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# Defining Bridge Parameters for HEC-RAS Bridge Modeling

In GeoHECRAS, the Bridge Parameters data panel of the Bridge & Culvert Data dialog box defines the bridge parameters to be used for all bridges (if multiple bridge openings) at a roadway crossing. This article describes how to use the Bridge Parameters data panel.

Follow the steps below to use the Bridge Parameters data panel:

1. Select the Bridge Parameters option from the Roadway Crossing Specifications dropdown combo box of the Bridge & Culvert Data dialog box.
2. The Bridge Parameters data panel will be displayed.

The following sections describe how to interact with the Bridge Parameters data panel of the Bridge & Culvert Data dialog box.

## Momentum Equation

This section defines the computational components to be included in the momentum equation. The Momentum Equation is one of the optional low flow methods used in computing flow through the bridge.

The section contains the following entries:

• Add friction component: This checkbox controls whether the momentum equation should include the friction loss component. This checkbox is checked by default.
• Add weight component: This checkbox controls whether the momentum equation should include the water weight component.

## Critical Depth Location

This section defines where the critical depth should be computed within the bridge opening.

If the program computes that the flow must pass through critical depth inside the bridge, critical depth will automatically be located inside the bridge at the most constricted cross section. If both cross sections are identical, the program will (by default) locate critical depth at the upstream inside cross section. However, if the user feels that it would be better to set critical depth inside the bridge at the downstream end, then this can be selected.

## Pressure Flow Criteria

This section defines how pressure flow is determined at a bridge opening. By default, the program uses the energy grade line elevation. Note that this does not change how pressure flow is calculated, only how the program checks for pressure flow at a bridge opening.

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