 |
||||
|
||||
|
|
|
 |
||
|
||||
      |
Measurement and Modeling of Wave-induced Sediment Resuspension in Nearshore Water
Collaborators
Barry Lesht, Argonne National Laboratory, (ANL web site)
Dave Schwab Great Lakes Environmental Research Laboratory
(GLERL Home)
Chin Wu, University of Wisconsin (UW
- Madison web site)
Executive Summary
To date, this project has concentrated on analyzing the extensive set of observations collected in 1998-2000. Subsurface pressure sensors were deployed during the unstratified period at various locations in southern Lake Michigan to measure the heights and periods of surface waves. Measurements of bottom current velocity and suspended sediment concentration were also made. Analysis of that data is now well advanced, and the effort will shift toward
- Analyzing additional data collected since 2000.
- Incorporating the resuspension model developed previously into the lake circulation model.
The resulting sediment transport model will be used to determine how well sediment transport paths can be simulated and to determine how sensitive the model is to different conditions of sediment availability.
Project Rationale
In shallow water (up to about 30-40 m depth) surface waves are the primary
cause of sediment resuspension; accurate modeling of wave-induced resuspension
is necessary if a lakewide sediment transport model is to be developed.
Deployments of tripods instrumented with sensors to make time series measurements
of subsurface pressure (to measure the height and period of surface waves),
bottom current velocity, and suspended sediment concentration were made
at various locations around the southern basin of Lake Michigan in 1998-2000.
Our analysis shows that a simple vertically-averaged model of sediment
resuspension does a good job of simulating resuspension events. However,
the observations also show numerous periods of high sediment concentration
when no resuspension occurs. These episodes are almost certainly due in
large part to advection of material resuspended elsewhere and then transported
past the mooring sites. One of the current goals of this research is to
determine how important advection of suspended sediment is, and how well
the model can simulate these movements.
Fig. 1. Locations of deployments between 1998-2000.
Project Plans
The resuspension model developed in 2004 will be incorporated into the 2d lake circulation model. The resulting model will then be run for different scenarios to determine how well the model can 1) simulate large-scale advection of suspended sediment in the lake, and 2) simulate sediment resuspension and transport under different conditions of sediment availability.
Revision of 2 previously submitted manuscripts - one describing the 1998-2000 data, and the other describing the fall 2003 data - will be completed, and analysis of the 2004 data will begin. Analysis of the 2004 data set will concentrate on the effects of temporal changes in particle size during resuspension events.
Accomplishments
A 2005 fall deployment in Lake Michigan was made in conjunction with Dr. Chin Wu from the University of Wisconsin in order to examine in detail the vertical distribution of resuspended sediments. An analysis of the fall 2003 deployment was completed. The results appear to show that the vertical distribution of sediment does not increase with increasing distance from the bottom. This is probably due to a change in the particle size with elevation.
An evaluation of the ability of the GLERL-Donelan wave model to predict resuspension events was completed. The results from 15 deployments (Fig. 1) show that although the errors introduced by using modeled wave parameters in place of observed waves can be almost completely compensated for by adjusting the resuspension coefficient in the resuspension model, the computed concentrations are frequently quite different from the observed sediment concentrations (Fig. 2). In addition, the values of this coefficient must be determined empirically for each site, since at present there is no way to predict the coefficient from either the water depth or the properties of the bottom sediment (Fig. 3). The results also show that most of the resuspended sediment is silt-sized (less than 0.06 mm) even in areas where silt-sized material is absent from the bottom sediment.
Fig. 2. Results from stations M04 (A), M09(B), and M11 (C). All observations were made in 2000. The black line is the bottom stress, the blue line the modeled sediment concentration near the bottom, the red line the observed concentration near the bottom, the yellow line the observed concentration 10 meters above the bottom, and the green line (M11 only), the observed concentration 25 meters above the bottom.
Fig. 3. Resuspension coefficients based on the observed (x) and modeled (+) wave parameters for all of the deployments compared to the water depth(A), mean particle diameter of the bed material (B), and mud fraction of the bottom sediment(C).
Publications
EADIE, B. J., D. J. SCHWAB, T. H. JOHENGEN, P. J. LAVRENTYEV, G. S. MILLER, R. E. Holland, G. A. LESHKEVICH, M. B. LANSING, N. R. MOREHEAD, J. A. ROBBINS, N. HAWLEY, D. N. Edgington, and P. L. VAN HOOF. Particle transport, nutrient cycling, and algal community structure associated with a major winter-spring sediment resuspension event in southern Lake Michigan. Journal of Great Lakes Research 28(3):324-337 (2002). http://www.glerl.noaa.gov/pubs/fulltext/2002/20020017.pdf
HAWLEY, N., B. M. Lesht, and D. J. SCHWAB. A comparison of observed and modeled surface waves in southern Lake Michigan and the implications for models of sediment resuspension. Journal of Geophysical Research 109(C10S03):11 (2004). http://www.glerl.noaa.gov/pubs/fulltext/2004/20040015.pdf
Lee, C.-H., D. J. SCHWAB, and N. HAWLEY. Sensitivity analysis of sediment resuspension parameters in coastal area of southern Lake Michigan. Journal of Geophysical Research 110(C03004):16 (2005). http://www.glerl.noaa.gov/pubs/fulltext/2005/20050018.pdf
Lesht, B.M., and HAWLEY, N., 2001. Using wave statistics to drive a simple sediment transport model, Proceedings of the 5th Conference on Ocean Wave Measurement and Analysis, 1366-1375.
LIU, P. C., and N. HAWLEY. Wave grouping characteristics in nearshore Great Lakes II. Ocean Engineering 29:1415-1425 (2002). http://www.glerl.noaa.gov/pubs/fulltext/2002/20020021.pdf
Last updated: 2006-07-20 mbl