Abstract
This paper presents observations on clear-water and live-bed contraction scour caused by subcritical flow along a large rectangular channel. Three contraction ratios (contraction width/approach–channel width) were used: 0.25, 0.50, and 0.75. Each ratio included a 45° transition linking the contraction to the approach channel. Contractions scour relates to three categories of contraction length: length shorter than flow-separation length at contraction entrance, length exceeds flow-separation length, and length is sufficiently long to develop uniform flow in contraction. Flow-choking was avoided. The experiments focused on the second category, herein termed intermediate-length contractions. Light detection and ranging (LiDAR) scans showed that maximum scour depths occurred at a flow vena contracta (formed within the contraction entrance), the entrance corners, and the contraction exit. The observed sour depth in the vena contracta exceeded the depths estimated using the existing HEC-18 equations for contraction-scour. The deepest scour occurred at entrance corners except for the smallest ratio, which produced a step scour.
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Data Availability Statement
Some or all of the data that support the findings of this study are available from the corresponding author upon reasonable request. The data include bed profiles (LiDAR scans), water-surface profiles, and flow velocities.
Acknowledgments
The writers thank Pete Lagasse, Paul Clopper, Will DeRosset, and Scott Zey (all at Ayres Associates) and the Panel for Project 24-47 (Revised Clear-Water And Live-Bed Contraction Scour Analysis) of the National Cooperative Highway Research Program for suggestions about the experiments, which the writers conducted for Ayres.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 147 • Issue 8 • August 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Aug 30, 2020
Accepted: Mar 15, 2021
Published online: Jun 2, 2021
Published in print: Aug 1, 2021
Discussion open until: Nov 2, 2021
ASCE Technical Topics:
- Channel flow
- Channels (waterway)
- Computer vision and image processing
- Engineering fundamentals
- Flow (fluid dynamics)
- Flow separation
- Fluid dynamics
- Fluid mechanics
- Hydraulic contraction
- Hydraulic engineering
- Hydraulic properties
- Hydraulic structures
- Hydraulics
- Hydrologic engineering
- Methodology (by type)
- Open channel flow
- Scour
- Subcritical flow
- Uniform flow
- Water and water resources
- Waterways
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Cited by
- Alireza Nowroozpour, Robert Ettema, Alireza Fakhri, A Reassessment of Contraction Scour at Bridge Waterways, Journal of Hydraulic Engineering, 10.1061/(ASCE)HY.1943-7900.0002031, 148, 12, (2022).