This is a presentation given at a meeting of the International Upper Great Lakes Study (IUGLS) in Detroit, MI, on the current status of the St. Clair Model.

1. 1-D HEC-RAS Hydraulic
Model of the St. Clair River
Detroit, MI
October 21, 2008

2. Introduction
• Two Major Questions:
– What effects have past dredging events
(1962) had on conveyance in the St. Clair
River?
– What effects have bathymetric changes in the
St. Clair River had on conveyance since
1971?

3. Introduction
• In response, I was given two objectives:
– Using the 2007 1-D model, fill in areas
dredged in 1962 to estimate change in
conveyance due to dredging.
– Using the 2007 (1971 resolution) bathymetry
provided by Environment Canada and the
1971 bathymetry, determine change in
conveyance since 1971 due to bathymetric
changes.

4. 1962 Dregding
• Locations of 1962
dredging provided by
the Army Corps of
Engineers, Detroit
District.

5. 1962 Dredging
• RAS cross-sections before and after
dredging.
St Clair Plan: Dredging 9/23/2008 St Clair Plan: 1) Reach1 10/19/2008
River = St. Clair River Reach = Main Ch-2 RS = 104 River = St. Clair River Reach = Main Ch-2 RS = 104
. .0239 . . .0239 .
178 0 0 Legend 178 0 0 Legend
2 2 2 2
6 6 6 6
176 4 4 WS Max WS 176 4 4 WS Max WS
174 Ground 174 Ground
Bank Sta Bank Sta
Elevation (m)
Elevation (m)
172 172
170 170
168 168
166 166
164 164
0 100 200 300 400 500 600 700 0 100 200 300 400 500 600 700
Station (m) Station (m)

6. 1962 Dredging
Final Result = +30.5 cms conveyance
change in the St. Clair River.

7. Bathymetric Changes since 1971
1971
St Clair Plan: 1) Reach1 10/19/2008
River = St. Clair River Reach = Main Channel RS = 147
. .0365 .
180 0 0 Legend
4 4
3 3
175 2 2 WS Max WS
170
Ground
Bank Sta
2007 (1971 Resolution)
Elevation (m)
165 St Clair Plan: 1) Reach1 10/19/2008
River = St. Clair River Reach = Main Channel RS = 147
160
.0432 .0365 .
180 0 Legend
155 4
3
150 175 2 WS Max WS
0 100 200 300 400 500 600 700
Ground
Station (m)
170
Bank Sta
Elevation (m)
2007 165
St Clair Plan: 1) Reach1 10/19/2008
River = St. Clair River Reach = Main Channel RS = 147
160
.0432 .0365 .
180 0 Legend 155
4
3
175 2 WS Max WS
Ground 150
170
0 100 200 300 400 500 600 700
Bank Sta
Elevation (m)
Station (m)
165
160
155
150
0 100 200 300 400 500 600 700
Station (m)

8. Bathymetric Changes since 1971
Final Result = +218 cms conveyance
change in the St. Clair River.
Flows: 1971 = 5526 cms;
2007 = 6110 cms;
2007 (res1971) = 5744 cms

9. Conclusions
• Dredging in 1962 has caused an increase
in conveyance of only 30.5 cms.
• Bathymetric changes since 1971 have
caused an increase in conveyance of 218
cms.
• During the study period of the current
project (1962 – present), bathymetric
changes have caused a greater increase
in conveyance than dredging.

10. Next Questions?
• Where does dredging impact conveyance
the most?
• What and where are the bathymetric
changes and how did they come about?

11. 1962 Dredging
• Using the 2007 RAS MC1
model, one reach
was replaced at a MC2 ES
time with the same
reach with dredged MC3
areas filled in.
MC4
EF
MC5

12. 1962 Dredging
Percent of Total /
Reach Flow Change (cms) Percent of Volume
MC1 1.3 0.17
MC2 8.0 2.55
MC3 13.2 1.31
MC4 2.4 1.28
MC5 10.6 1.57
* Total change in conveyance = 30.5 cms.

13. 1962 Dredging
MC1 MC3
MC2 MC4/MC5

14. Bathymetric Changes since 1971
• Using 1971 bathymetry, one reach was
replaced at a time with the same reach
from the 2007 bathymetry (1971
resolution).

15. Bathymetric Changes since 1971
Percent of Total /
Reach Flow Change (cms) Percent of Length
MC1 107.54 1.99
MC2 35.18 1.62
ES 3.56 0.17
MC3 55.25 0.81
MC4 6.06 0.46
EF -5.11 -0.39
MC5 8.46 0.32
* Total change in conveyance = 218 cms.

16. Bathymetric Changes since 1971
• Next Question:
– Can we define the location to be more exact?
• Yes: Reaches 1 and 2 (x-sections 147 –
102) were chosen and split into sub-
reaches of 3 to 4 measured cross-sections
each.

17. Bathymetric Changes since 1971
Main Channel 1 Main Channel 2
X-Sections Flow Change X-Sections Flow Change
147 – 145 0.27 119 – 117 -5.42
144 – 142 -0.52 116 – 114 1.26
141 – 139 22.60 113 – 111 8.63
138 – 136 51.15 110 – 108 9.99
135 – 133 -1.85 107 – 105 3.88
132 – 130 32.34 104 – 102 12.23
129 – 127 15.33 * Total change = 35.18 cms
126 – 124 14.87
123 – 120 -7.82
* Total change = 107.54 cms

18. Bathymetric Changes since 1971
St Clair Plan: 1) Reach1 10/19/2008
• Main Channel 2:
River = St. Clair River Reach = Main Ch-2 RS = 110
. .0239 .
178 0 0 Legend
2 2
6 6
176 4 WS Max WS
Changes in
4
174 Ground
Bank Sta
Elevation (m)
1971 172
Conveyance 170
168
seem to be due
166
164
0 100 200 300 400 500 600
to uncertainties
Station (m)
with altering the
St Clair Plan: 1) Reach1 10/19/2008
River = St. Clair River Reach = Main Ch-2 RS = 110
. .0239 .
178 0 0 Legend
2 2
2007 resolution.
176 6 6
4 4 WS Max WS
174 Ground
2007 Elevation (m)
172 Bank Sta
170
168
166
164
162
0 100 200 300 400 500 600
Station (m)

19. Bathymetric Changes since 1971
• Final Question: Which are the exact
cross-sections that are experiencing the
greatest bathymetric changes and why?
• To answer this question, we will examine
each measured cross-section between
141 and 136 to determine the exact
location where bathymetric changes have
been the most extreme.

20. Bathymetric Changes since 1971
141 - 139 138 - 136
X-Section Flow Change X-Section Flow Change
141 -3.46 138 15.12
140.05 5.33 137 43.44
140 2.85 136 1.26
* Total change = 51.15 cms
139.95 2.67
139.9 12.14
139 4.97
* Total change = 22.60 cms

21. Cross-Section #138
1971 2007
1971 2007
139.9
138

22. Final Results
• Full-scale:
– Dredging: change = 30.5 cms
– Bathymetric: change = 218 cms
• Local:
– Dredging: Main Channel 2 (MC1 was least)
– Bathymetric: Cross-section # 139.9 - 137

23. Discussion (1)
• In terms of any analysis concerned with the
dredging of 1962, the focus should be moved to
Main Channel 2 (west of Stag Island).
• In terms of other bathymetric changes since
1971, the area downstream of Blue Water
Bridge shows the greatest change (X-Sections
139.9 – 137)
• Downstream of the Blue Water Bridge is the
sand tongue identified by the Sediment TWG,
which may be the culprit.

24. Discussion (2)
• This sand tongue is thought to have been
created by large ships speeding up and
beginning their turn when under the Blue
Water Bridge. The large propellers may
stir up sediment in this area which is
deposited slightly downstream.
• Where is the sediment coming from if the
bottom of the main channel is armored, as
observed in videos and pictures taken by
the Sediment TWG?

25. Hypothesis
• There is increased
deposition in the ineffective
flow area during storms.
Ships speeding up and Ineffective
turning in this area may mix Ships Flow Area
the loose sediment
horizontally, causing it to be #137
washed downstream.
Effects would be greatest
immediately after a storm
event.