Fragility Curve Plugin

The Fragility Curve Plugin allows the user to define fragility curves (sometimes called system performance curves) and randomly sample failure elevations for use in a HEC-WAT Flood Risk Analysis (FRA) compute. A fragility curve represents the probability of a hydraulic structure, such as a dam or levee, breaching when the stream-side water surface reaches a certain elevation.  Typically, multiple fragility curves are defined for a structure, depending on the failure mode, such as over topping or piping.  During the HEC-WAT FRA compute, the Fragility Curve plugin chooses a failure mode (based on relative probability) and failure elevation from the fragility curve for that failure mode.  This sample failure elevation is passed as a data location in HEC-WAT that can be linked to the subsequent models in the simulation, such as HEC-RAS and HEC-ResSim.  The structure and the sampled elevation may have different meanings depending on the configuration of this model, most often applied to the HEC-RAS as a levee or dam breach elevation, where the river-side of a levee, or upstream side must exceed the elevation for the structure to breach.  Other models, such as HEC-ResSim require additional user-defined behavior to properly model the system's response when the failure elevation is exceeded.  Fragility curves and the resulting elevation can be resampled for every event, or once every realization, depending if the failure mode should be represented as natural variability or knowledge uncertainty.  Fragility curves may also include a loading duration, and sample from multiple failure modes for each structure.

Fragility Curves

A fragility curve could be used by a dam or a levee depending on the consuming model.  HEC-RAS models can use the output of the fragility curve at inline structures (usually dams) or lateral structures (usually levees).  HEC-ResSim can ingest the failure elevation as a scalar Global Variable but the user must set up logic to handle the resulting system behavior correctly.