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 Levee Fragility Curves and 

Safe Storage 

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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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