Welcome to CivilGEO Knowledge Base
Welcome to CivilGEO Knowledge Base
Welcome to CivilGEO Knowledge Base
Welcome to CivilGEO Knowledge Base
The GeoHECRAS software can model roadway crossing bridges and culverts by using the Bridge & Culvert Data command. The Bridge & Culvert Data command defines the bridge & culvert data, roadway deck geometry, bridge piers, sloping abutments, ineffective flow areas, bridge methodology & parameters, multiple opening stations, internal geometry, and more.
The user can define bridge data for 1D flow areas in the same way as defining bridge data for a 2D model. HEC-RAS provides the same low flow (energy, momentum, and Yarnell) and high flow (energy and pressure/weir) bridge modeling approaches for both 1D and 2D bridge modeling.
The following sections describe how to perform bridge modeling in GeoHECRAS.
The roadway crossing centerline must be first defined to represent a bridge or culvert in a 1D model. The roadway crossing centerline must be drawn from left to right looking in a downstream direction.
To define the roadway crossing centerline, the user can use the Draw Roadway Crossings or Assign Roadway Crossings commands to either manually draw the roadway crossing centerline or assign an already existing polyline as the roadway centerline. Refer to this article in our knowledge base to learn more about the Draw Roadway Crossings or Assign Roadway Crossings commands.
The software requires a minimum of four cross sections to be defined for modeling a roadway crossing. Two cross sections are defined at the downstream end of the roadway crossing structure. By contrast, the other two cross sections are defined at the upstream end of the roadway crossing structure. However, additional cross sections can also be defined upstream of the roadway crossing to account for additional backwater created upstream of the roadway crossing.
The two cross sections adjacent to the roadway crossing are placed in the full valley area adjacent to the roadway embankment. They represent the geometry of the river valley without the roadway embankment, which is the roadway fill area. These cross sections are called the Upstream Face Cross Section and the Downstream Face Cross Section since they are located very near the face of the roadway crossing structure.
The cross section drawn at the upstream end of the Upstream Face Cross Section is called the Approach Cross Section. This cross section is drawn upstream of the roadway crossing at a distance far enough where the impact of the flow contracting inward through the bridge or culvert opening is no longer felt. The cross section drawn downstream of the Downstream Face Cross Section is called the Exit Cross Section and is placed at a distance far enough in the downstream direction where the impact of the flow expanding outward is no longer considered significant.
Once the 1D roadway crossing is defined, the user can enter the data for the 1D bridge in the Bridge & Culvert Data dialog box.
Follow the steps below to enter the bridge data:
The following sections describe how to enter the bridge data and interact with the above dialog box.
This section of the Bridge & Culvert Data dialog box is used to switch between roadway crossings. Note that if the user opens the Bridge & Culvert Data dialog box by double-clicking the roadway crossing on Map View, that roadway crossing will be selected by default.
This section contains the following entries:
This section of the Bridge & Culvert Data dialog box allows the user to select the various roadway specifications from the Roadway Crossing Specifications dropdown combo box. The Roadway Crossing Specifications dropdown combo box lists the following roadway specifications:
The Deck Roadway data panel is displayed by default when the Bridge & Culvert Data dialog box is displayed. This data panel provides a table for entering and editing the roadway high chord and bridge opening low chord geometry. The data in the table is used to describe the area that is blocked due to the roadway bridge deck, road embankment, and bridge opening vertical abutments.
To learn more about the Deck Roadway data panel, refer to this article in our knowledge base.
The Culverts data panel is used to define the culverts at a roadway crossing. Select the Culverts option from the Roadway Crossing Specifications dropdown combo box.
The Culverts data panel will be displayed.
To learn more about the Culverts data panel, refer to this article in our knowledge base.
After entering the deck roadway and culverts data, the user can define bridge piers and sloping abutments that are inside of the bridge opening.
Select the Bridge Piers option from the Roadway Crossing Specifications dropdown combo box.
The Bridge Piers data panel will be displayed.
In the above panel, the user can enter the pier data in the same exact manner as required for a 2D bridge. To learn more about the Bridge Piers panel, refer to this article in our knowledge base.
Select the Sloping Abutments option from the Roadway Crossing Specifications dropdown combo box.
The Sloping Abutments data panel will be displayed.
The Sloping Abutments data panel is the same as for 2D bridges and works the same way. To learn more about the Sloping Abutments data panel, refer to this article in our knowledge base.
The user can define ineffective flow areas for the upstream and downstream cross sections outside of the bridge. If the user has included the left and right roadway approaches as part of the bridge, then it may be necessary to define ineffective flow areas for the outside cross sections in order to compute accurate headwater and tailwater elevations for the bridge curves.
Select the Ineffective Flow Areas option from the Roadway Crossing Specifications dropdown combo box.
The Ineffective Flow Areas data panel will be displayed.
This data panel contains the following two types of ineffective flow areas:
This section allows the user to define a left station and elevation and a right station and elevation for the ineffective flow area. Refer to this article in our knowledge base to learn more about Normal Ineffective Flow Areas.
This section allows the user to define up to 10 individual blocks for each cross section. Refer to this article in our knowledge base to learn more about Multiple Blocks Ineffective Flow Areas.
The Bridge Methodology data panel allows the user to define which computational methods HEC-RAS will use at a bridge opening. The user can also select the bridge opening types and bridge pier shapes using this data panel.
Select the Bridge Methodology option from the Roadway Crossing Specifications dropdown combo box.
The Bridge Methodology data panel will be displayed.
To learn more about the Bridge Methodology data panel, refer to this article in our knowledge base.
The Bridge Parameters data panel allows the user to define the bridge parameters to be used for all bridges (if multiple bridge openings) at a roadway crossing.
Select the Bridge Parameters option from the Roadway Crossing Specifications dropdown combo box.
The Bridge Parameters data panel will be displayed.
To learn more about Bridge Parameters data panel, refer to this article in our knowledge base.
The WSPRO Parameters data panel computes the water surface profile through a bridge by solving the energy equation. Select the WSPRO Parameters option from the Roadway Crossing Specifications dropdown combo box.
The WSPRO Parameters data panel will be displayed.
To learn more about the WSPRO Parameters data panel, refer to this article in our knowledge base.
The Multiple Openings data panel defines stagnation points for multiple opening roadway crossings. Select the Multiple Openings option from the Roadway Crossing Specifications dropdown combo box.
The Multiple Openings data panel will be displayed.
To learn more about the Multiple Openings data panel, refer to this article in our knowledge base.
The Internal Geometry data panel allows the user to edit the two-ground geometry cross sections inside of the bridge opening. This panel allows the user to change the station and elevation data, roughness coefficients, and main channel bank stations for each of the two internal bridge cross sections.
Select the Internal Geometry option from the Roadway Crossing Specifications dropdown combo box.
The Internal Geometry data panel will be displayed.
To learn more about the Internal Geometry data panel, refer to this article in our knowledge base.
The Build Bridge Opening data panel allows the user to define the geometry of the bridge opening by using span or abutment data. Select the Build Bridge Opening option from the Roadway Crossing Specifications dropdown combo box.
The Build Bridge Opening data panel will be displayed.
To learn more about the Build Bridge Opening data panel, refer to this article in our knowledge base.
This data panel analyzes differences between bridge opening data for any two selected scenarios, and then exports the Opening Comparison Analysis results table.
Select the Opening Comparison Analysis option from the Roadway Crossing Specifications dropdown combo box.
The Opening Comparison Analysis dialog box will be displayed.
This data panel contains three sections: Select Existing Roadway Crossing for Comparison, Perform Opening Comparison Analysis, and Opening Comparison Results. To know more about this data panel, refer to this article in our knowledge base.
The user can adjust the roadway geometry at any time during the modeling process. Select the Geometry Adjustment option from the Roadway Crossing Specifications section.
The Geometry Adjustment data panel will be displayed.
This data panel is similar to the Geometry Adjustment data panel of the 2D Bridge & Culvert Data dialog box. Refer to this article in our knowledge base to learn how to do the adjustment of the roadway geometry.
Select the Geometry Point Reduction option from the Roadway Crossing Specifications section.
The Geometry Point Reduction data panel will be displayed.
Refer to this article in our knowledge base to learn more about the Geometry Point Reduction data panel in roadway crossing.
The Profile Results data panel allows the user to select the analysis results. Select the Profile Results option from the Roadway Crossing Specifications section.
The Profile Results data panel will be displayed.
To learn more about the Profile Results data panel, refer to this article in our knowledge base.
After the user has defined the necessary data for the roadway crossing structure, the user needs to define the parameters necessary to create the HTAB (hydraulic table of rating curves). Note that this data is only used for unsteady flow simulations and is ignored for steady flow simulations. To change the flow data from steady to unsteady flow data, go to the Input ribbon menu, click the Scenario Manager dropdown menu, and then select the Scenario Manager command. The Scenario Manager dialog box will be displayed.
In the Scenario Manager dialog box, enable the Unsteady Flow Data radio button and add new unsteady flow data from the Unsteady flow dropdown combo box. Close the Scenario Manager dialog box and the current scenario flow data is now changed to unsteady flow.
The user can now select the Hydraulic Parameters – Bridges & Culverts command from the Rating Curves – Hydraulic Parameters dropdown menu of the Analysis ribbon menu to define the parameters.
The Hydraulic Parameters – Bridges & Culverts dialog box will be displayed.
The Select Roadway Crossing section allows the user to select the roadway crossing for purposes of defining the hydraulic parameters. This section contains three entries: River name, Reach name, and Roadway crossing river station.
The Family of Rating Curve Parameters section is used to define the limits of the family of rating curves that are developed for the roadway crossing. This section covers the following parameters:
This section defines the parameters necessary to compute the rating curves for the selected roadway crossing. This section covers the following parameters:
The Maximum headwater elevation defines the maximum elevation that the water surface can reach on the upstream side of the roadway crossing. Enter the maximum elevation that you expect the water surface to reach on the upstream side of the bridge in the Maximum headwater elevation entry field. Click on the […] button next to the Maximum headwater elevation entry field to pick the elevation from the roadway crossing plot. To learn more about the maximum headwater parameter settings, refer to this article in our knowledge base.
The Maximum tailwater elevation and Maximum flow parameters are optional. However, entering a maximum flow value is recommended as it will help control the limits of the hydraulic property table at the roadway crossing.
To learn more about the various parameters provided in this dialog box, refer to this article in our knowledge base.
When the data are defined, the user can click the [OK] button to save the entered data and close the dialog box.
After the user has entered the roadway crossing data, the user must run the analysis by selecting the Compute Unsteady command from the Analysis ribbon menu.
When the analysis run is complete, the software will then generate a family of rating curves for any 1D bridge openings and then perform the 1D flow analysis.
Once the model has finished running, the user can begin to view the output related to the 1D bridge hydraulics.
The software provides several types of output results for 1D bridges, as described below:
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