Time series of in situ measured velocity and suspended sediment concentration from Qiantang Estua... more Time series of in situ measured velocity and suspended sediment concentration from Qiantang Estuary (China), and estimates of turbulence and sediment stratification parameters are presented. The data span a period of 9 days, and after phase averaged, they are used to explore spring‐neap tidal variations in flow, turbulence, and sediment stratification. A local balance between shear production, sediment‐induced buoyancy flux, and dissipation is found to hold during ebb for both neap and spring tides. During flood elevated turbulence dissipation rates are observed, attributed to nonlocal turbulence, most likely due to horizontal advection. Our results show that the effect of sediment stratification is successfully parameterized by adding the Monin‐Obukhov length scale to the classical logarithmic layer theory. Flood‐ebb asymmetry in both Rig and Rf is observed, with higher values attained during flood due to the higher sediment concentrations and the corresponding weaker velocity shea...
Numerical simulations are used to study the response of Long Bay, South Carolina, a typical coast... more Numerical simulations are used to study the response of Long Bay, South Carolina, a typical coastal embayment with curved coastline located on the South Atlantic Bight, to realistic, climatologically defined, synoptic storm forcing. Synoptic storms, consisting of cold and warm fronts as well as tropical storms, are used as forcing under both mixed and stratified initial conditions. The analysis focuses on the development of cross-shore shelf circulation and the relative contributions of regionally defined cross-shore winds and alongshore bathymetric variation. The simulation results show that, under stratified conditions, the regionally defined offshore-directed wind component promotes upwelling during the developing stage of the cold front and enhances mixing during the decaying stage. No significant effect is found for warm front and tropical storm forcing conditions. Net cross-shore transports are induced at the southern and northern sides of the embayment that have opposing sign...
Acoustic current profilers were originally designed to measure 3-D flow structure but they also r... more Acoustic current profilers were originally designed to measure 3-D flow structure but they also record the intensity of the return echo. The latter is proportional to the number of backscatters present in the water column and can be used as a proxy for suspended sediment concentration. The potential for remote, rapid and simultaneous measurements of current and suspended sediment concentration (SSC) fields with increased vertical and horizontal spatial resolution drives the development of methods for converting acoustic intensity to SSC. In this study, we present simultaneously collected acoustic Doppler current profiler (ADCP, RDI Workhorse, 1200kHz) and suspended sediment concentration data, obtained with an optical backscatter sensor (OBS). These data are utilized to calibrate a simplified version of the sonar equation that converts the recorded by the ADCP echo intensity into SSC. This simplified sonar equation lumps a number of immeasurable quantities into two parameters Kc and...
Journal of Atmospheric and Oceanic Technology, 2019
A hybrid, empirical radar wave inversion technique that treats swell and wind waves separately is... more A hybrid, empirical radar wave inversion technique that treats swell and wind waves separately is presented and evaluated using a single 48-MHz radar unit and in situ wave measurements. This hybrid approach greatly reduces errors in radar wave inversion during swell seas. Our analysis suggests that, prior to the inversion, the second-order spectrum should be normalized using Barrick’s weighting function because this process removes harmonic and corner reflection peaks from the inversion and improves the results. In addition, the resulting calibration constants for the wind wave component are not wave-frequency dependent and are similar in magnitude to those found in previous studies using different operating-frequency radars. This result suggests radar frequency independence, although additional experimental verification is required. The swell component of the model presented here ignores the effect of swell’s propagation direction on the radar signal. Although this approach has sev...
Accurate estimates of Stokes drift are necessary to quantify Lagrangian transport and upper-ocean... more Accurate estimates of Stokes drift are necessary to quantify Lagrangian transport and upper-ocean mixing. These can be estimated from directional wave spectra. Here, a methodology for the reconstruction of such spectra is developed using partitioned bulk wave parameters provided by global wave models. These reconstructed spectra agree well with global wave model–simulated full spectra. Regional wave model simulations with reconstructed spectra as open boundary conditions lead to more accurate estimates of bulk wave parameters in the coastal ocean. Furthermore, the reconstructed directional spectra can be used to improve high-frequency (HF) radar–derived surface Lagrangian current estimates. Stokes drift vertical profiles from complete directional spectra are more accurate, and therefore coupled ocean circulation and wave models should incorporate spectral estimates for wave–current interaction studies. Based on model simulations conducted here, it is recommended that regional wave m...
An examination of the applicability and accuracy of the empirical wave inversion method in the pr... more An examination of the applicability and accuracy of the empirical wave inversion method in the presence of swell waves is presented. The ability of the method to invert Doppler spectra to wave directional spectra and bulk wave parameters is investigated using one-month data from a 12 MHz WERA High Frequency (HF) radar system and in-situ data from a wave buoy. Three different swell inversion models are evaluated: LPM (Lipa et al. 1981), WFG (Wang et al. 2016) and EMP, an empirical approach introduced in this study. The swell inversions were carried out using two different scenarios: (1) a single beam from a single radar site and two beams from a single radar site, and (2) two beams from two sites (a single beam per site) intersecting each other at the buoy location. The LPM method utilized using two beams from two different sites was found to provide the best estimations of swell parameters (swell height RMS error 0.24m) and showed a good correlation with the partitioned swell in-sit...
The South Carolina Coastal Erosion Study (SCCES) is a cooperative research program funded by the ... more The South Carolina Coastal Erosion Study (SCCES) is a cooperative research program funded by the U.S. Geological Survey Coastal and Marine Geology Program and managed by the South Carolina Sea Grant Consortium. The main objective of the study is to understand the factors and processes that control coastal sediment movement along the northern part of the South Carolina coast while
ABSTRACT As part of the South Carolina Coastal Erosion Study (SCCES) a nearshore field experiment... more ABSTRACT As part of the South Carolina Coastal Erosion Study (SCCES) a nearshore field experiment was carried out for five days in December 2003 just north of Myrtle Beach, South Carolina, providing measurements of the waves, currents and morphological evolution. This experiment occurred concurrently with an extensive field campaign several kilometers offshore which included measurements of the waves and currents on and near a significant sand shoal. The purpose of the nearshore experiment was to aid in the identification of the effect of the offshore shoal on the nearshore processes. The resulting dataset will be used for verification of numerical models being used to investigate the hydrodynamics of the region. The experiment was carried out from December 10 to December 15 and consisted of measurements of the waves and currents, extensive surveys of the bathymetry every day, grab samples of the sediments, and video imagery. The hydrodynamics were measured using two Sontek Triton downward-looking Acoustic Doppler Velocimeters and two Nortek AquaDopp profilers arranged in a cross-shore line from inside the swash to several surf zone widths past the breakers. The bathymetric surveying was accomplished using both a differential GPS system and a total station. Surveying was performed each day in order to capture the morphological changes. On the last day, seven sediment samples were taken along a single cross-section to determine the sediment characteristics across the beach. Additionally, a video camera was located on a balcony of the top floor of a nearby hotel providing an excellent field of view of the entire experimental area. Digital video was captured directly onto a computer during all daylight hours and many control points were surveyed in each day to facilitate rectification of the imagery. A variety of conditions were encountered during the experiment, including two storm fronts which passed through, generating wind speeds up to 15 m/s. The first storm generated waves from the south driving a longshore current towards the north. After several relatively calm days with nearly normal incident waves the second front passed through the area with strong wind and waves approaching the shore with a large angle of incidence from the north. This drove an extremely strong longshore current in excess of 1.4 m/s and caused significant morphological changes.
Time series of in situ measured velocity and suspended sediment concentration from Qiantang Estua... more Time series of in situ measured velocity and suspended sediment concentration from Qiantang Estuary (China), and estimates of turbulence and sediment stratification parameters are presented. The data span a period of 9 days, and after phase averaged, they are used to explore spring‐neap tidal variations in flow, turbulence, and sediment stratification. A local balance between shear production, sediment‐induced buoyancy flux, and dissipation is found to hold during ebb for both neap and spring tides. During flood elevated turbulence dissipation rates are observed, attributed to nonlocal turbulence, most likely due to horizontal advection. Our results show that the effect of sediment stratification is successfully parameterized by adding the Monin‐Obukhov length scale to the classical logarithmic layer theory. Flood‐ebb asymmetry in both Rig and Rf is observed, with higher values attained during flood due to the higher sediment concentrations and the corresponding weaker velocity shea...
Numerical simulations are used to study the response of Long Bay, South Carolina, a typical coast... more Numerical simulations are used to study the response of Long Bay, South Carolina, a typical coastal embayment with curved coastline located on the South Atlantic Bight, to realistic, climatologically defined, synoptic storm forcing. Synoptic storms, consisting of cold and warm fronts as well as tropical storms, are used as forcing under both mixed and stratified initial conditions. The analysis focuses on the development of cross-shore shelf circulation and the relative contributions of regionally defined cross-shore winds and alongshore bathymetric variation. The simulation results show that, under stratified conditions, the regionally defined offshore-directed wind component promotes upwelling during the developing stage of the cold front and enhances mixing during the decaying stage. No significant effect is found for warm front and tropical storm forcing conditions. Net cross-shore transports are induced at the southern and northern sides of the embayment that have opposing sign...
Acoustic current profilers were originally designed to measure 3-D flow structure but they also r... more Acoustic current profilers were originally designed to measure 3-D flow structure but they also record the intensity of the return echo. The latter is proportional to the number of backscatters present in the water column and can be used as a proxy for suspended sediment concentration. The potential for remote, rapid and simultaneous measurements of current and suspended sediment concentration (SSC) fields with increased vertical and horizontal spatial resolution drives the development of methods for converting acoustic intensity to SSC. In this study, we present simultaneously collected acoustic Doppler current profiler (ADCP, RDI Workhorse, 1200kHz) and suspended sediment concentration data, obtained with an optical backscatter sensor (OBS). These data are utilized to calibrate a simplified version of the sonar equation that converts the recorded by the ADCP echo intensity into SSC. This simplified sonar equation lumps a number of immeasurable quantities into two parameters Kc and...
Journal of Atmospheric and Oceanic Technology, 2019
A hybrid, empirical radar wave inversion technique that treats swell and wind waves separately is... more A hybrid, empirical radar wave inversion technique that treats swell and wind waves separately is presented and evaluated using a single 48-MHz radar unit and in situ wave measurements. This hybrid approach greatly reduces errors in radar wave inversion during swell seas. Our analysis suggests that, prior to the inversion, the second-order spectrum should be normalized using Barrick’s weighting function because this process removes harmonic and corner reflection peaks from the inversion and improves the results. In addition, the resulting calibration constants for the wind wave component are not wave-frequency dependent and are similar in magnitude to those found in previous studies using different operating-frequency radars. This result suggests radar frequency independence, although additional experimental verification is required. The swell component of the model presented here ignores the effect of swell’s propagation direction on the radar signal. Although this approach has sev...
Accurate estimates of Stokes drift are necessary to quantify Lagrangian transport and upper-ocean... more Accurate estimates of Stokes drift are necessary to quantify Lagrangian transport and upper-ocean mixing. These can be estimated from directional wave spectra. Here, a methodology for the reconstruction of such spectra is developed using partitioned bulk wave parameters provided by global wave models. These reconstructed spectra agree well with global wave model–simulated full spectra. Regional wave model simulations with reconstructed spectra as open boundary conditions lead to more accurate estimates of bulk wave parameters in the coastal ocean. Furthermore, the reconstructed directional spectra can be used to improve high-frequency (HF) radar–derived surface Lagrangian current estimates. Stokes drift vertical profiles from complete directional spectra are more accurate, and therefore coupled ocean circulation and wave models should incorporate spectral estimates for wave–current interaction studies. Based on model simulations conducted here, it is recommended that regional wave m...
An examination of the applicability and accuracy of the empirical wave inversion method in the pr... more An examination of the applicability and accuracy of the empirical wave inversion method in the presence of swell waves is presented. The ability of the method to invert Doppler spectra to wave directional spectra and bulk wave parameters is investigated using one-month data from a 12 MHz WERA High Frequency (HF) radar system and in-situ data from a wave buoy. Three different swell inversion models are evaluated: LPM (Lipa et al. 1981), WFG (Wang et al. 2016) and EMP, an empirical approach introduced in this study. The swell inversions were carried out using two different scenarios: (1) a single beam from a single radar site and two beams from a single radar site, and (2) two beams from two sites (a single beam per site) intersecting each other at the buoy location. The LPM method utilized using two beams from two different sites was found to provide the best estimations of swell parameters (swell height RMS error 0.24m) and showed a good correlation with the partitioned swell in-sit...
The South Carolina Coastal Erosion Study (SCCES) is a cooperative research program funded by the ... more The South Carolina Coastal Erosion Study (SCCES) is a cooperative research program funded by the U.S. Geological Survey Coastal and Marine Geology Program and managed by the South Carolina Sea Grant Consortium. The main objective of the study is to understand the factors and processes that control coastal sediment movement along the northern part of the South Carolina coast while
ABSTRACT As part of the South Carolina Coastal Erosion Study (SCCES) a nearshore field experiment... more ABSTRACT As part of the South Carolina Coastal Erosion Study (SCCES) a nearshore field experiment was carried out for five days in December 2003 just north of Myrtle Beach, South Carolina, providing measurements of the waves, currents and morphological evolution. This experiment occurred concurrently with an extensive field campaign several kilometers offshore which included measurements of the waves and currents on and near a significant sand shoal. The purpose of the nearshore experiment was to aid in the identification of the effect of the offshore shoal on the nearshore processes. The resulting dataset will be used for verification of numerical models being used to investigate the hydrodynamics of the region. The experiment was carried out from December 10 to December 15 and consisted of measurements of the waves and currents, extensive surveys of the bathymetry every day, grab samples of the sediments, and video imagery. The hydrodynamics were measured using two Sontek Triton downward-looking Acoustic Doppler Velocimeters and two Nortek AquaDopp profilers arranged in a cross-shore line from inside the swash to several surf zone widths past the breakers. The bathymetric surveying was accomplished using both a differential GPS system and a total station. Surveying was performed each day in order to capture the morphological changes. On the last day, seven sediment samples were taken along a single cross-section to determine the sediment characteristics across the beach. Additionally, a video camera was located on a balcony of the top floor of a nearby hotel providing an excellent field of view of the entire experimental area. Digital video was captured directly onto a computer during all daylight hours and many control points were surveyed in each day to facilitate rectification of the imagery. A variety of conditions were encountered during the experiment, including two storm fronts which passed through, generating wind speeds up to 15 m/s. The first storm generated waves from the south driving a longshore current towards the north. After several relatively calm days with nearly normal incident waves the second front passed through the area with strong wind and waves approaching the shore with a large angle of incidence from the north. This drove an extremely strong longshore current in excess of 1.4 m/s and caused significant morphological changes.
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Papers by George Voulgaris