Parametric study of levee saturation for undrained rapid drawdown analysis

Abstract

As infrastructure continues to age and natural disasters highlight weaknesses in this infrastructure, there has been an increased focus to analyze levees for rapid drawdown (RDD) failure; however, practitioners are lacking the guidance to do so. Geotechnical engineers have typically used multistage undrained methods to analysis the RDD condition in dams. In order to analyze the RDD condition for a levee with multistage undrained methods, the likely saturated zone within the levee must be determined, followed by the shear strength for both the saturated and unsaturated zones. The saturated zone can be estimated using transient seepage analysis. However, as there are more than 100,000 miles of levees in the United States alone, it is impractical to perform transient seepage analyses for multiple flood scenarios along every levee reach. Taking into account the considerable extent of levee reaches and the variance in material properties, levee geometry, and flood scenarios that may be experienced, it would be beneficial to have a quick and simple method to determine the approximate extent of the saturated zone within a levee at the end of a flood (i.e., the start of drawdown). In support of this broader goal, a chart-based method is presented that can be used to quickly estimate the saturated zone in a levee following a flood based on the soil properties, flood hydrograph, and levee geometry. This saturated zone can then be used as a starting point for undrained RDD analysis.