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Identifying Bridge Scour Susceptibility: A GIS-based Approach

Identifying Bridge Scour Susceptibility: A GIS-based Approach. Cassandra Rutherford Master of Science Candidate Department of Civil Engineering. Project Objective.

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Identifying Bridge Scour Susceptibility: A GIS-based Approach

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  1. Identifying Bridge Scour Susceptibility: A GIS-based Approach Cassandra Rutherford Master of Science Candidate Department of Civil Engineering

  2. Project Objective To develop a GIS-based method to evaluate the potential for scour at bridges and to identify those structures that are scour susceptible.

  3. Presentation Overview Bridge Scour Case Study GIS-based Approach Progress Available Data Future Work Methodology Questions

  4. Bridge Scour Bridge scour is the erosion of streambed soils and sediment that provide support for bridge foundations.

  5. Bridge Scour The primary variables that effect scour: • Bed materials • Channel protection • Channel and bridge geometry • Flow hydraulics

  6. Bridge Scour • Of the 832 bridge failures since 1950, 60% were related to scour. • $50 million spent annually in Federal aid for scour related bridge failures and repairs. • 3 bridges failures have resulted in the loss of 25 lives in the last 15 years.

  7. Bridge Scour Over the 49,186 bridges in Texas . . . • 40,814 bridges – over waterways • 688 bridges – scour critical

  8. Bridge Scour Scour critical bridges – structural integrity potentially jeopardized due to scour. Requires Level II Analysis. Level II Analysis – developed in HEC 18 requires on site investigation, bridge foundation information, modeling of stream

  9. Bridge Scour Scour susceptible bridges – likelihood that bridge may be vulnerable to scour. Current methods require large database of analyzed bridges for comparisons, or envelope curves based on historical scour measurements.

  10. GIS-based Approach Due to the large number of bridges, their spatial distribution, wide variety of data required and cost of performing Level II analysis, a robust method of analysis is required. GIS is an effective means for spatially storing the database, analyzing the data and presenting the results. Prioritization of bridges susceptible to scour can be more easily accomplished using a GIS scheme than previous methods.

  11. HEC GeoRas HEC GeoRas General Methodology Data Processing Validation Analysis

  12. Available Data USGS Harris County Surface-Water Data - daily stream flow and measurements provides gage location, channel width, cross section area, velocity, gage height, discharge and drainage area.

  13. Available Data Federal Highway Administration National Bridge Inventory (NBI) Database - electronic database coded by DOTs provides data on bridges such as structural type, number of spans, geometry, length, width, channel protection, etc.

  14. Available Data USDA – NRCS SSURGO Soil Data - shapefile of county along with multiple tables providing soil information such as classification, hydrologic group, sieve passing percents, soil erodibility factor, etc.

  15. HEC GeoRas HEC GeoRas General Methodology Data Processing Validation Analysis

  16. Case Study: Harris County

  17. Case Study: Harris County Datasets Used: Texas Bridge Database (NBI) USGS DEM (1:24,000) Harris County (TNRIS) Harris County data files Texas Counties shapefile (ESRI) Reach Files Version 3 (EPA) Harris County Soils shapefile (SSURGO) Harris County Stream gages (USGS) TIN Data for Buffalo Bayou (Dodson)

  18. Case Study: Harris County

  19. Case Study: Harris County

  20. Case Study: Harris County Erodibility

  21. Case Study: Harris County Bridges with Erosive Soils

  22. Case Study: Harris County Channel Protection < 6

  23. Case Study: Harris County Scour Susceptible Bridges

  24. Case Study: Buffalo Bayou Selected 2 Bridges on Buffalo Bayou to model total scour in HEC RAS

  25. HEC GeoRas HEC GeoRas General Methodology Data Processing Validation Analysis HEC GeoRas

  26. HEC GeoRAS Used to develop the spatial data required to generate a HEC-RAS import file with a defined 3-D stream network and 3-D cross sections

  27. HEC GeoRAS Buffalo Bayou Triangular Irregular Network (TIN) data is required. Contours are created to allow ArcView to refresh more quickly.

  28. HEC GeoRAS The following themes must be created: Stream Centerline Main Channel Banks Flow Path Centerline Cross-Sectional Cut Lines and Land Use

  29. HEC GeoRas HEC GeoRas General Methodology Data Processing Validation Analysis

  30. HEC RAS An accurate hydraulic models of river reach containing bridge must be developed before scour calculations can be performed.

  31. HEC RAS Scour calculations in HEC RAS require: Depth at bridge Velocity Number of piers

  32. HEC GeoRas HEC GeoRas General Methodology Data Processing Validation Analysis HEC GeoRas

  33. HEC GeoRAS Scour calculations results can be exported back into ArcView.

  34. HEC GeoRas HEC GeoRas General Methodology Data Processing Validation Analysis

  35. Current Progress • Text files correctly delimited and column headers properly determined • All non-digital data made into point shapefiles • Data correctly projected and combined in one project • Used method to select 6 scour susceptible bridges • Began initial HEC-GeoRAS and HEC RAS modeling

  36. Future Work • Generate HEC GeoRAS themes • Validate method by modeling 2 bridges and calculating the total scour using HEC RAS • Determine accuracy of the method • Automate GIS method

  37. Questions?

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