Last week, we discussed the importance of model reviews for the hydraulic modeling process which can help agencies assess flow conditions at roadway crossings more accurately.

Swiftly moving water at roadway crossings can cause bridge scour—the removal of sand, gravel, or other sediment from around bridge piers or abutments, which can compromise the integrity of a structure.

With one-dimensional modeling, flow directions are defined by the user during model setup. In a 2D model, flow directions are computed by the model at every element in the mesh.  This means multiple flow paths and flow splits are more accurately represented in a 2D model.

Example 2D hydraulic model showing flood flows at a typical roadway crossing on the South Platte River in Colorado. Flow direction is indicated by arrows and flood inundation limits by the color shading. (Credit CDOT)

With this improved representation of the flow paths and flow distribution at a crossing, engineers can develop better estimates of scour at each bridge component.  Furthermore, since the flow direction is computed in a 2D model, the angle of attack at bridge piers can be directly assessed rather that estimated.

To support use of 2D model results for bridge scour evaluation, FHWA has added specific scour tools in the SMS software interface for the SRH-2D model.  With these tools, averaged hydraulic parameters from specified locations can be computed and used in the FHWA Hydraulic Toolbox Bridge Scour Calculators, or other custom scour spreadsheets developed by users.

For more information on these new bridge scour tools, please explore the following links:

To learn more, please contact Scott Hogan or Laura Girard, Collaborative Hydraulics: Advancing to the Next Generation of Engineering (CHANGE) team co-leads.

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