ABSTRACT
Welcome to the second half of my final project. This comes to you from the University of Wisconsin-Madison. This is for Civil Engineering 514-Coastal Engineering, which is offered by the department of engineering.
My project was to determine the bottom velocities in the Duluth-Superior harbor. My first step in achieving these values was obtaining wind data from the nearest noaa station, this turned out to be the C-man fixed station DISW3 in Devils Island, Wisconsin. Wind speed and direction data, as well as others, can be downloaded, copied, and pasted into a spreadsheet for manipulation. I analyzed wind water waves and storm surge, in combination with seiche motions. I didn't consider boat traffic, although this is a major contributor to bottom velocities. My results showed that wind waves are more influential than storm surge, and that seasonal changes have a negligible impact on bottom velocities.
The first part of this project was a presentation.
If you would like to see more of the equations and numbers associated with
the previous discussion, please view this presentation.
PROJECT MOTIVATION
What interested me in pursuing this area for my project, was that I
have spent some time in the Duluth area. I have camped along
the North Shore, and have enjoyed skiing at Lutsen
“Mountain” in Duluth. I am also from Minnesota so choosing a
site ‘close to home’ also played a role in my decision. Independent
of personal reasons, I am interested in assessment and remediation of environmental
impacts.
In 1987 the International Joint Commission,
made up of Canadian and American government agencies, designated 43
Areas Of Concern in the Great Lakes Basin. The Duluth-Superior
Harbor was one of these AOC's.
These areas were sited based on their failure to meet criterion as defined
by the Great Lakes Water
Quality Agreement of 1978. The purpose of this agreement was
to maintain beneficial use of the area's ability to support aquatic life.
>From this agreement 14 Beneficial Use Impairment criterion were developed.
This is the first step in Remedial
Action Plans (RAP), namely to identify which of the 14 criterion are
being impaired. Beneficial use impairments are defined as a change
in the chemical, physical or biological integrity of the Great Lakes system,
which is potentially or actively causing an adverse inpact. To view
the impairments for the Duluth-Superior Harbor, click
here.
COASTAL ENVIRONMENT
The coastal environment of a region consists of its geologic and geographic
setting, the recreational uses and industrial developments, as well as
meteorological impacts that induce water level fluctuations. These
are some of the parameters I considered when evaluating the coastal environment
of the Lake Superior Basin and Upper Duluth Harbor. A good overview
of the physical
environment of the Duluth-Superior harbor including, Area Geography,
Climate, Geology, Soils, Physical Shoreline, Forestry, Wetlands,
Water Quality, Aquatic Nuisance Species, Land Use, and Minerals can be
found at the Office
of Coastal and Resource Management (OCRM) and National Oceanic and Atmospheric
Administration. Other useful physical
information about the Great Lakes basin can be found at the NOAA
Great Lakes Coast Watch site.
ISSUES AND APPROACHES
The beneficial use impairment I was considering in my project, was the
presence of contaminated sediments. I chose to look at the bottom
velocities that could cause resuspension and ultimately transport into
the Lake Superior basin. The next step was to identify the major
sources of water level fluctuations inducing bottom velocities. After
some literature review, I discovered the major contributors to be Storm
Surge, Wind Waves, and Boat Traffic in combination with the natural Seiche
motion of the harbor. Wind
data from the NOAA site was sufficient in determining bottom velocities
for Storm Surge and Wind Waves, but there was not any information available
on the bottom velocities caused by Boat Traffic. For this reason
I only considered the former. In addition to this I wanted to consider
how the magnitude of these energy sources varied from season to season.
RESULTS AND DISCUSSION
My results showed that the dominant cause of bottom velocites was Wind
Generated waves in combination with basin oscillation. The bottom
velocites due due Storm Surge varied across the seasons, but their magnitude
was several orders of magnitude less than that of the wind generated waves.
This fluctuation in bottom velocity with season was not observed in the
case of the wind generated waves. The average bottom velocity was
in the vicinity of 7cm/s. Whether or not this velocity would cause
resuspension is a matter of what kind of model one chooses to use.
In order for a representative model to be developed, on site testing should
be performed in the harbor. In this fashion threshold velocities
could be measured directly with some pecentage of certainty. The
size of sediment is a parameter that also contributes to whether a sediment
is suspended or not. In most cases contaminants impinge on the finer
fraction. This is due to their surface area and electro-static charge.
For this reason a sediment size distribution probability plot should be
created. Considering all of this information would be the most effective
way to model and monitor the transport of contaminated sediments in the
Duluth-Superior harbor.
Thank you for visting.
Brian Matthias Sperrazza
BS-Geology
and Geophysics
BS-Geological Engineering
REFERENCES
Stortz, K.R. and Sydor, M., "Transports in the Duluth-Superior Harbor", Journal of Great Lakes Research 1980, International Association for Great Lakes Research 6(3):223-231
Brassard, Pierre and Morris, William, "Resuspension and Redistribution of Sediments in Hamilton Harbour", Journal of Great Lakes Research 23(1):74-85, International Association for Great Lakes Research, 1997
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