Assign Channel Banks Command

Last updated on August 12, 2026

Channel bank locations identify the boundaries of the main channel within each cross section. HEC-RAS uses these stations to divide the cross section into the left overbank, main channel, and right overbank subsections. This subdivision affects conveyance, hydraulic radius, velocity distribution, and the application of Manning’s roughness values.

In GeoHECRAS, the Assign Channel Banks command allows the user to assign channel bank locations using polylines or polygons, assumed channel normal flow depth, defined channel width, HEC-RAS computed water surface elevations for low flow conditions, or end points of the cross sections. Selecting the correct method can reduce the time required to edit bank stations individually while maintaining consistency across a river reach.

Follow the steps below to use the Assign Channel Banks command:

From the Input ribbon menu, click the Assign Entities dropdown menu and select the Assign Channel Banks command.
The Assign Channel Banks dialog box will be displayed.

The Assign Channel Banks dialog box contains five panels, each representing a different method for assigning channel bank locations. The following sections describe each panel in detail and how to interact with the above dialog box.

Polyline/Polygon

The Polyline/Polygon panel assigns the channel bank locations by projecting the intersections of drawn polylines or polygons onto the cross sections. This method is useful when the channel edge is already digitized as a GIS layer or drawn on the Map View.

Selecting Cross Sections

The Select Cross Sections section is used to manually select the cross sections for assigning channel bank locations. If a cross section is already selected on the Map View prior to running this command, the same cross section will be shown selected within the table.

Alternatively, the user can click the [Pick] button to interactively select the cross sections from the Map View. The user can also click on the river reach, and all associated cross sections will be selected. Clicking the [Select All] button causes all the cross sections to be selected. The user can click the [Clear All] button to cancel the previous selection and redo the entire process.

In addition, the user can filter the specific river reaches to be shown in the table listing. Once the cross sections are selected, the number of selected cross sections will be displayed in the Total selected read-only field.

Selecting Channel Bank Elements

The Select Channel Bank Elements section allows the user to select the polylines or polygons to be associated as channel banks. Click the [Pick] button to select the bank polylines or polygons from the Map View. The software will first determine where the thalweg location is on the cross section. It will then move outward from the thalweg until a previously selected bank polyline or polygon edge is reached. The user can click the [Clear] button to cancel the previous selection and redo the entire process.

Process Channel Bank Elements

This section contains the Replace existing channel banks checkbox option. This option causes the software to replace already defined cross section channel banks for cross sections that are processed by defined channel bank polylines. By default, this checkbox option is checked.

Channel Depth

The Channel Depth panel is used to assign the channel bank locations at the cross sections using the assumed channel normal flow depth.

Selecting Cross Sections

The Select Cross Sections section allows the user to manually select the cross sections for assigning channel bank locations.

Assigning Bank Stations

The Assign Bank Stations section allows the user to define the channel depth and maximum channel width to construct channel bank locations. The software will first determine where the thalweg location is on the cross section. It will then move outward from the thalweg until the requested channel depth is reached within the maximum channel width specified.

The Channel depth entry field specifies the depth used to define the top of the channel. By default, the software uses a value of 3 ft.

The Maximum channel width entry field limits how far outward from the thalweg the search will extend. By default, the software uses a value of 300 ft. Clicking the […] button allows the user to measure the maximum channel width from the Map View.

Process Channel Bank Elements

Channel Width

The Channel Width panel is used to assign the channel bank locations at the cross sections using a defined channel width. This method works well where the channel width is reasonably uniform, and the thalweg is near the center of the channel.

Selecting Cross Sections

The Select Cross Sections section allows the user to manually select the cross sections for assigning channel bank locations.

Assigning Bank Stations

The Assign Bank Stations section allows the user to define a maximum channel width for assigning channel bank locations. The software will first determine where the thalweg location is on the cross section. It will then move outward from the thalweg equally until the requested channel width is reached. The Channel width entry field allows the user to enter a maximum channel width. By default, the software uses a value of 300 ft. The user can enter a different value or click the […] button to measure the maximum channel width from the Map View.

Process Channel Bank Elements

WSEL Results

The WSEL Results panel is used to assign channel bank locations using the computed water surface elevations for low flow conditions.

Selecting Cross Sections

The Select Cross Sections section allows the user to manually select cross sections for assigning channel bank locations.

Selecting Output Profile

The Select Output Profile section allows the user to select the computed water surface elevation profile to be used as baseline low flow and then move channel bank locations to the next point above the water surface. From the Water surface profile dropdown combo box, the user can select the previously computed water surface profile to use as the basis for bank assignment.

Bank Assignment

The Bank Assignment section provides the following options for controlling where exactly the channel bank location is placed relative to the water surface elevation:

Next existing ground point above water surface: When this option is selected, the software places the channel bank location at the next existing ground point on the cross section that rises above the selected water surface elevation.
Create new ground point above water surface: When this option is selected, the software creates a new ground point on the cross section above the water surface elevation plus the specified height offset and places the channel bank location at that new point. By default, the software uses a height of 1ft, but the user can enter a different value.

Cross Section (XS) End Points

The XS End Points panel is used to assign the leftmost and/or rightmost ground station of each cross section as the channel bank locations. This method is useful for schematic models or cross sections that have already been trimmed to the channel extents.

Selecting Cross Sections

The Select Cross Sections section allows the user to manually select cross sections for assigning channel bank locations.

Assigning Bank Stations

The Assign Bank Stations section provides the following options to select which end point of the cross section is used to construct channel bank locations:

Use leftmost ground station: When this checkbox option is checked, the software will use the leftmost ground station on the cross sections to be set as the channel bank location.
Use rightmost ground station: When this checkbox option is checked, the software will use the rightmost ground station on the cross sections to be set as the channel bank location.

Process Channel Bank Elements

Assigning Channel Banks

When the data have been defined in the Assign Channel Banks dialog box, click the [OK] button. The software will then look at each selected option and assign the channel bank locations to all selected cross sections.