Managing residual flood risk behind levees: Comparing USA, France, and Quebec (Canada)

Abstract

Although hydraulic infrastructure such as levees remain important for flood risk management in the USA, France, and Quebec (Canada), there is increasing emphasis on nonstructural measures, such as regulatory flood maps, to reduce exposure and vulnerability, for example, preventing people from building in high hazard areas. One key concept related to areas protected by levees is that of “residual risk”, that is, the risk from floods greater than the design standard of the levees (levee overtopping) and from levee breach. In this article, we review the legislative framework for regulatory flood maps in the USA, France, and Quebec (Canada) and compare how residual risk behind protective structures is taken into account (or not) in regulatory flood maps. We find big differences in how the USA, France and Canada manage residual risk behind the levees. While in France the area behind levees is part of the regulatory flood prone area, and land use restrictions, building codes, emergency measures and risk communication are mandatory, in the USA the area behind levees is only shown as part of the regulatory flood prone area if the levee is not accredited. In Quebec, regulatory flood maps in general follow the French approach with a few exceptions.

Managing rising residual flood risk: A national survey of Aotearoa‐New Zealand

“…This has led to continuous development in the floodplains and significantly increased flood risk profile nationwide in A‐NZ over time (Ministry for the Environment, 2008) and manifested in the recent floods experienced in Auckland. These pressures present challenges to how we manage and plan for present and future flood risks (Scott et al, 2013; Tullos, 2018), especially for the often unseen and lower profile residual flood risk—that is, the risk that remains after the implementation of risk treatment actions (Serra‐Llobet et al, 2022).…”

“…This is problematic because protective structures tend to offer a false sense of security, further encouraging floodplain development (White et al, 2001). Structural protection measures have adaptation limits (i.e., no absolute protection; Berkhout & Dow, 2023; Serra‐Llobet et al, 2022), which means they can fail through overtopping or breaches during extreme flood events. More investment is needed to upgrading the existing levees with outdated design standards, building new protective structures (giving more room for rivers and streams), or undertake managed retreat to keep up with increasingly more frequent and intense floods due to urban development and climate change (Collins, 2021; Lawrence et al, 2013).…”

“…With regard to flood risk however, it has taken on increasing importance as flood risk management moved away from the conventional river engineering view of hazard control to a more holistic understanding of the concept of risk (Bubeck et al, 2017; Serra‐Llobet et al, 2022). This includes, inter alia, the consideration of residual risk behind the protective measures (Serra‐Llobet et al, 2022), resilient spatial planning approaches (White et al, 2010), or the implementation of concepts, such as creating more room for rivers (Dottori et al, 2020; Rijke et al, 2012). Yet, literature specifically on residual risk as a component of effective flood risk management remains scarce (Wagner et al, 2021).…”

“…Yet, literature specifically on residual risk as a component of effective flood risk management remains scarce (Wagner et al, 2021). In a recent comparative study between the United States, France, and Quebec (Canada), Serra‐Llobet et al (2022) found significant variability in how residual flood risk is managed. For example, in the US residual flood risk is depicted in the national regulatory Flood Insurance Rate Maps (FIRMs) under the National Flood Insurance Program (NFIP).…”

“…It is therefore imperative to understand how and to what extent the country's flood risk management practices considers, analyses, and treats residual flood risk and how this is understood, communicated, and utilized in land‐use planning decisions. Importantly, if the country's present flood risk governance does not understand and act on residual flood risk, insurance penetration may reduce, posing difficult decisions for risk managers, land‐use planners, and ultimately the community in managing pre‐existing or new development (Serra‐Llobet et al, 2022). To fill this gap in research, this article aims to draw on practitioners' knowledge from A‐NZ through a national survey to understand how present and future residual flood risk is evaluated and managed across the country.…”