Paul A. Work

Cross-Shore Variation of Wind-Driven Flows on the Inner Shelf in Long Bay, South Carolina, United States

and exceeded 0.1 N/m 2 , vertical mixing occurred, the two-layered flow pattern disappeared, and currents were directed alongshore with the wind at all sites and throughout the water column. In the fall, near-bed flows close to the shore (water depth <7 m) were often reduced compared to or opposed those measured farther offshore under southwestward winds. A simplified analysis of the depth-averaged, alongshore momentum balance illustrates that the alongshore pressure gradient approached or exceeded the magnitude of the alongshore wind stress at the same time that the nearshore alongshore current opposed the wind stress and alongshore currents farther offshore. In addition, the analysis suggests that the wind stress is reduced closer to shore so that the alongshore pressure gradient is large enough to drive the flow against the wind.

Waves Initiative within SEACOOS

This article describes the efforts and progress in the area of surface waves, detailing the development of the in situ measuring stations operating in the SEACOOS region. The development and operation of 2 cabled near-shore directional wave installations are described, with some results on near-shore wave climatology developed from those stations. This is followed by a description of a wave buoy observational activity that included an intercomparison of surface wave parameters measured by the buoy with those measured by an RD Instruments acoustic Doppler current profiler. Lastly, a large section of the article is dedicated to describing research and development activities designed to evaluate the use of HF Radar technology for wave measurements.

Wind Speed Dependence of Single-Site Wave-Height Retrievals from High-Frequency Radars

Abstract 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 with increasing wind speed.

Estimation of suspended sediment concentration in rivers using acoustic methods.

Acoustic Doppler current meters (ADV, ADCP, and ADP) are widely used in water systems to measure flow velocities and velocity profiles. Although these meters are designed for flow velocity measurements, they can also provide information defining the quantity of particulate matter in the water, after appropriate calibration. When an acoustic instrument is calibrated for a water system, no additional sensor is needed to measure suspended sediment concentration (SSC). This provides the simultaneous measurements of velocity and concentration required for most sediment transport studies. The performance of acoustic Doppler current meters for measuring SSC was investigated in different studies where signal-to-noise ratio (SNR) and suspended sediment concentration were related using different formulations. However, these studies were each limited to a single study site where neither the effect of particle size nor the effect of temperature was investigated. In this study, different parameters that affect the performance of an ADV for the prediction of SSC are investigated. In order to investigate the reliability of an ADV for SSC measurements in different environments, flow and SSC measurements were made in different streams located in the Aegean region of Turkey having different soil types. Soil samples were collected from all measuring stations and particle size analysis was conducted by mechanical means. Multivariate analysis was utilized to investigate the effect of soil type and water temperature on the measurements. Statistical analysis indicates that SNR readings ob tained from the ADV are affected by water temperature and particle size distribution of the soil, as expected, and a prediction model is presented relating SNR readings to SSC mea surements where both water temperature and sediment characteristics type are incorporated into the model. The coefficients of the suggested model were obtained using the multivariate anal ysis. Effect of high turbidity conditions on ADV performance was also investigated during and after rain events.

Beach Profile Model with Size-Selective Sediment Transport. II: Numerical Modeling

AbstractBeach profile evolution is a dynamic phenomenon that often leads to threatening consequences such as severe beach erosion and shoreline retreat. A new comprehensive morphodynamic model is introduced in this study that includes representation of bedload and suspended size-selective sediment transport and cross-shore sediment grain-sorting models. The model is capable of simulating the changes in cross-shore bathymetry and sediment grain size composition observed under laboratory conditions for both erosive- and accretive-type equilibrium beach profiles. The new model is most advantageous for scenarios with poorly sorted sediments or sites with strong cross-shore variability in sediment grain sizes. Information on sediment size composition in the domain and its history is also provided by the new model, which can be useful for engineering, recreational, or biological considerations.

Identification of Swell in Nearshore Surface Wave Energy Spectra

An approach for routine identification of swell and sea in nominally fully developed, omnidirectional, surface water wave energy spectra measured in arbitrary water depth is developed, applied, and discussed. The methodology is an extension of earlier work with deepwater spectra and involves identifying the frequency at which wave steepness is maximized and relating this to the swell separation frequency. The TMA parameterized spectrum is employed to establish a relationship between the two frequencies so that the methodology can be used when wind data are unavailable. The methodology is developed for finite water depth and tested using a dataset that includes both acoustic Doppler current profiler and wave buoy data, recorded simultaneously at the same location. For cases where the sea and swell are clearly, visually distinguishable in the omnidirectional spectra, the new method accurately distinguishes between the two, but it can also be used to identify sea and swell in unimodal spectra.

Bacteriophage Tracer for Fecal Contamination Sources in Coastal Waters

Septic systems are designed for on-site treatment of wastewater, often for individual households with dependence on homeowner maintenance. They frequently become overloaded and fail, short-circuiting wastewater treatment within the tank, allowing untreated wastes into groundwater or surface water. Current methods for detection of such leaks rely on the use of inert dye and are often inadequate. The work described here included development and testing of bacteriophage-based tracking approaches to improve assessment of on-site sewage disposal systems and identification of leaks. The hypothesis is that a benign bacteriophage can be used to detect chronically failing septic systems with greater sensitivity and longevity than inert dye technology. Testing was conducted in both open waterway and coastal groundwater systems subject to astronomical tidal forcing. Results in open (surface) water demonstrated correlation between dye and phage presence initially, but the phage was detectable at greater distances and longer durations than the dye. Phage detection in groundwater did not correlate with dye presence, and revealed that phage moves more quickly through soils than dye. Details of the development, testing, and deployment of the bacteriophage tracer are provided, illuminating both the pros and cons of the approach. The ultimate advantage is that the use of a sentinel bacteriophage improves detectability of failing septic systems in coastal and other environments. This approach may thus be useful for establishing new science-based criteria for the installation of new septic systems in coastal areas.

Beach Profile Model with Size-Selective Sediment Transport. I: Laboratory Experiment and Sensitivity Study

AbstractThe response of physical models of beach profiles to random breaking waves was studied to investigate size-selective sediment transport and cross-shore profile evolution. Three types of beach profiles with different sediment mixtures were considered and subjected to waves until profiles reached equilibrium. Size-selective sediment transport was evident in the experiments, with the mean sediment size varying up to 20% along the beach profiles. Consistent coarsening and fining of the surface sediment in the experiments revealed size-selective sediment transport governed by cross-shore variations in energy dissipation, affecting important beach profile features such as sandbar structures and offshore and foreshore slopes. The theoretical basis of the transport phenomenon was described by analyzing the relationship between the transport processes and essential wave and hydrodynamic parameters obtained using a new set of numerical models. The results showed that beach profile changes and associated sed...

Directional Bimodality in Nearshore, Surface Water Wave Energy Spectra, Georgia, USA:

Surface water wave measurements in coastal Georgia, USA are considered. The dataset includes non-directional wave energy spectra measured via pressure transducers at two locations; non-directional, wave buoy-derived observations at a third; and directional wave buoy observations at a fourth, closest to shore. Mean depths at the observation sites range from 14 to 44 m. Measurements of non-directional surface wave energy spectra and the resulting bulk wave parameters (height, period) are compared at the four locations to reveal spatial and temporal variations. Directional characteristics of the waves are investigated at the nearshore site. A new, simple definition for directionally bimodal spectra is proposed and applied. The importance of directional bimodality when considering problems that are sensitive to wave direction, such as longshore sediment transport, is demonstrated. Neglect of directional bimodality via the use of a single mean wave direction can lead to significant errors in computation of longshore sediment transport, and potentially even the incorrect sign on computed quantities.

Mesoscale Wave Energy Dissipation Over Heterogeneous Sediments

Abstract : Measurements describing the evolution of wave energy spectra as waves propagate across a large shoal are described. The shoal is shore oblique, 2 km by 10 km in extent, with relief of up to three meters over bathymetry with ambient depth 10-12 m. The region is sediment starved, and bottom roughness displays spatial variability due to rock outcrops. Field measurements intended to investigate the effects of this shoal on waves, currents, and sediment transport in its lee reveal strong cross-shore gradients in energy density and energy flux, well outside of the surf zone, in conditions of minimal wind, which are attributed to bottom friction. The dissipation displays the expected frequency dependence, in that it decreases in significance as wave frequency increases, but this trend is not as strong as available theoretical predictions would suggest.