Simulating suspended sediment dynamics in shallow-water wave- and current-driven environments

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Sediment dynamics driven by waves and currents in shallow-water estuarine environments impacts many physical and biological processes and is important to the estuary-wide sediment budget. However, observational restrictions have limited our ability to understand the physics governing sediment entrainment and mixing in these environments. Nonlinear interactions between waves and currents, and sediment-induced stratification, result in complex near-bed physics that impacts the vertical transport of both mass and momentum throughout the water column. An Eulerian based sediment transport model is developed, along with a method for reducing the spin-up time for turbulent channel flow simulations. With proper initial conditions, the method leads to over a factor of six savings in the computational expensive associated with spin-up relative to traditional methods. Direct numerical simulation is then applied to study wave, current, and sediment interactions in combined wave- and current-driven flows with low Reynolds number (laminar) waves. Simulated conditions are relevant to wind-waves propagating into shallow-water, fine sediment environments. In contrast to the effects of high Reynolds number waves, low Reynolds number waves are found to accelerate currents by reducing vertical turbulent momentum transport. However, the wave velocity is unaffected by the currents, and resembles the Stokes theoretical wave solution for all conditions simulated. We also show that sediment entrainment and near-bed sediment dynamics are controlled by waves, although current-generated turbulence is required for vertical mixing. As is the case for steady currents, the downward settling flux is balanced by the upward turbulent flux throughout most of the water column. Near-bed sediment-induced stratification is also shown to suppress vertical transport of mass and momentum by stabilizing infrequent but intense mixing events. The stabilization reduces both the vertical Reynolds stress and vertical turbulent sediment flux, leading to accelerated currents and reduced suspended sediment concentrations. Near-bed reductions in vertical Reynolds stresses also reduce turbulence production but increase vertical shear. The increased shear acts as a feedback mechanism that eventually outweighs suppression of the Reynolds stress and increases turbulence production higher in the water column. Unlike mean shear, if the vertical turbulent sediment flux is restricted at any point in the water column, the magnitude of the mean suspended sediment concentration gradient decreases at all heights above the restriction. As a result, the effects of sediment-induced stratification on vertical turbulent sediment fluxes are more pronounced than on vertical turbulent momentum fluxes.


Type of resource text
Form electronic resource; remote; computer; online resource
Extent 1 online resource.
Place California
Place [Stanford, California]
Publisher [Stanford University]
Copyright date 2018; ©2018
Publication date 2018; 2018
Issuance monographic
Language English


Author Nelson, Kurt Shaun
Degree supervisor Fringer, Oliver B. (Oliver Bartlett)
Thesis advisor Fringer, Oliver B. (Oliver Bartlett)
Thesis advisor Koseff, Jeffrey Russell
Thesis advisor Monismith, Stephen Gene
Degree committee member Koseff, Jeffrey Russell
Degree committee member Monismith, Stephen Gene
Associated with Stanford University, Civil & Environmental Engineering Department.


Genre Theses
Genre Text

Bibliographic information

Statement of responsibility Kurt Nelson.
Note Submitted to the Civil & Environmental Engineering Department.
Thesis Thesis Ph.D. Stanford University 2018.
Location electronic resource

Access conditions

© 2018 by Kurt Shaun Nelson
This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).

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