Vertical variation in diffusion coefficient within sediments
Chandler, I. D. (2012) Vertical variation in diffusion coefficient within sediments. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2581603~S1
River ecosystems can be strongly in
uenced by contaminants in the water column,
in the pore water and attached to sediment particles. Current models [TGD, 2003]
predict exposure to sediments based on equilibrium partitioning between dissolved
and suspended-particle-sorbed phase in the water column despite numerous studies
showing significant direct mass transfer across the sediment water interface. When
exchange across the interface (hyporheic exchange) is included in modelling the
diffusion coefficient is assumed to be constant with depth.
The overall aims of this research were to quantify the vertical variation in diffusion
coefficient below the sediment water interface and asses the use of a modified
EROSIMESS-System (erosimeter) in the study of hyporheic exchange.
The modified erosimeter and novel fibre optic
uorometers measuring in-bed
concentrations Rhodamine WT were employed in an experimental investigation.
Five different diameter glass sphere beds (0.15 to 5.0mm) and five bed shear velocities
(0.01 to 0.04m/s) allowed the vertical variation in diffusion coefficient to be
quantified to a depth of 0.134m below the sediment water interface.
The vertical variation in diffusion coefficient can be described using an exponential
function that was found to be consistent for all the parameter combinations
tested. This function, combined with the scaling relationship proposed by O'Connor
and Harvey  allows a prediction of the diffusion coefficient below the sediment
water interface based on bed shear velocity, roughness height and permeability.
1D numerical diffusion model simulations using the exponential function compare
favourably with the experimental data.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||G Geography. Anthropology. Recreation > GB Physical geography
T Technology > TA Engineering (General). Civil engineering (General)
|Library of Congress Subject Headings (LCSH):||River sediments -- Mathematical models, Pollutants -- Mathematical models|
|Official Date:||May 2012|
|Institution:||University of Warwick|
|Theses Department:||School of Engineering|
|Supervisor(s)/Advisor:||Pearson, Jonathan, Dr. ; Guymer, Ian|
|Sponsors:||Engineering and Physical Sciences Research Council (EPSRC) (CASE/CNA/07/75) ; Unilever (Firm)|
|Extent:||xviii, 237 leaves : ill., charts|
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