Physical Sciences and Mathematics Commons^™

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 …

Controls On Floc Size In A Continental Shelf Bottom Boundary Layer, Paul Hill, George Voulgaris, John Trowbridge

George Voulgaris

Simultaneous in situ observations of floc size, waves, and currents in a continental shelf bottom boundary layer do not support generally accepted functional relationships between turbulence and floc size in the sea. In September and October 1996 and January 1997, two tripods were deployed in 70 m of water on the continental shelf south of Woods Hole, Massachusetts. On one a camera photographed particles in suspension 1.2 m above the bottom that had equivalent circular diameters larger than 250 um, and on the other, three horizontally displaced acoustic current meters measured flow velocity 0.35 m above the bottom. The tripods …

Measurements And Three-Dimensional Modeling Of Nearshore Circulation On A South Carolina Beach, Nirnimesh Kumar, George Voulgaris, John Warner

George Voulgaris

A numerical modeling system for simulating nearshore surf zone conditions and tidal processes is presented and evaluated with in situ data. The modeling system is comprised of the Regional Ocean Modeling System (ROMS v 3.0), a three-dimensional numerical ocean model, coupled with Simulating Waves Nearshore (SWAN), a spectral wave propagation model. The system has been modified with a new vertical distribution of radiation stress terms for applications in very shallow waters. The model performance is evaluated by comparing simulations to hydrodynamic data (wave height, direction, longshore and cross-shore currents) collected in the surf zone in northern South Carolina, U.S. Model …

Cross-Shore Variation Of Wind-Driven Flows On The Inner Shelf In Long Bay, South Carolina, United States, Benjamin Gutierrez, George Voulgaris, Paul Work

George Voulgaris

The cross-shore structure of subtidal flows on the inner shelf (7 to 12 m water depth) of Long Bay, South Carolina, a concave-shaped bay, is examined through the analysis of nearly 80 days of near-bed (1.7–2.2 m above bottom) current observations acquired during the spring and fall of 2001. In the spring and under northeastward winds (upwelling favorable) a two-layered flow was observed at depths greater than 10 m, while closer to the shore the currents were aligned with the wind. The two-layered flow is attributed to the presence of stratification, which has been observed under similar conditions in the …

Lateral Circulation And Suspended Sediment Transport In A Curved Estuarine Channel: Winyah Bay, Sc, Usa, Yong Hoon Kim, George Voulgaris

George Voulgaris

Shipborne vertical profiles of flow and suspended sediment concentration collected on a transect, across a curved, nonsymmetrical estuarine channel are presented. Analysis of the transient cross-channel momentum balance equation shows that the lateral circulation pattern is controlled by the interaction between centrifugal and lateral baroclinic forcings although those two might not be necessarily in balance as suggested earlier by Seim and Gregg (1997). Instead, differential along-channel advection and local acceleration appear to influence greatly lateral circulation dynamics. During ebb when the water column is highly stratified, the interaction between centrifugal acceleration and opposite-directed lateral baroclinic forcing results in weak lateral …

Geomorphic Analysis Of Tidal Creek Networks, Karyn Novakowski, Raymond Torres, L Gardner, George Voulgaris

George Voulgaris

The purpose of this study is to determine if concepts in terrestrial channel network analysis provide insight on intertidal creek network development and to present new metrics for their analysis. We delineated creek network geometry using high-resolution digital images of intertidal marsh near Georgetown, South Carolina. Analyses reveal that intertidal creek networks may be topologically random. Length-area relationships suggest that salt marsh and terrestrial networks have similar scaling properties, although the marsh networks are more elongate than terrestrial networks. To account for recurrent water exchange between creek basins at high tide, we propose that the landscape unit of geomorphic analyses …

Analysis Of Fluvial Suspended Sediment Load Contribution Through Anthropocene History To The South Atlantic Bight Coastal Zone, U.S.A., K Mccarney-Castle, George Voulgaris, A J. Kettner

George Voulgaris

Discerning the effects of anthropogenic activities (i.e., reservoir construction, land use change), as opposed to those of natural processes (i.e., climate variability), on suspended sediment flux has become an increasingly difficult challenge. This contribution presents water and suspended sediment flux from five major watersheds that discharge into the southeastern U.S. Atlantic, a region that is currently considered sediment starved. Three periods of Anthropocenetime were defined and evaluated: (1) “pre-European conditions” (1680–1700), (2) “pre-dam conditions" (1905-1925), and (3) "post-dam conditions" (1985-2005). Physical and hydrologic watershed data were used to run a climate-driven hydrological transport numerical model (HydroTrend) to estimate …

Effects Of Low Tide Rainfall On Intertidal Zone Material Cycling, Raymond Torres, Miguel Goni, George Voulgaris, Charles Lovell, James Morris

George Voulgaris

Sediment transport by rainfall-runoff processes is well documented for terrestrial landscapes but few studies have focused on rainfall-runoff effects in intertidal areas. Here we present geochemical analyses performed on sediment samples collected during low tide irrigation experiments, and tidal channel turbidity measurements taken during natural rainfall over North Inlet Marsh, South Carolina. Order of magnitude approximations indicate that a single 10 minute storm may entrain 8-15% of the local annual average sediment accumulation. This rainfall-entrained material is enriched in organic nitrogen and marine algal matter, and therefore of high nutritional quality.

Evaluation Of The Acoustic Doppler Velocimeter (Adv) For Turbulence Measurements, George Voulgaris, John Trowbridge

George Voulgaris

Accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in this paper. Simultaneous measurements of open-channel flow were undertaken in a 17-m flume using an ADV and a laser Doppler velocimeter. Flow velocity records obtained by both instruments are used for estimating the true (‘‘ground truth’’) flow characteristics and the noise variances encountered during the experimental runs. The measured values are compared with estimates of the true flow characteristics and values of variance (^u92&, ^w92&) and covariance (^u9w9&) predicted by semiempirical models for open-channel flow. The analysis showed that the ADV sensor can measure mean velocity and Reynolds stress within …

Forcing And Dynamics Of Seafloor-Water Column Exchange On A Broad Continental Shelf, William Savidge, Ann Gargett, Richard Jahnke, James Nelson, Dana Savidge, R Short, George Voulgaris

George Voulgaris

Relict sediments of elevated permeability characterize the majority of continental shelves globally (Emery, 1968). In these settings, interactions between benthic boundary layer (BBL) flows and seabed topography generate pressure fluctuations that drive advective and dispersive porewater transport, dramatically increasing the magnitude and variability of porewater solute and particulate exchange across the sediment-water interface (Huettel et al., 1996; Huettel and Rusch, 2000). On broad shallow shelves with a relatively large area-to-volume ratio, the seafloor’s role is magnified. Energetic events may reorganize bedforms across a significant fraction of the shelf, leading to altered exchange dynamics that may persist long after the organizing …

Tidal Asymmetry And Residual Circulation Over Linear Sandbanks And Their Implication On Sediment Transport: A Process-Oriented Numerical Study, Rosario Sanay, George Voulgaris, John Warner

George Voulgaris

A series of process-oriented numerical simulations is carried out in order to evaluate the relative role of locally generated residual flow and overtides on net sediment transport over linear sandbanks. The idealized bathymetry and forcing are similar to those present in the Norfolk Sandbanks, North Sea. The importance of bottom drag parameterization and bank orientation with respect to the ambient flow is examined in terms of residual flow and overtide generation, and subsequent sediment transport implications are discussed. The results show that although the magnitudes of residual flow and overtides are sensitive to bottom roughness parameterization and bank orientation, the …

Shelf Edge Tide Correlated Eddies Along The Southeastern United States, Dana Savidge, Jonathan Norman, Colton Smith, Julie Amft, Trent Moore, Catherine Edwards, George Voulgaris

George Voulgaris

High frequency radar observations in the Southeastern United States have revealed sequences of small short‐lived cyclonic eddies along the shoreward edge of the Gulf Stream, that spin up as the local tide turns alongshelf antiparallel to the Stream. Eddies propagate equatorward along the shelf edge, sometimes progressing shoreward before dissipating one to three hours later. They are distinctly different from Gulf Stream meander eddies, which propagate poleward. In this article, radar and mooring data are used to establish three important aspects of these neweddies: they represent an instability process operating at a previously unidentified frequency, scale, and cross‐Stream position; they …

Wind Speed Dependence Of Single-Site Wave-Height Retrievals From High-Frequency Radars, Brian Haus, Lynn Shay, Paul Work, George Voulgaris, Rafael Ramos, Jorge Martinez-Pedraja

George Voulgaris

Wave-height observations derived from single-site high-frequency (HF) radar backscattered Doppler spectra are generally recognized to be less accurate than overlapping radar techniques but can provide significantly larger sampling regions. The larger available wave-sampling region may have important implications for observing system design. Comparison of HF radar–derived wave heights with acoustic Doppler profiler and buoy data revealed that the scale separation between the Bragg scattering waves and the peak energy-containing waves may contribute to errors in the single-site estimates in light-to-moderate winds. A wave-height correction factor was developed that explicitly considers this scale separation and eliminates the trend of increasing errors …

Subtidal Inner Shelf Currents Off Cartagena De Indias, Caribbean Coast Of Colombia, Mauro Maza, George Voulgaris, Bulusu Subrahmanyam

George Voulgaris

Seasonal trends in inner shelf subtidal circulation off the coast of Cartagena de Indias, Colombia, are examined through the analysis of current profiles, hydrographic, meteorological and satellite data collected from 1999 to 2002. During the dry season (December–April) the water column is well-mixed and along-shelf currents flow southwestward following the steady trade winds. In the rainy season (May –November) the water column experiences continuous events of stratification and the along-shelf currents flow northeastward, opposing the weak southwestward winds. In the dry season the along shelfcirculation is mostly driven by wind forcing, while in the rainy season, the circulation is set …

Evaluation Of Beach Nourishment Evolution Models Using Data From Two South Carolina Beaches: Folly Beach And Hunting Island, Sc, Usa, Harry Weathers, George Voulgaris

George Voulgaris

Beach nourishment is a common method used for mitigating coastal erosion. However, it is also a costly undertaking and requires an appropriate cost-to-benefit analysis. Although the costs can be estimated relatively easily, the benefits are directly related to the life expectancy of the proposed project. With this in mind, three existing beach replenishment time-evolution models (the Linear Erosion, the Verhagen, and the One-Line models) were compared for their ability to represent data from two beach nourishment projects that have taken place in South Carolina, USA, at Folly Beach and Hunting Island. Another newly introduced model that combines the One-Line model …

Introduction And Tribute, George Voulgaris, Timothy Kana, Jacqueline Mitchell

George Voulgaris

No abstract provided.