Assessment of Floodplain Vulnerability during Extreme Mississippi River Flood 2011 Allison E. Goodwell, † Zhenduo Zhu, † Debsunder Dutta, † Jonathan A. Greenberg, ‡ Praveen Kumar, †, * Marcelo H. Garcia, † Bruce L. Rhoads, ‡ Robert R. Holmes, § Gary Parker, † David P. Berretta, ∥ and Robert B. Jacobson ⊥ † Department of Civil and Environmental Engineering, University of Illinois at Urbana−Champaign, 205 North Mathews Avenue, Urbana, Illinois 61801-2352, ‡ Department of Geography, University of Illinois at Urbana−Champaign, 605 East Springfield Avenue Champaign, Illinois 61820, United States § U.S. Geological Survey, Office of Surface Water, ∥ U.S. Army Corps of Engineers, Memphis District, and ⊥ U.S. Geological Survey CERC, Columbia, Missouri 65201-9634, United States * S Supporting Information ABSTRACT: Regional change in the variability and magnitude of flooding could be a major consequence of future global climate change. Extreme floods have the capacity to rapidly transform landscapes and expose landscape vulnerabilities through highly variable spatial patterns of inundation, erosion, and deposition. We use the historic activation of the Birds Point-New Madrid Floodway during the Mississippi and Ohio River Flooding of 2011 as a scientifically unique stress experiment to analyze indicators of floodplain vulnerability. We use pre- and postflood airborne Light Detection and Ranging data sets to locate erosional and depositional hotspots over the 540 km 2 agricultural Floodway. While riparian vegetation between the river and the main levee breach likely prevented widespread deposition, localized scour and deposition occurred near the levee breaches. Eroded gullies nearly 1 km in length were observed at a low ridge of a relict meander scar of the Mississippi River. Our flow modeling and spatial mapping analysis attributes this vulnerability to a combination of erodible soils, flow acceleration associated with legacy fluvial landforms, and a lack of woody vegetation to anchor soil and enhance flow resistance. Results from this study could guide future mitigation and adaptation measures in cases of extreme flooding. ■ INTRODUCTION Extreme floods can transform landscapes, impact lives, and cause loss of property and livelihood. Because predicted changes in precipitation and climate patterns could affect regional flood frequency, 1 it is imperative that we develop appropriate flood mitigation and adaptation measures. 2 Recent studies have called for the urgent development of strategies for disaster resilience 3,4 and the need to assess landscape vulnerability. 5 Large floods, such as the extreme Mississippi and Ohio River Floods of Spring 2011, 6 create highly variable spatial patterns of erosion and deposition. 7,8 These localized areas, or “hotspots”, of change expose underlying landscape vulnerabilities and provide opportunities to retrospectively assess their causes in order to guide future actions. We treat this modern historical flood as a scientifically unique field-scale stress test, 9 and analyze the indicating factors of hotspots of floodplain vulnerability to erosion and deposition. Erosion and deposition associated with overbank flow, lateral migration, and avulsive cutoffs shape the floodplains and control soil properties along large meandering rivers such as the Lower Mississippi. In this region, these processes over time allow for the development of a highly productive agricultural landscape. To protect these valuable lands from flooding, humans have built levees that hydrologically disconnect them from the river. To manage extreme floods, that threaten nearby communities or the structural integrity of the levees, the modern arsenal of flood-control techniques includes intentional levee breaches or spillway activations in optimal locations. 10,11 One such location is the Birds Point New Madrid (BPNM) Floodway, an agricultural region located west of the Mississippi River just south of its confluence with the Ohio River, near the city of Cairo, Illinois (Figure 1a,b). Current policy which was established following the disastrous 1927 Flood permits levees surrounding the BPNM Floodway to be intentionally breached during extreme floods to prevent upstream and downstream Received: October 25, 2013 Revised: February 4, 2014 Accepted: February 10, 2014 Article pubs.acs.org/est © XXXX American Chemical Society A dx.doi.org/10.1021/es404760t | Environ. Sci. Technol. XXXX, XXX, XXX−XXX