Levee and Dam Breach Modeling

1
Levee and Dam Breach Modeling
2
Two Levee Failure Tools

• Simple failure by overtopping or by prescribed
  elevation and duration
• Specify vertical and horizontal failure rates
• Simulate Levee Erosion Piping, overtopping,
  breach channel or collapse

3
Simplified Levee Failure
Levee failure width
Levee crest elevation
Vertical failure rate
Horizontal failure rate
Levee failure base elevation
Floodplain elevation
4
Breach Erosion Component

• NWS Breach Program Code Embedded in the FLO-2D
  model (Fread, 1988)
• Both Piping and Overtopping Breach Failures
• Failure with Impervious Core
• Considers Potential Channel Side Slope Collapse
  and Wedge Collapse

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Pipe Breach Failure
Pipe Expansion
ZD
Specify Pipe Elevation
1
ZU
Pipe Breach
TW Submergence
1
1
Pipe Outlet 1 ft gt Floodplain Elev.
Pipe Collapses into a Channel
6
Overtopping Breach Failure
Rectangular Channel Enlargement
Breach Expansion
Side Slope Slump
Weir Control
ZD
1
Channel Flow
Trapezoid Channel Enlargement
ZU
1
1
Breach Channel Erosion
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FLO-2D BREACH Model

• FLO-2D - flood routing and provides reservoir
  water surface and tailwater elevations
• BREACH computations FLO-2D timestep
• Modified the sediment transport capacity
  computations
• Adjusted the sediment distribution in breaches
• Implemented sediment conservation routines
• Bulks water flows automatically for the levee or
  dam sediment BF 1./(1. Cv)

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FLO-2D Breach Computation Sequence

• Piping Failure
• If upstream water surface gt pipe elevation
  piping initiates
• User specifies initial pipe elevation with outlet
  1 ft above downstream embankment toe
• With pipe enlargement or collapse channel
  breach flow occurs
• Channel breach flow discharge controlled by
  weir flow and hydraulics computed by open channel
  flow consider TW submergence
• Compute sediment transport capacity, distribute
  erosion to pipe or channel breach geometry
  widen breach

9
FLO-2D Breach Computation Sequence

• Overtopping Failure
• Overtopping discharge computed by FLO-2D
  initiates flow is channel breach
• Breach flow initiates and combines with
  overtopping discharge
• Channel breach flow discharge controlled by
  weir flow and hydraulics computed by open channel
  flow
• Split flow into crest slope and DS face slope
• Compute sediment transport capacity, distribute
  erosion to pipe or channel breach geometry
  widen breach
• Breach geometry transition to trapezoidal channel
  with side slope collapse
• Upstream face erosion

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Primary Breach Data Parameters

• Embankment geometry side slopes, crest width
  and length
• Pipe breach elevation and width/depth ratio
• D50 core, shell and riprap material
• Sediment parameters unit weight, porosity,
  cohesive strength
• n-values for shell and core
• Grass on downstream face

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Primary Breach Data Parameters

• Line 1 has the global dam or levee breach
  geometry data.
• 1 IBR G1, GZU, GZD, GZC, GCRESTWIDTH,
  GCRESTLENGTH, GBRBOTWIDMAX, GBRTOPWIDMAX,
  GBRBOTTOMEL, GWEIRCOEF
• Line 2 is the global impervious dam or levee
  core data.
• 2 IBR G2, GD50C, GPORC, GUWC, GCNC, GAFRC,
  GCOHC, GUNFCC
• Line 3 is the global dam or levee shell data.
• 3 IBR G3, GD50S, GPORS, GUWS, GCNS, GAFRS,
  GCOHS, GUNFCS
• Line 4 is the global breach ratio, dam or levee
  face grass parameters, maximum sediment
  concentration, riprap sediment mean size and
  gradation.
• 4 IBR G4, GBRATIO, GGRASSLENGTH, GGRASSCOND,
  GGRASSVMAXP, GSEDCONMAX, GD50DF, GUNFCDF,
  GBREACHTIME
• LINES 5 thru 10 ARE OPTIONAL DATA FOR
  INDIVIDUAL BREACH LOCATIONS
• REPEAT LINES 5 thru 10 FOR EACH SPECIFIED
  BREACH GRID ELEMENT
• Line 5 is the prescribed individual breach grid
  element and breach direction.
• 5 IBR B, IBREACHGRID, IBREACHDIR
• Line 6 has the prescribed individual breach dam
  or levee geometry data.

GLOBAL PARAMETERS
SPECIFIC GRID ELEMENT PARAMETERS
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Levee Breach Simulation

• River overflow to floodplain road embankment

Levee breach failure
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Levee Output

• LEVOVERTOP.OUT Levee overtopping discharge by
  direction.
• LEVEE OVERTOPPING DISCHARGE (CFS OR CMS)
  POSITIVE DISCHARGE REPRESENTS INFLOW TO NODE
• LEVEE ELEMENTS WITH NO OVERTOP DISCHARGE ARE
  NOT REPORTED
• DISCHARGE IS REPORTED BY DIRECTION
• GRID ELEMENT TIME TOTAL DISCHARGE
  N E S W
  NE SE SW NW
• 4036 15.30
  17.01 0.00 0.00 0.00
  0.00 0.00 0.00 17.01
  0.00
• 15.40
  5.11 0.00 0.00
  0.00 0.00 0.00 0.00
  5.11 0.00
• 15.50
  32.60 0.00 0.00
  0.00 0.00 0.00 0.00
  32.60 0.00
• 15.60
  122.73 0.00 0.00
  0.00 0.00 0.00 0.00
  122.73 0.00
• 15.70
  168.69 0.00 0.00
  0.00 0.00 0.00 0.00
  168.69 0.00
• 15.80
  1.49 0.00 0.00
  0.00 0.00 0.00 0.00
  1.49 0.00
• 16.00
  39.32 0.00 0.00
  0.00 0.00 0.00 0.00
  39.32 0.00
• 16.10
  206.82 0.00 0.00
  0.00 0.00 0.00 0.00
  206.82 0.00
• PEAK Q 17.62 2993.68
• 17.70
  48.15 0.00 0.00
  0.00 0.00 0.00 0.00
  48.15 0.00
• 17.80
  54.75 0.00 0.00
  0.00 0.00 0.00 0.00
  54.75 0.00
• 17.90
  69.32 0.00 0.00
  0.00 0.00 0.00 0.00
  69.32 0.00

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Levee Output

• LEVEE.OUT Levee failure data and discharge
  through the levee.
• LEVEE FAILURE DISCHARGE (POSITIVE Q IS FLOW OUT
  OF NODE)
• GRID ELEMENT FAILURE DIRECTION WS
  ELEV. FAILURE WIDTH DISCHARGE TIME
• 
  
  (M) (CMS)
  (HRS)
• THE LEVEE IN GRID ELEMENT 4957 IN
  DIRECTION 4 FAILED AT TIME 0.06 HOURS
  WS ELEV 330.02 CREST ELEV 329.99
• THE LEVEE IN GRID ELEMENT 6702 IN
  DIRECTION 1 FAILED AT TIME 0.07 HOURS
  WS ELEV 330.02 CREST ELEV 329.99
• THE LEVEE IN GRID ELEMENT 6702 IN
  DIRECTION 5 FAILED AT TIME 0.07 HOURS
  WS ELEV 330.02 CREST ELEV 329.99
• THE LEVEE IN GRID ELEMENT 6702 IN
  DIRECTION 8 FAILED AT TIME 0.07 HOURS
  WS ELEV 330.02 CREST ELEV 329.99
• 4957
  4 330.00
  2.39 2.08
  0.10
• 6702
  1 329.99
  2.32 1.37
  0.12
• 6702
  5 329.99
  2.32 1.37
  0.13
• 6702
  8 329.99
  2.32 1.37
  0.15
• THE LEVEE IN GRID ELEMENT 7353 IN
  DIRECTION 3 FAILED AT TIME 0.13 HOURS
  WS ELEV 330.02 CREST ELEV 329.99
• THE LEVEE IN GRID ELEMENT 7462 IN
  DIRECTION 7 FAILED AT TIME 0.13 HOURS
  WS ELEV 330.02 CREST ELEV 329.99
• THE LEVEE IN GRID ELEMENT 6919 IN
  DIRECTION 3 FAILED AT TIME 0.14 HOURS
  WS ELEV 330.02 CREST ELEV 329.99
• 4957 4
  330.01
  3.39 23.46 0.20
• 6702
  1 329.97
  3.32 19.98
  0.20

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Levee Output

• LEVDEFICIENCY.OUT - The levee freeboard deficit
  is listed in this file. Five levels of freeboard
  deficit are reported
• 0 freeboard gt 3 ft (0.9 m)
• 1 2 ft (0.6 m) lt freeboard lt 3 ft (0.9 m)
• 2 1 ft (0.3 m) lt freeboard lt 2 ft (0.6 m)
• 3 freeboard lt 1 ft (0.3 m)
• 4 levee is overtopped by flow.

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Levee Freeboard Deficiency
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Levee Issues

• Safe Storage Uncertified Levees
• Uncertified Levee Failure Reaches
• Multiple breach locations (how to find them)
• By water surface elevation and duration
• By water contact
• By depth below the crest
• Other
• Negotiate with FEMA

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Water Supply Reservoir Dam Break Model in Florida
Jim OBrien FLO-2D Software, Inc.
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DamBreak Estimated Area of Inundation
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Initial Attempts to Estimate Area of Inundation
using DamBreak
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FLO-2D Estimated Area of Inundation South
Breach
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Mapper Delineated North Breach
Area of Inundation
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More Results Time to 1 ft
Hours
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Mapper Delineated North Breach
Risk Hazard Mapping
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Next Levee fragility curves and safe storage.