Highways in the Coastal Environment: Assessing Extreme Events - FHWA Hydraulic Engineering Circular 25 (HEC-25), Vol. 2

"Highways in the Coastal Environment: Assessing Extreme Events" (HEC-25 Vol. 2) was developed by the Federal Highway Administration (FHWA) to provide technical guidance for assessing vulnerabilities of highway infrastructure in coastal areas to climate change and extreme weather events. In particular, the manual identifies methods for quantifying exposure of coastal transportation facilities to sea-level rise, storm surge, and wave action. The information provided in the manual can be used to inform risk and vulnerability assessments, planning, and design guidelines for infrastructure. It is intended to be used by engineers, roadway designers, planners, and others involved with planning, designing, or constructing transportation infrastructure in coastal environments.

In Chapter 2, the manual describes coastal processes (e.g. tides, storm surge, waves) that affect transportation asset vulnerability. It identifies different models that are available for simulating these coastal processes, and describes how climate change is likely to affect those processes, focusing in particular on sea-level rise data and projections. This section also summarizes any unique aspects of coastal processes for four different coastal regions in the United States: the Gulf of Mexico and South Atlantic, the mid-Atlantic and New England, the Great Lakes, and the Pacific. For example, tsunamis cause more damage along the Pacific coast of the U.S. than other coastal regions.

Chapter 3 focuses on how the manual can be used, identifying tools and methods available for quantifying risk (both probability of certain flood magnitudes and consequences of flooding). While HEC-25, Vol. 2 is intended primarily to help assess exposure of assets to coastal processes and climate change impacts, it also briefly addresses the other two aspects of vulnerability, discussing methodologies for assessing sensitivity of coastal transportation infrastructure and how adaptive capacity and adaptation countermeasures factor in.

Chapter 4 of the manual includes more detail on how to quantify exposure of assets to storm surge and wave action, while considering climate change and sea-level rise projections. It presents three different levels of effort that can be used in this analysis, depending on the quality of assessment required: Use of Existing Data and Resources; Original Modeling of Storm Surge and Waves; or Modeling in a Probabilistic Risk Framework. The manual identifies steps for gathering or developing the information needed to conduct each level of analysis for each of the four U.S. coastal regions.

Finally, Chapter 5 includes case studies on how climate change and extreme weather events in coastal areas have been factored into exposure and vulnerability assessments for transportation infrastructure and facilities. The case studies include:

- San Francisco Bay Area's Adapting to Rising Tides pilot project (a Level 1 analysis example),

Gulf Coast Phase 2 study (a Level 2 example), and

- Synthetic Storm Analysis on the Florida Coast (as a Level 3 example).


The HEC-25, Vol. 2 manual is one of the Hydraulic Engineering Circular documents provided by the FHWA, and is a standalone supplement to the first HEC-25 document on highways in coastal environments. The primary HEC-25 manual, developed in 2008, provides more general guidance to be used in planning, design, and operation of coastal highways.



Publication Date: October 2014

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  • Assessment guide


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