An outfall is the point where wastewater or stormwater is discharged from a drainage system, sewer system, or treatment plant into a larger body of water such as a sea, lake, river, or ocean. It is typically the endpoint of a network of pipes or conduits that collect and transport the water or wastewater from various sources (such as industries, homes, or storm drains) to this final point of release into the environment. In hydrology, outfalls are terminal nodes of the drainage system used to define the final discharge point under dynamic wave flow routing. For other flow routing methods such as a kinematic wave, the terminal outfall behaves as a junction. Refer to this article in our knowledge base to learn more about terminal outfall.
In GeoSTORM software, terminal outfalls can be drawn or assigned using Draw Terminal Outfalls and Assign Terminal Outfalls commands. Refer to this article in our knowledge base to learn how to incorporate terminal outfalls into the stormwater project.
After adding terminal outfalls, the user can use the Terminal Outfall Data command to define additional data and view the corresponding output results.
Follow the steps below to use the Terminal Outfall Data command:
- From the Input ribbon menu, click the Terminal Outfalls dropdown menu and select the Terminal Outfall Data command.
- The Terminal Outfall Data dialog box will be displayed.
The following sections describe how to use the Terminal Outfall Data command and interact with the above dialog box.
Selecting Outfall
The Select Outfall section allows the user to select the terminal outfall for defining the terminal outfall data. The user can create a new terminal outfall, copy existing terminal outfall data to a new terminal outfall, and delete a terminal outfall. In addition, the user can navigate between terminal outfalls and enter a description detailing the defined terminal outfall.
The following options are provided in this section:
- Outfall ID
This dropdown combo box lists all the terminal outfalls defined in the current scenario. Click on the edit option (i.e., the pencil icon) to edit the terminal outfall ID. The Up and Down arrow buttons allow the user to switch between the next adjacent downstream and upstream terminal outfalls. Note that the Up and Down arrow buttons will be disabled (i.e., grayed out) if the current scenario contains only one terminal outfall. Alternatively, the user can click the […] button to select the terminal outfall from the Map View.
- Description
This optional text field allows the user to enter additional information that describes the selected terminal outfall.
- New
The [New] button allows the user to draw a new terminal outfall on the Map View. Note that the ID of every newly created terminal outfall must be unique.
- Copy
The [Copy] button allows the user to create a copy of the selected terminal outfall on the Map View along with its associated data.
- Delete
The [Delete] button allows the user to delete the selected terminal outfall from the current scenario.
- Less/More
The [< Less] and [More >] buttons at the Select Outfall header allow the user to hide and display the right side of the dialog box containing the Computed Results plot for terminal outfalls. This allows the dialog box to be smaller in size when the user does not want to see the plot view.Note: From the Scenario Manager dialog box, selecting Rational Method as the hydrology analysis engine hides the plot view. This is because, for the Rational Method, there is no concept of time and hence no concept of routing flows as the analysis assumes steady-state peak flows at all nodes.
Outfall Specifications
This section allows the user to define general options for the selected terminal outfall.
Terminal Outfall Definition
The following options are provided in this section:
- Outfall type
This dropdown combo box allows the user to define the type of outfall boundary condition.
The following outfall boundary condition types are available:- Critical Depth – The outfall water surface elevation is set to the minimum elevation between the critical flow depth and the normal flow depth in the connecting conduit.
- Fixed WSEL – The outfall water surface elevation is defined as a fixed elevation.
- Normal Depth – The outfall water surface elevation is defined based on the normal flow depth in the connecting conduit.
- Tidal Boundary – The outfall water surface elevation is defined in a table of tide elevation versus time.
- Time Series – The outfall water surface elevation is defined from a time series of elevation.
Note: Based upon the selected outfall boundary condition type, the content of the Terminal Outfall Definition section will be changed.
- Backflow flap gate
This checkbox option allows the user to define whether a flap gate will be enabled to prevent backflow (or flow reversal) at the terminal outfall. By default, this checkbox option will be disabled (i.e., grayed out).This entry field defines the invert elevation of the terminal outfall. - Invert elevation
This entry field defines the invert elevation of the terminal outfall. - Downstream link slope (H:V)
This read-only entry field displays the slope for connecting links that constitute one of the following elements:- Pipes
- Routing Reach
- Roadway Segment
- Roadway Crossing (i.e., Culvert)
- Fixed water surface elevation
This entry field allows the user to define the water surface elevation at the terminal outfall. Note that this entry field is only available when Fixed WSEL is selected as the outfall type.
Tidal Boundary Definition
This tabbed panel allows the user to define the tidal boundary data for the terminal outfall, which describes how the tidal elevation at the terminal outfall changes over time. Selecting this panel displays a data table with Time from Midnight and Tidal Elevation columns. The Time from Midnight column defines the elapsed time from 12:00 AM midnight. The Tidal Elevation column defines the tidal elevation at each specified time. Note that this tabbed panel is only available when Tidal Boundary is selected as the outfall type.
Tidal WSEL Plot
The Plot tabbed panel displays a graphical plot corresponding to the data defined in the Tidal Boundary Definition tabbed panel.
Time Series Definition
This tabbed panel allows the user to define the time series data for the terminal outfall, which describes how the water surface elevation at the terminal outfall changes over time. Selecting this panel displays a data table with Time from Midnight and Water Surface Elevation columns. The Time from Midnight column defines the elapsed time from 12:00 AM midnight. The Water Surface Elevation column defines the water surface elevation at each specified time. Note that this tabbed panel is only available when Time Series is selected as the outfall type.
Time Series WSEL Plot
The Plot tabbed panel displays a graphical plot corresponding to the data defined in the Time Series Definition tabbed panel.
Computational Results
This section provides a summary of stormwater computational results for the selected terminal outfall.
The following results are provided in this section:
- Peak flow rate
This read-only field displays the peak flow rate that occurred at the terminal outfall during the storm event. - Maximum WSEL
This read-only field displays the maximum water surface elevation that occurred at the terminal outfall during the storm event. - Maximum water depth
This read-only field displays the maximum water depth that occurred at the terminal outfall during the storm event. - Stored water volume
This read-only field displays the total stored water volume that occurred at the terminal outfall during the storm event.