Bridge Contraction and Lateral Spillslope Scour

This research investigated: Effects and zone of influence of choked flows; Lateral erosion of bridge spillslopes; Bedrock interdiction by scour, and Scour downstream from chocked-flow conditions. The present study had two goals: (i) Definition of scour zone downstream from choked flows; and (ii) Computation of lateral spillslope erosion through the stream power theory. In order to accomplish these objectives, the following tasks were delineated and carried out: (i) Theoretical analysis to develop stream power relationships for severely contracted channel segments through bridges; (ii) Field survey; (iii) Hydraulic modeling of chocked flows; and (iv) Sediment modeling to determine scour. Stream power analysis enhanced the accuracy of BRI-STARS computations for the computation of spillslope scour through bridge openings. Computed bed elevation and water surface profiles through Murphy Creek showed the transition of subcritical upstream flows to supercritical downstream flows between the northbound and southbound bridges and matched the trend and magnitude of observed channel widening and erosion patterns very closely. This powerful approach, combined with angle of repose failure and implementation of bedrock controls provides engineers a very important design tool. For the Richeau Creek case where the approach channel was severely constricted, hydraulic computations show that discharges that match observed water surface elevations are smaller than previously estimated. The peak discharge corresponding to the 50-year flood frequency was shown to match the observed high-water mark and the relative magnitude of the computed scour agrees with field observations. For the Cottonwood case using the post-flood cross sections through the study reach, computations showed relatively minor additional scour for the 50-year, 4-hr hydrograph. These computations showed that the historical floods that occurred in Cottonwood Creek has altered the channel geometry. Computations show an additional 4 to 5 ft of scour at the bridge crossing the Cottonwood Creek for the 50-year event. Using computer modeling, the Wyoming Department of Transportation (WYDOT) Bridge Program will use the results of this research in predicting the limits of anticipated spillslope scour and the design of scour countermeasures at complex sites such as those of Murphy Creek, Richeau Creek, and Cottonwood Creek.

• Corporate Authors:

  Hydrau-Tech, Incorporated

  333 West Drake Road, Suite 40
  Fort Collins, CO  United States  80526

  Wyoming Department of Transportation

  Research Center, 5300 Bishop Boulevard
  Cheyenne, WY  United States  82009-3340

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Molinas, Albert
  • Bailey, William
• Publication Date: 2006-11

Language

• English

Media Info

• Media Type: Print
• Edition: Final Report
• Features: Appendices; Figures; Photos; References;
• Pagination: 73p

Subject/Index Terms

• TRT Terms: Bedrock; Bridges; Channels (Waterways); Computer models; Erosion; Hydraulics; Scour; Sediments; Theory
• Uncontrolled Terms: Bridge contraction; Choked flows (Open channels); Downstream; Spillslopes; Stream power analysis; Upstream; Water surface profiles
• Subject Areas: Bridges and other structures; Design; Highways; Hydraulics and Hydrology; I24: Design of Bridges and Retaining Walls; I26: Water Run-off - Freeze-thaw;

Filing Info

• Accession Number: 01046421
• Record Type: Publication
• Report/Paper Numbers: FHWA-WY-06/06F
• Files: TRIS, USDOT, STATEDOT
• Created Date: Apr 14 2007 7:36AM