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J. Steven Fries, 1999 - 2000 Graduate Student Researcher

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J. Steven Fries


Steve successfully defended his thesis titled “Enhancement of Fine Particle Deposition To Permeable Sediment” on September 13, 2001. The thesis abstract follows.

Predictions of deposition rate are integral to the transport of many constituents including contaminants, organic matter, and larvae. Review of the literature demonstrates a general appreciation for the potential control of deposition by bed roughness, but no direct tests involving flat sediment beds. Understanding the mechanisms at work for flat sediment beds would provide the basis for exploring more complicated bed conditions and the incorporation of other transport processes, such as bioturbation and bedload transport.

Generally, fine particle deposition rates are assumed to be equivalent to the suspension settling velocity, therefore, deposition rates in excess of settling are considered enhanced. Flume observations of deposition were made using treatments that covered a wide range of flow, particle, and bed conditions. Specific treatments demonstrated large enhancements (up to eight times settling). Delivery of particles to the interface is important, but models based on delivery alone failed to predict the observed enhancement.

This necessitated the development of a new model based on a balance between delivery and filtration in the bed. Interfacial diffusion was chosen as a model for particle delivery. Filtration of particles by the bed is a useful framework for retention, but the shear in the interstitial flow may introduce additional factors not included in traditional filtration experiments.

The model performed well in prediction of flow conditions, but there remained a discrepancy between predictions and observed deposition rate, especially for treatments with significant enhancement. Fluid flow predictions by the model, such as slip at the sediment water interface and fluid penetration into the sediment, appeared to be supported by flume experiments. Therefore, failure to predict the magnitude of enhancement was attributed to the filtration efficiency. A weakness of this deposition model is the lack of an observable mechanism to drive diffusion and filtration. Emerging techniques to directly measure fluid and particle motion at the interface could reveal these mechanisms. The observation of enhanced deposition to flat sediment beds reinforces the importance of permeable sediments to the mediation of transport from the water column to the sediment bed.

Background


Ph.D., MIT/WHOI Joint Program
B.S. in Civil Engineering / Engineering Public Policy (Minor: Environmental Engineering)
Carnegie Mellon University Received December 1994

J. Steven Fries graduate research centered around flume studies identifying the mechanisms controlling deposition of fine particles with a focus on sediment transport, interfacial flows, and permeability at the sediment-water interface. The focus of his doctoral thesis is the observation of enhanced fine particle deposition to flat, sand beds. A simple mathematical model for deposition which incorporates settling of particles, diffusion across the sediment-water interface, and filtration within the sand bed was developed to predict scenarios where deposition maybe enhanced. In addition to his graduate thesis, he has pursued projects involving biological effects on sediment transport. Ripple formation and migration within benthic assemblages changes the near-bed flows and potential for deposition within the patch. He has also worked with fellow students to incorporate the technique of particle image velocimetry (PIV) into flume studies of turbulence and particle deposition.


Last updated: August 19, 2008
 


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