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

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.

Presentation Overview Bridge Scour Available Data Methodology Case Study Progress Future Work Questions GIS-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 Scour

The primary variables that effect scour: Bed materialsBed materials Channel protectionChannel protection Channel and bridge geometryChannel and bridge geometry Flow hydraulicsFlow hydraulics

Bridge Scour Of the 832 bridge failures since 1950, 60% were related to 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.$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.3 bridges failures have resulted in the loss of 25 lives in the last 15 years.

Bridge 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 critical scour critical

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

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

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. 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. Prioritization of bridges susceptible to scour can be more easily accomplished using a GIS scheme than previous methods.

General Methodology HEC GeoRas Data Processing Analysis Validation

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

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

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

HEC GeoRas General Methodology Data Processing Validation Analysis

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)

Case Study: Harris County

Erodibility

Bridges with Erosive Soils

Case Study: Harris County Channel Protection Channel Protection < 6 NNot over water 9None needed 8Well vegetated 7Minor damage 6Slumping 5Eroded 4Extensive erosion 3Protection failing 2State of collapse 1Bridge closed

Scour Susceptible Bridges Case Study: Harris County

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

HEC GeoRas General Methodology Data Processing Analysis HEC GeoRas Validation

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

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

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

HEC GeoRas General Methodology Data Processing Analysis Validation

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

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

HEC GeoRas General Methodology Data Processing Analysis HEC GeoRas Validation

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

Data Processing HEC GeoRas General Methodology Validation Analysis

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

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

Questions?