Barry M. Lesht, Environmental Research Division, Argonne National Laboratory

Objectives:

1. Determine threshold criteria for initiation of resuspension of the bottom sediments in the Lake Michigan coastal region associated with episodic events,
2. Estimate the magnitude and direction of the horizontal near-bottom sediment flux during episodic transport events.

Approach:

• An instrumented tripod was deployed at several locations in the southern basin of the lake to make long time-series observations of physical and sedimentological conditions within the benthic boundary layer.
• Tripod measurements include horizontal current velocity, water temperature (2 levels), wave height and period, suspended sediment concentration (2 levels, inferred from beam attenuation), and bottom configuration (digital photography).

Results:

• Spring transport events result from surface-wave induced resuspension of local sediments.
• Resuspension events are not limited to the spring, but occur throughout the year whenever wave conditions exceed critical threshold.
• Horizontal near-bottom sediment flux during events can approach 100 kg/m²/day.
• Simple resuspension models using wave orbital velocity as forcing can simulate events with good accuracy.
• See also Detailed Results (MS Word, 34pp, 475 K).

Summary of Argonne EEGLE Tripod Deployments

Deployment	Location	Depth	Dates	Data Hours	Events
98-1	Wind Point, WI	15m	04/02/98-04/30/98	669.5	4
98-2	Oak Creek, WI	25m	07/23/98-08/24/98	770.5	0
98-3	Oak Creek, WI	25m	10/28/98-12/01/98	815.5	2
99-1	St. Joseph, MI	20m	02/25/99-04/19/99	0.0	-
99-2	St. Joseph, MI	20m	04/20/99-06/01/99	1032.0	1
99-3	South Haven, MI	18m	10/15/99-11/17/99	787.5	5
00-1	Milwaukee, WI	20m	02/28/00-04/18/00	1194.0	4
00-2	Milwaukee, WI	20m	04/19/00-05/16/00	0.0	-
00-3	Milwaukee, WI	20m	05/16/00-06/08/00	0.0	-
00-4	Muskegon, MI	25m	09/12/00-present