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Temporal Variability in Cohesive Sediment Dynamics in a Partially Mixed Estuary, the York River Estuary, Virginia, USA: A Numerical Study Developed from Observations.

Record Type:	Electronic resources : Monograph/item
Title/Author:	Temporal Variability in Cohesive Sediment Dynamics in a Partially Mixed Estuary, the York River Estuary, Virginia, USA: A Numerical Study Developed from Observations./
Author:	Tarpley, Danielle Rae Nicole.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
Description:	221 p.
Notes:	Source: Dissertations Abstracts International, Volume: 81-11, Section: B.
Contained By:	Dissertations Abstracts International81-11B.
Subject:	Physical oceanography. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27960225
ISBN:	9798643196365

Temporal Variability in Cohesive Sediment Dynamics in a Partially Mixed Estuary, the York River Estuary, Virginia, USA: A Numerical Study Developed from Observations.
Tarpley, Danielle Rae Nicole.

Temporal Variability in Cohesive Sediment Dynamics in a Partially Mixed Estuary, the York River Estuary, Virginia, USA: A Numerical Study Developed from Observations. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 221 p.

Source: Dissertations Abstracts International, Volume: 81-11, Section: B.

Thesis (Ph.D.)--The College of William and Mary, 2020.

This item must not be sold to any third party vendors.

Fine-grained material such as silts and clays are the predominant sediment type in low energy systems such as micro-tidal embayments and estuaries. Due to its cohesive nature, fine sediment typically moves through marine systems as aggregated particles, or flocs, rather than as individual mineral grains. The particle's components, local hydrodynamics, and concentration influence floc size, density, and fall velocity. These, in turn, impact suspended sediment transport, which complicates predictions of the fate of sediment for water quality, contaminant distribution, and dredging purposes in these systems. This dissertation used a state-of-the-art modeling system and observations to examine the variability in sediment distribution due to cohesive processes along a partially mixed estuary and to determine the role of flocculation on sediment transport for a muddy site within the York River estuary, Virginia. The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system was used to simulate the hydrodynamics and suspended sediment transport in a muddy estuarine system. The model accounted for flocculation dynamics with a population balance model, FLOCMOD, changes in the erosion of sediment from the bed due to compaction or bed consolidation, and sediment-induced density gradients.The sensitivity of the sediment distribution was performed using an idealized two-dimensional (vertical and longitudinal) model that produced key estuarine features such as salinity-driven circulation and an estuarine turbidity maximum (ETM). The reference model included the effects of flocculation, bed consolidation, and sediment-induced density gradients. Results from the reference model were compared to test cases, each of which removed one of these processes. This showed that the effects of flocculation on suspended sediment concentrations (SSC) were most significant in the surface waters and in the ETM; whereas bed consolidation decreased SSC along the full length of the estuary. Another test case demonstrated that calculations of SSC and median floc diameter (D50) were sensitive to the number of sediment classes used to represent the floc population.The capabilities of the idealized two-dimensional estuary were extended and used to examine the contribution of flocculation compared to other sediment transport mechanisms such as advection, diffusion, settling, and erosion. The dominant processes that impacted the sediment mass balance in the idealized estuary were flocculation, vertical diffusion, and erosion. Next, the D50 produced by FLOCMOD in the idealized estuary was compared to a theoretical equilibrium floc size (Deq) estimated based on the ratio of SSC to the square root of the shear rate (G). This analysis also produced an estimate for a timescale for flocculation. In general, D50 reached Deq in the bottom boundary of the estuary when the flocculation timescales were on the order of minutes. However, immediately above the sediment bed, Deq was very similar to D50 when erosion was minimal or when finer flocs were eroded from the bed. However, the computed D50 most often differed widely from Deq, indicating that equilibrium theory was not appropriate for much of the idealized estuary.To facilitate the direct application of the flocculation model to the York River estuary, a one-dimensional (vertical) model was designed using observations of hydrodynamics and floc properties from the Claybank site for the vertical water column structure. The sensitivity of SSC and floc distribution to the parameterization of FLOCMOD was assessed using a model representing a spring-neap tidal cycle. The SSC was more sensitive to parameterization in the bottom boundary layer, D50 was less sensitive than SSC, and the grain size distribution width (spread) was more sensitive to the fractal dimension. Model results were then compared to observations to choose parameters to represent the floc population in the York River estuary. Parameterization was challenging, but the preferred representation for the York floc population had a low relative error for SSC and acceptable error for the distribution mode and spread. For the spring-neap tidal cycle in general, vertical diffusion, settling, and erosion accounted for more sediment mass transport than flocculation, but flocculation played an important role in the vertical distribution of sediment via changes in floc size.

ISBN: 9798643196365Subjects--Topical Terms:

3168433
Physical oceanography.
Subjects--Index Terms:

Bed consolidation

Temporal Variability in Cohesive Sediment Dynamics in a Partially Mixed Estuary, the York River Estuary, Virginia, USA: A Numerical Study Developed from Observations.
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245 1 0 $a Temporal Variability in Cohesive Sediment Dynamics in a Partially Mixed Estuary, the York River Estuary, Virginia, USA: A Numerical Study Developed from Observations.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2020
300 $a 221 p.
500 $a Source: Dissertations Abstracts International, Volume: 81-11, Section: B.
500 $a Advisor: Harris, Courtney K.;Friedrichs, Carl T.
502 $a Thesis (Ph.D.)--The College of William and Mary, 2020.
506 $a This item must not be sold to any third party vendors.
520 $a Fine-grained material such as silts and clays are the predominant sediment type in low energy systems such as micro-tidal embayments and estuaries. Due to its cohesive nature, fine sediment typically moves through marine systems as aggregated particles, or flocs, rather than as individual mineral grains. The particle's components, local hydrodynamics, and concentration influence floc size, density, and fall velocity. These, in turn, impact suspended sediment transport, which complicates predictions of the fate of sediment for water quality, contaminant distribution, and dredging purposes in these systems. This dissertation used a state-of-the-art modeling system and observations to examine the variability in sediment distribution due to cohesive processes along a partially mixed estuary and to determine the role of flocculation on sediment transport for a muddy site within the York River estuary, Virginia. The Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system was used to simulate the hydrodynamics and suspended sediment transport in a muddy estuarine system. The model accounted for flocculation dynamics with a population balance model, FLOCMOD, changes in the erosion of sediment from the bed due to compaction or bed consolidation, and sediment-induced density gradients.The sensitivity of the sediment distribution was performed using an idealized two-dimensional (vertical and longitudinal) model that produced key estuarine features such as salinity-driven circulation and an estuarine turbidity maximum (ETM). The reference model included the effects of flocculation, bed consolidation, and sediment-induced density gradients. Results from the reference model were compared to test cases, each of which removed one of these processes. This showed that the effects of flocculation on suspended sediment concentrations (SSC) were most significant in the surface waters and in the ETM; whereas bed consolidation decreased SSC along the full length of the estuary. Another test case demonstrated that calculations of SSC and median floc diameter (D50) were sensitive to the number of sediment classes used to represent the floc population.The capabilities of the idealized two-dimensional estuary were extended and used to examine the contribution of flocculation compared to other sediment transport mechanisms such as advection, diffusion, settling, and erosion. The dominant processes that impacted the sediment mass balance in the idealized estuary were flocculation, vertical diffusion, and erosion. Next, the D50 produced by FLOCMOD in the idealized estuary was compared to a theoretical equilibrium floc size (Deq) estimated based on the ratio of SSC to the square root of the shear rate (G). This analysis also produced an estimate for a timescale for flocculation. In general, D50 reached Deq in the bottom boundary of the estuary when the flocculation timescales were on the order of minutes. However, immediately above the sediment bed, Deq was very similar to D50 when erosion was minimal or when finer flocs were eroded from the bed. However, the computed D50 most often differed widely from Deq, indicating that equilibrium theory was not appropriate for much of the idealized estuary.To facilitate the direct application of the flocculation model to the York River estuary, a one-dimensional (vertical) model was designed using observations of hydrodynamics and floc properties from the Claybank site for the vertical water column structure. The sensitivity of SSC and floc distribution to the parameterization of FLOCMOD was assessed using a model representing a spring-neap tidal cycle. The SSC was more sensitive to parameterization in the bottom boundary layer, D50 was less sensitive than SSC, and the grain size distribution width (spread) was more sensitive to the fractal dimension. Model results were then compared to observations to choose parameters to represent the floc population in the York River estuary. Parameterization was challenging, but the preferred representation for the York floc population had a low relative error for SSC and acceptable error for the distribution mode and spread. For the spring-neap tidal cycle in general, vertical diffusion, settling, and erosion accounted for more sediment mass transport than flocculation, but flocculation played an important role in the vertical distribution of sediment via changes in floc size.
590 $a School code: 0261.
650 4 $a Physical oceanography. $3 3168433
653 $a Bed consolidation
653 $a Cohesive
653 $a Estuary
653 $a Flocculation
653 $a FLOCMOD
653 $a Sediment-induced stratification
690 $a 0415
710 2 $a The College of William and Mary. $b School of Marine Science. $3 3281332
773 0 $t Dissertations Abstracts International $g 81-11B.
790 $a 0261
791 $a Ph.D.
792 $a 2020
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=27960225