Montauk Point Research Articles

Planning and design of three USACE New York District projects

The United States Army Corps of Engineers (USACE) New York District (NYD) has had a tremendous impact on an approximately $6 billion comprehensive coastal storm risk management program in the last 10 years since Hurricane Sandy caused significant damage in the New York (NY) and New Jersey (NJ) area. There was 2013- 2014 emergency repair and restoration to existing beach nourishment and navigation projects, but also USACE NYD accomplished the planning and design for multiple coastal storm risk management projects in the NY and NJ area. Of those projects, specific coastal risk reduction features are described for the Sea Bright to Manasquan, NJ; East Rockaway Inlet to Rockaway Inlet, NY; and Montauk Point Lighthouse Stabilization, NY. The planning and design for these projects exemplifies resilience principles and planned adaptability to withstand the challenges of the dynamic coastal environment. The USACE NYD is faced with numerous challenges such as environmental restrictions, politics, real estate, sea level change, etc.; the magnitude of coastal planning, design and construction that has occurred over these past 10 years for the NYD studies and projects demonstrates the fortitude of collaboration combined with current and innovative engineering principles.

War against Prohibition: Italians and Booze in New York City, 1920–1933

War against Prohibition: Italians and Booze in New York City, 1920–1933

A “splendid flying field” in Indianapolis: Aviation and Speedway Spectacles in the Great War Era

A “splendid flying field” in IndianapolisAviation and Speedway Spectacles in the Great War Era Brian M. Ingrassia (bio) In 1917, Carl Graham Fisher offered the facilities of the Indianapolis Motor Speedway to the United States federal government for the training of military aviators and the building of aircraft. He asserted that the Speedway, constructed nearly a decade earlier in 1909, was the best place in America to carry out such work. The government partly took Fisher up on his offer, and the 328-acre facility became a focal point for World War I aviation. By autumn of that year, Fisher was mapping and marking cross-country flying routes throughout the lower Great Lakes region; he even began imagining aerial routes along the transcontinental highways he had spearheaded earlier in the decade, especially the east-west Lincoln Highway. In so doing, Fisher seemed to lay the foundation for an aviation network centered on Indianapolis. The war’s aftermath, however, saw the Speedway turn in a different direction. In May 1919, racing returned to Indianapolis in a form made more dangerous than ever before by wartime technological developments. And although there was serious discussion of turning the raceway into an airport in the mid-1920s, the track’s owners chose spectacle over commercial or military utility, cementing the facility’s identity as a site for thrilling motor sports. The story of Great War aviation at Indianapolis, which remains obscured in standard narratives, has a threefold significance.1 First, as historian Mark Foster implies in his brief treatment of the subject, the Speedway’s wartime service was part of Carl Fisher’s project of developing transportation infrastructures connecting early-1900s people and cities.2 Second, it shows that the Midwest, as historian Kristin Hoganson has perceptively argued, was not disconnected from global currents; rather, the region contributed to larger projects of nationalism and imperialism.3 Third, the story hints [End Page 109] at how Midwesterners adopted and adapted transportation technologies for innovative purposes not limited to utilitarian movement of people or goods. Scholar Jason Weems contends that aircraft helped Midwesterners comprehend their region, a former frontier based on a seemingly “infinite notion of the future.” By the twentieth century, though, the “very grid that had once led settlers to a manifest destiny now appeared to lock them in place.”4 Settled in the middle, they turned to modern technologies and cultural spectacles. After World War I, Fisher and his fellow racing moguls had an opportunity to transform the Hoosier track into a regional aviation hub, but instead they doubled down on popular culture, maintaining the IMS grounds as a place for racing before then selling the facility to famed Great War aviator Eddie Rickenbacker right as the postwar economy peaked in 1927. Airplanes may have offered early-1900s Americans a near-utopian “instrument of reform, regeneration, and salvation,” yet motor sport impresarios ultimately chose the racing spectacle.5 The Speedway became a place where Midwesterners fashioned a modernity based on culture as much as upon commerce. The central figure in this story, Carl Fisher, was the guiding spirit behind Indianapolis’s speedway, which itself was modeled on the Brooklands automotive and aerial facility built in Surrey, England, in 1907. Fisher, who made a fortune through a headlamp company called Prest-O-Lite, used his wealth to promote automotive travel, pop-culture spectacles, and real-estate ventures in Miami Beach, Florida, and Montauk Point, Long Island. Fisher was like a playful version of Henry Ford, shaping American landscapes and mobility in his own distinctive way. He and three other Hoosier industrialists—James Allison, Arthur Newby, and Frank Wheeler—built Indianapolis’s famous speedway as a tar-and-gravel track in early 1909 and then, after a series of deadly crashes that summer, repaved it with three million vitrified bricks later that year. In its early years, Indianapolis’s speedway held both auto races and aviation contests, making the regional metropolis a focal point for transportation-based spectacle. By 1911, the 2.5-mile oval held its first 500-mile race, which marked its claim to global fame. When the U.S. entered the Great War, aviation was still an important part of the...

Dynamics of the periphery current in Rhode Island Sound

Observations reveal a near-surface circulation around the periphery of Rhode Island Sound (RIS) that occurs in summer stratified conditions and disappears in winter when weak solar insolation and wind stirring result in strong vertical mixing. According to a series of numerical simulations and theoretical analysis, we attribute the summer intensification of this “periphery current” to a circulation produced by seasonal bottom thermal fronts often observed from May to September. The strength of the thermal fronts is proportional to the surface solar radiation. Meanwhile, the simulations capture a continuous topographically rectified tidal residual current in RIS and a pair of opposite-sign headland eddies around Montauk Point in Block Island Sound (BIS). Our analysis suggests the importance of nonlinear vorticity advection and frictional torques in BIS. On the other hand, the vorticity balance shows the importance of velocity torque by contributing to the opposite headland gyres, while the effect by planetary vorticity stretching is negligible over BIS but important in RIS.

A Regression-Based Approach for Cool-Season Storm Surge Predictions along the New York–New Jersey Coast

AbstractA multilinear regression (MLR) approach is developed to predict 3-hourly storm surge during the cool-season months (1 October–31 March 31) between 1979 and 2012 using two different atmospheric reanalysis datasets and water-level observations at three stations along the New York–New Jersey coast (Atlantic City, New Jersey; the Battery in New York City; and Montauk Point, New York). The predictors of the MLR are specified to represent prolonged surface wind stress and a surface sea level pressure minimum for a boxed region near each station. The regression underpredicts relatively large (≥95th percentile) storm maximum surge heights by 6.0%–38.0%. A bias-correction technique reduces the average mean absolute error by 10%–15% at the various stations for storm maximum surge predictions. Using the same forecast surface winds and pressures from the North American Mesoscale (NAM) model between October and March 2010–14, raw and bias-corrected surge predictions at the Battery are compared with raw output from a numerical hydrodynamic model’s [the Stevens Institute of Technology New York Harbor Observing and Prediction System (SIT-NYHOPS)] predictions. The accuracy of surge predictions between the SIT-NYHOPS output and bias-corrected MLR model at the Battery are similar for predictions that meet or exceed the 95th percentile of storm maximum surge heights.

Two-dimensional hydrodynamic modeling of circulation in Great South Bay and New York Bight

A two-dimensional depth-averaged boundary-fitted hydrodynamic model is used to study circulation in Great South Bay and New York Bight Region. The model domain included portions of New York Bight from Cape May, New Jersey to Montauk Point at the end of Long Island Sound, New York Harbor, Great South Bay and the adjoining rivers in New York and New Jersey. The model forcing functions consisted of tidal elevations along the open boundaries and winds. Model predictions of surface elevations at Fire Island Inlet and Moriches Inlet Coast Guard Stations showed good comparison with observations, with correlation coefficients exceeding 0.960. The simulated tidal currents showed good comparisons with observations with root mean square errors less than 10% and correlation coefficients exceeding 0.910. The model predicted low-frequency currents showed favorable comparison with observations, with correlation coefficients of 0.808 and 0.605, respectively for the east–west and north–south components. Observations and model simulations show that the subtidal currents with speeds of 10–20cm/s are generated due to alongshore wind over the continental shelf.

Modeling regional sediment transport and shoreline response in the vicinity of tidal inlets on the Long Island coast, United States

A new numerical model was developed to simulate regional sediment transport and shoreline response in the vicinity of tidal inlets based on the one-line theory combined with the reservoir analogy approach for volumetric evolution of inlet shoals. Sand bypassing onshore and sheltering effects on wave action from the inlet bar and shoals were taken into account. The model was applied to unique field data from the south coast of Long Island, United States, including inlet opening and closure. The simulation area extended from Montauk Point to Fire Island Inlet, including Shinnecock and Moriches Inlets. A 20-year long time series of hindcast wave data at three stations along the coast were used as input data to the model. The capacity of the inlet shoals and bars to store sand was estimated based on measured cross-sectional areas of the inlets as well as on comprehensive bathymetric surveys of the areas around the inlet. Several types of sediment sources and sinks were represented, including beach fills, groin systems, jetty blocking, inlet bypassing, and flood shoal and ebb shoal feeding. The model simulations were validated against annual net longshore transport rates reported in the literature, measured shorelines, and recorded sediment volumes in the flood and ebb shoal complexes. Overall, the model simulations were in good agreement with the measured data.

Beach Nourishment, Shoreline Change, and Dune Growth at Westhampton Beach, New York, 1996-2009

Abstract Westhampton Beach is located on the barrier island between Moriches Inlet and Shinnecock Inlet, along the south shore of Long Island, New York. This vulnerable area has been subject to a number of beach erosion control measures under the authority of the Fire Island to Montauk Point, New York Beach Erosion and Hurricane Protection (FIMP) project as well as the related Westhampton Interim Project The Westhampton Interim Project, initiated in 1996, provided for beachfill placement, dune construction west of the groin field, periodic beachfill renourishment until 2027, and a tapering of the groins at the western edge of the groin field in order to provide a smooth transition to the downdrift barrier beaches. Project coastal processes monitoring since 1996 has shown that the shoreline position in the project area has been stable and there has been volumetric growth of the dune field west of the groin field. The 10-year average volumetric loss in the project area of 180,000 cubic yards per year is ver...

MODELING SHORELINE RESPONSE AND INLET SHOAL VOLUME DEVELOPMENT ON LONG ISLAND COAST, UNITED STATES

A new numerical model was developed to simulate regional sediment transport, shoreline response in the vicinity of tidal inlets, and inlet shoal volume growth based on the one-line model of shoreline change combined with the reservoir concept for volumetric evolution of inlet shoals. Sand bypassing onshore and sheltering effects on wave action from the inlet bar and shoals were taken into account. The model was applied to unique field data from the south coast of Long Island, United States, including inlet opening and closure. The simulation area extended from Montauk Point to Fire Island inlet, including Shinnecock and Moriches Inlets (Figure 1). A 20-year time series of hindcast wave data at three stations along the coast were used as input data to the model. Several types of sediment sources and sinks were represented, including beach fills, groin systems, jetty blocking, inlet bypassing, and flood shoal and ebb shoal feeding. The model simulations were validated against annual net longshore transport rates reported in the literature, measured shorelines, and recorded sediment volumes in the flood and ebb shoal complexes. Overall, the model simulations were in good agreement with the measured data.

Turbulence in coastal fronts near the mouths of Block Island and Long Island Sounds

Measurements of turbulence were performed in four frontal locations near the mouths of Block Island Sound (BIS) and Long Island Sound (LIS). These measurements extend from the offshore front associated with BIS and Mid-Atlantic Bight Shelf water, to the onshore fronts near the Montauk Point (MK) headland, and the Connecticut River plume front. The latter feature is closely associated with the major fresh water input to LIS. Turbulent kinetic energy (TKE) dissipation rate, ε, was obtained using shear probes mounted on an autonomous underwater vehicle. Offshore, the BIS estuarine outflow front showed, during spring season and ebb tide, maximum TKE dissipation rate, ε, estimates of order 10 − 5 W/kg, with background values of order 10 − 6 to 10 − 9 W/kg. Edwards et al. [Edwards, C.A., Fake, T.A., and Bogden, P.S., 2004a. Spring–summer frontogenesis at the mouth of Block Island Sound: 1. A numerical investigation into tidal and buoyancy-forced motion. Journal of Geophysical Research 109 (C12021), doi:10.1029/2003JC002132.] model this front as the boundary of a tidally driven, baroclinically adjusted BIS flow around the MK headland eddy. At the entrance to BIS, near MK, two additional fronts are observed, one of which was over sand waves. For the headland site front east of MK, without sand waves, during ebb tide, ε estimates of 10 − 5 to 10 − 6 W/kg were observed. The model shows that this front is at the northern end of an anti-cyclonic headland eddy, and within a region of strong tidal mixing. For the headland site front further northeast over sand waves, maximum ε estimates were of order 10 − 4 W/kg within a background of order 10 − 7 –10 − 6 W/kg. From the model, this front is at the northeastern edge of the anti-cyclonic headland eddy and within the tidal mixing zone. For the Connecticut River plume front, a surface trapped plume, during ebb tide, maximum ε estimates of 10 − 5 W/kg were obtained, within a background of 10 − 6 to 10 − 8 W/kg. Of all four fronts, the river plume front has the largest finescale mean-square shear, S 2 ~ 0.15 s − 2 . All of the frontal locations had local values of the buoyancy Reynolds number indicating strong isotropic turbulence at the dissipation scales. Local values of the Froude number indicated shear instability in all of the fronts.

Interplay of Wind Forcing and Buoyant Discharge off Montauk Point: Seasonal Changes to Velocity Structure and a Coastal Front

Abstract Seasonal-mean currents in fall, winter, and spring on the bathymetrically complex continental shelf 15–65 m deep off Montauk Point, outside Block Island Sound, are analyzed using moored profiling current-meter records from a 2.5-yr period. A sharp boundary, or coastal front, occurs where strong, shallow, generally southwestward flow that weakens nearly linearly with increasing depth meets deeper flow nearly opposite in direction (fall/winter) or markedly weaker (spring). Velocities veer clockwise (counterclockwise) with increasing depth inshore (offshore) of the front. Evidence is presented that thermal wind balance holds without major frictional modification: it accounts for the veering, and the seasonal-mean horizontal density gradients it implies are generally toward the southeast quadrant in agreement with limited hydrographic measurements. Substantial seasonal changes in flow and frontal attributes occur because of the interplay of annual cycles in wind forcing and buoyant discharge. In fall and winter, upwelling-favorable wind causes nearshore setdown of sea surface height and an inshore-directed barotropic pressure gradient: shallow down-coast (alongshore to the south and west) currents weaken, and deep currents are up-coast. In spring, buoyant discharge peaks and winds weaken: shallow down-coast flow strengthens and deep flow weakens. The front extends to the seafloor, with attachment depth shallowest in winter, deepest in spring, and intermediate in fall; its width is smaller in fall than in winter. Buoyant discharge theory based on bottom boundary layer density advection dynamics captures these seasonal shifts. Cross-shelf circulation includes offshore (onshore) shallow (deep) motion; deep onshore motion appears enhanced near a canyon and persistent through all three seasons, suggesting wind-driven upwelling is not solely responsible.

Networked Acoustic Modems for Real-Time Data Telemetry from Distributed Subsurface Instruments in the Coastal Ocean: Application to Array of Bottom-Mounted ADCPs

Abstract Through the winter and spring of 2002, networked acoustic modems demonstrated real-time wireless data telemetry from an array of bottom-mounted acoustic Doppler current profilers (ADCPs) on the inner continental shelf 20–60 m deep off of Montauk Point, New York. To achieve typical temporal and spatial sampling needs for data assimilative numerical modeling, the array spanned 10 km × 10 km and transmitted data each ∼2 h. Network nodes included five sensors, each an ADCP with acoustic modem housed in a trawl-resistant bottom frame; five repeaters that are individual acoustic modems on near-bottom taut-wire moorings; and two gateways, each a buoy with a subsurface acoustic modem and topside cellular modem allowing for two-way communication with the shore. Deliveries from an ADCP adjacent to the gateway buoy were more than 97% successful through both winter and spring. Deliveries from ADCPs 5 km from the gateway averaged 25% (86%) reliability in winter (spring). Winter performance degrades because of upward-refracting sound speed profiles that limit direct acoustic paths, and strong winds that disrupt sea surface reflectivity and increase ambient noise. Reliability improved up to 36% due to the receive-all gateway mode, and more than doubled for certain node pairs due to a handshake protocol incorporating an automatic repeat request. Shore-based network control demonstrated adaptive sampling by changing ADCP vertical and temporal resolution, and network data path rerouting in response to unplanned events, such as trawling impacts. Networked acoustic modems are well suited for coastal ocean-observing systems, particularly at sites such as this where seafloor cables and surface buoys are vulnerable to fishing and shipping activities.

The structure of the coastal density front at the outflow of Long Island Sound during spring 2002

South of the eastern end of Long Island (Montauk Point) along the Eastern U.S. coast, a coastal density front forms between the buoyant outflow plume of the Long Island Sound (LIS) and the denser shelf waters offshore. During a 2-day cruise in April 2002, measurements of the density and velocity structure of this front were obtained from high-resolution CTD and ADCP data. Transects show the front intersecting the bottom inshore of the 30 m isobath and shoaling offshore. Variability in the location of the front is small offshore of the 40 m isobath, yet tidal excursions of the front along the bottom are significant (5 km) inshore of this depth. The frontal structure of the LIS plume was similar to observations of bottom-trapped coastal density fronts and shelf break fronts. A coastal jet in the along front direction was the main feature of the mean velocity field and was found to be in thermal wind balance with the mean density field. Stronger than expected offshore velocities near the surface, most likely a result of wind forcing, were the only exception to these similarities. In addition, analysis of temperature and salinity gradients along isopycnals gives evidence of secondary cross-frontal circulation and detachment of the bottom boundary layer. Characteristics of the LIS plume are used to evaluate recent analytical models of bottom-trapped coastal density fronts and bottom-advected plume theory, finding good agreement.

Spring‐summer frontogenesis at the mouth of Block Island Sound: 2. Combining acoustic Doppler current profiler records with a general circulation model to investigate the impact of subtidal forcing

The use of a one‐layer inverse model to improve the fidelity of a three‐dimensional primitive equation model is explored in the region just south of Block Island Sound in the Middle Atlantic Bight. The inverse model, based on the theory of Bennett and McIntosh, produces a solution to the linear, shallow‐water equations that minimizes model‐data misfit and the resulting open boundary velocity variance. The Massachusetts Institute of Technology general circulation model is configured regionally and includes realistic tidal forcing, surface warming, and wind stress, as well as climatological buoyancy gradients between the estuary and the shelf. A 15 day record from two acoustic Doppler current profiler moorings, deployed in spring 2000 south of the entrance of Block Island Sound, allows assessment of the forward model and provides data to improve subtidal boundary conditions. Model‐data misfit decreases notably for both the depth‐averaged and vertically sheared flow, indicating that improvements to the depth‐averaged circulation positively impact the three‐dimensional circulation in this shallow shelf environment. The role of wind stress in modulating the position of the buoyant plume that characterizes the regional hydrography is also examined. A distinctly three‐dimensional circulation is observed, with a growing offshore plume at the mouth of the sound during northward stress followed by rapid alongshelf advection during periods of southwestward or weak winds. Although, on the timescales considered here, wind stress forcing dominates the buoyancy‐driven motion, it is overwhelmed by the tidally driven rectified flow just south of Montauk Point, which provides the inshore boundary of the front even in downwelling favorable conditions.

Spring‐summer frontogenesis at the mouth of Block Island Sound: 1. A numerical investigation into tidal and buoyancy‐forced motion

The generation and underlying dynamics of late‐spring temperature and salinity fronts at the mouth of Block Island Sound in the Mid‐Atlantic Bight are examined using a three‐dimensional general circulation model. The model is forced by tidal velocities at its outer boundaries, an estuary/shelf salinity gradient, and surface warming. Runs representing the period from 18 April to 23 May 2000 are investigated through direct examination of the model results and diagnostic calculations that isolate individual processes. Three mechanisms are identified as significantly contributing to the location and structure fronts observed in this region. Vertical mixing produces the necessary horizontal temperature structure within and near Block Island Sound, but the southern frontal boundary is further affected by the subtidal circulation, which is divided into two components defined using a momentum budget analysis. Tidal currents over the complex bathymetry leads to nonlinearly rectified flows, including a headland eddy south of Montauk Point. Circumscribing this feature is a baroclinically adjusted, buoyant outflow from the Long Island Sound estuary. While modifications to the buoyancy forcing can modify the frontal position, it necessarily remains offshore of the tidally driven circulation. Analysis of the salinity anomaly fluxes indicates that both tidal and mean advection are responsible for the overall transport of buoyancy.

Networked Acoustic Modems for Real-Time Data Delivery from Distributed Subsurface Instruments in the Coastal Ocean: Initial System Development and Performance

Results are reported from field tests of networked acoustic modems used for wireless real-time delivery of oceanographic measurements from a distributed array of subsurface instruments in coastal waters. The network demonstrated consists of sensor nodes, repeater nodes, gateway nodes, and a shore-based control center. Sensors are oceanographic instruments interfaced with acoustic modems, deployed in trawl-resistant bottom frames with azimuthally omnidirectional acoustic signaling needed for flexible network rerouting. Repeaters are individual acoustic modems to relay data so the array covers a larger area; only these relatively low-cost nodes are suited for deployment unprotected from trawlers. Gateways are buoys with acoustic modems interfaced to cellular telephone modems for communication between the underwater network and the shore. The experiment site is the inner continental shelf off Montauk Point, New York, and Block Island, Rhode Island, with a U.S. Coast Guard navigation buoy equipped as a gateway. Conditions span a variety of sound-speed profiles, water depths (∼25–50 m), and seasons. Long-term average rates of successful transmissions fall to about 50% at a range of 3–4 km in the typically adverse shallow-water acoustic channel. This is adequate for networked acoustic modems to be cost effective in providing quantities of data typically required for data assimilative modeling of coastal oceanographic processes. Modem range degrades in association with increased winds; numerically modeled rays indicate that direct paths between nodes commonly do not exist. Networking functions demonstrated include handshaking protocols, receive-all gateway mode, and rerouting of data pathways from shore in response to a repeater node that is trawled out.

The isotopic composition of carbon monoxide at Montauk Point, Long Island

We present the seasonal cycle of the stable isotopes of CO (13CO and C18O) along with CO concentration from samples collected weekly at Montauk Point, Long Island, between October 1996 and October 1997. The seasonal cycle of the stable isotopes is similar in shape to studies carried out at more pristine locations, but the isotopic values are quite different as a result of differing relative strengths of seasonal sources. We also observe a fairly strong correlation between oxygen-18 and CO concentration, indicating one predominant source in this region (fossil fuel combustion). The observed isotopic seasonality can help constrain relative source strengths as certain sources have characteristic isotopic signatures. We use a simple isotope chemistry model to simultaneously solve for the relative strengths of the major sources during the sampling period. We find that fossil fuel combustion is the most predominant source, with only small contributions from nonmethane hydrocarbon oxidation and biomass burning, even during the summer and fall months.

A mesoscale sediment budget for Long Island, New York

A sediment budget encompassing the 140-km shoreline from Montauk Point to Fire Island Inlet, New York, derived longshore transport rates for 25 coastal cells using comparative surveys. The study area along the south shore of Long Island, a generally straight coast of mainland and barrier island beaches, includes the eroding headland at Montauk Point, three jettied inlets, two groin fields, and three barrier beaches. Bridging between small-scale (quantitative) surveys and large-scale regional geology, the sediment budget provides a mesoscale view and quantitative estimates of key coastal processes in the area. Results integrate changes between the foredunes and lower foreshore to the estimated depth of closure (−9 to −12 m below mean sea level) for a 24.5-year period (1955–1979). Beach fills and losses to washovers and breach channels are incorporated in the analysis.The results confirm net westerly transport and provide the first evidence that shoaling in Fire Island Inlet (long estimated to be ~ 400,000 m3/yr) is due primarily to cannibalization of the immediate updrift compartments, particularly erosion of the foreshore below mean low water. This lowers estimates of longshore transport rates along most of the study area compared with previous estimates. The offshore source attributed by others to account for Fire Island's stability appears to be trailing ebb shoals lagging behind inlet migration. Jettied inlets in the central study area intercept some longshore transport but since stabilization (circa 1955) have been ebb dominant, preserving the littoral budget seaward of the strandline; littoral losses to the lagoons by inlets or washovers were insignificant over the period. However, breach channels, if not closed soon after storms, were found to offset years of ebb dominance in jettied inlets by depositing major flood deltas. Beach fills had measurable and positive effect on the sediment budget along the western half of the study area through the early 1970s. The volume of beach fills since 1975 has diminished to about 10% of the earlier rate. A field of 15 groins in the central study area is shown to trap 100% of the longshore transport and produce a local drift reversal. Rates of accretion within the groin cells and erosion along the downdrift compartment dwarf the average rates of change for the majority of littoral compartments in the study area.

Scanning electron microscope evidence for offshore‐onshore sand transport at Fire Island, New York, USA

ABSTRACTBalancing the sediment budget of the Atlantic shoreline of Long Island has proved to be problematic because more sediment has been found to be moving westward in littoral drift than was estimated to be supplied by wave erosion of the Ronkonkoma terminal moraine at Montauk Point. There is a need for the existence of an additional, possibly offshore source. As part of a larger Atlantic shore study, 11 beach samples from Fire Island were compared with samples representing the known glacial source at Montauk Point, and also with four offshore samples to the south. Comparisons were based upon quartz sand grain surface texture patterns derived by scanning electron microscope checklist analysis. Initial evidence of an offshore‐onshore link was provided by qualitative results examining surface texture variability between samples, illustrated by photographic evidence and written notes. This evidence was confirmed consistently during quantitative analysis. In particular, canonical variate analysis grouped two offshore samples representing deposits of buried glacial to fluvioglacial lobes with beach samples from Fire Island in adjacent onshore locations or slightly downdrift. In addition, canonical variate analysis and factor analysis using the spssx package, together with cluster analysis using the ARTHUR package, depicted the main factors and texture variables largely responsible for sample discrimination. The significance of both the offshore‐onshore link and the associated factors influencing quartz grain surface texture was revealed by the fact that they are strongly related to each other and to the regional geomorphology.

Origin, evolution, and distribution of shoreface sand ridges, Atlantic inner shelf, U.S.A.

A computer mapping system was employed to document the location of 259 shoreface-attached and detached sand ridges in water <20 m deep and the temporal and spatial distribution of 309 historical and active tidal inlets along the U.S. Atlantic coast (Montauk Point, New York, to Miami Beach, Florida). This database was compiled through the analysis of over 600 historical maps, 50 bathymetric charts, and other published data. A genetic relationship between the location of certain historical and active tidal inlets and shoreface-attached sand ridges is documented. It is inferred that ebb-tidal deltas provided the initial sand source for the development of many shoreface-attached sand ridges. Although shoreface-attached sand ridges appear to have several different modes of formation, a two-step process for the development of most shoreface-attached and detached sand ridges along U.S. Atlantic barrier island and cape coastlines is proposed: (1) sand is deposited as ebb-tidal deltas or river deltas along the lower shoreface and/or inner continental shelf prior to or during transgression, followed by (2) further transgression, which reworks the deltaic sand bodies into linear sand ridges at the base of the shoreface by shelf processes. The best-developed shoreface sand ridge fields along the U.S. Atlantic shelf lie adjacent to shorelines characterized by all of the following: (1) transgression, (2) mixed energy, wave-dominated barrier islands, and (3) laterally migrating tidal inlet systems. Tidal inlet systems are natural sediment sinks that capture sand carried by longshore sediment transport. Ebb-tidal delta deposits associated with these migrating tidal inlets provide the initial sand body for the development of shoreface-attached sand ridges. The oblique orientation and linear form of shoreface-attached sand ridges appear to be a function of shoreline transgression, lateral inlet migration, and wave reworking of ebb-tidal delta deposits concentrated along an ebb-tidal delta retreat path. Shelf processes act as modifying agents in the evolution of sand ridges during and after ebb-tidal delta deposition. In general, shoreface-attached sand ridges are poorly developed or absent along eroding headlands, spits, and barrier island shorelines characterized by naturally stabilized tidal inlets. These latter inlets and shoreline types are dominated or influenced by one or all of the following: (1) antecedent topography, (2) higher tidal ranges, (3) larger tidal prisms, (4) lower wave energies, or (5) finer grain sizes. The coupling of shoreline and shallow marine sedimentary processes during a transgression is critical to the origin, evolution, and distribution of shoreface sand ridges in the study area. Modern shoreface-attached sand ridges are also known to occur in different coastal and shelf settings where large amounts of sediment were supplied to the shoreface and inner shelf during, or immediately before, transgression. Commonly observed vertical and lateral interrelationships of Holocene shoreface-attached sand ridges and tidal inlets or distributary channels have important ramifications for the development of shelf sandstone facies models. In addition, the geometric relationship documented in this study provides predictive petroleum and hard mineral exploration models of the spatial and temporal distribution of shoreface and shelf sand ridges.