1. Home
  2. Knowledge Base
  3. GeoHECRAS
  4. River Junction Data Command

River Junction Data Command

The River Junction Data command allows the user to define/edit attribute data for river reaches.

Follow the steps below to use the River Junction Data command:

  1. From the Input ribbon menu, click on the River Reaches dropdown menu and select the River Junction Data command.
    River Junction Data Input ribbon menu commandAlternatively, the user can double-click the river junction node on the Map View to open the River Junction Data command.
  2. The River Junction Data dialog box will be displayed.
    River Junction Data dialog box

The following sections describe how to use the River Junction Data command and interact with the above dialog box.

Junction Specifications

This section allows the user to define the river reach data for the selected river junction.
Junction Specifications section

The following data are provided in this section:

  • River junction node
    This dropdown combo box lists the river junctions already defined in the model. The user can select a desired river junction node to edit.

    Click the [Pick] button to directly select a river junction from the Map View. On clicking the [Pick] button, the dialog box will temporarily disappear and the user will be prompted to select the river junction from the Map View. After selecting the river junction, the user will be returned to the dialog box with the river junction selected. To abort the selection process, press the [Esc] key or right-click and choose Cancel from the displayed context menu.
    Note that if the user opens the River Junction Data dialog box by double-clicking the river junction on Map View, then that river junction will be selected by default.
    Click the pencil icon to rename the selected river junction. Note that the river junction name must be unique. Otherwise, the Duplicate Junction Name dialog box will be displayed with the following message:

    Duplicate Junction Name dialog boxTo abort the rename operation, press the [Esc] key.

  • Steady flow computation mode
    This dropdown combo box allows the user to select the computational method to be used at the junction when performing steady flow hydraulic computations. The following methods are available in the dropdown combo box:
    Steady flow computation mode dropdown combo box

    1. Energy Equation
      This method is used to model the water surface profile at a river junction. The energy equation does not consider the angle of the tributary entering or leaving the main channel. In most situations, the amount of energy loss due to the angle of the tributary flow is insignificant and hence this is the preferred computational approach to use. By default, this method is shown selected in the dropdown combo box.
    2. Momentum Equation
      This method is used to consider the angle of the tributary entering or leaving the main channel. In situations where the angle of the tributary can cause significant energy losses, the momentum equation is the more appropriate computational approach to use.

      When this computational method is selected, an additional Angle (deg) column will be available in the Confluence Junction and Split Flow Junction sections data table. This column is used to enter the angle of the tributary relative to the main river. For river reaches that are considered to be the main channel, the angle should be left at 0.
      In addition, the following checkbox options get enabled on selecting the Momentum Equation method:

      Include friction component and Include weight component checkboxesThe Include friction component checkbox option is used to include the friction force component in the momentum equation. By default, this checkbox option is checked.

      The Include weight component checkbox option is used to include the weight component in the momentum equation. By default, this checkbox option is unchecked.
  • Unsteady flow computational mode
    This dropdown combo box is used to select the computational method to be used at the junction when performing unsteady flow hydraulic computations. The following methods are available in the dropdown combo box:
    Unsteady flow computational mode dropdown combo box

    1. Force Equal WSEL
      This method makes some simplifying assumptions for the unsteady state hydraulics at the junction. If the junction is a normal flow combining junction, then all cross sections that bound the junction are given the same water surface elevation during a time step, based upon the computed water surface elevation at the downstream side of the junction. This simplifying assumption requires that the cross sections be placed fairly close together around the junction, depending upon the slope of the stream. If the cross sections are spaced too far apart, then model stability problems may arise. By default, this method is shown selected in the dropdown combo box.
    2. Energy Balance
      This method performs an energy balance across the junction to compute the water surface elevation, rather than forcing the water surface elevations to be the same. It is useful when junction reach lengths are fairly lengthy or when the river reach has a moderate to a steep slope.
  • Description
    This entry field allows the user to describe the location of the river junction in more detail.

Junction Type

The dialog box automatically defines the types of river junctions of the selected node. The software determines the type of junction based upon the number of river reaches that are connected to the node, as well as the direction of the river reaches. The user cannot override the selected junction type radio button option.

The following types of junctions are available in the dialog box:

Undefined Junction

This radio button selection section defines the junction as undefined when the following conditions have not been met:

  • Three or more river reaches connected to the junction node
  • Only one river reach pointing downstream towards or downstream from the junction node

Undefined Junction radio button section

Confluence Junction

This radio button selection section defines data for river confluences, where rivers combine flow into a single reach. This junction type requires the following conditions to be met:

  • Three or more river reaches connected to the junction node
  • One river reach pointing downstream from the junction node

The following data corresponds to this radio button selection section:
Confluence Junction radio button section

  • Upstream reaches
    The Upstream reaches contain a table listing the upstream river reaches that contribute flow to the confluence. Each row in the table has read-only fields that show a contributing river reach. However, for each river reach, the flow distance from the cross section upstream of the junction and to the cross section downstream of the junction can be defined. In addition, when using the Momentum Equation method in the Steady flow computation method dropdown, the flow angle the river reach makes to the main river channel needs to be defined.

    The user can click the [Compute] button to automatically compute junction flow lengths when inserting a junction into the middle of an existing river reach or digitizing a new reach into the middle of an existing river reach.
  • Downstream river & reach
    This read-only field lists the downstream river reach.

Split Flow Junction

This radio button selection section is used to define data for split flow diversions, where a river splits into two (or more) river reaches. This junction type requires the following conditions to be met:

  • Three or more river reaches connected to the junction node
  • One river reach pointing downstream towards the junction node

The following data corresponds to this radio button selection section:
Split Flow Junction radio button section

  • Upstream river & reach
    This read-only field lists the upstream river reach.
  • Downstream reaches
    The Downstream reaches contain a table listing the downstream river reaches that split flow away from the junction. Each row in the table has read-only fields that show a split flow river reach. However, for each river reach, the flow distance from the cross section upstream of the junction and to the cross section downstream of the junction needs to be defined. In addition, when using the Momentum Equation method in the Steady flow computation method dropdown, the flow angle the split flow river reach makes to the main river channel needs to be defined.

    The user can click the [Compute] button to automatically compute junction flow lengths when inserting a junction into the middle of an existing river reach or digitizing a new reach into the middle of an existing river reach.
  • Balance (Optimize) steady flow diversions
    This checkbox option causes the HEC-RAS steady flow analysis to balance the flow between the downstream river reaches. It optimizes the amount of flow in the river reach until the computed energy grade elevation for the cross sections just downstream of the junction is within a specified tolerance (0.02 ft.). By default, this checkbox option is unchecked.

About the Author cxscvlgeo

  • Was this Helpful?
  • YesNo

Was this article helpful?

Related Articles