Multistate Overflow Fragility Models for Homogenous Inland Levees with Noncohesive Sediments

Abstract

Existing efforts for analyzing the overflow fragility of inland levees have focused primarily on breach and incorporated simplified definitions of breach for that purpose. The intermediate events that are precursors of a breach have not been analyzed, and several key performance measures including the duration of overflow, discharge rate, and time to the intermediate and breach events, which can inform decisions on evacuation and recovery planning, have not been investigated. This study, for the first time, provides a set of two-dimensional fragility models with an initial water level before surge and peak surge elevation as intensity measures. Fragility models are developed for the class of homogenous levees with noncohesive sediments. Breach formation is modeled through the Dam/Levee Breach model, and failure probabilities are derived using Monte Carlo Simulation (MCS). Unlike existing fragility models, the new class of fragility models accurately represents key performance failure events in levees including initiation of a breach, local geotechnical instabilities, and breach development. These models can be used in risk analysis frameworks to probabilistically account for local geotechnical failures and breach scenarios. Furthermore, probabilistic models for the time of peak discharge rate, breach peak outflow, and volume of water outflow are developed based on stochastic simulations of the flood performance of levees. A power model is investigated for representing breach peak outflow and is compared with previous deterministic models. The proposed model for breach peak outflow can be integrated with hydraulic inundation modeling to probabilistically estimate the inundated area downstream of levees.