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Pilot Channels Command

The Pilot Channels command allows the user to define a pilot channel along the river reach. Pilot channels are used for unsteady flow modeling. In order to stabilize unsteady flow models, placing a thin pilot channel along the river reach helps the model to converge to a stable solution. A pilot channel acts as a cushion of water during the computations, greatly speeding up the unsteady flow computations. The user can graphically adjust the pilot channel in the river profile view, selecting the region to apply the pilot channel cut along the river reach. This is helpful when the channel bottom is highly irregular along the river reach. Creating a uniform pilot channel slope along the river reach tends to dampen out the effects of the channel bottom irregularities.

Follow the steps below to use the Pilot Channels command:

  1. From the Input ribbon menu, select the Cross Sections dropdown menu and then choose the Pilot Channels command.
    Pilot Channels command from the Cross Sections dropdown of Input ribbon menu
  2. The Pilot Channels dialog box will be displayed.
    Pilot Channels dialog box

The following sections describe the Pilot Channels command and how to interact with the above dialog box.

Selecting River Reach

The Select River Reach section allows the user to select the river and the reach for defining the pilot channels.

Note that if a river reach has been preselected from the Map View prior to running this command, then the selected river reach will be displayed in the River name and Reach name dropdown combo boxes.

If the model contains a single river and reach, then it will automatically be selected in the River name and Reach name dropdown combo boxes. If the model contains multiple rivers and reaches, then the user can select the desired river and the reach from the River name and Reach name dropdown combo boxes.

Alternatively, the user can click the [Pick] button to select the river and the reach from the Map View. Clicking on the [Pick] button causes the Pilot Channels dialog box to temporarily disappear. The software will then prompt the user to select the river reach from the Map View. After selecting a river reach, the Pilot Channels dialog box will be redisplayed with the river reach shown as selected. The selected river reach is highlighted on the Map View. To abort the selection process, the user can press the [Esc] key or right-click and select Cancel from the displayed context menu.

In addition, a graphical plotting displaying a longitudinal view of the river reach and the pilot channels along the river reach is provided in this section.

Pilot Channel Editing

This section allows the user to define the parameters for creating a pilot channel. It includes the parameters for defining channel invert over a range of cross sections and the parameters to define a pilot channel cut for the selected cross sections.

The user can select either of the following panels to define pilot channels:

  • Draw Invert
  • Project Slope
  • Interpolate Invert

Draw Invert

This tabbed panel allows the user to draw the channel invert (channel bottom) along the existing river reach. Click the [Draw] button, and then draw channel invert on the graphical plot available under the Select River Reach section. When finished, right-click and choose Done from the displayed context menu. The software will then automatically compute the required channel invert. Note that the drawn pilot invert should be sloped downward going downstream for the best computational result.
Draw Invert panel

After drawing the pilot channel invert, the user should manually specify the pilot channel width and Manning’s n value in the Pilot Channel Data section to stabilize unsteady flow models.

Project Slope

This tabbed panel allows the user to enter an elevation for the invert of the pilot channel and project it on a slope over the range of cross sections.
Project Slope panel

Follow the steps below to define a new channel bottom slope:

  1. Click on the Downstream cross section dropdown combo box and then select the cross section that will be used as the downstream most river station. By default, the software selects the cross section at the downstream end of the river reach.
    Downstream cross section dropdown combo box
  2. Click on the Upstream cross section dropdown combo box and then select the cross section that will be used as the upstream most river station. By default, the software selects the cross section at the upstream end of the river reach.
    Upstream cross section dropdown combo boxAlternatively, click the [Pick] buttons adjacent to the Downstream cross section and Upstream cross section dropdown combo boxes and select the corresponding cross sections from the Map View. After clicking the [Pick] button, the Pilot Channels dialog box will temporarily disappear. The software will then prompt the user to select the associated cross section from the Map View. After selecting the cross section, the Pilot Channels dialog box will be redisplayed with the cross section shown selected.
  3. Define the Pilot channel width.
  4. Specify the Pilot Channel Manning’s n value, which should be equal to or higher than the main channel n value. Clicking on the […] lookup button will display a Manning’s Roughness lookup table dialog box.
    Manning's Roughness dialog box
  5. Define the Pilot channel invert elevation.
  6. From the Cut options section, select the desired option for applying the pilot cut for each of the cross sections within the selected range. The following options are available:
    • The Same cut to all cross sections radio button option is used to define the same pilot cut for each of the cross section in the selected cross section range.
    • The Project from downstream XS at slope (V:H) radio button option allows the user to enter elevation for the most downstream cross sections and have the invert elevations for other cross sections computed by projecting cuts on a constant slope upstream.
    • The Project from upstream XS at slope (V:H) radio button option allows the user to enter elevation for the most upstream cross section of the range and have the invert elevations for all other cross sections computed by projecting a user-specified slope downstream.
  7. Click the [Apply] button.

Interpolate Invert

This tabbed panel allows the user to define an invert elevation for the downstream most and the upstream most cross sections, and then automatically interpolate invert elevations for all the cross sections in between the selected range.
Interpolate Invert panel

Follow the steps below to interpolate invert elevations:

  1. Click the Downstream cross section dropdown combo box and then select the cross section that will be used as the downstream most river station for applying channel invert.
  2. Click the Upstream cross section dropdown combo box and then select the cross section that will be used as the upstream most river station for applying channel invert.
  3. Define the Pilot channel width.
  4. Specify the Pilot channel Manning’s n value, which should be equal to or higher than the main channel n value.
  5. Define the Downstream XS pilot channel invert elevation and the Upstream XS pilot channel invert elevation.
  6. Click the [Apply] button.

Pilot Channel Data

This section provides a table that displays the final pilot channel values for each of the cross sections. The user can modify the table directly and change any value on a cross section-by-cross section basis. Any update in the pilot channel data is automatically reflected in the table.
Pilot Channel Data section

Selected Cells Group Editing

This section allows the user to quickly enter/edit the pilot channel data in the pilot channel summary table (described above).

Follow the steps below to update the pilot channel data:

  1. Select desired cells in the Pilot Channel Data table.
  2. Click the Define change dropdown combo box and then select one of the options for updating the cell’s value and enter the change coefficient.
    Define change dropdown combo box
    The following options are available:

    • Add Constant: This option adds a constant value to the selected cell’s value.
    • Multiply By Factor: This option multiplies the selected cell’s value by a user-defined number.
    • Apply Value: This option replaces the selected cell’s value with the user-specified value.
  3. Click the [Apply Change] button to apply the defined pilot channel adjustment. Note that the [Apply Change] button is only available when a group editing option other than the default No Change option is selected.

When all the pilot channel information has been defined in the Pilot Channels dialog box, click the [OK] button, and the software will create a new pilot channel geometry.

About the Author Chris Maeder

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