Physical Sciences and Mathematics Commons^™

Inner-Shelf Circulation And Sediment Dynamics On A Series Of Shoreface-Connected Ridges Offshore Of Fire Island, Ny, John Warner, Jeffrey List, William Schwab, George Voulgaris, Brandy Armstrong, Nicole Marshall

George Voulgaris

Locations along the inner-continental shelf offshore of Fire Island, NY, are characterized by a series of shoreface-connected ridges (SFCRs). These sand ridges have approximate dimensions of 10 km in length, 3 km spacing, and up to ∼8 m ridge to trough relief and are oriented obliquely at approximately 30° clockwise from the coastline. Stability analysis from previous studies explains how sand ridges such as these could be formed and maintained by storm-driven flows directed alongshore with a key maintenance mechanism of offshore deflected flows over ridge crests and onshore in the troughs. We examine these processes both with a limited …

Temporal And Spatial Evolution Of Wave-Induced Ripple Geometry: Regular Versus Irregular Ripples, Timothy Nelson, George Voulgaris

George Voulgaris

Concurrent observations of inner shelf near bed hydrodynamics and acoustic imagery of the seabed are used to relate wave-induced ripple geometry (wavelength and orientation) to near bed directional wave velocities. The observations were collected on the continental shelf of the South Atlantic Bight at water depths of 9.5 and 30 m off the coasts of South Carolina (median size 177 mm) and Georgia (388 mm), respectively. 2-D spectral analysis techniques are performed on the imagery to automate detection of ripple wavelength, orientation, and irregularity. Our analysis shows that ripple irregularity is a time-dependent process dependent on magnitude, direction, and duration …

Alongshore Momentum Balance Analysis On A Cuspate Foreland, Nirnimesh Kumar, George Voulgaris, Jeffery H. List, John C. Warner

George Voulgaris

Nearshore measurements of waves and currents off Cape Hatteras, North Carolina, U.S.A, are used to investigate depth-averaged subtidal circulation and alongshore momentum balances in the surf and inner shelf region around a cuspate foreland. Data were collected on both sides of the cape representing shorefaces with contrasting shoreline orientation (north-south vs. northwest-southeast) subjected to the same wind forcing. In the nearshore, the subtidal flow is aligned with the local coastline orientation while at the cape point the flow is along the existing submerged shoal, suggesting that cape associated shoals may act as an extension of the coastline. Alongshore momentum balance …

Sediment Resuspension, Flocculation And Settling In A Macrotidal Estuary, Ya Ping Wang, George Voulgaris, Yan Li, Yang Yang, Jianhua Gao, Jia Chen, Shu Gao

George Voulgaris

Estuarine boundary layer and water column in situ measurements of hydrodynamics, sediment resuspension and sediment particle size distribution are presented for a macrotidal environment in SE China. Vertical and tidal variability of sediment size and its relation to turbulence and hydrodynamic forcing are examined using time-series from two week long experiments after they are phase averaged to reconstruct typical neap and spring tidal cycles. In situ particle size distributions obtained using laser diffraction show clear evidence of flocculation processes that change dynamically during the tidal cycle. Mean particle size of particles in suspension is found to be one order of …

Predicting Wave-Induced Ripple Equilibrium Geometry, Timothy R. Nelson, George Voulgaris, Peter Traykovski

George Voulgaris

A comprehensive database of existing (since 1954) field and laboratory measurements of ripple geometry is compiled and combined with newly collected field data to examine the performance of ripple equilibrium predictors. Re-analysis of this enlarged ripple geometry data set reveals that ripples formed from monochromatic waves scale differently than ripples formed from random waves for many existing ripple predictors. Our analysis indicates that ripple wavelengths from the two data sets collapse into a single scaling when the semi-orbital excursion and sediment grain diameter are used as normalizing factors. Ripple steepness remains relatively constant for both regular and irregular wave conditions …

Holocene Sediment Distribution On The Inner Continental Shelf Of Northeastern South Carolina: Implications For The Regional Sediment Budget And Long-Term Shoreline Response, Jenny Denny, William Schwab, Wayne Baldwain, Walter Barnhadt, Paul Gayes, Robert Morton, John Warner, Neil Driscoll, George Voulgaris

George Voulgaris

High-resolution geophysical and sediment sampling surveys were conducted offshore of the Grand Strand, South Carolina to define the shallow geologic framework of the inner shelf. Results are used to identify and map Holocene sediment deposits, infer sediment transport pathways, and discuss implications for the regional coastal sediment budget.

The thickest deposits of Holocene sediment observed on the inner shelf form shoal complexes composed of moderately sorted fine sand, which are primarily located offshore of modern tidal inlets. These shoal deposits contain ∼67 M m3 of sediment, approximately 96% of Holocene sediment stored on the inner shelf. Due to the lack …

Storm-Induced Inner-Continental Shelf Circulation And Sediment Transport: Long Bay, South Carolina, John Warner, Charlene Silvester, Brandy Armstrong, George Voulgaris, Timothy Nelson, William Schwab, Jane Denny

George Voulgaris

Long Bay is a sediment-starved, arcuate embayment located along the US East Coast connecting both South and North Carolina. In this region the rates and pathways of sediment transport are important because they determine the availability of sediments for beach nourishment, seafloor habitat, and navigation. The impact of storms on sediment transport magnitude and direction were investigated during the period October 2003–April 2004 using bottom mounted flow meters, acoustic backscatter sensors and rotary sonars deployed at eight sites offshore of Myrtle Beach, SC, to measure currents, water levels, surface waves, salinity, temperature, suspended sediment concentrations, and bedform morphology. Measurements identify …

Implementation Of The Vortex Force Formalism In The Coupled Ocean-Atmosphere-Wave-Sediment Transport (Coawst) Modeling System For Inner Shelf And Surf Zone Applications., Nirnimesh Kumar, George Voulgaris, John Warner, Maitane Olabarietta

George Voulgaris

No abstract provided.

Radon As An Indicator Of Limited Cross-Shelf Mixing Of Submarine Groundwater Discharge Along An Open Ocean Beach In The South Atlantic Bight During Observed Hypoxia, Clayton Mccoy, Richard Viso, Richard Peterson, Susan Libes, Brent Lewis, John Ledoux, George Voulgaris, Erik Smith, Denise Sanger

George Voulgaris

Amongst other ocean state parameters, the development of a wave measurement program was supported as part of the Southeast U.S. Atlantic Coastal Ocean Observing System (SEACOOS). The program focused on supporting nearshore wave measurements using both cabled and autonomous systems but also examined the feasibility of using HF Radar systems for remote estimation of wave parameters. The nearshore stations have provided a significant database on directional wave climate for a number of nearshore locations in the region that provide valuable information to coastal engineers and managers for sustainable development along the coast of the southeastern United States. The ability of …

Wind-Speed Inversion From Hf Radar First-Order Backscatter Signal, W Shen, Klaus-Werner Gurgel, George Voulgaris, Thomas Schlick, D Stammer

George Voulgaris

Land-based high-frequency (HF) radars have the unique capability of continuously monitoring ocean surface environments at ranges up to 200 km off the coast. They provide reliable data on ocean surface currents and under slightly stricter conditions can also give information on ocean waves. Although extraction of wind direction is possible, estimation of wind speed poses a challenge. Existing methods estimate wind speed indirectly from the radar derived ocean wave spectrum, which is estimated from the secondorder sidebands of the radar Doppler spectrum. The latter is extracted at shorter ranges compared with the first-order signal, thus limiting the method to short …

Implementation And Modification Of A Three-Dimensional Radiation Stress Formulation For Surf Zone And Rip-Current Applications, Nirnimesh Kumar, George Voulgaris, John Warner

George Voulgaris

Regional Ocean Modeling System (ROMS v 3.0), a three-dimensional numerical ocean model, was previously enhanced for shallow water applications by including wave-induced radiation stress forcing provided through coupling to wave propagation models (SWAN, REF/DIF). This enhancement made it suitable for surf zone applications as demonstrated using examples of obliquely incident waves on a planar beach and rip current formation in longshore bar trough morphology (Haas and Warner, 2009). In this contribution, we present an update to the coupled model which implements a wave roller model and also a modified method of the radiation stress term based on Mellor (2008, 2011a,b,in …

A Case History Of The Science And Management Collaboration In Understanding Hypoxia Events In Long Bay, South Carolina, Usa., Denise Sanger, Debra Hernandez, Susan Libes, George Voulgaris, Braxton Davis, Erik Smith, Rebecca Shufford, Dwayne Porter, Eric Koepfler, Joseph Bennet

George Voulgaris

Communication of knowledge between the scientific and management communities is a difficult process complicated by the distinctive nature of professional career goals of scientists and decision-makers. This article provides a case history highlighting a collaboration between the science and management communities that resulted from a response to a 2004 hypoxia, or low dissolved oxygen, event in Long Bay, off Myrtle Beach, South Carolina. A working group of scientists and decision-makers was established at the time of the event and has continued to interact to develop a firm understanding of the drivers responsible for hypoxia formation in Long Bay. Several factors …

Waves Initiative Within Seacoos, George Voulgaris, Brian Haus, Paul Work, Lynn Shay, Harvey Seim, Robert Weisberg, James Nelson

George Voulgaris

Amongst other ocean state parameters, the development of a wave measurement program was supported as part of the Southeast U.S. Atlantic Coastal Ocean Observing System (SEACOOS). The program focused on supporting nearshore wave measurements using both cabled and autonomous systems but also examined the feasibility of using HF Radar systems for remote estimation of wave parameters. The nearshore stations have provided a significant database on directional wave climate for a number of nearshore locations in the region that provide valuable information to coastal engineers and managers for sustainable development along the coast of the southeastern United States. The ability of …

Exploring The Persistence Of Sorted Bedforms On The Inner-Shelf Of Wrightsville Beach, North Carolina, Benjamin Gutierez, George Voulgaris, Robert Thieler

George Voulgaris

Geological studies offshore of Wrightsville Beach, North Carolina reveal subtle large-scale regions of coarse sand with gravel and shell hash (widths between 100 and 200 m and negative relief of ∼1 m) that trend obliquely to the coast. It was previously suggested that these regions serve as conduits for sand exchange between the shoreface and inner shelf during storm-associated downwelling. Consequently they were classified as rippled scour depressions. More recently, the role of alongshore flows and self-organization as a result of inhibited settling of fine sand has been discussed. In this study, 45 days of near-bed current measurements were analyzed …

Effect Of Channel Bifurcation On Residual Estuarine Circulation: Winyah Bay, South Carolina, Yong Kim, George Voulgaris

George Voulgaris

The residual circulation pattern of Winyah Bay, the fourth largest estuary on the eastern coast of the US, is examined using stationary and shipborne current measurements during periods of low freshwater discharge. The estuary has a complex morphology with a single channel and narrow banks at the river entrance and the bay mouth, and a bifurcated channel system (main and western channels, respectively) in the middle part that appears to affect the residual circulation. Overall, the upper (single channel morphology) and middle (dual-channel morphology) parts of the estuary exhibit a baroclinic residual circulation. The presence of bifurcated channels in the …

Internal Waves Revealed By Synthetic Aperture Radar (Sar) Imagery In The Vicinity Of The Eastern Cretan Arc Straits (Eastern Mediterranean), Adonis Velegrakis, E. Oikonomou, A. Theocharis, M Collins, H Kontoyannis, V Papadopoulos, George Voulgaris, T. Wells, E. Balopoulos

George Voulgaris

Internal waves have been detected on ERS-1 SAR images obtained during late summer over the eastern Cretan Straits, an area characterised by complex regional physiography, bottom topography, flow regime and stratification patterns of the upper part of the water column. Analysis of the imaged characteristics of the internal waves has revealed a strong diversity in form, propagation direction and type of sea surface modulation, which indicates various mechanisms of generation. Analysis of the currents recorded over the area shows that, although semi-diurnal tidal currents are present, these are of low magnitude in comparison with the overall flow and, therefore, tidal …

The In Situ Passive Acoustic Measurement Of Shingle Movement Under Waves And Currents: Instrument (Tosca) Development And Preliminary Results, George Voulgaris, Michael Wilkin, Michael Collins

George Voulgaris

An instrumented platform (TOSCA) is described for monitoring coarse-grained sediment transport in high (wave and tidal) energy environments. The system consists of a number of sensors which measure: instantaneous current velocities at three levels; sea surface elevation; and self-generated noise (SGN) caused by intercollision of particles in transit. SGN is related to transport rates, on the basis of laboratory calibration; this, in turn, allows a correlation with simultaneous near-bed shear stress to be established. During the field measurements, PC-based real-time data transmission is realised through the use of a (buoyed) radio telemetry system.

TOSCA has been deployed in eastern Christchurch …