Evaluation of PierScour Equations for CoarseBed Streams
By Katherine J. Chase and Stephen R. Holnbeck
U.S. Geological Survey
Scientific Investigations Report 20045111
In cooperation with the
Montana Department of Transportation
Abstract
Streambed scour at bridge piers is among the leading causes of bridge failure
in the United States. Several pierscour equations have been developed to
calculate potential scour depths at existing and proposed bridges. Because
many pierscour equations are based on data from laboratory flumes and from
cohesionless silt and sandbottomed streams, they tend to overestimate scour
for piers in coarsebed materials. Several equations have been developed to
incorporate the mitigating effects of large particle sizes on pier scour, but
further investigations are needed to evaluate how accurately pierscour depths
calculated by these equations match measured field data.
This report, prepared in cooperation with the
Montana Department of Transportation, describes the evaluation of five
pierscour equations for coarsebed streams. Pierscour and associated
bridgegeometry, bedmaterial, and streamflowmeasurement data at bridges over
coarsebed streams in Montana, Alaska, Maryland, Ohio, and Virginia were
selected from the Bridge Scour Data Management System. Pier scour calculated
using the Simplified Chinese equation, the Froehlich equation, the Froehlich
design equation, the HEC18/Jones equation and the HEC18/Mueller equation for
flood events with approximate recurrence intervals of less than 2 to 100 years
were compared to 42 pierscour measurements. Comparison of results showed that
pierscour depths calculated with the HEC18/Mueller equation were seldom
smaller than measured pierscour depths. In addition, pierscour depths
calculated using the HEC18/Mueller equation were closer to measured scour
than for the other equations that did not underestimate pier scour. However,
more data are needed from coarsebed streams and from less frequent flood
events to further evaluate pierscour equations.
Contents
Abstract
Introduction
Purpose and scope
Description of pierscour data used to evaluate equations
Methods of data collection
Comparison of data sets used to develop and evaluate
equations
Description of pierscour equations for coarsebed streams
Simplified Chinese equation
Froehlich equation
Froehlich design equation
HEC18/Jones equation
HEC18/Mueller equation
Evaluation of pierscour equations for
coarsebed streams
Simplified Chinese equation
Froehlich equation
Froehlich design equation
HEC18/Jones equation
HEC18/Mueller equation
Summary statistics for calculated and
measured pier scour
Summary and conclusions
References cited
ILLUSTRATIONS
 Map showing States from which pierscour data were compiled
 Graphs showing comparison of calculated to measured pier scour for five equations
 Graph showing distribution of residual depth of pier scour
TABLES
 Hydrologic and hydraulic data for selected pierscour sites
 Summary of pierscour measurements
 K_{1}, K_{2}, and K_{3 }correction factors for the HEC18/Jones equation
 Summary of scour measurement data used to develop the HEC18/Mueller equation
 Comparison of calculated pier scour to measured pier scour from five equations
 Summary statistics for calculated pier scour for five pierscour equations and measured pier scour
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