Levee Fragility Curves and Safe Storage
8/2/2019 Fragility Curves
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Levee Fragility Curves and
Safe Storage
8/2/2019 Fragility Curves
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Safe Storage
Relates to the concept of leveeremoval for FEMA mapping.
Safe storage has been consideredon several projects including arecent FLO-2D model FIS Study
approved by FEMA.
Safe storage concept can be linked
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Safe Storage Concept
Even the levees in the poorest
condition will store some water
before failure initiates.
Safe storage may only extend 1 or
2 ft above the toe of the levee butconstitutes a large volume of water.
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Levee Safe Storage
Safe Storage = ?
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Safe Storage Issues
• For the Sacramento River Basin, this volumeof storage would significantly reduceddownstream flood volumes and peak
discharges (floodwave attenuation).
• When safe storage elevation isexceeded…levee removal vs. leave breach?
For what reach length?
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Levee Fragility Curves
Fragility represents a link between a
geotechnical risk model and predicted watersurface elevations with a flood model.
Implicitly defines levee failure risk for hazardmapping.
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Background
• Levee core and shell materials varysignificantly especially in older levees
• Levees often failure before overtoppingdue to piping
• Breach expands to complete failure while
flood waters are still rising
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orpsDevelope
FragilityCurves on
theSacrament
River
Method:
1. Select curve
2. Select likely failurepoint
3. Determine distanc
below crest
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Levee Geotechnical Investigation
• Core and shell material
Percent fines vs. local spoil material
• Construction methodsCompaction vs. spoils
• Foundation condition
Sand boils
Field inspection, in-situ borings, lab testing
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Fragility Curve Data
FS1 0.03 6.0 FS1 0.15 3.5
FS1 0.50 2.5 FS1 0.85 1.0 FS1 0.95 0.0 FS2 0.03 9.0
FS2 0.15 5.5 FS2 0.50 4.0 FS2 0.85 2.0 FS2 0.98 0.0
Curve ID LFP Dist. Below Crest
Create Fragility Curves Data in BREACH.DAT
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Assign Levee Fragility Failure Dat
C FS3 0.5
P 3450 FS1 0.5P 3558 FS1 0.9P 3559 FS2 0.7
P 3669 FS3 0.5P 3670 FS4 0.5P 3782 FC1 0.3P 3783 FS1 0.5
GLOBAL DATA
INDIVIDUALLEVEEELEMENTDATA
Assign Levee Element, Select Curve ID, and LFP in LEVEE.DA
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Results
• FLO-2D finds the breach based on thehydraulics and the weak levees
• Breach can occur anywhere at any time• FLO-2D initiates piping based on water
surface and prescribed duration
• Pipe expands to channel breach tocollapse to complete failure
B fi f FLO D F ili C
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Benefits of FLO-2D Fragility Curve
• Combines geotechnical characteristics
with flood routing hydraulics for a spatialassessment of levee failure and floodwaveattenuation
• Identifies flood risk as a function of leveefailure
•Different levee LPF will results in differentareas of flooding
Fragility Curve Simulation
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