Companion Guide to Video May 2015

www.fhwa.dot.gov/federal-aidessentials

Did you know that scour, the erosion around 

a bridge’s foundation caused by flooding, is 

the single greatest cause of bridge failures? 

In fact, following several dramatic bridge 

failures, the U.S. Congress required the 

Federal Highway Administration, or FHWA, 

to apply an improved approach to the 

agency’s scour program to responsibly 

manage the risk of scour-related challenges 

with our Nation’s highway bridges. This 

approach is based on gathering accurate 

data and then using that data to assess the 

risk to the public. 

Every bridge or culvert in an agency’s 

inventory with a span of 20 feet or greater 

must be appraised for risk of scour. 

Structures determined to be vulnerable to 

scour need a plan of action for mitigating 

the risk and associated resources for 

carrying out the plan. 

Is your agency tasked with managing a 

scour program for structures in its 

inventory? If so, how will your agency 

develop plans of action that are appropriate 

for level of risk and achievable within its 

budgetary constraints? 

Let’s begin by exploring the primary 

elements of a risk-based scour program. 

Then we’ll illustrate how a local public 

agency, or LPA, might develop a 

sustainable program. 

To develop a risk-based scour program, a 

multi-disciplinary team, consisting of 

engineers, engineering managers, and even 

public safety professionals, starts with a list 

Federal-aid Program Overview

FHWA Bridge Scour Program

Developing a Risk-Based Scour Program

Implementing an action plan for scour-critical structures
Federal-aid Essentials for Local Public Agencies

of structures that are both publically owned 

and 20-feet long or greater. 

For each structure on the list, the team 

develops a risk appraisal. Using bridge 

inspection data or engineering assessment, 

the scour potential of a bridge is 

determined. For example, a bridge that 

doesn’t cross a waterway would be 

identified as having no potential for scour, 

whereas a bridge subject to failure during 

the appraised flood event would be 

identified as scour critical. 

Risk appraisal considers the consequence 

of failure by asking such questions as: 

• What is the benefit of the bridge to 

the community? 

• Do commuters, emergency services, 

and commerce depend on it every 

day?

• What is the cost of mitigating the risk 

of scour? 

For each structure identified in the risk 

appraisal as scour critical, the agency team 

develops a plan of action, which specifies 

the management and public safety strategy. 

For some structures, the plan of action will 

specify long-term monitoring. 

For example: 

• When will the structure be 

monitored? 

• What is the indication of failure? 

• Under what conditions will it be 

closed and reopened?

• What is the planned detour route? 

For other structures, however, the plan of 

action will specify countermeasures to 

mitigate scour. For example, an agency 

might plan a structure retrofit with deeper 
Federal-aid Essentials for Local Public Agencies

pile foundations or its banks reinforced with 

rip-rap. Typically, agencies use cost-benefit 

analyses to determine if long-term 

monitoring or countermeasures are the 

most appropriate plan of action. 

Monitoring floods, closing and opening 

bridges, detouring traffic, and installing 

countermeasures require a commitment of 

agency resources. For this reason, the 

scour program identifies the resources so 

that agency management can consider the 

cost of the scour plan of action as it 

balances priorities. 

Let’s see how a LPA develops its risk 

assessment and scour plan of action for one 

scour-critical bridge. 

A county bridge inspector reports that the 

footing of a bridge has been undermined, 

making the bridge scour-critical. The scour 

program management team, including the 

public works director, the head of streets 

and maintenance, the fire chief, and the 

sheriff, discuss the importance of the bridge. 

The safety and service of the bridge are 

vital because it carries several school buses 

and provides the only access to a 

subdivision for emergency services. 

Until the scour problem can be addressed, 

the team agrees that the county bridge 

inspectors will monitor the bridge during 

floods and provide direction to the sheriff 

when the bridge needs to be closed and 

allowed to be reopened to traffic. 

When the team meets again, it learns that in 

order to keep the bridge in service, the 

county will install rip-rap. The $70,000 cost 

of the rip-rap and the short-term monitoring 

of the bridge are budgeted. Once the rip-rap 

is installed, the public works director will 

remove the bridge from the list of scourcritical bridges and revise the cost of scour 

program monitoring. 

Scour is the single most common cause of 

bridge failure. Your agency’s best defense 

against scour is a thoughtfully managed 

program. However, to be effective the 

program must be fully implemented. As

illustrated by our example, agencies need to 

update their scour programs when 

management priorities change, bridge 

conditions change, or as countermeasures 

are implemented. 
Federal-aid Essentials for Local Public Agencies

While the FHWA encourages agencies to 

use a risk-based approach when developing

a scour program, each agency develops its 

own criteria for establishing priorities. When 

developing or updating your scour program, 

contact your State department of 

transportation. It can provide its scour 

program policy, guidance on how to 

proceed with the process, and may even 

offer document templates.
Federal-aid Essentials for Local Public Agencies

The content of this 

document is not a 

substitute for 

information obtained 

from State departments 

of transportation, 

appropriate FHWA 

Division Offices, and 

applicable laws. 

Scenarios have been 

simplified for emphasis 

and do not necessarily 

reflect the actual range of 

requirements applicable 

to the scenario or this 

topic. This document

was created under 

contract number 

DTFH61-14-P-00163 by 

the Federal Highway 

Administration, U.S. 

Department of 

Transportation, and is 

offered to the public to 

heighten and focus 

awareness of Federal-aid 

requirements within the 

local public agencies 

community and 

reinforces the 

importance of these 

necessary policies, 

procedures, and 

practices.

This Companion Resource 

is the script content for 

the video production of 

the same name. 

Additional Resources

• FHWA library of technical guidance and policy memos for Bridge Scour 

issues

http://www.fhwa.dot.gov/engineering/hydraulics/policymemos.cfm

• FHWA Hydraulic Program office website with links to technical 

information on scour

http://www.fhwa.dot.gov/engineering/hydraulics/scourtech/scour.cfm

• This online training provides guidance on developing a Plan of Action 

(POA) for scour critical bridges. Available through the NHI.

http://www.nhi.fhwa.dot.gov/training/course_search.aspx?sf=0&course

_no=135085

• This FHWA memorandum provides guidance on applying risk concepts 

and data utilization; collectively, these activities are referred to as the 

FHWA Scour Program

http://www.fhwa.dot.gov/engineering/hydraulics/scourtech/scour.cfm

• HEC-18 presents the state of knowledge and practice for the design, 

evaluation and inspection of bridges for scour

http://www.fhwa.dot.gov/engineering/hydraulics/scourtech/scour.cfm

• HEC-23 is a two-volume document set that identifies and provides 

design guidelines for bridge scour and stream instability 

countermeasures

http://www.fhwa.dot.gov/engineering/hydraulics/scourtech/counter.cf

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