The following is one of over 75 programs & documentation included with Hydro-CD by Dodson

HY-9: Scour

VERSION/DATE: Version 5.0, 1995




HYDRAULIC ENGINEERING CIRCULAR NO. 18 (HEC-18) EVALUATING SCOUR AT BRIDGES (3rd Edition), November 1995, By US Department of Transportation, Federal Highway Administration

HYDRAULIC ENGINEERING CIRCULAR NO. 20 (HEC-20) Stream Stability at Highway Structures (2nd Edition), November 1995 By US Department of Transportation, Federal Highway Administration


HY9 - The program is based on FHWA HEC-18 "Evaluating Scour at Bridges". The program is designed to assist the user in using the equations presented in chapter 4 of the procedures. HEC-18 provides procedures for the design, evaluation and inspection of bridges for scour. 


1. Designing new and replacement bridges to resist scour,

2. Evaluating existing bridges for vulnerability to scour,

3. Inspecting bridges for scour,

4. Providing scour countermeasures, and

5. Improving the state-of-practice of estimating scour at bridges.


The most common cause of bridge failures is floods with the scouring of bridge foundations being the most common cause of flood damage to bridges. The hydraulic design of bridge waterways is typically based on flood frequencies somewhat less than those recommended for scour analysis in this publication. During the spring floods of 1987, 17 bridges in New York and New England were damaged or destroyed by scour. In 1985, 73 bridges were destroyed by floods in Pennsylvania, Virginia, and West Virginia. A 1973 national study for the FHWA of 383 bridge failures caused by catastrophic floods showed that 25 percent involved pier damage and 72 percent involved abutment damage.[1] A second more extensive study in 1978 [2] indicated local scour at bridge piers to be a problem about equal to abutment scour problems. A number of case histories on the causes and consequences of scour at major bridges are presented in Transportation Research Record 950.[3]


The purpose of this document is to provide guidelines for identifying stream instability problems at highway-stream crossings and for the selection and design of appropriate countermeasures to mitigate potential flood damages to bridges and other highway components at stream crossings.


Approximately 86 percent of the 577,000 bridges in the National Bridge Inventory (NBI) are built over streams. A large proportion of these bridges span alluvial streams that are continually adjusting their beds and banks. Many, especially those on more active streams, will experience problems with scour and bank erosion during their useful life. The magnitude of these problems is demonstrated by the average annual flood damage repair costs of approximately $50 million for highways on the Federal-aid system. The Federal-aid system contains less than half of all bridges in the NBI.
2012 - Walter P. Moore & Associates, Inc. - Houston, TX, USA