The Input | Cross Sections | Automated Draw Cross Sections command causes the software to automatically create cross sections along a river reach. The software will attempt to uniformly space cross sections along the river reach, creating cross sections that are perpendicular to the river reach. Where adjoining cross sections might cross each other, the software will intelligently bisect the cross section point of intersection and then run the adjoining cross sections parallel to each other. This command works well except for extremely sinuous sections of a river reach where cross sections would cross multiple adjacent cross sections.
Selecting this command will display the Automated Draw Cross Sections dialog box.
The following sections are used for defining data while automatically drawing cross sections along a river reach.
River Reach Selection
This section is used to select the river reach(es) that will be used to automatically draw cross sections along. The following options are provided:
- All river reach alignments – This option causes all the defined river reaches within a model to have cross sections created along them. This option works well when there is only one river reach in a model and the user wants the software to immediately start creating cross sections along it.
- Selected river reach alignments – This option is used to interactively select river reaches from the Map View for automatically drawing cross sections along it. 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 river reaches to select them. When done selecting river reaches, right-click and choose Done from the displayed context menu or press the [Enter] key. The Automated Draw Cross Sections dialog box will redisplay showing the number of river reaches selected.
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.
Cross Section Specifications
This section is used to define a maximum cross section spacing and cross section width. Note that the maximum cross section width field is ignored if the user has implemented the Cross Section Geometry Extraction Control section.
Cross Section Placement
This section is used to define automated cross section placement in the following special circumstances:
- River networks with existing junctions
- Control cross sections at the upstream and downstream face locations of roadway crossings
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 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 automatically drawn cross section 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 by extending outward or trimming back 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.
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. In addition, the cross section flow lengths are automatically determined.