Effect of Tidal Stage on Sediment Concentrations and Turbulence by Vessel Wake in a Coastal Plain Saltmarsh

Richard Styles,Michael A Hartman

doi:10.3390/jmse7060192

Abstract

Vessel generated waves can impact shoreline stability and habitat structure in many waterways. Sheltered regions, such as coastal plain saltmarshes, support fragile ecosystems and can be particularly vulnerable to the effects of unregulated vessel operations. Instruments for measuring currents and sediment concentration were deployed in a coastal plain saltmarsh to examine the small-scale physical characteristics of the vessel wake generated by recreational craft typical of this environment. The response to vessel wake varied sharply depending upon the stage of the tide. At low tide, waves breaking on the exposed bank produced high concentrations of suspended material that were transported offshore through turbulent diffusion. When the water elevation exceeded the toe of the marsh scarp, the concentration and turbulent kinetic energy exhibited less of a statistically significant variation in response to vessel passage. For the most energetic flows, the vessel orbital velocities were dwarfed by turbulent fluctuations generated by the sheared tidal boundary layer. While further research is required, preliminary findings indicate that the dissipation of vessel wake energy may stimulate or enhance shear generated turbulence if the characteristic wave period is similar to the characteristic time scale of the energy containing eddies.

Highlights

IntroductionVessel generated waves in shallow water can impact shoreline stability and habitat structure in many waterways [1,2,3,4]
Vessel generated waves in shallow water can impact shoreline stability and habitat structure in many waterways [1,2,3,4]. These impacts are linked to sediment transport processes, which are associated with dissipation and turbulence generation similar to wind waves, tides, or other energetic forcing mechanisms
The purpose of this paper is to present the results of a field study to examine the hydrodynamic and sediment transport characteristics of vessel wake in an intertidal saltmarsh as a function of tidal stage focusing on small-scale physical processes

Summary

Introduction

Vessel generated waves in shallow water can impact shoreline stability and habitat structure in many waterways [1,2,3,4]. These impacts are linked to sediment transport processes, which are associated with dissipation and turbulence generation similar to wind waves, tides, or other energetic forcing mechanisms. Unlike wind waves or tides, vessel generated waves propagate as discrete packets, and the resulting energy dissipation, turbulence generation, and sediment transport are short lived. The impact of vessel wake in estuaries with sufficient fetch is often dwarfed by the integrated effect and persistence of wind wave attacks [5]. Different regions of the same estuary can experience much weaker wave conditions due to fetch limitations in areas that are sheltered from the more exposed open bay, thereby allowing vessel wake to represent the dominant form of wave energy

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Results