QUANTIFYING THE COSTS AND BENEFITS OF MANAGED RETREAT: INSIGHTS FROM VALMEYER’S GAINS AND GREATER OLIVE BRANCH’S LOSSES

Author

Rajee Tamrakar, Southern Illinois University CarbondaleFollow

Date of Award

8-1-2025

Degree Name

Master of Science

Department

Geography and Environmental Resources

First Advisor

Remo, Jonathan

Abstract

With climate change intensifying flood risk, managed retreat - the strategic relocation of communities away from high-risk areas has garnered increasing interest as a flood mitigation strategy. Since the “Great Flood of 1993,” full and partial managed retreat initiatives have been implemented along the upper Mississippi River and its major tributaries. This study contrasts two levee-protected communities in Illinois - Valmeyer, which successfully relocated after the 1993 Harrisonville Levee breach which inundated 90% of its buildings, and the Greater Olive Branch (GOB) area where repeated breaches of the Len Small Levee inundated ~50% of its buildings, leading to voluntary buyouts after the 2011 flood. This study employs a combination of hydrodynamic modeling, flood loss estimation, and benefit-cost analysis (BCA) for both historical and hypothetical levee breach scenarios to estimate potential flood losses and assess the cost-effectiveness of managed retreat strategies for Valmeyer and the Greater Omaha Basin (GOB). Flood depths generated through hydrodynamic simulations were used to estimate structure-level damages and calculate Expected Annual Damages (EADs), which served as the basis for BCA. The BCA produces benefit-cost ratios (BCRs), which were computed using actual and estimated relocation or buyout costs, with ratios ≥1.0 being considered cost-effective (benefits outweigh the cost of relocation). U.S. Census demographic and socioeconomic data were used to assess potential differences in baseline social vulnerability between the communities before the floods, and to assess the longitudinal changes of these indicators through time after the relocation and buyout programs were implemented. The flood loss modeling results show both communities experienced substantial damage under the assessed flood scenarios, with annual expected damages of up to $4.0 million in Valmeyer and $0.8 million in GOB. Valmeyer’s relocation was cost-effective under scenarios that produced flood depths and inundation extents similar to or greater than the 1993 levee breach, with BCRs ranging from 1.08 to 1.5. For assessed GOB flood scenarios, relocation was not found to be cost-effective, as many affected buildings were located on relatively higher ground within the floodplain, which limited flood damage. However, targeted buyouts across GOB for the most flood-prone buildings were found to be cost-effective with BCRs ranging from 1.23 to 3.24. Socioeconomic, political, and geographic indicators of social vulnerability revealed that before the floods, Valmeyer’s vulnerability indicators were relatively lower than GOB. In addition, Valmeyer had a greater adaptive capacity characterized by stronger governance, community cohesion, and geographic centralization. Conversely, GOB was more geographically dispersed and had no formal governance from a local municipal corporation like Valmeyer. The longitudinal assessment showed Valmeyer experienced a decline in its population initially after relocation, followed by substantial growth (more than doubling of the community’s population) between 2000 and 2010, with an influx of younger, more affluent external households. From 2010 to 2020, the community stabilized, maintaining gains in socioeconomic conditions and associated decreases in vulnerability indicators. GOB exhibited a slow decline in population and an increase in certain social vulnerability variables between 1990 and 2010, followed by a more rapid decline in population and further increases in vulnerability between 2010 and 2020. This population decline may be attributed, at least in part, to the voluntary buyouts undertaken after the 2011 flood. These findings suggest that the success of retreat and buyouts does not depend only on the magnitude of flood risk but also on the underlying social, economic, and institutional capacities of the community. This research provides a data-driven basis for evaluating managed retreat as both a post-disaster recovery strategy and a proactive flood adaptation measure that communities facing similar challenges can adopt to reduce future flood risk.