FLOOD04125

• County: Statewide
• Basin: Statewide
• Title: Interim Procedures for Evaluating Scour at Bridges
• Date: 9/1/1988
• Prepared By: Federal Highway Administration
• Floodplain - Doc Type: Educational/Technical/Reference Information

Objectives

The primary objective of the proposed stLody is collecting "COlOr data for th..
purpose of 1) evaluating ex Isting scour-pr'ediction equations and 2) perhaps
developing improved scour-prediction equations. A secondary ovJective i::l to
assess alternative methods of scour data collection; onsite measurements are
considered a necessity at this time, but aeophysical techniques may prove to
be superior in the fUture. Following is a list of specific components of the
Objectives for the proposed study.

1. Perfor~ onsite measurements to collect scour data during high-
flow events to define the occurrence and extent of local scour,
constriction scour, and(or) genera! scour, at (::>number<:=)
selected sites.

2. Apply geophysical techniques at lu>allisome<:=} sites at the
the beginning of the study to determine past scour depths and
near the end of the study to obtain another lIM!asurement of scour
depths that occurred during the study perioa.

3. Compare locai scour depths measured onsite with iocal "cour
depths estimated using published local scour prediction equatior,s
and evaluate the adequacy of those prediction equations.

4. Using regression analyses, and(or) other curve-fitting techniques,
attempt to develop Improved scour-prediction equations. D.ta
to be anaiyzed wouid not necessarily be rest/'icted to the data
collected in this study if similar data could be obtained from
compatible scour studies being conducted elsewhere.

5. Compare scour data measured onsite with scour data defined by
geophysical techniques and assess onsite measurements versus
geophysical techniques with respect to cost, ease of use, safety,
accuracy, etc.

, Approach

Background

Many recent technical and Journal articles pertainlfig to bridge scour and
related topics (Jones 1984; Laursen 1984; MurillO 1986) emphasize the need
for onsite measurement of scour at bridges during hign-flow events. Lack 01'
confidence in which scour prediction equation(s) to use for a particular set
of circumstances has prompted an increased interest in developing data bases
that reflect full-scale, prototype field conditions.

A pilot study was conducted by the U. S. Geological Survey (USGS) in coop-
eration'with the Federal Highway Administration (FHWA) to develop and test
guidelines for onsite measurellM!nts of scour at bridges during high flows
(Jarrett and Boyle, 1986). That studt presented two alternative approaches
for future ocour studies. The onsite measurement part of this proposed scour
study for (:>..>study area<:=] is based upon the "limited approach" described by
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