JULY 1993 FLOOD DAMAGE TO US-71 BRIDGE OVER BRUSHY CREEK, CARROLL COUNTY, IOWA: CASE STUDY

The flood of 1993 inundated much of the upper Mississippi River Basin, resulting in significant damage at numerous sites in Iowa. A record flood on Brushy Creek resulted in failure of the US-71 bridge 14.5 km south of Carroll, Iowa. Development of a computer flow model at the site and analysis of scour for the failed bridge and its replacement are included. On the basis of data from plans, topographic maps, and a United States Geological Survey (USGS) crest stage gage at the site, the computer model was developed using WSPRO (a USGS/FHWA computer program for Water Surface Profile Computations). To construct the computer model, cross sections were developed, and Manning's roughness coefficients "n" were assigned, such that known stage elevations were produced for a given flow. The model was then used to estimate flood flows during the event. Scour was estimated using the WSPRO data, soil boring data, and procedures from HEC-18, "Evaluating Scour at Bridges". Long-term aggradation or degradation, contraction scour, and local pier scour were all evaluated. The case study allowed verification of HEC-18 procedures and formulas based on an actual flood event versus a laboratory flume study. The scour analysis predicted scour below the pile tips at the piers, and the bridge failed when the piers were undermined--good evidence of the validity of HEC-18 scour calculations. The computer program WSPRO and the scour procedures from HEC-18 as analysis tools that can be used to assess stream flows, scour potential, and design adequacy are presented.

Language

  • English

Media Info

  • Features: Figures; Photos; References; Tables;
  • Pagination: p. 38-46
  • Monograph Title: 1993 Midwest floods and water quality best management practices
  • Serial:

Subject/Index Terms

Filing Info

  • Accession Number: 00713557
  • Record Type: Publication
  • Files: TRIS, TRB
  • Created Date: Nov 16 1995 12:00AM