Managing New Orleans flood risk in an uncertain future using non-structural risk mitigation

Over four years after Hurricane Katrina devastated the Gulf Coast, the long-term future of the City of New Orleans remains uncertain. This dissertation addresses one of New Orleans' most critical challenges: how to make the city more resilient and less vulnerable to future flood damages. Despite recent upgrades to the protection system surrounding the city designed to protect against floods with a 1-in-100 (1%) annual chance of occurrence, New Orleans remains vulnerable to lower-frequency, high-damage events. In addition, uncertain factors that influence flood risk, including coastal land loss and subsidence, rising sea levels, and population recovery and growth, may lead to increasing risk over time. Current proposals for risk reduction in New Orleans and South Louisiana, however, have not fully accounted for these key uncertain drivers.Analysis results reveal that flood risk estimates vary considerably by scenario and across different locations within the city. Non-structural risk mitigation strategies appear to provide cost-effective risk reduction in high-risk neighborhoods and help to hedge against futures in which damages from 1% annual recurrence (or more frequent) events are greater than expected. However, substantial residual risk remains from lower frequency (1-in-400 or 1-in-1,000 annual chance) events even with large investments in non-structural risk mitigation. Scenarios that yield excessive residual damage typically include high rates of coastal land loss outside of the protection system and levees that degrade over time, suggesting that wetlands restoration and continued investments in structural protection remain critical to successful New Orleans flood risk management.Rather than focus on additional large-scale structural infrastructure investments, this dissertation considers proposals to augment the existing protection system with "non-structural" risk mitigation programs. Non-structural risk mitigation includes incentives for elevating existing or new structures, revised building codes, incentives for relocation to lower risk areas, and land use restrictions designed to curtail future growth in the floodplain. This research estimates the risk reduction benefits and implementation costs of non-structural risk mitigation strategies focused on single-family homes in New Orleans. I draw from existing risk models to develop a low-resolution scenario generator, NOLArisk, designed to produce first-order estimates of property risk from 2011-2060 across a range of uncertain future scenarios. I then apply exploratory modeling and Robust Decision Making (RDM) methods to (a) suggest strategies that balance risk reduction and implementation costs across many or most plausible futures, and (b) identify scenarios in which current alternatives yield negative net economic benefits or excessive levels of residual risk.