Identifying Bridge Scour Susceptibility: A GIS-based Approach

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.



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


• 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.


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


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


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


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.


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.


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


Data Processing

Validation Analysis

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)




Erodibility Erodibility


Bridges with Erosive Soils Bridges with Erosive Soils


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: 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


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


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.


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


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


Data Processing

Analysis

HEC GeoRas

Validation


Scour calculations Scour calculations

results can be results can be

exported back exported back

into ArcView.into ArcView.

Data Processing HEC

GeoRas

HEC GeoRas


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?

Identifying Bridge Scour Susceptibility: A GIS-based Approach

Documents

bridge scour susceptibility

historical scour

harris county case study

harris county datasets

bridge foundations

bridges failures

harris countybridges

related bridge failures