Draw and Assign Cross Sections Command (GeoSTORM)

Cross sections are located at intervals along a stream to characterize the flow-carrying capability of the stream and the adjacent floodplain. The cross sections should extend across the entire floodplain, should be perpendicular to the anticipated flow lines, and must not intersect with each other. Sometimes it is necessary to layout cross sections in a curved or dog-leg alignment to meet these requirements.

In GeoSTORM, cross sections can be defined by either drawing or assigning polylines on the Map View using the following commands:

• Draw Cross Sections
• Assign Cross Sections

Drawing/Assigning Cross Sections

The Draw/Assign Cross Sections command allows the user to manually draw or assign polylines on the Map View as cross sections.

Follow the steps below to use the Draw/Assign Cross Sections command:

1. From the Input ribbon menu, click the Cross Sections dropdown menu and select the Draw Cross Sections or Assign Cross Sections command.
2. The following dialog box(s) will be displayed:
   • Draw Cross Sections:
     
     
   • Assign Cross Sections:
     
     

The following sections describe how to use the Draw Cross Sections and Assign Cross Sections commands and interact with the above dialog boxes.

Drawing Cross Sections

In the Draw Cross Sections dialog box, the Draw Cross Section Polylines section allows the user to draw single or multiple polylines on the Map View as cross sections.

Follow the steps below to draw cross sections:

1. Click the [Draw] button and the dialog box will temporarily disappear. If the Draw curvilinear polyline checkbox option is checked, then the curvilinear polyline segments can be drawn on the Map View.
   
2. The status bar (shown under the Map View) will prompt the user to draw cross section polyline(s).
3. After drawing cross section polyline(s), press the [Enter] key or right-click and select Done from the displayed context menu.
4. The Draw Cross Section dialog will be redisplayed, and the polyline(s) will be drawn as cross section(s) on the Map View.

Assigning Cross Sections

In the Assign Cross Sections dialog box, the Select Cross Section Polylines section allows the user to manually assign single or multiple polylines on the Map View as cross sections.

Follow the steps below to assign cross sections:

1. Click the [Pick] button and the dialog box will temporarily disappear.
   
2. The status bar (shown under the Map View) will prompt the user to select single or multiple polylines.
3. After selecting the polyline(s), press the [Enter] key or right-click and select Done from the displayed context menu.
4. The Assign Cross Sections dialog box will be redisplayed, and the selected polylines will be assigned as cross sections on the Map View. Click the [Clear] button to cancel the previous selection and redo the entire process.

Other Specifications

This section is common to both the Draw Cross Sections and Assign Cross Sections dialog boxes. The following panels are available in this section:

• Extraction Data
• Other Data
• Roughness

Extraction Data

This panel allows the user to define the data extraction specifications for the selected cross sections.

Note: The Extract Elevation Data checkbox option needs to be checked to enable the content of the Extract Elevation Data and Cross Section Geometry Extraction Control subsections.

Extract Elevation Data

This subsection defines the Terrain elevation source used to extract cross section geometry. Depending upon the terrain elevation source selected, different options are provided to specify additional elevation data information.

The following options are available in the Terrain elevation source dropdown combo box:

• CAD Drawing
• Elevation Grid
• GIS Contours
• LandXML Data
• Terrain Surface
• TIN Surface

CAD Drawing

If the user selects CAD Drawing as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when CAD Drawing is selected as the terrain elevation source:

• CAD drawing layer: This dropdown combo box allows the user to select the CAD drawing layer available in the project.
• Drawing layers: Clicking the [Define] button adjacent to the Drawing layers entry displays the CAD Drawing Layers dialog box, allowing the user to define the properties of the drawing layers, as shown below.
  

Elevation Grid

If the user selects Elevation Grid as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following option is displayed when the Elevation Grid is selected as the terrain elevation source:

• Elevation grid layer: This dropdown combo box allows the user to select the elevation grid layer available in the project.

GIS Contours

If the user selects GIS Contours as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when GIS Contours is selected as the terrain elevation source:

• GIS polyline layer: This dropdown combo box allows the user to select the GIS polyline layer type.
• Elevation attribute: This dropdown combo box allows the user to select the elevation attribute type.

LandXML Data

If the user selects LandXML Data as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when the LandXML Data is selected as the terrain elevation source:

• TIN surface layer: This dropdown combo box allows the user to select the TIN surface layer type.
• TIN surface: This dropdown combo box allows the user to select the TIN surface type.

Terrain Surface

If the user selects Terrain Surface as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following option is displayed when the Terrain Surface is selected as the terrain elevation source:

• Terrain surface layer: This dropdown combo box allows the user to select the terrain surface layer type.

TIN Surface

If the user selects TIN Surface as the terrain elevation source, the content of the Extract Elevation Data subsection changes, as shown below.

The following options are displayed when the TIN Surface is selected as the terrain elevation source:

• TIN surface layer: This dropdown combo box allows the user to select the TIN surface layer type.
• TIN surface: This dropdown combo box allows the user to select the TIN surface type.

Cross Section Geometry Extraction Control

This subsection allows the user to control the amount of cross section geometry to extract for the assigned/drawn cross section polyline. This assures that an adequately deep enough cross section is created on both sides of the river reach. The software will try to compute the cross-section geometry data up to the specified depth and within the maximum width defined in this subsection.

If the selected polyline does not extend outward far enough to get the cross section depth specified, the software will automatically extend the constructed cross section further outward. Similarly, if the selected polyline extends too far outward for the depth specified, the software will automatically trim the constructed cross section.

Other Data

This panel allows the user to assign bank stations for the cross sections using channel width, channel depth, or bank polylines/polygons. The Assign Bank Stations checkbox needs to be checked to enable the content of the Other Data panel.

Assign Bank Stations

This subsection is used to construct channel bank locations based upon the selected option.

The following options are provided in this subsection:

• Define by channel width
  This radio button option is used to assign the bank stations using a defined channel width. The software first identifies the thalweg location on the cross section, then extends outward from the thalweg symmetrically until the desired channel width is achieved. Clicking the […] button allows the user to measure the channel width from the Map View.

• Define by channel depth
  This radio button option is used to assign the bank stations using an assumed normal flow depth and a maximum channel width search distance. The software first identifies the thalweg location on the cross section, then extends outward from the thalweg until the desired channel depth is reached while staying within the specified maximum channel width. Clicking the […] button allows the user to measure the maximum channel width from the Map View.

• Define by bank polylines/polygons
  This radio button option is used to assign the bank stations using selected polylines or polygons. Using the corresponding [Pick] buttons, the user can interactively select individual polylines or polygons on the Map View to be associated as bank stations. The user can click the [Clear] button to cancel the previous selection and redo the entire process. The software will first identify the thalweg location on the cross section, then extend outward from the thalweg until it reaches a previously selected bank polyline or polygon edge.

Roughness

During the extraction of the cross section geometry, the software will automatically assign a default Manning’s roughness for the left overbank, channel, and right overbank areas. However, the user can adjust these values in the Manning’s Roughness subsection of this panel.

Note that clicking the […] lookup button displays the Manning’s Roughness dialog box. This dialog box provides a reference to Manning’s roughness coefficients for some commonly used surface materials.