Assign Multiple Cross Sections command

The Input | Cross Sections | Assign Multiple Cross Sections command enables the user to quickly assign a selection of existing polylines as cross sections on the Map View and have the software extract the cross section geometry from the underlying ground terrain.

Selecting this command will display the Assign Multiple Cross Sections dialog box.

Assign Multiple Cross Sections dialog box

The following sections are used for defining data in assigning multiple polylines as cross sections.

Select Cross Section Polylines

This section is used to interactively select polylines from the Map View for assigning as cross sections. Click on the [Pick] button and the dialog box will temporarily disappear. A prompt will be displayed at the status line, informing the user what to do next. Within the Map View, click on polylines to select them.

To select all of the polylines on the same map data layer, first select one polyline on the Map View. Then right-click and choose Select Similar from the displayed context menu. The software will then select all of the polylines contained on that layer.

When done selecting polylines, right-click and choose Done from the displayed context menu or press the [Enter] key. The Assign Multiple Cross Sections dialog box will redisplay showing the number of polylines selected.

Note that selected polylines must overlay only one existing river reach for this command to operate. See this section on defining river reaches.In addition, cross sections cannot already exist for the river reach. If cross sections already exist, then instead use the Assign Cross Sections command as described here.

Cross Section River Stationing

This section is used to define the river stationing to be used for the constructed cross sections. Define the downstream most cross section river station, along with the river stationing to be used for the upstream cross sections. Cross sections can be numbered using a fixed increment or by the river chainage alone the river reach. The river chainage can be in miles or feet if working in US units, or kilometers or meters if working in metric (SI) units.

Process Selected Cross Section Polylines

This section is used to define whether the selected polylines should be deleted after the cross sections are constructed. By default the delete selected polylines checkbox is unchecked.

Extract Elevation Data

This optional section is used to define the elevation data source to be used for extracting the cross section geometry. Depending upon the elevation data source type that is selected, different options are provided to specify additional elevation data information.

See this section for information on the types of terrain elevation data that can be used for constructing cross sections.

If the checkbox for this section is unchecked, then the subsequent sections below it are unavailable (i.e., grayed out). In addition, no geometry will be created when the cross sections are created. The cross sections will just be a flat horizontal lines at elevation 0.

Cross Section Geometry Extraction Control

This optional section is used to control the amount of cross section geometry to extract for the selected polylines. This assures the user that adequately deep cross sections are created on both sides of the river reach. The software will attempt to retrieve the cross section geometry data to the depth specified within the maximum cross section width specified.

If the selected polylines do not extend outward far enough to get the cross section depth requested, the software will automatically extend the constructed cross sections further outward. Similarly, if the selected polylines extend too far outward for too large of a depth, the software will automatically trim the constructed cross sections.

Assign Bank Stations

This optional section is used to construct channel bank locations based upon an assumed normal flow depth and a maximum channel width search distance. The software will first determine where the thalweg location is on a cross section. It will then move outward from the thalweg until the requested channel depth is reached within the maximum channel width specified.

Note that there are other methods for assigning channel bank stations, as described in this section.

Assignment of Manning’s Roughness and Flow Lengths

During the construction of the cross sections, the software will automatically assign a default Manning’s roughness for the left overbank, channel, and right overbank areas. See this section on how to define the default roughness values for the software to use.In addition, the cross section flow lengths are automatically determined.

About the Author Chris Maeder

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