This project will test the hypothesis that measured increases in flood levels on the Lower Mississippi River are linked to progressive increases in levee heights and extent along the river. In order to test this hypothesis, we will develop a geodatabase of levee emplacement and growth during the past 100-125 years along the Lower Mississippi River, empirically test the correlation between observed levee expansion and increases in flood levels, and compare the results of this empirical model with 1-D and 2-D hydraulic modeling results. Archival levee maps and surveys will be compiled, digitized, all horizontal and vertical coordinates registered to a common datum, and used to parameterize increases in levee extent and heights through the study region over various spatial and temporal sampling windows. These metrics of levee growth will be tested for significant correlations with increases in flood levels over time quantified by specific-gage analysis of a spectrum of overbank flow conditions. Finally, four targeted modeling reaches will be modeled using 1-D and 2-D simulations in order to test the causal links between levee expansion and the hydrological signature. This methodology is designed as an analysis of levee impacts that is: quantitative, empirical, and system-wide.
In spite of up to $1.1 billion annually spent on flood-control infrastructure, economic damages from floods in the U.S. have risen dramatically during the 20th century. A growing body of evidence suggests that a significant portion of this increase results from physical magnification of flooding driven by levee expansion and other river engineering activities. This project will provide a quantitative, empirical, and system-wide analysis of the impacts of levee construction upon flood response, focusing upon the Lower Mississippi River. The goal is to provide a practical tool for evaluating flood-control and floodplain projects. Specifically, this research should provide an empirical tool for quantifying the impact of each new increment of levee acreage or levee height on flood-stage response. At present, without such a system-scale, empirical tool, large increases in levee-protected acreage and levee heights are occurring, resulting in billions of dollars of infrastructure recently constructed or planned on U.S. floodplains.
