Date of Award

7-31-2018

Document Type

Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

First Advisor

Erin E. Hackett

Second Advisor

Richard N. Peterson

Third Advisor

Richard F. Viso

Additional Advisors

Diane Fribance

Abstract

Erosion and water quality degradation have been observed in Singleton Swash in Myrtle Beach, SC, and have been hypothesized to be related to migration of the beach-face channel. Dredging this channel temporarily fixes erosional threats to nearby infrastructure but the effects on water quality are not well understood. It is hypothesized that variations in dissolved oxygen (DO) concentration (used here as a proxy for water quality) within the water column are related to changes in vertical mixing and transport due to oceanic tidal forcing. This study utilizes current meters, pressure sensors, and optical DO probes to measure and study the relationships between flow characteristics, DO, and water level. Correlation analysis is used to examine the influence of each physical process on dissolved oxygen variations as well as to explore the relationships between hydrodynamic variables. Results show that larger tidal ranges are associated with higher mean levels of DO concentration in the swash. The larger tidal ranges are linked to greater magnitude currents, and due to tidal asymmetries in the swash, flood currents are stronger than ebb currents. Stronger currents are also linked to larger Reynolds shear stress indicating increased mixing on flood tides relative to ebb tides. It is concluded that the combined transport of oxygenated waters into the swash on large flood tides, and its subsequent mixing due to strong currents, result in increased DO concentrations in the swash. This result is also supported by the direct correlation found between DO concentration and tidal ranges. Health of the ecosystem depends on strong currents and higher magnitude Reynolds shear stress to maintain high DO concentrations within the system. It was found in Hoffnagle (2015) that lower beach-face elevations correlate with larger tidal ranges in the swash; thus, maintenance of the beach-face swash channel is imperative to support a large tidal range and therefore overall ecosystem health.

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