Revised Clear-Water and Live-Bed Contraction Scour Analysis

This report provides state transportation engineers and other practitioners with revised scour contraction estimation equations for use on live-bed and clear-water channels with fine sand and introduces a new computational paradigm that results in less variability. Under NCHRP Project 24-47, “Revised Clear-Water and Live-Bed Contraction Scour Analysis,” Ayres Associates developed live-bed and clear-water contraction scour equations for risk-based bridge design. This study introduces the concept of calculating contraction scour at the “vena-contracta,” which is formed where the flow enters the contracted channel. Except for corner (abutment) scour at the contraction entrance, the scour depth in the vena-contracta region gives the deepest scour along a contracted channel. The Research Team developed a regression equation from data obtained from flume experiments to estimate a vena-contracta correction coefficient, Kv. Using modeling and laboratory tests from Colorado State University, this study re-examined the FHWA’s Hydraulic Engineering Circular No. 18 (HEC-18) equations used for the clear-water and live-bed conditions and the NCHRP Project 24-20, “Estimation of Bridge Scour Depths at Bridge Abutments,” scour equations used for estimating the contraction scour component of abutment scour. Both contraction scour prediction methods were adjusted to include the vena-contracta coefficient. These revised equations are for use when estimating both live-bed and clear-water contraction scour in channels whose beds are formed of fine sand and have the width-to-depth ratio and entrance conditions comparable with those used for this study.

• Record URL:
  http://www.trb.org/Main/Blurbs/182156.aspx
• Availability:
  • Find a library where document is available. Order URL: http://worldcat.org/isbn/9780309674072
• Supplemental Notes:
  • A Training Manual is available as NCHRP Web-Only Document 294: Revised Clear-Water and Live-Bed Contraction Scour Analysis Training Manual, and the PowerPoint presentation supporting the manual is available on the TRB website (www.trb.org) by searching for “NCHRP Research Report 971”.
• Authors:
  • Lagasse, P F
  • Ettema, R
  • DeRosset, W M
  • Nowroozpour, A
  • Clopper, P E
• Publication Date: 2021

Language

• English

Media Info

• Media Type: Digital/other
• Features: Figures; Photos; References; Tables;
• Pagination: 177p
• Serial:
  • NCHRP Research Report
  • Issue Number: 971
  • Publisher: Transportation Research Board
  • ISSN: 2572-3766

Subject/Index Terms

• TRT Terms: Bridge abutments; Bridge design; Channels (Waterways); Contraction; Equations; Hydraulics; Sand; Scour
• Subject Areas: Bridges and other structures; Design; Highways; Hydraulics and Hydrology;

Filing Info

• Accession Number: 01777877
• Record Type: Publication
• ISBN: 9780309674072
• Report/Paper Numbers: NCHRP Project 24-47
• Files: TRIS, TRB, ATRI
• Created Date: Jul 26 2021 5:59PM