Highways in the River Environment — Floodplains, Extreme Events, Risk, and Resilience

This manual provides technical guidance and methods for assessing the vulnerability of transportation facilities to extreme events and climate change in riverine environments. The focus is quantifying exposure to extreme flood events considering climate change and other sources of nonstationarity. It is anticipated that there will be multiple uses for this guidance including risk and vulnerability assessments, planning activities, and design procedure development. The manual provides an overview of federal policies affecting floodplains and floodplain development including Federal Highway Administration (FHWA) and Federal Emergency Management Agency (FEMA) policies as they affect transportation. It also provides a description of extreme and other flood events and provides an overview of the rainfall/runoff and statistical models designers use for hydrologic design. The manual also discusses the uncertainty associated with hydrologic models. With a view toward future design, the manual explains the concept of nonstationarity and two important drivers for nonstationarity: climate change and land use/land cover changes. The manual introduces several tools for identifying and adjusting for trends in the historical record, as well as techniques for projecting floods. The manual provides an overview of climate modeling including descriptions of global climate models (GCMs), regional climate models (RCMs), statistical downscaling, and emissions scenarios. To provide guidance to planners and engineers who plan, design, and maintain the nation’s transportation infrastructure, the manual establishes a context based on the principles of risk and resilience. The manual describes the probabilistic nature of flood events and describes a larger assessment framework to provide cost-effective transportation assets. The manual provides an analysis framework and specific guidance for addressing nonstationarity, including climate change, based on five levels of analysis. The guidance recognizes that all plans and projects do not merit the same attention. Finally, the manual provides case studies to illustrate several of the concepts included in the manual.