Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour

The goal of this study was to conduct a field-oriented evaluation, coupled with advanced laboratory techniques, of channel degradation in a stream of the Deep Loess Region of western Iowa, namely Mud Creek. The Midwestern United States is an ideal place for such a study considering that ~$1 Billion of infrastructure and farmland has been lost recently to channel degradation. A common form of channel degradation in this region is associated with the formation of knickpoints, which naturally manifest as short waterfalls within the channel that migrate upstream. As flow plunges over a knickpoint face, scouring of the downstream bed creates a plunge pool. This downcutting increases bank height, facilitating bank failure, stream widening, and damage to critical bridge infrastructure. The authors conducted a state-of-the-art geotechnical analysis of the sediments from the knickpoint face, plunge pool, and adjacent stream banks to determine the areas of the streambed near the bridge infrastructure that favor knickpoint propagation. Soil characterization using particle size distributions and Gamma Spectroscopy identified a stratigraphic discontinuity at the elevation where the knickpoint forms. An automated surveillance camera was established to monitor the location of the knickpoint face relative to a fixed datum and provide a first-order approximation of its migration rate, which was approximately 0.9 m over a 248-day study period. Surveys conducted of the stream reach also facilitated information about knickpoint migration. Flow measurements using Large-scale Particle Image Velocimetry were conducted during the study to understand the hydrodynamic conditions at the site. The results of this research will assist local and federal transportation agencies in better understanding the following: (1) principal geotechnical and hydrodynamic factors that control knickpoint propagation, (2) identify necessary data for extraction and analysis to predict knickpoint formation, (3) provide mitigation measures such as grade control structures (e.g., sheet-pile weirs, bank stabilization measures) near bridge crossings to control the propagation of knickpoints and prevent further damage to downstream infrastructure.

• Supplemental Notes:
  • This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
• Corporate Authors:

  Mid-America Transportation Center

  University of Nebraska-Lincoln
  2200 Vine Street, PO Box 830851
  Lincoln, NE  United States  68583-0851

  Research and Innovative Technology Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Papanicolaou, A N Thanos
  • Admiraal, David M
  • Wilson, Christopher
  • Kephart, Clark
• Publication Date: 2012-4

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Figures; Photos; References; Tables;
• Pagination: 63p

Subject/Index Terms

• TRT Terms: Bridge abutments; Bridge piers; Channel flow; Geotechnical engineering; Scour; Structural analysis
• Uncontrolled Terms: Knickpoints
• Geographic Terms: Iowa
• Subject Areas: Bridges and other structures; Geotechnology; Highways; Hydraulics and Hydrology; I24: Design of Bridges and Retaining Walls;

Filing Info

• Accession Number: 01480989
• Record Type: Publication
• Report/Paper Numbers: MATC-UI-UNL: 471/424, 25-1121-0001-471, 25-1121-0001-424
• Files: UTC, TRIS, RITA, ATRI, USDOT
• Created Date: May 8 2013 11:29AM