 U.S. Department of Transportation Federal Highway Administration |
MEMORANDUM |
| Subject: | INFORMATION: HEC-17 – Highways in the River Environment: Extreme Events, Risk and Resilience | Date: | August 1, 2016 |
| From: | Joseph (Joe) Krolak, P.E. Principal Hydraulic Engineer |
Reply to Attn. of: | HIBT-20 |
| To: | FHWA Division Bridge Engineers & Staff State DOT Hydraulic & Drainage Engineers |
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The FHWA Office of Bridges and Structures (HIBS), working with the Office of the Natural Environment (HEPN) and the Resource Center, are releasing Hydraulic Engineering Circular (HEC) 17, "Highways in the River Environment: Extreme Events, Risk and Resilience"1 (.pdf). In doing so, FHWA acknowledges the efforts of the team at Kilgore Consulting and Management, authors of the manual.
This HEC-17 manual is a major and significant update that provides technical guidance and methods for assessing the nexus of riverine and transportation as it relates to floods, floodplain policies, extreme events, climate change, risks, and resilience. An important focus is quantifying exposure to extreme flood events considering climate change and other sources of nonstationarity.
This focus aligns with FHWA policies and procedures relating to consideration of change, and effects of change upon a project's hydrology and hydraulics. For example, almost exactly 60 years ago, at the very beginning of the Interstate Highway System, the August 10, 1956 Policy and Procedure Memorandum 20-4 required:
"Designs for all [Interstate] culverts and bridges over streams shall … accommodate floods at least as great as that for a 50-year frequency or the greatest flood of record, whichever is the greater, with the runoff based on the land development expected in the watershed 20 years hence ...."
Today, the consideration of such change, particularly change associated with climate and extreme events, necessitates FHWA's goal that HEC-17 provides the transportation community with our understanding of the best current, actionable, science informed approaches to address such change in the river environment. In doing so, FHWA believes that this manual provides a complement to our October 2014 HEC-25, "Highways in the Coastal Environment: Assessing Extreme Events – Volume 2."
Specifically, HEC-17 describes and discusses:
- FHWA and other floodplain policies and guidance
- Uncertainty associated with hydrologic models
- Nonstationarity and two drivers: climate change and land use/land cover changes
- Several tools for identifying and adjusting for trends in the historical record
- Techniques for projecting floods
- Global/regional climate models, downscaling techniques, and emissions scenarios
- Risk and resilience and the probabilistic nature of flood events
Recognizing that all plans and projects do not merit the same attention, HEC-17 also provides a five level analysis framework and specific guidance for addressing non-stationarity, including climate change. Finally, the manual provides case studies to illustrate several of the concepts.
In releasing this technical manual, FHWA understands that all of these topics only reflect an initial placeholder of a rapidly evolving scientific and engineering consensus effort.
For example, AASHTO, NCHRP, and other organizations are undertaking relevant and important research and studies that will increase our understanding of the science and advance the state of the practice. In recognition, FHWA plans to collect and update such information and provide further HEC-17 (and HEC-25) editions as these advances in knowledge and practice become available.
A limited number of printed copies of HEC-17 have been sent to Hydraulic and Drainage engineers in State DOT and FHWA offices.
To assist a wider audience, HIBS has posted HEC-17 on our website; now available for downloading at FHWA Hydraulics. Additionally, FHWA anticipates several future outreach efforts, including a presentation at the 2016 National Hydraulic Engineering Conference in Portland, Oregon, on August 11, 2016.
If you have any questions, please feel free to contact Joe Krolak at (202) 366-4611 (Joe.Krolak@dot.gov) or Brian Beucler, Office of Bridges and Structures at (202) 366-4598 (Brian.Beucler@dot.gov).
cc:
FHWA Hydraulics Discipline Team
Office of the National Environment
1 In April 1981, FHWA produced the 1st edition of HEC-17: "Design of Encroachments on Flood Plains Using Risk Analysis." This 2nd edition expands upon and supplements that April 1981 1st edition. However, FHWA believes the risk analyses in the 1st edition still provide useful approaches and practices for the transportation community.