HR: 0800h
AN: H31B-1293    [Abstracts]
TI: Enhancement of Solute Transfer into Sediment by Water Surface Wave Motion
AU: * Qian, Q
EM: qian0037@umn.edu
AF: St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, #2 Third Ave. SE, Minneapolis, MN 55414 United States
AU: Voller, V R
EM: volle001@umn.edu
AF: St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, #2 Third Ave. SE, Minneapolis, MN 55414 United States
AU: Stefan, H G
EM: stefa001@umn.edu
AF: St. Anthony Falls Laboratory, Department of Civil Engineering, University of Minnesota, #2 Third Ave. SE, Minneapolis, MN 55414 United States
AB: A critical environmental problem is the solute transfer from surface water into sub-aqueous sediment. If a water body has a perfectly horizontal water surface and exhibits no bed forms solute transfer into the bed sediments will be controlled by molecular diffusion. If, however, surface waves or bed forms are present the resulting pressure differences along the water-sediment surface can establish a flow field in the sediment, which in turn will enhance the transfer of the solute from the water body into its sediments. To better understand this enhancement, a model of solute transfer across the sediment-water interface under a standing surface wave is developed. This model simulates the combined effect of advection and diffusion transfer to arrive at a one-dimensional depth dependent dispersion coefficient that characterizes solute transfer into the sediment. A Peclet number, based on wave height, permeability of the sediment, and molecular diffusion coefficient of the sediment, is defined as the single dimensionless parameter to characterize the relative magnitude of advection to diffusion in the 2-D flow through the sediment. The 2-D concentration distributions are then averaged at each depth. The work demonstrates that the one-dimensional solute concentration vs. depth profile is essentially independent of any numerical dispersion present in the solute field predictions. The resulting one-dimensional (1-D) concentration profile with depth was then matched to the solution of an unsteady 1-D vertical dispersion equation. A depth-variable dispersion coefficient (D_d) is thus determined by inverse modeling. Results show that the dispersion coefficient (D_d) is not only a function of depth but also a function of Peclet number and time. However, after a brief initial period, the depth-variable distribution of the dispersion coefficient becomes independent of time. In general, the dispersion coefficient (D_d) can be several orders of magnitude larger than the molecular diffusion coefficient. The calculated dispersion coefficient increases linearly with the Peclet number and for a give Peclet number it decreases often exponential with depth from the sediment-water interface. Also, with an increase in Peclet number the flow through the sediment also gains greater penetration. The Penetration depths (d_p) of the solute into the sediment are therefore Peclet number dependence. Hence, using a molecular diffusion coefficient alone to describe solute transport in permeable beds can lead to erroneous predictions.
DE: 1719 Hydrology
DE: 1830 Groundwater/surface water interaction
DE: 1847 Modeling
DE: 1856 River channels (0483, 0744)
DE: 1871 Surface water quality
SC: Hydrology [H]
MN: Fall Meeting 2005