Cassandra Rutherford

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Identifying Bridge Scour Susceptibility A
GIS-based Approach

• Cassandra Rutherford
• Master of Science Candidate
• Department of Civil Engineering

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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.

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Presentation Overview

Bridge Scour
Case Study
Progress
GIS-based Approach
Available Data
Future Work
Methodology
Questions
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Bridge Scour

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

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Bridge Scour

• The primary variables that effect scour
• Bed materials
• Channel protection
• Channel and bridge geometry
• Flow hydraulics

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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.

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Bridge Scour

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

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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

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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.

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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.

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General Methodology

Data Processing
Validation
Analysis
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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.

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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.

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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.

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General Methodology

Data Processing
Validation
Analysis
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Case Study Harris County

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Case Study Harris County

• Datasets Used
• Texas Bridge Database (NBI)
• USGS DEM (124,000) 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)

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Case Study Harris County

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Case Study Harris County

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Case Study Harris County

• Erodibility

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Case Study Harris County

• Bridges with Erosive Soils

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Case Study Harris County

• Channel Protection
• 
  lt 6

N Not over water
9 None needed
8 Well vegetated
7 Minor damage
6 Slumping
5 Eroded
4 Extensive erosion
3 Protection failing
2 State of collapse
1 Bridge closed
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Case Study Harris County

• Scour Susceptible Bridges

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Case Study Buffalo Bayou

• Selected 2 Bridges on Buffalo Bayou to model
  total scour in HEC RAS

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General Methodology

Data Processing
Validation
Analysis
HEC GeoRas
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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
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HEC GeoRAS

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

• The following themes must be created
• Stream Centerline
• Main Channel Banks
• Flow Path Centerline
• Cross-Sectional Cut Lines
• and Land Use

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General Methodology

Data Processing
Validation
Analysis
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HEC RAS

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

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HEC RAS

• Scour calculations
• in HEC RAS require
• Depth at bridge
• Velocity
• Number of piers

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General Methodology

Data Processing
Validation
Analysis
HEC GeoRas
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HEC GeoRAS

• Scour calculations
• results can be
• exported back
• into ArcView.

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General Methodology

Data Processing
Validation
Analysis
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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

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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

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Questions?