Jul 10 2012

Hydraulic Design of Safe Bridges

The Federal Highway Administration (FHWA) recently published a new manual, Hydraulic Design Series Number 7 (HDS 7), that has very close ties to our blog because of its content and some of its authors.

safe bridge

While you can download the HDS 7 manual for free from the FHWA website, we are going to be posting some portions of it that might be helpful to readers of this blog.  At the end of this series we plan on interviewing Lyle Zevenbergen and John Hunt, so if you have any questions about the manual make sure to comment on the posts and we will try to incorporate some of them into the interview.

Before we get to the discussions about modeling, here is a little introduction to the manual.


The Federal Highway Administration provides oversight of the Nation’s bridges through the National Bridge Inspection Standards (NBIS) and other regulatory policies and programs. Bridge failures resulting from both natural and human factors led the U.S. Congress to express its concern about the safety, approaches, and oversight of the Nation’s bridges.

Within the Conference Report for the Departments of Transportation and Housing and Urban Development, and Related Agencies Appropriations Act, 2010 (H.R. Rep. No. 111-366), the Congress recommended that the “… (FHWA) use a more risk-based, data-driven approach to its bridge oversight” to improve bridge safety. Congress stated its intention to monitor the progress that FHWA makes in identifying new approaches to bridge oversight, completing initiatives, and achieving results from its efforts. Congress directed that FHWA apply funds to focus and achieve these activities.

To address the conference report, FHWA undertook a combination of activities that contribute to four primary outcomes: more rigorous oversight of bridge safety; full NBIS compliance by all States; improved information for safety oversight and condition monitoring; and qualified and equipped bridge inspection personnel.

As hydraulic issues remain a leading factor in bridge failures, FHWA recognized that these activities need to include efforts to better collect, understand and deploy more recent and robust guidance and techniques to the accepted state of hydraulic and waterway related practice. [HDS 7] is one of the products of these efforts.


The purpose of HDS 7, Hydraulic Design of Safe Bridges, is to provide technical information and guidance on the hydraulic design of bridges. HDS 7 replaces the HDS 1 manual “Hydraulics of Bridge Waterways” (FHWA 1978) for guidance of bridge hydraulic analyses. Bridges should be designed as safely as possible while optimizing costs and limiting impacts to property and the environment. Many significant aspects of bridge hydraulic design are discussed. These include regulatory topics, specific approaches for bridge hydraulic modeling, hydraulic model selection, bridge design impacts on scour and stream instability, and sediment transport.

The impacts of bridge design and construction on the economics of highway design, safety to the traveling public, and the natural environment can be significant. An economically viable and safe bridge is one that is properly sized, designed, constructed, and maintained. In general, although longer bridges are more expensive to design and build than shorter bridges, they cause less backwater, experience less scour, and can reduce impacts to the environment. Increased scour from too short a bridge can require deeper foundations and necessitate countermeasures to resist these effects. A properly designed bridge is one that balances the cost of the bridge with concerns of safety to the traveling public, impacts to the environment, and regulatory requirements to not cause harm to those that live or work in the floodplain upstream and downstream of the bridge.

2 pings

  1. History of Hydraulic Bridge Design » Hydraulically Inclined

    […] « Hydraulic Design of Safe Bridges […]

  2. Looking Back at Tropical Storm Irene: What Went Right (Video) » Hydraulically Inclined

    […] the maintenance and long-term cost was greatly depreciated. FHWA’s HDS 5 manual as well as the new HDS 7 deal with some of these issues. These videos are a terrific look at dealing with large storm events […]

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