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Cassandra RutherfordCassandra RutherfordMaster of Science CandidateMaster of Science Candidate
Department of Civil EngineeringDepartment of Civil Engineering
Identifying Bridge Identifying Bridge Scour Susceptibility: Scour Susceptibility:
A GIS-based ApproachA GIS-based Approach
Project ObjectiveProject Objective
To develop a GIS-based method to To develop a GIS-based method to evaluate the potential for scour at evaluate the potential for scour at bridges and to identify those bridges and to identify those structures that are scour structures that are scour susceptible.susceptible.
Presentation OverviewPresentation Overview
Bridge ScourBridge Scour
Available DataAvailable Data
MethodologyMethodology
Case StudyCase Study
ProgressProgress
Future WorkFuture Work
QuestionsQuestions
GIS-based ApproachGIS-based Approach
Bridge scour is the Bridge scour is the
erosion of streambed erosion of streambed
soils and sediment soils and sediment
that provide support that provide support
for bridge foundations.for bridge foundations.
Bridge ScourBridge Scour
Bridge ScourBridge Scour
The primary variables that effect scour:The primary variables that effect scour:
• Bed materialsBed materials
• Channel protectionChannel protection
• Channel and bridge geometryChannel and bridge geometry
• Flow hydraulicsFlow hydraulics
Bridge ScourBridge Scour
• Of the 832 bridge failures since 1950, Of the 832 bridge failures since 1950, 60% were related to scour.60% were related to scour.
• $50 million spent annually in Federal $50 million spent annually in Federal aid for scour related bridge failures and aid for scour related bridge failures and repairs.repairs.
• 3 bridges failures have resulted in the 3 bridges failures have resulted in the loss of 25 lives in the last 15 years.loss of 25 lives in the last 15 years.
Bridge ScourBridge Scour
Over the 49,186 Over the 49,186
bridges in Texas . . . bridges in Texas . . . • 40,814 bridges –40,814 bridges –
over waterways over waterways • 688 bridges – 688 bridges –
scour criticalscour critical
Bridge ScourBridge Scour
Scour critical bridges – structural integrity Scour critical bridges – structural integrity potentially jeopardized due potentially jeopardized due
to scour. Requires Level II Analysis.to scour. Requires Level II Analysis.
Level II Analysis – developed in HEC 18 Level II Analysis – developed in HEC 18 requires on site investigation, bridge requires on site investigation, bridge foundation information, modeling of stream foundation information, modeling of stream
Bridge ScourBridge Scour
Scour susceptible bridges – likelihood that Scour susceptible bridges – likelihood that bridge may be vulnerable to scour.bridge may be vulnerable to scour.
Current methods require large database of Current methods require large database of analyzed bridges for comparisons, or analyzed bridges for comparisons, or envelope curves based on historical scour envelope curves based on historical scour measurements.measurements.
GIS-based ApproachGIS-based Approach
Due to the large number of bridges, their Due to the large number of bridges, their spatial distribution, wide variety of data spatial distribution, wide variety of data required and cost of performing Level II required and cost of performing Level II analysis, a robust method of analysis is analysis, a robust method of analysis is required. GIS is an effective means for required. GIS is an effective means for spatially storing the database, analyzing the spatially storing the database, analyzing the data and presenting the results.data and presenting the results.
Prioritization of bridges susceptible to scour Prioritization of bridges susceptible to scour
can be more easily accomplished using a GIS can be more easily accomplished using a GIS scheme than previous methods.scheme than previous methods.
General MethodologyGeneral Methodology
HEC GeoRas
HEC GeoRas
Data Processing
Analysis Validation
Available DataAvailable Data
USGS Harris County USGS Harris County Surface-Water DataSurface-Water Data
- daily stream flow and measurements- daily stream flow and measurements provides gage location, channel width, provides gage location, channel width,
cross section area, velocity, gage cross section area, velocity, gage height, discharge and drainage area.height, discharge and drainage area.
Available DataAvailable Data
Federal Highway Federal Highway AdministrationAdministration
National Bridge Inventory (NBI) National Bridge Inventory (NBI)
DatabaseDatabase
- electronic database coded by DOTs- electronic database coded by DOTs
provides data on bridges such as structural provides data on bridges such as structural type, number of spans, geometry, length, type, number of spans, geometry, length, width, channel protection, etc.width, channel protection, etc.
Available DataAvailable Data
USDA – NRCSUSDA – NRCS
SSURGO Soil Data SSURGO Soil Data
- shapefile of county along with multiple - shapefile of county along with multiple tables providing soil information such tables providing soil information such as classification, hydrologic group, as classification, hydrologic group, sieve passing percents, soil erodibility sieve passing percents, soil erodibility factor, etc.factor, etc.
HEC GeoRas
HEC GeoRas
General MethodologyGeneral Methodology
Data Processing
Validation Analysis
Case Study: Harris CountyCase Study: Harris County
Case Study: Harris CountyCase 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)
Case Study: Harris CountyCase Study: Harris County
Case Study: Harris CountyCase Study: Harris County
Case Study: Harris CountyCase Study: Harris County
Erodibility Erodibility
Case Study: Harris CountyCase Study: Harris County
Bridges with Erosive Soils Bridges with Erosive Soils
Case Study: Harris CountyCase Study: Harris County
Channel ProtectionChannel Protection
< 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
Scour Susceptible BridgesScour Susceptible Bridges
Case Study: Harris CountyCase Study: Harris County
Case Study: Buffalo BayouCase Study: Buffalo Bayou
Selected 2 Bridges on Buffalo Bayou 2 Bridges on Buffalo Bayou to model total scour in HEC RASto model total scour in HEC RAS
HEC GeoRas
HEC GeoRas
General MethodologyGeneral Methodology
Data Processing
Analysis HEC
GeoRas
Validation
HEC GeoRASHEC 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
HEC GeoRASHEC GeoRAS
Buffalo BayouBuffalo Bayou
Triangular Irregular Triangular Irregular Network (TIN) data is Network (TIN) data is required. Contours required. Contours are created to allow are created to allow ArcView to refresh ArcView to refresh
more quickly. more quickly.
HEC GeoRASHEC GeoRAS
The following themes must be created:The following themes must be created:
Stream Centerline Stream Centerline
Main Channel Banks Main Channel Banks
Flow Path Centerline Flow Path Centerline
Cross-Sectional Cut Lines Cross-Sectional Cut Lines
and Land Useand Land Use
HEC GeoRas
HEC GeoRas
General MethodologyGeneral Methodology
Data Processing
Analysis Validation
HEC RASHEC RAS
An accurate hydraulic models of river An accurate hydraulic models of river reach containing bridge must be reach containing bridge must be
developed before scour calculations developed before scour calculations can be performed.can be performed.
HEC RASHEC RAS
Scour calculations Scour calculations
in HEC RAS require:in HEC RAS require:
Depth at bridgeDepth at bridge
VelocityVelocity
Number of piersNumber of piers
HEC GeoRas
HEC GeoRas
General MethodologyGeneral Methodology
Data Processing
Analysis
HEC GeoRas
Validation
HEC GeoRASHEC GeoRAS
Scour calculations Scour calculations
results can be results can be
exported back exported back
into ArcView.into ArcView.
Data Processing HEC
GeoRas
HEC GeoRas
General MethodologyGeneral Methodology
Validation Analysis
Current ProgressCurrent Progress
• Text files correctly delimited and Text files correctly delimited and column headers properly determinedcolumn headers properly determined
• All non-digital data made into point All non-digital data made into point shapefiles shapefiles
• Data correctly projected and combined Data correctly projected and combined in one projectin one project
• Used method to select 6 scour Used method to select 6 scour susceptible bridgessusceptible bridges
• Began initial HEC-GeoRAS and HEC Began initial HEC-GeoRAS and HEC RAS modelingRAS modeling
Future WorkFuture 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
Questions?Questions?