50-Year Flood in the Lower Illinois River: Sensitivity of Spillway and Levee Failure Option Parameters in the UNET Model

Abstract

The one-dimensional unsteady-state hydraulic model (UNET) was developed by the U.S. Army Corps of Engineers and has been used for flood protection in some large rivers. In its use for the real-time management of levee and drainage districts for flood protection, such as on the Mississippi River Basin, the required number of simulations for combinations of scenarios would present a great challenge for modelers to provide data for operational-mode decision making. The goal of this paper is to identify the most sensitive parameters for the spillway, simple levee failure, and complicated levee failure options in UNET so that simulations for real-time operation can focus on the most sensitive parameters without sacrificing much modeling accuracy. The sensitivity analysis was performed for the 50-year frequency flood in the lower Illinois River during which the Thompson Lake Levee and Drainage District or the Emiquon Area were used as temporary flood storage by using a state-of-the-art variance-based sensitivity analysis method—extended Fourier amplitude sensitivity test (FAST). The first-order and total-effect sensitivity indexes computed from the FAST method were used to evaluate the affect of the parameters to flood-peak reduction. As a result, the least and most sensitive variables for the spillway, simple levee failure, and complicated levee failure options in UNET were identified, and this knowledge helps significantly reduce the number of simulations for management scenarios by focusing on only the most sensitive parameters.