TITLE SLIDE OPTION 1 PRESENTATION TITLE HERE KEEP LEFT JUSTIFIED“The views, opinions and findings contained in this report are those of the authors(s) and should not be construed as an official Department of the Army position, policy or decision, unless so designated by other official documentation.”
Alex Nelson, P.E. Hydraulic Engineer, St. Paul District
SAME Meeting 25 April 2018
MODELING MISSISSIPPI RIVER DREDGING STRATEGIES AFTER THE LOCK CLOSURE AT UPPER ST. ANTHONY FALLS
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GOAL • With the closure of Upper St.
Anthony Falls in 2015 to reduce the spread of invasive carp, new channel management strategies have been considered due to reduced navigation in upper pools.
• This sediment modeling study is meant to inform dredging decisions in combination with other methods and information.
https://www.mprnews.org/story/2015/06/08/upper-st-anthony-lock#gallery
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SEDIMENT MODELING CAVEAT “Why would you want to study something as complicated as sediment transport?”
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- Albert Einstein to his son Hans Albert Einstein (paraphrased)
“Due to the physical complexities of sediment transport and large uncertainties in observations and empirical equations, sediment calibration may be successful within a factor of two.”
- Most sediment modelers, probably
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http://www.startribune.com/july-31-big-river-big-trouble-dredges-work-ot-to-open-mississippi-river/269919531/
BLUF • Alternative 1 (No dredging above USAF)
average change from 2008-2015 • Pool 2 +4% • Pool 3 +1% • Upper Pool 4 +6% • Total (USAF to LP) -15%
• Alternative 2 (No dredging above LD1) average change from 2008-2015 • Pool 2 +4% • Pool 3 +2% • Upper Pool 4 +8% • Total (USAF to LP) -24%
• However, reductions in overall dredging are almost lost by the end of a decade
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0
50
100
150
SAF Pool 1 Pool 2 Pool 3 Pool 4 (Upper)
Dr ed
ge d
Vo l.
(C Y)
Baseline Dredging Alt. 1 (USAF) Alt. 2 (LD1)
0
50
100
150
200
250
300
350
400
450
Dr ed
ge d
Vo l.
(C Y)
Baseline Dredging Alt. 1 (USAF) Alt. 2 (LD1)
BACKGROUND • Purpose: To model channel
maintenance alternatives for the reach above USAF to identify downstream maintenance impacts through Lake Pepin
• 1D Sediment Transport Model in HEC-RAS
• Capture dam operations and backwater flow splits
• Calibrate to measured dredging (2007-2015)
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Lake Pepin Pool 3
(USAF & LSAF) Lock & Dam No. 1, Minneapolis, MN
Lock & Dam No. 2, Hastings, MN
Lock & Dam No. 3, Red Wing, MN
BACKGROUND • Average number of lockages, 2013-2017
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https://www.bloomingtonmn.org/deals-packages/paradise-cruises-3-OFF-Any-Public-Cruise
https://mississippiriver.natgeotourism.com/content/lock-and-dam-no-1/mspf16be21f1d48ecab8
Dredging in Pool 3 and Upper Pool 4
HYDRAULIC VALIDATION • Calibrated to stage and flow at dams and control points
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No. 3
HYDRAULIC VALIDATION • Calibrated
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HYDRAULIC VALIDATION • Calibrated to measured flow splits in Pool 2 & 3
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HYDRAULIC VALIDATION • Calibrated to measured flow splits in Pool 2 & 3
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SEDIMENT 18
Minnesota River
St. Croix River
St. Croix River
St. Paul, MN
5: Sediment Quality and Characteristic Data • Flow-load relationships and suspended sediment gradations from USGS data
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higher than measured dredging
• Base condition model is not perfect at each location for each year, but is fairly representative of the system globally and annually
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OVERALL RESULTS 24
Uncertainty for new equilibrium timeframe
CONCLUSIONS • Temporary reductions in overall dredging quantities for both alternatives
• Halting dredging above USAF appears to approach a new equilibrium within a decade
• Halting dredging above LD1 shows trend of reaching new equilibrium beyond a decade
• Increased downstream dredging is minimal immediately after implementation, but dredging quantities downstream offset the upstream reductions over time
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CONCLUSIONS • Alternative 1 (No dredging above USAF)
average change from 2008-2015 • Pool 2 +4% • Pool 3 +1% • Upper Pool 4 +6% • Total (USAF to LP) -15%
• Alternative 2 (No dredging above LD1) average change from 2008-2015 • Pool 2 +4% • Pool 3 +2% • Upper Pool 4 +8% • Total (USAF to LP) -24%
• However, reductions in overall dredging are almost lost by the end of a decade
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0
50
100
150
SAF Pool 1 Pool 2 Pool 3 Pool 4 (Upper)
Dr ed
ge d
Vo l.
(C Y)
Baseline Dredging Alt. 1 (USAF) Alt. 2 (LD1)
0
50
100
150
200
250
300
350
400
450
Dr ed
ge d
Vo l.
(C Y)
Baseline Dredging Alt. 1 (USAF) Alt. 2 (LD1)
CONCLUSIONS • Alternative 1 (USAF)
• Projected to balance dredging quantities within a decade • By one to two decades, Pool 1 is expected to absorb all dredging offsets
• Alternative 2 (LD1) • Projected to balance dredging quantities in a little more than a decade • In the next forty years, Pool 2 is expected to absorb 95% of dredging offsets
(5% in Pool 3)
FUTURE • Model can be used as a
tool to investigate sediment deposition in Lake Pepin or to assess the disposition of Lock and Dam No. 1
• Future improvements with new HEC-RAS 5.0.4 Sediment could offer better calibration of the model and more stable model runs for longer record
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U.S. Army Corps of Engineers, St. Paul District
(651) 290-5789 TEL (651) 764-0465 CEL
alexander.g.nelson@usace.army.mil
U.S. Army Corps of Engineers St. Paul District (MVP) 180 5th St E, Suite 700 St. Paul, MN 55104
Modeling Mississippi River dredging strategies after the lock closure at Upper St. Anthony Falls
GOAL
OVERALL RESULTS