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Levee Fragility Curves and Safe Storage

Safe Storage. Relates to the concept of levee removal for FEMA mapping. Safe storage has been considered on several projects including a recent FLO-2D model FIS Study approved by FEMA.Safe storage concept can be linked to fragility curves.. Safe Storage Concept. Even the levees in the poorest

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Levee Fragility Curves and Safe Storage

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    1. Levee Fragility Curves and Safe Storage

    2. Safe Storage Relates to the concept of levee removal for FEMA mapping. Safe storage has been considered on several projects including a recent FLO-2D model FIS Study approved by FEMA. Safe storage concept can be linked to fragility curves.

    3. 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 but constitutes a large volume of water.

    5. Safe Storage Issues For the Sacramento River Basin, this volume of storage would significantly reduced downstream flood volumes and peak discharges (floodwave attenuation). When safe storage elevation is exceeded…levee removal vs. leave breach? For what reach length?

    6. Levee Fragility Curves Fragility represents a link between a geotechnical risk model and predicted water surface elevations with a flood model. Implicitly defines levee failure risk for hazard mapping.

    7. Background Levee core and shell materials vary significantly especially in older levees Levees often failure before overtopping due to piping Breach expands to complete failure while flood waters are still rising

    8. Corps Developed Fragility Curves on the Sacramento River

    9. Levee Geotechnical Investigation Core and shell material Percent fines vs. local spoil material Construction methods Compaction vs. spoils Foundation condition Sand boils Field inspection, in-situ borings, lab testing

    10. Fragility Curve Data

    11. Assign Levee Fragility Failure Data

    12. Results FLO-2D finds the breach based on the hydraulics 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 to collapse to complete failure

    13. Benefits of FLO-2D Fragility Curves Combines geotechnical characteristics with flood routing hydraulics for a spatial assessment of levee failure and floodwave attenuation Identifies flood risk as a function of levee failure Different levee LPF will results in different areas of flooding

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