Hydrodynamic behavior of the Cape Fear River estuarine system, North Carolina

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  • July 17, 2019
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  • Becker, May Ling
    • Affiliation: College of Arts and Sciences, Department of Marine Sciences
Abstract
  • Transport in estuaries depends on the relative strengths of dominant forcing mechanisms, which may include tides (which generate turbulence), river input (which adds buoyancy), and wind (which may act as a remote forcing in the coastal ocean or a local forcing over the estuary). In this study, we investigate the major physical mechanisms that influence circulation in the Cape Fear River Estuary (CRFE), a partially mixed estuary that is representative of other estuaries along the southeast Atlantic coast from southern North Carolina through northern Florida. First, we describe differences in velocity and stratification at along-channel sections of the estuary for relatively low-flow conditions based on historical data. Then, we discuss the influence of river inflow on the salinity intrusion using different methods of determining discharge in order to investigate the appropriate means of incorporating flow history into the discharge value. Finally, we discuss the role of tidal forcing based on findings of a field data study designed to characterize estuarine behavior during differing tidal conditions. Specifically, velocity, salinity, and tidal-height data were collected for an along-channel segment of the CFRE during two separate periods representing high versus low ranges, and mechanisms influencing observed differences are described. Results indicate the salinity structure and circulation are impacted by tidal-range differences that vary over an approximately 29-day period, intra-tidal variations, and sub-tidal variations in freshwater input. For low-flow conditions, the system exhibits characteristics of a two-layer estuarine system in which density driven-circulation enhances inflow near the bottom while fresher, less dense water flows out near the surface. Specifically, 1) over 90 percent of the variability in the length of the salinity intrusion over a five-year period can be explained based on peaks in river discharge using the hydrologic flood exponential decay model, 2) intra-tidal and tidal-range variations significantly influence stratification, 3) these variations impact circulation including the along-channel velocity structure, and 4) salinity characteristics are critically linked to turbulent mixing characteristics and the strength of stratification within the water column.
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  • In Copyright
Advisor
  • Luettich, Richard A.
Degree granting institution
  • University of North Carolina at Chapel Hill
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  • Open access
Date uploaded
  • October 19, 2010

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