1-D HEC-RAS Hydraulic Model of the St. Clair River

Detroit, MI

October 21, 2008

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?

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.

1962 Dregding

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

1962 Dredging

• RAS cross-sections before and after dredging.

0 100 200 300 400 500 600 700164

166

168

170

172

174

176

178

St Clair Plan: Dredging 9/23/2008 River = St. Clair River Reach = Main Ch-2 RS = 104

Station (m)

Ele

vatio

n (m

)

Legend

WS Max WS

Ground

Bank Sta

.0264

.0239 .0264

0 100 200 300 400 500 600 700164

166

168

170

172

174

176

178

St Clair Plan: 1) Reach1 10/19/2008 River = St. Clair River Reach = Main Ch-2 RS = 104

Station (m)

Ele

vatio

n (m

)

Legend

WS Max WS

Ground

Bank Sta

.0264

.0239 .0264

1962 Dredging

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

Bathymetric Changes since 1971

0 100 200 300 400 500 600 700150

155

160

165

170

175

180

St Clair Plan: 1) Reach1 10/19/2008 River = St. Clair River Reach = Main Channel RS = 147

Station (m)

Ele

vatio

n (m

)

Legend

WS Max WS

Ground

Bank Sta

.0432

.0365 .0432

0 100 200 300 400 500 600 700150

155

160

165

170

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180

St Clair Plan: 1) Reach1 10/19/2008 River = St. Clair River Reach = Main Channel RS = 147

Station (m)

Ele

vatio

n (m

)

Legend

WS Max WS

Ground

Bank Sta

.0432 .0365 .0432

1971

2007

0 100 200 300 400 500 600 700150

155

160

165

170

175

180

St Clair Plan: 1) Reach1 10/19/2008 River = St. Clair River Reach = Main Channel RS = 147

Station (m)

Ele

vatio

n (m

)

Legend

WS Max WS

Ground

Bank Sta

.0432 .0365 .0432

2007 (1971 Resolution)

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

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.

Next Questions?

• Where does dredging impact conveyance the most?

• What and where are the bathymetric changes and how did they come about?

1962 Dredging

• Using the 2007 RAS model, one reach was replaced at a time with the same reach with dredged areas filled in.

MC1

MC3

ES

EF

MC5

MC2

MC4

1962 Dredging

Reach Flow Change (cms)

Percent of Total / 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.

1962 Dredging

MC1

MC2

MC3

MC4/MC5

Bathymetric Changes since 1971

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

Bathymetric Changes since 1971

Reach Flow Change (cms)

Percent of Total / 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.

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.

Bathymetric Changes since 1971

X-Sections Flow Change

147 – 145 0.27

144 – 142 -0.52

141 – 139 22.60

138 – 136 51.15

135 – 133 -1.85

132 – 130 32.34

129 – 127 15.33

126 – 124 14.87

123 – 120 -7.82

X-Sections Flow Change

119 – 117 -5.42

116 – 114 1.26

113 – 111 8.63

110 – 108 9.99

107 – 105 3.88

104 – 102 12.23

Main Channel 1 Main Channel 2

* Total change = 107.54 cms

* Total change = 35.18 cms

Bathymetric Changes since 1971

• Main Channel 2: Changes in Conveyance seem to be due to uncertainties with altering the 2007 resolution.

0 100 200 300 400 500 600162

164

166

168

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172

174

176

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St Clair Plan: 1) Reach1 10/19/2008 River = St. Clair River Reach = Main Ch-2 RS = 110

Station (m)

Ele

vatio

n (m

)

Legend

WS Max WS

Ground

Bank Sta

.0264

.0239 .0264

0 100 200 300 400 500 600164

166

168

170

172

174

176

178

St Clair Plan: 1) Reach1 10/19/2008 River = St. Clair River Reach = Main Ch-2 RS = 110

Station (m)

Ele

vatio

n (m

)

Legend

WS Max WS

Ground

Bank Sta

.0264

.0239 .0264

1971

2007

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.

Bathymetric Changes since 1971

X-Section Flow Change

141 -3.46

140.05 5.33

140 2.85

139.95 2.67

139.9 12.14

139 4.97

* Total change = 22.60 cms

X-Section Flow Change

138 15.12

137 43.44

136 1.26

* Total change = 51.15 cms

141 - 139 138 - 136

Cross-Section #138

1971 2007

139.9

138

1971 2007

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

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.

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?

Hypothesis

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

#137

IneffectiveFlow AreaShips