences between faunas collected in 1996 and 1997, and in the 1940s and 1960s include a strong decrease in relative abundance of Eggerella advena over all LIS, an increase in relative abundance of Ammonia beccarii in western LIS, and a decrease in species diversity. The decreased diversity suggests that environmental stress caused the faunal changes. Oxygen isotope data for E . excavatum clavatum indicate that a change in salinity is not a probable cause. Carbon isotope data suggest that the supply of organic matter to the benthos increased since the early 1960s, with a stronger increase in western LIS where algal blooms have occurred since the early 1970s, possibly as a result of nutrient input by waste water treatment plants. These blooms or the resulting episodes of anoxia/hypoxia may have played a role in the increased relative abundance of A. beccarii. There is no clear explanation for the decreased abundance of E. advena , but changes in the phytoplankton composition (thus food supply) are a possible cause. Benthic foraminiferal faunal and stable isotope data have excellent potential as indicators of physicochemical environmental changes and their effects on the biota in LIS.

An Overview of the Lena River Delta Setting: Geology, Tectonics, Geomorphology, and Hydrology

Abstract: The Lena River Delta, largest in the Arctic, occupies 32,000 km 2 . It has a complicated structure caused by neotectonic block-movements, which formed an island archipelago with elevation differences as large as 60 m of distinct geological units. The modern active delta occupies spaces between older islands of the archipelago, and is just beginning to protrude into the open sea. The hydrologic pattern in the delta also shows the influence of tectonism. Numerous earthquakes during last century with magnitudes as large as 6 suggest that tectonic movement is continuing. Radiocarbon dating shows that the modern delta has been built during the second half of the Holocene. The total advance of the delta during this time was 120-150 km. The Lena River is considered the main sediment source for the Laptev Sea. The latest investigations give the suspended sediment load in the lower Lena River at 21 Mt/y, but only 2 m height. The sand island is characterized by typical lake-thermokarst relief, but no volumes of underground ice large enough to explain this relief are known. The elongated lake depressions and lakes are oriented about 2-8 o True. In the middle of generally 1- to 2-m-deep lakes are equally oriented hollows as deep as 25 m. The lakes are degrading because of erosion by stream channels draining them. The lake-thermokarst relief on the north slope of the island is partly or totally destroyed by erosion processes. Thus the Lena Delta is characterized by several unique features that are either poorly understood or unexplained.

Holocene Depositional Patterns, Neotectonics and Sundarban Mangroves in the Western Ganges-Brahmaputra Delta

Abstract: Litho- and chronostratigraphic analyses of radiocarbon-dated cores are utilized herein to distinguish Holocene deltaic and underlying transgressive units and late Pleistocene alluvial deposits in the western Ganges-Brahmaputra delta. Regional distribution of these facies indicates that neotectonic displacement, including differential land subsidence, of delta plain sectors is one of the major controls of late Quaternary depositional patterns in this depocenter. The spatial and temporal configuration of Holocene deltaic sediment thickness, mud and sand layers, peats interstratified in Holocene sequences, and modern mangrove forests that form the Sundarbans are attributed to NE-SW, and to a lesser extent NW-SE, neotectonic trends. Holocene sedimentary and stratigraphic configurations closely parallel geological structures, some of them deep seated, that affected this region during most of the Tertiary and have continued to the present. Extensive mangrove forests developed along the NE-SW zone of thickened Holocene deltaic deposits. Their present configuration is related to natural factors, such as eastward tilting of the delta, rapid sediment accumulation (to 0.7 cm/yr), marked land subsidence (to 0.5 cm/yr), and increasing anthropogenic influences, including large-scale land reclamation and decreased river flow influx. The diverse and extensive mangrove tracts of the delta have significant environmental and economic implications for the rapidly growing population, including serving as a buffer zone that helps to reduce the impact of landward-driven tides, storms and cyclones. Interpretation of Holocene facies in the subsurface by means of radiocarbon-dated cores provides a mean to more precisely define the interaction between contemporary Holocene depositional patterns and neotectonics. This information, in turn, can be utilized to develop realistic measures needed to minimize further degradation of this biologically unique ecosystem.

Hydro-isostatic and tectonic influences on emergent Holocene paleoshorelines in the Mariana Islands, Western Pacific Ocean

Abstract: Emergent paleoreef flats and paleoshoreline notches in the Mariana Islands document the effects of a mid-Holocene highstand in regional hydro-isostatic sea level and post-mid-Holocene forearc uplift of selected islands. Global hydro-isostatic calculations imply for Micronesia an a really variable magnitude of 0.6-2.7 m for the mid-Holocene highstand, relative to modern sea level, and radiocarbon ages for emergent reef flats and rubble terraces indicate a peak during the interval 4750-2250 yrs BP. In the tectonically stable region of Micronesia southeast of the Mariana Islands, emergences of paleoshorelines by 1.1-2.4 m closely match hydro-isostatic expectations for each island group. In the Mariana Islands, Saipan, Tinian, and southern Guam display emergent mid-Holocene paleoreef flats and paleoshoreline notches standing 1.2-2.0 m above modern counterparts, within the range of 0.8-2.1 m expected from hydro-isostatic theory. With allowance for minor tectonic subsidence locally, average hydro-isostatic emergence for the Mariana Islands is estimated as 1.8 m. Northern Guam and Rota display paleoshoreline emergences in excess of hydro-isostatic expectation, implying 0.8 m and 1.2 m of post-mid-Holocene tectonic uplift, respectively. Subduction of an oceanic seamount chain beneath the segment of the forearc belt beneath Rota and northern Guam probably accounts for subregional tectonic uplift, and also for enhanced interplate coupling responsible for anomalous seismicity. Post-mid-Holocene drawdown in relative sea level influenced the development of attractive environments for human settlement, which began in the Mariana Islands c. 3500 yrs BP.

Radiocarbon Dates in China's Holocene Yangtze Delta: Record of Sediment Storage and Reworking, Not Timing of Deposition

Abstract: Evaluation of conventional and AMS radiocarbon dates, obtained for 65 Holocene sediment samples in 20 cores collected in the Yangtze delta, China, indicates that only about one in 4 dates falls within an expected time range. In this Holocene deltaic system, most radiocarbon-dated samples do not become progressively younger upcore, and there is no direct relationship between age and depth . About one in 6 dates is too young, recording locally truncated stratigraphic sections. Of particular note are the nearly two-thirds of all radiocarbon dates that record ages that are much too old, by 1000 to 10,000 years (23% are of Pleistocene age). This phenomenon results from the introduction of old carbon during sediment storage and reworking along the dispersal path between headlands and the coast. Thus, rather than recording final time of Holocene deposition at deltaic core sites, dates in Yangtze delta sediment appear to indicate a time lapse that occurred during storage and transport cycles in the fluvial valley and delta plain. There is no simple, obvious or universal solution to this radiocarbon-dating problem in deltaic sequences. The problem warrants attention since reliable dating of Holocene sequences is essential for measurement of rates of sediment accumulation and delta margin subsidence relative to sea level, two of the parameters needed to help implement protection measures along the vulnerable low-lying Yangtze delta coast. At present, a multi-method dating approach (amino acid racemization, isotopic analyses, archaeological determination, and others) would constrain sediment age, and provide a more reliable measure of deposition time in such settings than by radiocarbon dating alone.

Sedimentary Petrology of a Declining Reef Ecosystem, Florida Reef Tract (U.S.A.)

Abstract: Petrologic evaluation of biogenic sediments collected shelf-wide along the Florida reef tract in 1989 revealed three principal components: coral, the calcareous green alga Halimeda, and mollusc. The dominant grain was dependent in part upon local morphology that controlled composition and vitality of the biota. Either Halimeda or mollusc grains prevailed in sands off the upper Keys. In the middle and lower Keys, Halimeda grains prevailed nearshore and coral grains offshore. Comparison with similar analyses of samples collected in 1952 and 1963 indicates that, over 37 years, the relative abundance of molluscan grains more than doubled in the upper Keys and that of particulate coral tripled in the middle Keys. These changes can be interpreted in the context of physical and biological events that affected Florida Keys reefs over that period of time. In the 1970s, outbreaks of extremely cold water killed even representatives of the hardiest coral species. In the 1980s, black-band and white-band diseases decimated the major reef-building acroporid corals, and the pivotal herbivore, Diadema antillarum, disappeared. Although Diadema is a major coral bioeroder, the sea urchin is also essential to healthy reef growth. The increase in coral debris in the middle Keys may be related to Hurricane Donna in 1960, but it is also consistent with the prediction of accelerated bioerosion by boring organisms in response to increased plankton productivity. Plankton productivity is stimulated by nutrients from Florida Bay and by well-documented eutrophication of nearshore environments. In the upper Keys, where reefs are somewhat removed from bay and nearshore influence, a relative decrease in coral debris over the 37 years may reflect proliferation of algae and algae-grazing molluscs as well as suppressed rates of bioerosion in the absence of Diadema. Human activities have substantially increased the natural flux of fixed nitrogen to coastal systems worldwide. Waters in the Florida Keys are no exception. Spatial and temporal trends in sediment constituents are compared to a previously published model that predicts the response of benthic biota to changes in nutrient supply. As adapted to interpret changes observed in reef-tract sediments, the model provides insights into the natural nutrient gradient along the Florida reef tract.

Relationships Among Sea-Floor Structure and Benthic Communities in Long Island Sound at Regional and Benthoscape Scales

Abstract: Long Island Sound is comprised of a rich and spatially heterogeneous mix of sea-floor environments which provide habitat for an equally diverse set of assemblages of soft-sediment communities. Information from recent research on the geomorphological and chemical attributes of these environments, as well as from studies of the hydrodynamics of the Sound, provide the opportunity to develop a landscape, or "benthoscape" framework for understanding the soft-sediment ecology of this estuary and for guiding future research focusing on structure and function at multiple spatial scales. This contribution reviews past research on benthic communities in Long Island Sound and addresses how they may be shaped by sea-floor characteristics at regional and benthoscape scales. At the regional scale (i.e. the entire Sound), differences in benthic community composition correspond to the distribution of general sedimentary environments. However, significant variation in community structure also occurs at the benthoscape scale (within regions) related to local variations in sediment properties, and physical and biogenic topographic features. Several topical areas in particular need further research in Long Island Sound, including temporal dynamics of benthic communities relative to sea-floor structure and the interaction between the dynamics of benthoscapes and hydrologic seascapes.

Growth and Nutrition of Baldcypress Families Planted Under Varying Salinity Regimes in Louisiana, USA

Abstract: Saltwater intrusion from the Gulf of Mexico is one important factor in the destruction of baldcypress ( Taxodium distichum (L.) Rich.) swamps along the Louisiana Gulf Coast, USA. Recent restoration efforts have focused on identification of baldcypress genotypes with greater tolerance to saline conditions than previously reported. To date, salt tolerance investigations have not been conducted under saline field conditions. In 1996, therefore, three plantations were established with 10 half-sib genotype collections of baldcypress in mesohaline wetlands. Tree survival and growth were measured at the end of two growing seasons, and foliar ion concentrations of Na, Cl, K, and Ca and available soil nutrients were measured during the 1996 growing season. In general, soil nutrient concentrations exceeded averages found in other baldcypress stands in the southeastern United States. Seedlings differed among sites in all parameters measured, with height, diameter, foliar biomass, and survival decreasing as site salinity increased. Average seedling height at the end of two years, for example, was 196.4 em on the lowest salinity site and 121.6 cm on the highest. Several half-sib families maintained greater height growth increments (ranging from 25.5 to 54.5 cm on the highest salinity site), as well as lower foliar ion concentrations of K, Cl, and Ca. Results indicate that genotypic screening of baldcypress may improve growth and vigor of seedlings planted within wetlands impacted by saltwater intrusion.

Holocene Sedimentation in Lagoa dos Patos Lagoon, Rio Grande do Sul, Brazil

Abstract: Lagoa dos Patos in southern Brazil is part of the largest lagoonal system in South America. The Holocene lagoonal sediments of the Lagoa dos Patos, mostly muds, have an average thickness of about 6 m as determined by 297 km of 7.0 kHz echograms. Holocene muddy sedimentation developed over a probable Upper Pleistocene coastal plain, whose surface has a sub-bottom reflector that could not be penetrated by the energy of a 7.0 kHz seismic wave. The characteristics of this reflecting surface suggest indurated Pleistocene muds and/or sediments that are coarser than the overlying muddy deposits of Holocene lagoon. Based on stratigraphic correlation and the local sea level curve, we estimate that Holocene sedimentation started about 8.0 ka ago. This yields an average deposition rate of 0.75 mm/ yr. A broadly comparable average rate of 0.52 ± mm/yr was obtained for cored intervals between 14 C samples from the upper part of these muddy Holocene lagoon deposits.

Plant diversity as a suitable tool for coastal dune vulnerability assessment.

Abstract: The investigation reported here is concerned with the use of plant diversity measures for coastal dune monitoring. The original set of recorded plant species on dune systems was broken into 3 functionally homogeneous groups, which allow ecological comparisons among foredune vegetation on a much wider sense than traditional taxonomic approaches. Plant diversity was measured both, as species richness and as the rate of species number increase with area. Plant diversity values were tested as a dependent variable of a coastal dune vulnerability Index. Increasing coastal dunes vulnerability, caused by natural or human events, lowered the rate of species increase with area within the plant functional type associated to prograding foredunes. Results suggest that plant diversity within this functional type, measured as the slope of the species-area curve, may be used as a management tool for predicting coastal dune vulnerability.

Comparative Impacts of the 1982-83 and 1997-98 EI Nino Winters on the Central California Coast

Abstract: Although most indices suggest the 1997-98 El Nino-Southern Oscillation (ENSO) was more intense than the 1982-83 ENSO event, the coastline of central California sustained approximately $14 million in damages during the 1982-83 winter, more than double the economic impact experienced during the 1997-98 winter. We attribute the difference in coastal response to a combination of oceanographic and anthropogenic factors. During 1982-83, the large wave events tended to coincide with more southerly and higher velocity winds, increasing set-up along the shoreline and beach erosion due to offshore-directed flow. These large wave events also occurred during very high tides, causing the waves to break closer to shore and to strike the coast with more energy, increasing their impact on coastal structures and property. During the 1997-98 winter, however, the largest waves arrived during lower tides and coincided with lower wind velocities. The northwesterly winds reduced set-up along the shoreline and caused net onshore flow, decreasing wave impact. Another important factor contributing to the disproportionate damage between the winters was the higher percentage of shoreline that had been armored by 1997. Most areas significantly damaged in 1982-83 winter were protected by more substantial seawalls or revetments during the 1997-98 ENSO event. Improving the understanding of variations in coastal response to extreme storm events is essential to bolstering the resiliency of our coastal communities.

Grain-Size-Selective Aeolian Sand Transport on a Nourished Beach

Abstract: The grain-size-selective aeolian processes that take place after a beach nourishment were studied on the island of Ameland in the Netherlands. The beach and foredunes were sampled both before and after nourishment. Grain-size distributions of surface and subsurface sand, wind-laid sand and sand in transport were analysed. The unreworked fill is only moderately sorted and exhibits a large spatial variation. Marine reworking results in a decrease of shell fragments and a decrease in fines on the foreshore, with the exception of the swash mark. During aeolian sand transport, aeolian decoupling results in a backshore with surface lag deposits with moderately sorted sand containing a substantial amount of shell fragments and silt, and patches of sand with less shell fragments. Wind-laid nourishment sand, i.e., the nourishment sand that is blown to the dunes, contains only small amounts of these shell fragments and the sand is finer and better sorted than the nourishment beach sand. However, the nourishment sand that is blown to the foredunes still deviates from the wind-laid native sand; it is more poorly sorted and more negatively skewed. Furthermore, the wind-laid nourishment sand contains significantly more coarse material, i.e., shell fragments, than the wind-laid native sand, which will lead to an increase in calcium carbonate content in the foredunes.

Contaminant distribution and accumulation in the surface sediments of Long Island Sound

Abstract: The distribution of contaminants in surface sediments has been measured and mapped as part of a U.S. Geological Survey study of the sediment quality and dynamics of Long Island Sound. Surface samples from 219 stations were analyzed for trace (Ag, Ba, Cd, Cr, Cu, Hg, Ni, Pb, V, Zn and Zr) and major (AI, Fe, Mn, Ca, and Ti) elements, grain size, and Clostridium perfringens spores. Principal Components Analysis was used to identify metals that may co-vary as a function of common sources or geochemistry. The metallic elements generally have higher concentrations in fine-grained deposits, and their transport and depositional patterns mimic those of small particles. Fine-grained particles are remobilized and transported from areas of high bottom energy and deposited in less dynamic regions of the Sound. Metal concentrations in bottom sediments are high in the western part of the Sound and low in the bottom scoured regions of the eastern Sound. The sediment chemistry was compared to model results (SIGNELL et al., 1998) and maps of sedimentary environments (KNEBEL et al., 1999) to better understand the processes responsible for contaminant distribution across the Sound. Metal concentrations were normalized to grain-size and the resulting ratios are uniform in the depositional basins of the Sound and show residual signals in the eastern end as well as in some local areas. The preferential transport of fine-grained material from regions of high bottom stress is probably the dominant factor controlling the metal concentrations in different regions of Long Island Sound. This physical redistribution has implications for environmental management in the region.

Comparison of the Performance of Three Adjacent and Differently Constructed Beach Nourishment Projects on the Gulf Peninsula of Florida

Abstract: Detailed beach-profile monitoring was conducted at the three phases of Sand Key beach nourishment on the Gulf Coast of Florida. The nourishment at Indian Rocks Beach, Indian Shores, and Redington Beach was monitored during six years, four years, and eight years respectively after nourishment. Quarterly or more frequent beach and nearshore profile surveys were conducted in order to determine short-term (1 year) and long-term (4 to 8 years) rates of shoreline and beach-nearshore volume changes. The overall performance of the Sand Key beach nourishment is excellent. Redington Beach project has already exceeded the design lifetime of 7 years, and Indian Rocks Beach and Indian Shore projects are likely to exceed the design lifetime. The measured beach-nearshore volume loss is small: 31% at Indian Rocks Beach over six years, 30% at Indian Shores over four years, and only 10% at Redington Beach during eight years. Performance of beach nourishment is influenced by many factors. Those that are directly related to the three nourishment projects include: (1) relative location in the regional longshore sediment transport regime, (2) magnitude of wave energy, (3) sediment characteristics of the borrow material, (4) local reversal and/or gradient in longshore transport, (5) presence of hard structures, (6) adjacent beach nourishment, (7) variation of shoreline orientation, and (8) sand transfer and beach-fill construction technique. The shoreline and beach-nearshore volume change patterns at the three nourishment projects were different due to the different degrees of influence from the above factors, however, construction style is deemed to be an important contributor. The much less costly dragline and conveyor belt transfer technique used in the construction of Indian Shores project does not prove to be most cost effective for long-term performance.

Near-bed currents and suspended sediment transport in saltmarsh canopies

Abstract: A field study was undertaken to measure near-bed current velocity, water level and suspended sediment concentration on unvegetated mudflat, and in recently developed Scirpus mariquete and Spartina alterniflora canopies in the Changjiang Estuary, China. Near-bed current (a combination of both tidal currents and wave motion) velocities were up to 50 cm s -1 in saltmarsh canopies and on the mudflat. Near-bed current velocity within a saltmarsh canopy was generally less than that on the mudflat, regardless of the phase of the tides or the tidal current direction. Mean near-bed current velocity was reduced by 16% within the estuarine saltmarsh canopy compared to open mudflat. Reductions in near-bed current velocities within the saltmarsh canopy were larger during ebb tide than flood tide. Suspended sediment concentrations were found to be lower within the estuarine saltmarsh canopies compared to the unvegetated mudflat.

Resonant reflection of waves over sinusoidally varying topographies

Abstract: The propagation of monochromatic waves over an arbitrarily varying topography is studied theoretically. The varying topography is first represented by a finite number of small steps. A theoretical model is then developed by formulating the diffraction of monochromatic waves by abrupt depth changes, through the eigenfunction expansion method. Not only the propagating mode but also the evanescent modes are included in the model. The model developed is applied to the study of the Bragg reflection of monochromatic waves caused by a singly-sinusoidally varying topography. The effects of the oblique incidence of waves are also investigated. The model solutions are compared with available experimental data. The model is also used to investigate the Bragg reflection of monochromatic waves over a doubly sinusoidally varying topography. The reflection coefficients calculated are compared with laboratory measurements and other numerical results. A reasonable agreement is observed.

Mercury in Long Island Sound Sediments

Abstract: Mercury (Hg) concentrations were measured in 394 surface and core samples from Long Island Sound (LIS). The surface sediment Hg concentration data show a wide spread, ranging from 600 ppb Hg in westernmost LIS. Part of the observed range is related to variations in the bottom sedimentary environments, with higher Hg concentrations in the muddy depositional areas of central and western LIS. A strong residual trend of higher Hg values to the west remains when the data are normalized to grain size. Relationships between a tracer for sewage effluents (C. perfringens) and Hg concentrations indicate that between 0-50 % of the Hg is derived from sewage sources for most samples from the western and central basins. A higher percentage of sewage-derived Hg is found in samples from the westernmost section of LIS and in some local spots near urban centers. The remainder of the Hg is carried into the Sound with contaminated sediments from the watersheds and a small fraction enters the Sound as in situ atmospheric deposition. The Hg-depth profiles of several cores have well-defined contamination profiles that extend to pre-industrial background values. These data indicate that the Hg levels in the Sound have increased by a factor of 5-6 over the last few centuries, but Hg levels in LIS sediments have declined in modern times by up to 30 %. The concentrations of C. perfringens increased exponentially in the top core sections which had declining Hg concentrations, suggesting a recent decline in Hg fluxes that are unrelated to sewage effluents. The observed spatial and historical trends show Hg fluxes to LIS from sewage effluents, contaminated sediment input from the Connecticut River, point source inputs of strongly contaminated sediment from the Housatonic River, variations in the abundance of Hg carrier phases such as TOC and Fe, and focusing of sediment-bound Hg in association with westward sediment transport within the Sound.

Predicting Threshold Entrainment Mass for a Boulder Beach

Abstract: The critical threshold mass for boulders composing a beach is the mass of the largest stone entrained by the hydraulic forces associated with wave breaking and swash run-up. For any given storm event there is a maximum boulder mass that can be moved and another slightly larger boulder that has the minimum mass necessary to remain stable. Two equations are derived: one to estimate critical threshold mass and another to estimate minimum stable mass for boulders on a beach. The equations incorporate: stone density, beach slope, breaking wave height, water depth, wave period, run-up height, maximum swash velocity and average swash velocity. In both equations the wave force applied to the beach face is scaled relative to the elevation that wave energy raises the water surface. Scaling the wave force relative to the run-up elevation results in a critical threshold formula. This is given as equation (45). Its predictions accurately match field data giving the largest boulder transported on a beach during storm events. Scaling the wave force relative to the breaking wave height at the toe of the beach results in a stability formula. This is given as equation (46). It predicts stable mass in the range defined by the Hudson formula. Equation (46) has an advantage over the Hudson formula by incorporating the physically important parameters of wave period and swash velocity. Both equations could be useful in the initial evaluation and design of dynamic revetments constructed with quarry stone.

Holocene Relative Sea Level Changes in Disko Bugt, West Greenland

Abstract: An investigation of Holocene relative sea level (RSL) changes in Disko Bugt has been carried out with the purpose of reconstructing, with a good resolution in time and space, the Holocene RSL changes of a smaller part of Greenland, and thereby to allow testing of modern models for RSL changes in Greenland. This paper summarises the results of the investigation. The Holocene marine limit in Disko Bugt has been mapped, four RSL curves representing the Early - Middle Holocene emergence of different parts of Disko Bugt have been constructed, and attempts have been made to reconstruct the Late Holocene RSL changes within the region. Important conclusions are: 1. The rate of Early-Middle Holocene relative land rise increases towards the margin of the Greenland Ice Sheet. 2. RSL reached present sea level earlier in areas close to the Greenland Ice Sheet than in areas at greater distances from the Greenland Ice Sheet. 3. RSL fell below present sea level between 2 and 4 ka BP. 4. Submergence has occurred since ca. 1 ka BP.

Distribution of Surficial Sediment in Long Island Sound and Adjacent Waters: Texture and Total Organic Carbon

Abstract: The surficial sediment distribution within Long Island Sound has been mapped and described using bottom samples, photography, and sidescan sonar, combined with information from the geologic literature. The distributions of sediment type and total organic carbon (TOC) reveal several broad trends that are largely related to the sea-floor geology, the bathymetry, and the effects of modern tidal- and wind-driven currents. Sediment types are most heterogeneous in bathymetrically complex and shallow nearshore areas; the heterogeneity diminishes and the texture fines with decreasing bottom-current energy. Lag deposits of gravel and gravelly sand dominate the surficial sediment texture in areas where bottom currents are the strongest (such as where tidal flow is constricted) and where glacial till crops out at the sea floor. Sand is the dominant sediment type in areas characterized by active sediment transport and in shallow areas affected by fine-grained winnowing. Silty sand and sandsilt-clay mark transitions within the basin from higher- to lower-energy environments, suggesting a diminished hydraulic ability to sort and transport sediment. Clayey silt and silty clay are the dominant sediment types accumulating in the central and western basins and in other areas characterized by long-term depositional environments. The amount of TOC in the sediments of Long Island Sound varies inversely with sediment grain size. Concentrations average more than 1.9% (dry weight) in clayey silt, but are less than 0.4% in sand. Generally, values for TOC increase both toward the west in the Sound and from the shallow margins to the deeper parts of the basin floor. Our data also suggest that TOC concentrations can vary seasonally.