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Over 220 linear miles of geophysical data, including sidescan sonar and chirp sub-bottom profiles, were collected in 2016 and 2017 by the US Army Corps of Engineers and the US Fish and Wildlife Service in the upper Niagara River. In addition, 36 sediment grab samples were collected to groundtruth the geophysical data. These data were used to map the spatial distribution of fine-grained sediment, including volume data in certain locations, along the shallow shorelines of the upper Niagara River. Overall, the most extensive deposits were spatially associated with either small tributaries or with man-made structures that modified the natural flow of the system. Extensive beds of submerged aquatic vegetation (SAV) were also mapped. Although always associated with a fine-grained matrix, the SAV beds were patchy in distribution, which might reflect subtle differences in the grain size of the sediment matrix or could simply be a function of variations in species or growth. The maps generated from this effort can be used to guide sampling plans for future studies of contamination in fine-grained sediment regions.

Over six linear miles of shallow acoustic reflection geophysical data were collected in an 800 ft by 300 ft survey region at Ogdensburg Harbor, Ogdensburg, NY. To better accommodate modern commercial vessels and expand the harbor’s capacity, the current navigable depth of -19 ft Low Water Depth (LWD) needs to be increased to -28 ft LWD, and an accurate map of the nature of the riverbed material (e.g., unconsolidated sediment, partially indurated glacial till, or bedrock) is required to effectively plan for removal. A total of 28 boreholes were previously collected to map the stratigraphy, and the effort revealed significant spatial variability in unit thickness and elevation between adjacent boreholes. To accurately map this variable stratigraphy, chirp sub-bottom profiles were collected throughout the region, with an average line spacing of 13 ft. These sub-bottom data, validated and augmented by the borehole data, resulted in high-resolution spatial maps of stratigraphic elevation and thickness for the study area. The data will allow for more accurate assessment of the type and extent of different dredging efforts required to achieve a future uniform depth of -28 ft LWD for the navigable region.

Observations from high resolution bathymetric surveys on the coast of North Carolina indicate areas with shore-parallel depth contours and other areas with shore-oblique sandbars. These shore-oblique bars are large-scale morphological features that extend up to 1000 m from shore, and previous studies have shown that they are spatially correlated with higher shoreline change rates and induce erosional hotspots. To investigate the influence the oblique sandbar morphology has on nearshore wave transformation and energy distribution, a non-hydrostatic wave model is used with the bathymetry corresponding to two areas with shore-parallel depth contours and two areas with shore-oblique sandbars. The model is applied with a horizontal resolution of 5 m and a boundary condition representative of the directional spectrum of a typical southeast swell event. An idealized approach with relatively short alongshore model domains and cyclic lateral boundary conditions is adopted due to limited availability of high resolution bathymetry, however this approach elucidates the influence of shore-oblique sandbars on the nearshore hydrodynamics. The numerical results show that higher alongshore variability in depth due to the shore-oblique bars drive large alongshore changes in cross-shore wave energy flux and cause spatial variability in dissipation in the nearshore region. The simulations indicate that alongshore variations in wave energy caused by the shore oblique bars results in a 50–75 % reduction in wave setup and a 25–40 % decrease in alongshore velocity averaged across the surf zone for the conditions investigated. The results suggest that wave-driven hydrodynamics can influence nearshore sediment dynamics to create erosional zones compared to areas with shore-parallel bathymetric contours, since the morphology of shore-oblique sandbars are an important control on wave energy that impacts the beach.

In order to investigate the effect of wave processes on the geotechnical characteristics of topmost sediments, a Portable Free Fall Penetrometer (PFFP) was deployed in the energetic nearshore zone of the U.S. Army Corps of Engineers' Field Research Facility (FRF) in Duck, NC. A total of 335 deployments were conducted from the FRF's 560 m long pier over six non-consecutive days in September and October of 2016. During the surveying period, significant wave heights varied between Hs = 0.8–2.4 m measured at a water depth of 17.4 m. The results showed that the sediment strength is affected by the wave climate. The derived average maximum quasi-static bearing capacities (qsbc), which reflects sediment strength, during low energy wave periods (September 22–24 and 26; Hs = 0.8–1.3 m) ranged between 67 and 73 kPa with maximum qsbc values of 120–136 kPa, while the average values were 47–59 kPa with a maximum qsbc of 82–98 kPa during the high energy wave periods (October 5–6; Hs = 2.4 m). Results also showed that the sediment strength decreased in the shallow water depth regions in spite of the increase in the particle size distribution, due to the increasing wave impact on the seabed within the shallow water region. The area where seabed strength variations were affected by the wave action became wider in the cross-shore direction as the wave height increased. Results further showed that the strength of the topmost sediment layers varied spatially along the profile and temporarily with variations in significant wave height. This likely reflects the impact of waves on sediment strength.

Numerical models predicting surfzone waves and shoreline runup in field situations are often initialized with shoreward propagating (sea-swell, and infragravity) waves at an offshore boundary in 10–30 m water depth. We develop an offshore boundary condition, based on Fourier analysis of observations with co-located current and pressure sensors, that accounts for reflection and includes nonlinear phase-coupling. The performance of additional boundary conditions derived with limited or no infragravity observations are explored with the wave resolving, nonlinear model SWASH 1D. In some cases errors in the reduced boundary conditions (applied in 11 m depth) propagate shoreward, whereas in other cases errors are localized near the offshore boundary. Boundary conditions that can be implemented without infragravity observations (e.g. bound waves) do not accurately simulate infragravity waves across the surfzone, and could corrupt predictions of morphologic change. However, the bulk properties of infragravity waves in the inner surfzone and runup are predicted to be largely independent of ig offshore boundary conditions, and dominated by ig generation and dissipation.

Runup on ocean beaches includes steady wave setup and oscillating swash, often decomposed into wind generated sea-swell (SS), and lower frequency infragravity (IG) waves. We show that the numerically fast, open-source numerical model 1D SWASH predicts accurately the bulk properties of runup observed on two natural beaches (one steep and one shallow sloped) for a range of incident wave conditions. The runup tongue shape was measured with a scanning lidar, and the waterline location was defined in both the observations and model with a 10 cm depth threshold. Runup is reasonably accurately predicted with energetic (e.g. 5 m significant height) incident waves, even though the assumption of 1D bound waves significantly overpredicts infragravity energy at the offshore boundary in 10 m depth. The model-data comparisons are limited by statistical chatter, often larger in runup than offshore because runup energy is concentrated in the relatively narrow infragravity IG band with low effective degrees of freedom.

The rigour of extracting friction angles, and eventually lower-bound bearing strength, in sandy beach settings through slope angles determined from digital images (visual spectrum) is explored. Digital images of topographic sand features using hand-held cameras, an unmanned aerial vehicle and a panchromatic satellite sensor are analysed to determine average slope angles using three-dimensional reconstruction. Greyscale gradients and shadows are utilised in the satellite images to extract slope estimates. The slope angles matched tilt table results of samples from the same locations at the Duck, NC, and Claytor Lake, VA, field sites. Direct shear testing of sample material suggest friction angles of ∼33° and ∼35°, respectively. The authors test a potential pathway to derive lower-bound bearing strength using these remotely sensed slope angles. Preliminary results are encouraging, but likely sensitive to the impact of moisture content, differences between the maximum and the observed slope angle and internal friction angles.

A non-hydrostatic wave model (SWASH) that phase-resolves the free surface and fluid motions in the water column is applied to investigate wave transformation and the spatial distribution of wave breaking over different morphological features. The model is forced using observed directional energy spectra and results are compared to wave observations collected outside the surf zone using acoustic wave sensors, and over a 100 m nearshore transect using high-frequency measurements of the sea surface from a LIDAR sensor mounted on the beach dune at the Field Research Facility in Duck, NC. The model is applied to four cases with different wave conditions and bathymetry, tested for sensitivity of model parameters to these different natural conditions, and used to predict the spatial variability in wave breaking and correlation between energy dissipation and morphologic features. Model results compare very well with observations of spectral evolution outside the surf zone, and generally well with the remotely sensed observations of wave transformation inside the surf zone with R = 0.85-0.93 for Hs along the cross-shore transect. In particular the model is able to spatially resolve wave shoaling and dissipation at the shore break at the same location as observed in the LIDAR data. The results indicate that nearshore morphology has a significant effect on the spatial distribution of wave energy dissipation. Alongshore variability in bathymetry due to bars, rip channels, and larger morphological features such as the scour depression under the pier, causes large alongshore changes in cross-shore wave energy flux that influence the location and intensity of wave breaking.

The transformation of surface gravity waves from 11 m depth to runup was observed on the low-sloped (1/80) Agate Beach, Oregon, with a cross-shore transect of current meters, pressure sensors, and a scanning lidar. Offshore wave heights H0 ranged from calm (0.5 m) to energetic (>7 m). Runup, measured with pressure sensors and a scanning lidar, increases linearly with (H0L0)1/2, with L0 the deep-water wavelength of the spectral peak. Runup saturation, in which runup oscillations plateau despite further increases in (H0L0)1/2, is not observed. Infragravity wave shoaling and nonlinear energy exchanges with short waves are included in an infragravity wave energy balance. This balance closes for high-infragravity frequencies (0.025–0.04 Hz) but not lower frequencies (0.003–0.025 Hz), possibly owing to unmodeled infragravity energy losses of wave breaking and/or bottom friction. Dissipative processes limit, but do not entirely damp, increases in runup excursions in response to increased incident wave forcing.

A Radar Inlet Observation System (RIOS) collected hourly X-band radar data at the wave dominated Oregon Inlet, NC, for 9 months from September 2016 to May 2017. The intensity of the radar backscatter, predominantly associated with surface wave shoaling and breaking, was time-averaged to provide an implied measure of bedforms superimposed on the ebb-tidal delta. Eulerian and Lagrangian motion tracking analyses determined the bedform alongshore migration rates over the study period; these were found to be significantly correlated to estimates of longshore sediment flux based on offshore wave parameters given by Ashton and Murray (2006). Although the exact magnitude of sediment transport cannot be directly estimated from bedform migration, the correlation does support an underlying assumption that sediment transport varies proportionally in both magnitude and direction to average bedform movements. The implications of these findings were further explored through application of the sediment transport model to a year long period of continuous offshore wave data (20 Oct 2016 to 20 Oct 2017). The predicted net transport of 90,000 m3 southward during this year is consistent with a previous estimate of inlet bypassing (Dolan and Glassen 1973). However, pronounced and opposing seasonal transport patterns were an order of magnitude higher than the yearly net, and could lead to significant inter-annual variability in alongshore sediment transport with similar dynamic response in ebb-delta morphodynamics at Oregon Inlet.

Observations of waves and setup on a steep, sandy beach are used to identify and assess potential applications of spatially dense lidar measurements for studying inner-surf and swash-zone hydrodynamics. There is good agreement between lidar- and pressure-based estimates of water levels (r2 = 0.98, rmse = 0.05 m), setup (r2 = 0.92, rmse = 0.03 m), infragravity wave heights (r2 = 0.91, rmse = 0.03 m), swell–sea wave heights (r2 = 0.87, rmse = 0.07 m), and energy density spectra. Lidar observations did not degrade with range (up to 65 m offshore of the lidar) when there was sufficient foam present on the water surface to generate returns, suggesting that for narrow-beam 1550-nm light, spatially varying spot size, grazing angle affects, and linear interpolation (to estimate the water surface over areas without returns) are not large sources of error. Consistent with prior studies, the lidar and pressure observations indicate that standing infragravity waves dominate inner-surf and swash energy at low frequencies and progressive swell–sea waves dominate at higher frequencies. The spatially dense lidar measurements enable estimates of reflection coefficients from pairs of locations at a range of spatial lags (thus spanning a wide range of frequencies or wavelengths). Reflection is high at low frequencies, increases with beach slope, and decreases with increasing offshore wave height, consistent with prior studies. Lidar data also indicate that wave asymmetry increases rapidly across the inner surf and swash. The comparisons with pressure measurements and with theory demonstrate that lidar measures inner-surf waves and setup accurately, and can be used for studies of inner-surf and swash-zone hydrodynamics.

Storms can have long-term impacts on the groundwater flows and subsurface salinity structure in coastal aquifers. Previous studies have shown that tides, wave driven infiltration, and storm surge elevate the groundwater level within the beach (Nielsen 1999, Cartwright 2004). The resulting bulge of high groundwater propagates inland, and may cause flooding up to several days after a storm has passed (Gallien 2016). In addition, waves, tides, and storm surge force saltwater to infiltrate into the aquifer above the fresher terrestrial groundwater, and storm-driven pulses of salinity may persist for months (Robinson et al. 2014). Here, observations of groundwater heads and salinities collected continuously for three years are used to examine the effects of ocean storms, wind-driven fluctuations in sound water levels, and morphological changes on a barrier island aquifer.

Grain size on the surface of natural beaches has been observed to vary spatially and temporally with morphology and wave energy. The stratigraphy of the beach at Duck, North Carolina, USA was examined using 36 vibracores (~1-1.5 m long) collected along a cross-shore beach profile. Cores show that beach sediments are finer (~0.3 mm) and more uniform high up on the beach. Lower on the beach, with more swash and wave action, the sand is reworked, segregated by size, and deposited in layers and patches. At the deepest measurement sites in the swash (~-1.4 to -1.6 m NAVD88), which are constantly being reworked by the energetic shore break, there is a thick layer (60-80 cm) of very coarse sediment (~2 mm). Examination of two large trenches showed that continuous layers of coarse and fine sands comprise beach stratigraphy. Thicker coarse layers in the trenches (above mean sea level) are likely owing to storm erosion and storm surge elevating the shore break and swash, which act to sort the sediment. Those layers are buried as water level retreats, accretion occurs and the beach recovers from the storm. Thinner coarse layers likely represent similar processes acting on smaller temporal scales.

Nearshore regions act as an interface between the terrestrial environment and deeper waters. As such, they play important roles in the dispersal of fluvial sediment and the transport of sand to and from the shoreline. This study focused on the nearshore of Poverty Bay, New Zealand, and the processes controlling the dispersal of sediment from the main source, the Waipaoa River. Hydrodynamics and sediment-transport in water shallower than 15 m were observed from April through mid-September 2006. This deployment afforded observations during 3–4 periods of elevated river discharge and 5 dry storms. Similar wind, river discharge, wave, current, and turbidity patterns were characterized during three of the wet storms. At the beginning of each event, winds blew shoreward, increasing wave heights to 2–3 m within Poverty Bay. As the cyclonic storms moved through the system the winds reversed direction and became seaward, reducing the local wave height and orbital velocity while river discharge remained elevated. At these times, high river discharge and relatively small waves enabled fluvially derived suspended sediment to deposit in shallow water. Altimetry measurements indicated that at least 7 cm was deposited at a 15 m deep site during a single discharge event. Turbidity and seabed observations showed this deposition to be removed, however, as large swell waves from the Southern Ocean triggered resuspension of the material within three weeks of deposition. Consequently, two periods of dispersal were associated with each discharge pulse, one coinciding with fluvial delivery, and a second driven by wave resuspension a few weeks later. These observations of nearfield sediment deposition contradict current hypotheses of very limited sediment deposition in shallow water offshore of small mountainous rivers when floods and high-energy, large wave and fast current, oceanic conditions coincide. Consistently shoreward near-bed currents, observed along the 10 m isobath of Poverty Bay, were attributed to a combination of estuarine circulation, Stokes drift, and wind driven upwelling. Velocities measured at the 15 m isobath, however, were directed more alongshore and diverged from those at the 10 m isobath. The divergence in the currents observed at the 10 and 15 m locations seemed to facilitate segregation of coarse and fine sediment, with sand transported near-bed toward the beach, while suspended silts and clays were exported to deeper water.

Over the late Holocene highstand, the shoreline at Poverty Bay, NZ migrated 12 km seaward, fed by sediment from the Waipaoa river. Paleo-shorelines indicate steadily decelerating progradation, possibly signaling changes in forcing on the Waipaoa Sedimentary System. To isolate the cause of this progradation slowdown we reconstruct late Holocene tectonics and stratigraphy over the Waipaoa coastal plain and nearshore from 7 ka–present. We find that decreasing rates of sediment storage by coastal progradation were driven by increasing tectonic storage in the steadily subsiding but rapidly growing coastal plain, such that net terrestrial storage remained constant at ∼ 0.8 Mt/yr. Hence changes in shoreline migration were due to autogenic increases in accommodation rather than allogenic changes in forcing. Furthermore, while the Waipaoa sediment load is primarily mud, reconstructions suggest that progradation was largely controlled by the supply of coarse-grained sediment. Our results suggest that in coastal systems such as the Waipaoa, where progradation is confined and wave energy is high, net accumulation of muds occurs only behind the prograding sandy shoreface, which shelters them from wave attack. Accounting for mud storage in the Waipaoa coastal plain and Poverty Bay suggests that export of muddy sediment to the Waipaoa shelf remained roughly constant at ∼ 2.0 Mt/yr from 7 ka until the onset of anthropogenic deforestation in the 19th century.

The inner shelves of active, energetic continental margins are frequently defined as regions of sediment segregation and fine-sediment bypassing. The Waiapu River, North Island, New Zealand presents an opportunity to study fine-sediment segregation and strata formation in a spatially constrained, highly energetic, aggradational setting, with one of the highest sediment yields on earth. We present evidence that the inner shelf of the Waiapu River plays a significant role in both the fate of fine-grained (

Recent studies of continental margins suggest that small, high-yield rivers are capable of generating shelf sediment-gravity flows, an idea that fundamentally alters our understanding of material flux from the continents to the ocean. Discharge measurements indicate that the Waiapu River, North Island, New Zealand reaches hyperpycnal concentrations (> 36 kg m− 2) on a yearly basis. This study contrasts shelf-edge basins with a broad trough along the shelf-edge off the Waiapu River, testing whether there is evidence that shelf sediment-gravity flows propagate to topographic lows. Observations and measurements through geochemical and sedimentological analyses of sediment cores, EM1002 swath bathymetry, and Chirp sub-bottom profiles suggest differing transport modalities on the outer shelf. In general a southern trough-shaped region exhibits high terrigenous inputs and non-steady-state 210Pb profiles, whereas the northern basins contain steady-state 210Pb profiles and increased marine influence. Sediment-gravity flows dominate accumulation in the southern region, whereas within the northern portion, surface plume sedimentation is indicated. Overall this study suggests that sediment-gravity flows could be bypassing the northern basins, perhaps a result of oceanographic influences and bathymetric steering as they seek a more direct route across the shelf.

This study demonstrates the physical concurrence of shore-oblique bars and gravel outcrops in the surf zone along the northern Outer Banks of North Carolina. These subaqueous features are spatially correlated with shoreline change at a range of temporal and spatial scales. Previous studies have noted the existence of beach-surf zone interactions, but in general, relationships between nearshore geological features and coastal change are poorly understood. These new findings should be considered when exploring coastal zone dynamics and developing predictive engineering models. The surf zone and nearshore region of the Outer Banks is predominantly planar and sandy, but there are several discrete regions with shore-oblique bars and interspersed gravel outcrops. These bar fields have relief up to 3 m, are several kilometers wide, and were relatively stationary over a 1.5 year survey period; however, the shoreward component of the bar field does exhibit change during this time frame. All gravel outcrops observed in the study region, a 40 km longshore length, were located adjacent to a shore-oblique bar, in a trough that had width and length similar to that of the associated bar. Seismic surveys show that the outcrops are part of a gravel stratum underlying the active surface sand layer. Cross-correlation analyses demonstrate high correlation of monthly and multi-decadal shoreline change rates with the adjacent surf-zone bathymetry and sediment distribution. Regionally, areas with shore-oblique bars and gravel outcrops are correlated with on-shore areas of high short-term shoreline variability and high long-term shoreline change rates. The major peaks in long-term shoreline erosion are onshore of shore-oblique bars, but not all areas with high rates of long-term shoreline change are associated with shore-oblique bars and troughs.

A poor understanding of the physical environment often hinders management of marine artefacts. A study was conducted of an early-18th-century shipwreck to test whether the wreckage could have settled through ∼3.5 m of substrate. Results indicate that the wreck could have settled via episodic scour processes driven by storms and tidal inlet migration. A numerical model, modified to include characteristics of the underlying geology, predicts continued scour under moderate waves. Scour processes appear to have been interrupted by an erosion-resistant underlying layer, so that the wreck now remains exposed, subject to degradation. A generalized approach to predict burial or exposure of other shallow-water artefacts is developed. © 2006 The Authors

This work describes a newly-discovered spatial correlation between paleo-channels and nearshore morphology along the barrier islands of northeastern North Carolina and southeastern Virginia, U.S. mid-Atlantic coast. These nearshore morphological features include regions of shore-oblique sandbars and coincident gravel outcrops that previously have been linked to erosional hotspots at the shoreline. These new findings have direct bearing on both nearshore morphodynamics and shoreline management. Paleo-channels were identified in the chirp seismic record and compared to shore-oblique sandbar locations discerned from bathymetric data and corroborated by gravel outcrops depicted in the side scan record. Both graphical correlation and statistical cross-correlation analyses revealed a significant spatial relationship between these features, with higher statistical correlation for channels > 500 m wide. Seismic records also indicate that the gravel outcrops seen on the updrift flanks of the shore-oblique bars are surface expressions of the underlying geology. We hypothesize that these outcrops are composed of relict channel fill sediments that interact with the hydrodynamic regime to produce sorted bedforms. The bathymetric anomalies then serve to alter incident wave energy and affect shoreline behavior. The spatial and temporal stability of these features over several years and through a variety of wave conditions suggests some degree of underlying geologic control. While the mechanisms responsible for this relationship remain speculative, these results may bridge the gap between studies focusing on framework geology and its influence on shoreline change and those that investigate bar morphodynamics and the initiation of sorted bedforms.

Beach and nearshore morphology, defined primarily by slope and sandbar development, is very dynamic and is largely controlled by waves, currents and regional sediment characteristics. Results presented here challenge this long-established concept and suggest that underlying, framework geology may also exert a first-order control on nearshore morphology by influencing the stability and/or persistent re-establishment of large-scale sandbar morphology and position as well as surface sediment characteristics. Repeated sub-bottom chirp and swath bathymetry surveys of the nearshore (2–10 m depths) covering over 56 km of the North Carolina Outer Banks and Southeastern Virginia indicate the following: (1) development of shore-oblique sandbars adjacent to large gravel outcrops that are surface exposures of the underlying geologic strata, (2) identical re-development or sustained maintenance of large-scale sandbar morphology and position before and after very energetic conditions, (3) vertical and horizontal heterogeneity of lithology and grain-size and a minimum volume of sand, ranging from 0 to 1.5 m thick, and (4) close spatial alignment between the location of outcrops/shore-oblique bars and shoreline erosional hotspots. A hypothesis is proposed from these findings that links framework geology to bar morphodynamics and sorted bedforms and, ultimately, erosional hotspots. Sediment transport and shoreline evolution models based solely on waves and currents and an assumption of unlimited and uniform sediment may be inadequate in similar heterogeneous, sand-limited regions.

Bottom-water hypoxia (≤ 2 mg l -1 dissolved oxygen (DO)) greatly modifies the benthic habitat of estuaries, depending upon spatial extent, duration, and frequency. Bottom-water hypoxia often develops under conditions of density stratification, which inhibits vertical mixing, and warm temperatures, which enhance biological oxygen demand. Long-term, mid-channel data from the Neuse River Estuary in North Carolina permitted evaluation of how stratification and temperature combined to affect DO concentrations at the bottom. Salinity stratification (∆S) and water tempera- ture (T ) explained respectively 30 and 23% of the variance in bottom-water DO concentrations. The amount of salinity stratification required to induce bottom-water hypoxia declined with increasing water temperature. About 80% of observed hydrographic profiles exhibited bottom hypoxia when ∆S exceeded 5 psu and T exceeded 20°C. Using cross-channel hydrographic surveys as verification, we derived a general set of methods to estimate the lateral extent of low-DO bottom water from mid- channel hydrographic profiles. The method involves cross-estuary and along-estuary extrapolation based on assumption of a flat oxycline. Occasional violation of this assumption resulted in modest overestimation in cross-channel extent of low DO. Application of this method produced estimates ranging from 0 to 116 km 2 of bottom area (0 to 42% of the estuarine study area) exposed to hypoxia over all sample dates in summer 1997. The maximal bottom area exposed to hypoxia corresponded closely with an independent estimate of the area (100 km 2 ) that experienced almost complete mor- tality of Macoma spp. clams, the key benthic resource for demersal fishes and crabs. Consequently, mid-channel hydrographic profiles taken along the mid-channel of the estuary can be employed to assess the spatial scale of bottom habitat degradation due to hypoxia.

Understanding across-margin transport has long been recognized as crucial for wise management of our coastline and shelf waters. Issues related to sewage outfalls, nutrient and pollutant dispersal, carbon export, and shoreline sediment budgets all require an understanding of these processes. Across-margin transport of water and sediment at cuspate foreland headlands has been largely unrecognized, and the processes responsible for this export unappreciated. We examined physical process on Cape Lookout Shoal, a cape-associated shoal on the North Carolina continental shelf, through numerical modeling and field observations of near-bottom currents. The cuspate foreland setting of the northern South Atlantic Bight has been previously characterized as wave-dominated with a principal alongshore directed sediment transport and physical circulation forced by wave and wind-driven currents along the inner and mid-shelf. Our findings instead suggest that a seaward-directed, tidal-driven headland flow many play a significant role in the direction of net sediment transport on the shoal and ultimately its location and long-term maintenance. The shoal's location relative to the promontory-induced residual eddies and the region of active deposition differs from traditionally held ideas on sedimentary processes at headland-related sand banks. In addition, the headland flows may also serve as a first-order mechanism for rapidly exporting nearshore and estuarine waters to the outer-shelf.

The sedimentary processes of a cape-associated shoal are an integral component of the sediment budget of the surrounding cuspate foreland shoreline. The manner in which sediment is delivered to a shoal and the fate of this sediment, once delivered, have important implications to shoreline management and yet remain largely unstudied. Modern sedimentary processes and the recent depositional history of Cape Lookout Shoal, a large cape-associated shoal in the mixed-energy environment of the North Carolina continental shelf, were examined in a field-intensive study through high-resolution seismic profiles, hydraulic probes, near-bottom current meters, sediment grab samples, and detailed bathymetric surveys. Our findings indicate that: (1) the sediment budget of the up-drift littoral cell is coupled directly to Cape Lookout Shoal, (2) the sedimentary processes of the shoal remain active down its entire length but at a diminishing level with distance from the shore, and (3) the shoal serves as a long-term sink for littoral-zone sediment and limits sediment exchange between adjacent littoral cells and shelf regions. We present evidence suggesting that the position and morphology of Cape Lookout Shoal are not controlled by underlying erosion-resistant strata and that the shoal appears to have developed in the late Holocene after the shelf was scoured by the transgressing shoreface.

Radar Inlet Observing System (RIOS) remotely senses waves, currents, and bathymetry at tidal inlets and river mouths. RIOS utilizes a 25kW X-band, coherent-on-receive radar to measure wave parameters at 3m resolution up to 3km radius from the antenna. Data acquisition and processing are fully automated and capable of hourly observations and web posting from a small, mobile trailer. Wave shoaling and breaking, obtained from the time series of radar spikes generated by the roughened surface of waves, are used to infer water depths and identify the position of shoals and channels. The ability of RIOS to measure wave orbital velocities (radial components) in order to determine mean surface currents is also investigated. Results from a field experiment at New River Inlet, North Carolina in April-May 2012 indicate RIOS accurately characterized the location and morphology of shoals and channels across the ebb tidal delta over a range of quiescent and storm conditions. The magnitude of RIOS-measured surface currents were substantially less than in-situ observations and showed great sensitivity to sea surface roughness.

[1] Despite the acknowledged influence of coastal geological framework on the behavior of beaches and barrier islands and a wealth of geological and bathymetric observations from the inner shelf, quantitatively connecting those observations to shoreline behavior has been difficult. Nearshore geologic and morphologic variability described by recent research is not well represented by conventional geologic parameters, such as mean grain size and shoreface slope, used in most shoreline change models. We propose that total nearshore sediment volume, as calculated to a continuous seismic reflection surface, provides a flexible and robust metric for use in the prediction of shoreline change. This method of determining the volume of sediment in the nearshore accounts for three-dimensional sandbar morphologies and heterogeneous seafloor sediments. The decadal-scale shoreline change rate for northeastern North Carolina is significantly correlated to the volume of sediment in the nearshore when a geologically defined base is used in volume determinations, suggesting that the shallow stratigraphic framework of transgressive coasts is an important influence on decadal shoreline behavior. Nearshore sediment volume was overestimated when an arbitrary depth-constant baseline was used and was not correlated to decadal shoreline change. This implies that a volume metric which accounts for both framework geology and variable seafloor morphology better represents the geologic character of the shoreface and may help to improve existing models of shoreline change. An empirical model of regional shoreline erosion potential demonstrates the importance of incorporating nearshore sediment volume, shallow framework geology, and surface morphology when predicting seasonal to decadal shoreline evolution.

An experimental mixed-sediment mound has been constructed 7 km south of the mouth of the Cape Fear River, NC. The objectives of the study include: (1) document the fate of the mound, (2) document sediment characteristics over the long term; and (3) investigate the generation of turbidity associated with the mound. Directional wave information, vertical current profiles, surface-sediment samples, suspended-sediment concentration measurements, and repetitive high-resolution bathymetric and sub-bottom surveys have been obtained since April 2001. Results to date indicate that the mound has remained intact while the mound crest may be creeping toward shore in response to the prevailing wave and current conditions. Sedimentary characteristics appear to be cyclical in response to local processes. The general trend is that over time the high concentration of fines winnow out leaving a predominantly sand pavement on the mound surface until the next storm event. In addition, turbidity levels over the mound were found to not be anomalously high in comparison to ambient levels. This study is important for model development and dredging operations implementation.

Numerous regional geophysical mapping efforts have taken place along the mid-Atlantic coast over the past 20 years, illuminating the relationship between relict geology and coastal processes. Results have demonstrated that variability in the structural framework of the coastal plain is important in controlling regional-scale shoreline evolution and sediment availability. Furthermore, variations in the geologic character (grain size, consolidation, composition, morphology, etc.) of the shelf and nearshore have been linked to long-term (centennial and greater) and short-term (decadal to centennial) shoreline evolution. Despite these spatial relationships, little information regarding the variability of geologic properties is accounted for in numerical models of shoreline change, leading to outputs that do not accurately characterize natural and human-induced shoreline behavior.

Few observational techniques are capable of simultaneously mapping the shoreline and nearshore sand bars at high resolution and over large distances, especially during storms when waves are large and visibility is reduced. Proof-of-concept experiments were undertaken to test the feasibility of using X-band radar, mounted on a beach vehicle with dual-channel global positioning system (GPS), to rapidly map the swash and nearshore bars over several kilometers. Bar and Swash Imaging Radar (BASIR), a mobile system developed in collaboration with Imaging Science Research, was evaluated under varying wave heights and storm conditions through comparisons with bathymetric profiles and video along the North Carolina Outer Banks. The video, operated by Oregon State University Coastal Imaging Lab and the U.S. Army Corps of Engineers Field Research Facility in Duck, North Carolina, utilizes a similar technique of time averaging and multiple-image merging to map sand bars. Significant correlation and relativel...

A new research program focusing on sediment dispersal across the active margin of the New Zealand east coast has provided the foundation for a holistic understanding of the transport and fate of terrestrial materials in the coastal ocean. Field studies began in January 2005 with two acoustic mapping and shallow seabed sampling expeditions to the shelf and slope off the Waipaoa River (Figure l), and in February 2006, the specially designed French research vessel (R/V) Marion Dufresne II collected seven long (up to 25 meters) piston cores from the study area for stratigraphic control. Both the 2005 and 2006 expeditions are part of the U.S. National Science Foundation (NSF) MARGINS Source-to-Sink (S2S) initiative.