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

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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.

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

  1. 1. 1-D HEC-RAS HydraulicModel of the St. Clair River Detroit, MI October 21, 2008
  2. 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. 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. 4. 1962 Dregding• Locations of 1962 dredging provided by the Army Corps of Engineers, Detroit District.
  5. 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. 6. 1962 DredgingFinal Result = +30.5 cms conveyance change in the St. Clair River.
  7. 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 StaElevation (m) Station (m) 165 160 155 150 0 100 200 300 400 500 600 700 Station (m)
  8. 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. 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. 10. Next Questions?• Where does dredging impact conveyance the most?• What and where are the bathymetric changes and how did they come about?
  11. 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. 12. 1962 Dredging Percent of Total /Reach Flow Change (cms) Percent of VolumeMC1 1.3 0.17MC2 8.0 2.55MC3 13.2 1.31MC4 2.4 1.28MC5 10.6 1.57* Total change in conveyance = 30.5 cms.
  13. 13. 1962 DredgingMC1 MC3 MC2 MC4/MC5
  14. 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. 15. Bathymetric Changes since 1971 Percent of Total /Reach Flow Change (cms) Percent of LengthMC1 107.54 1.99MC2 35.18 1.62ES 3.56 0.17MC3 55.25 0.81MC4 6.06 0.46EF -5.11 -0.39MC5 8.46 0.32* Total change in conveyance = 218 cms.
  16. 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. 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. 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. 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. 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. 21. Cross-Section #138 1971 2007 1971 2007139.9 138
  22. 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. 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. 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. 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.

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