USGS Scientific Investigations Report 2007-5260
Prepared in cooperation with the Alabama Department of Transportation
By K.G. Lee and T.S. Hedgecock
U.S. Geological Survey Scientific Investigations Report 2007-5260, 56 pages (Published online, March 2008)
This report is available in PDF format:
SIR 2007-5260 (
) (6 MB)
The U.S. Geological Survey, in cooperation with the Alabama Department of Transportation, made observations of clear-water contraction scour at 25 bridge sites in the Black Prairie Belt of the Coastal Plain of Alabama. These bridge sites consisted of 54 hydraulic structures, of which 37 have measurable scour holes. Observed scour depths ranged from 1.4 to 10.4 feet. Theoretical clear-water contraction-scour depths were computed for each bridge and compared with observed scour. This comparison showed that theoretical scour depths, in general, exceeded the observed scour depths by about 475 percent. Variables determined to be important in developing scour in laboratory studies along with several other hydraulic variables were investigated to understand their influence within the Alabama field data. The strongest explanatory variables for clear-water contraction scour were channel-contraction ratio and velocity index. Envelope curves were developed relating both of these explanatory variables to observed scour. These envelope curves provide useful tools for assessing reasonable ranges of scour depth in the Black Prairie Belt of Alabama.
Abstract
Introduction
Purpose and Scope
Acknowledgments
Description of Study Area
Previous Investigations
Theoretical Bridge Scour
Contraction Scour
Theoretical Live-Bed Contraction Scour
Theoretical Clear-Water Contraction Scour
Pier Scour
Site Selection
Data Assumptions
Justification for the Assumption of Clear-Water Scour
Justification for the Assumption of Large Flood Flows
Historical Floods
Risk Analysis
Justification for the Assumption of Equilibrium-Scour Conditions
Approach
Estimation of Hydrologic Data
Estimation of Hydraulic Data
Measurement of Actual Scour Depths
Computation of Theoretical Scour Depths
Comparison of Actual and Theoretical Scour Depths
Variables Influencing Clear-Water Contraction Scour
Median Grain Size
Velocity Variables
Channel-Contraction Ratio
Hydraulic Ratios
Contraction Ratios
Depth Variables
Other Variables
Development of the Alabama Clear-Water Contraction Scour Envelope Curves
Application of the Alabama Contraction-Scour Envelope Curves
Summary
References Cited
Appendix A. Alabama bridge-scour study sites and reference numbers for figure 7
Appendix B. Photographs of selected Alabama bridge-scour study sites
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Suggested citation: Lee, K.G., and Hedgecock, T.S., 2008, Clear-water contraction scour at selected bridge sites in the Black Prairie Belt of the Coastal Plain in Alabama, 2006: U.S. Geological Survey Scientific Investigations Report 2007–5260, 56 p. (available online at https://pubs.water.usgs.gov/sir2007-5260).
For more information, please contact K.G. Lee.
U.S. Department of the Interior |
U.S. Geological Survey
Persistent URL: https://pubs.water.usgs.gov/sir2007-5260
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