Numerical Modeling Analysis of the Katrina Cut Rubble Mound

Numerical Modeling Analysis of the Katrina Cut
Rubble Mound Structure
Gordon Thomson, PE, D.CE
Samantha Danchuk, PE, Ph.D.
Chris Day, PE
Mark Saunders, PE
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Outline
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Project Location
History of Breaching
Katrina Cut
Emergency Structure
Risk Assessment and Modeling
– Calibration
– Inputs
– Results
 Summary
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Project Location
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Project Location
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Project Location
Mobile
Bay
Mississippi Sound
Dauphin Island
Katrina Cut
Pelican
Island
Petit
Bois
Island
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History of Dauphin Island Breaching
1917
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History of Dauphin Island Breaching
1925
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History of Dauphin Island Breaching
1940
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History of Dauphin Island Breaching
February 1992
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History of Dauphin Island Breaching
March 2000
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History of Dauphin Island Breaching
May 2005
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History of Dauphin Island Breaching
June 2006
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History of Dauphin Island Breaching
February 2008
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History of Dauphin Island Breaching
May 2010
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History of Dauphin Island Breaching
September 2011
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Katrina Cut
Hurricane Ivan
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Katrina Cut
7.5 feet deep
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Katrina Cut
Katrina Cut
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Katrina Cut
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Emergency Barrier
 Emergency barrier constructed during Deepwater
Horizon Spill to limit oil flowing into Mississippi Sound
 Designed and constructed by Thompson Engineering
under an emergency permit
 Rubblemound with sand core
ALDOT Class 5 riprap
D=2.75 feet, 130pcf
Grade “A” riprap
D=1.6 feet, 130pcf
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Emergency Barrier
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Emergency Barrier
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Risk Assessment
 State has requested to leave the structure in place
 Goal of risk assessment is to provide information to
permitting agencies
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Risk Assessment
 Life Cycle Based Analysis
– Quantify risks associated with structure
• Breaching
• Sediment transport
• Impact to private property, navigation, SAV, pipelines
– Compare with and without structure condition
over a 50 year period
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Model Input
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Model Input
 50 year simulations
 Repeated historic storm record in sequence
– 1917 to 1967
– 1960 to 2010
 Average conditions based on 20 year WIS record
– Non-storm waves were broken into 12 bins
 Performed using two sea level rise scenarios
– USACE guidance for low and high SLR
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Model Input
 Morfac and storm history for 1917 to 1967
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Model Calibration
 Calibrated for storm response and long-term
volumetric change
– Repeated Katrina breach
– 20 year calibration run
 Model verification using Hurricane Ivan and
Hurricane Isaac
– Shoreline and volume changes
– Breach width
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Model Calibration
2005 LIDAR Survey
Delft3D Model Prediction
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Model Calibration
20-year Calibration Run
1991 to 2010 Volumetric Change
Yellow dots are observed changes
Dotted lines are DELFT3D results
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Model Results: With Structure
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Model Results: With Structure
 Structure promotes
longshore transport
initially
 Breach forms in low lying
area adjacent to structure
 Structure is flanked, cross
shore transport
dominates
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Model Results: With Structure
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Model Results : With Structure
Eastern end of the
dike structure
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Model Results: Without Structure
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Model Results: Without Structure
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Model Results
Number of Parcels
Private Property (Land) Loss
Note – Most likely scenario
(more storms,
low / observed sea level rise)
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Model Results
Hurricane Isaac
Feet
0.5
0.3
0.2
0
-0.2
-0.3
-0.5
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Model Results
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Model Results
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Summary
 Method for 50 year life cycle analysis
– Historic storm record
– Longer calibration period
 Specific findings
– No breaching along developed section until a major storm event in year 20
– No difference in breaching potential along inhabited area between the
with and without structure scenario
– Breaching expected adjacent to structure during next major storm
– Loss of property indistinguishable between with and without structure
(within expected model accuracy)
– Future land loss expected regardless of presence of structure
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Contact
Gordon Thomson, P.E. D.CE
Director
Gordon.Thomson@cbi.com
(561) 361-3147
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