Baseline Risk Assessment for Herbert Hoover Dike

A risk assessment (RA) was conducted for 27 miles of Herbert Hoover Dike to better understand and estimate the Baseline failure risk. Unique aspects of this risk assessment included the following: high stillwater levels persisting for almost a year; highly dynamic and spatially variable wind loading; short-duration wind setup reduces likelihood of piping; dike length increases probability of failure; and multiple breaches with overlapping inundation areas that affect failure probability and consequences and risk evaluations.
A wide range of stillwater and wind loading combinations were considered. Following a potential failure modes analysis (PFMA), failure modes were included: piping through foundation, embankment piping, piping along conduits, piping along structures through embankment, embankment and flood wall instability, and overwash and overtopping. System response probabilities (SRPs) were estimated using toolboxes, analyses and expert judgment. Life-loss and economic consequences were estimated. RA calculations were performed using DAMRAE-HHD, which includes length effects. Uncertainties were explored using sensitivity analyses. Estimated risks were evaluated against the US Army Corps of Engineers (USACE) tolerable risk guidelines (TRG).