SA/2D Connection Data Command - Knowledge Base on CivilGEO

Storage areas define the elements (i.e., reservoirs, lakes, detention ponds, storage nodes, etc.) where there are one or more inflows and only one computed outflow. Inflow comes from other elements in the model, such as drainage basins, routing reaches, or diversions. If there is more than one inflow, all inflow is added together before computing the outflow. It is assumed that the water surface in the storage area pool is level.

2D flow areas are regions of a model whereby the flow through that particular region will be computed with the HEC-RAS two-dimensional flow computation algorithms. 2D flow areas are defined by laying out a polygon representing the outer boundary of the 2D flow area and then specifying the computational mesh.

In GeoHECRAS, SA/2D connections are used to link two storage areas together with a hydraulic structure or two 2D flow areas, or a storage area to a 2D flow area. The user can draw SA/2D connections interactively on the map view or assign the already imported GIS shapefiles as SA/2D connections. The software also allows the user to place a hydraulic structure in the middle of a 2D flow area to control how flow travels from one series of cells to another series of cells. SA/2D connections can consist of a weir and gated spillway, culverts, a bridge, just a weir, rating curves, or a linear routing option. To learn how to draw SA/2D connections, refer to this article in our knowledge base.

To establish a hydraulic connection between two storage areas, 2D flow areas, or inside a 2D flow area, the SA/2D Connection Data dialog box will be used.

Follow the steps below to use the SA/2D Connection Data command:

From the Input ribbon menu, click the SA/2D Connections dropdown menu and select the SA/2D Connection Data command.
The SA/2D Connection Data dialog box will be displayed.

The following sections describe how to use the SA/2D Connection Data command and interact with the above dialog box.

Selecting SA/2D Connection

The Select SA/2D Connection section allows the user to switch between SA/2D connections.
Select SA/2D Connection section

The following options are provided:

SA/2D connection ID
This dropdown combo box lists all the SA/2D connections that are defined in the model. It allows the user to select a SA/2D connection that has already been defined. Clicking the pencil icon allows the user to edit the selected SA/2D connection ID.

The user can navigate between the previous and next SA/2D connections using the up and down arrow buttons. Alternatively, the user can click the […] button to select the SA/2D connection from the Map View.

Note that the up and down arrow buttons will be disabled (i.e., grayed out) when the model contains only a single SA/2D connection.
Description
This text field allows the user to enter additional information that describes the selected SA/2D connection.
New
The [New] button allows the user to create a new SA/2D connection. Note that the SA/2D connection name should be unique. Otherwise, a warning dialog box is displayed, and the user is then returned to the SA/2D connection ID field to change the ID.
Copy
Clicking the [Copy] button causes the software to copy existing SA/2D connection data to a new SA/2D connection. When this command is executed, the software automatically provides a unique default name for the duplicated SA/2D connection. The cursor is then placed into the SA/2D connection ID. The user can go with the default name or enter a different valid and unique ID before moving on to add any other data.
Delete
The [Delete] button allows the user to delete the current SA/2D connection from the project.
Less/More
The [< Less] and [More >] buttons at the Select SA/2D Connection header allow the user to hide and display the right side of the dialog box containing the SA/2D Connection Plot. This causes the dialog box to diminish in size when the user does not want to see the plot view.
Convert to Breakline
Clicking the [Convert to Breakline] button causes the software to convert the selected SA/2D connection into a breakline.

SA/2D Connection Specifications

The following sections describe the SA/2D connection specifications. Click on the dropdown selector at the SA/2D Connection Specifications entry to display the various data panels that define the SA/2D connection data.

Connection Data Panel

This panel provides the connection details for the selected SA/2D connection. By default, the Connection Data panel is shown when the SA/2D Connection Data command is selected.
Connection Data Panel

Connection Details

This section is used to define the connection details for the selected SA/2D connection.

Note that if the structure is drawn between two storage areas, a storage area and a 2D flow area, or between two 2D flow areas, the user will need to define the From and To locations. If the structure is drawn completely inside of a single 2D flow area, then the To and From connections are automatically set to the 2D area.

The following options are provided:

From SA/2D area ID
This dropdown combo box allows the user to select the storage area or 2D flow area ID that the water flows from. Alternatively, the user can click the [Pick] button to select the storage area or 2D flow area from the Map View.
To SA/2D area ID
This dropdown combo box allows the user to select the storage area or 2D flow area ID that the water flows to. Alternatively, the user can click the [Pick] button to select the storage area or 2D flow area from the Map View.

Clicking on the [Reverse Connection] button causes the software to reverse the SA/2D connection selected in the From SA/2D area ID and the To SA/2D area ID dropdown combo boxes. When the user clicks this button, a confirmation dialog box is displayed as shown below.
Reverse SA/2D Connection confirmation dialog box

Clicking on the [Reverse Direction] button causes the software to reverse the geometry of the SA/2D connection. Note that this button is disabled (grayed out) if the storage area or 2D flow area is not selected. When the user clicks this button, a confirmation dialog box is displayed as shown below.
Reverse SA/2D Connection Geometry confirmation dialog box

2D Weir Polyline Cell Spacing

This section is used to define the cell spacing values along the storage area or 2D flow area connection polyline. The following options are provided:

Cell spacing along weir polyline
This entry represents the cell spacing along the storage area or 2D flow area connection polyline. If this entry is left blank, then the cell spacing used in the vicinity of the storage area or 2D flow area connection will be used. Click the […] button to measure the SA/2D connection cell spacing from the Map View.
Relaxed cell spacing in 2D flow area
This entry represents the cell spacing further away from the storage area or 2D flow area connection polyline. This value should not be the same as the Cell spacing along weir polyline value, or many cell errors may be introduced along the polyline. Click on the […] button to measure the SA/2D connection cell spacing from the Map View.

Connection Structure

This section is used to define the type of routing that will be used for the selected SA/2D connection. The following option is provided:

Structure type
This dropdown combo box allows the user to select the type of routing for the selected SA/2D connection from the following options:
1. Structure Routing: This option is used for both storage area and 2D flow area structures.
2. Linear Routing: This option is used for storage area structures only.

Based on the type of routing selected by the user, the other data panels in the SA/2D Connection Specifications dropdown combo box get enabled or disabled.

Culvert Flow Direction

This section is used to control the culvert flow direction for all culverts defined for the selected SA/2D connection. The following option is provided:

All culverts
This dropdown combo box allows the user to select the culvert flow direction from the following options:
1. No Flap Gates: This means that flow can move in both directions through the culverts. By default, this option is selected.
2. No Negative Flow: This means that flow can only move in the positive flow direction through the culverts (Downstream).
3. No Positive Flow: This means that flow can only move in the negative direction through the culverts (upstream).

Weir Only Computations

This section is used to define the computational method for the selected SA/2D connection. Note that this dropdown combo box is only available for the weir structure type. For other structure types, it is disabled (grayed out). The following option is provided:

Computation type
This dropdown combo box allows the user to define the weir computational method, which can be one of the following:
1. At Each Time Step
2. As Curves (faster)

2D Flow Area Internal Overflow Computation

This section is used to define the computational method for flow going over the top of the structure to be computed for the selected SA/2D connection. The following option is provided:

Computation type
This dropdown combo box allows the user to select the overflow computational method, which can be one of the following:
1. Weir Equation: If this option is chosen, all flow over the top of the hydraulic structure is computed with the weir equation. By default, this option is selected.
2. 2D Computation (No Gates/Culverts): If this option is chosen, the flow over the top of the structure is computed as normal 2D flow between cells.

Overflow Weir Panel

This panel provides overflow weir geometry specifications for the selected SA/2D connection.
Overflow Weir Panel

Overflow Weir Crest Geometry

This section provides a table for entering and editing storage area or 2D flow area connection overflow weir geometry. The geometry of the overflow weir is entered from left to right station looking in a downstream direction. The user enters stations and elevations at the top of the overflow weir. Everything below the defined crest geometry elevations is considered solid ground.

The right-click context menu of the table displays the commands to cut, copy, and paste data to and from the Windows clipboard as well as insert and delete rows to and from the table. In addition, the user can also export the table data to Excel or pdf format and delete the table data.

Overflow Weir Specifications

This section is used to define the dimensions of the overflow weir. The following options are provided:

Structure width (parallel to flow)
This entry field is used to specify the width of the overflow weir structure (measured along the flow direction). By default, the software uses a value of 10 ft. Alternatively, the user can click the [Pick] button to measure the structure width from the Map View.
Overflow weir crest shape
This dropdown combo box allows the user to define the spillway shape at the overflow weir. This is used to reduce the weir flow coefficient due to the submergence effect of weir flow submergence. Weir flow submergence occurs when the tailwater begins to drown out the weir flow. Two options are available: Broad Crested and Ogee.

If the user has selected the Ogee as overflow weir crest shape, two additional parameters: Spillway approach height and Design energy head are displayed in the Overflow Weir Specifications section.
Spillway approach height
This entry field is used to define the height, which is equal to the elevation of the spillway crest minus the mean elevation of the ground just upstream of the spillway.
Design energy head
This entry field is used to define the height, which is equal to the energy grade line elevation minus the elevation of the spillway crest.
Weir coefficient
This entry field allows the user to specify the coefficient of discharge for use in the weir flow equation for overflow. Note that different coefficients are used depending on units such as US Units or Metric (SI) Units. By default, the software uses a value of 2.6. Clicking on the […] button will display a lookup dialog box containing weir coefficients.
Note that if the Ogee shaped weir is selected, the user can compute the weir coefficient based on the approach and design energy head with a click of the [Compute] button.

Culverts Panel

This panel is used to define culvert specifications for the selected SA/2D connection.
Culverts Panel

Note that the contents of this panel are the same as the Culverts panel contained in the Bridge & Culvert Data dialog box, except that the entry Distance to Upstream Cross Section is missing in Culvert Dimensions section.

Note that this entry applies to all of the culverts defined for the selected SA/2D connection.

To learn more about this panel, refer to this article in our knowledge base.

Gates Panel

This panel provides gate specifications for the selected SA/2D connection.
Gates Panel

Gate Groups

The Gate Group is automatically assigned to “Gate #1” when the first-time user opens the Gate panel. The user can enter up to 20 different gate groups at each SA/2D connection, and each gate group can have up to 25 identical gate openings. If all of the gate openings are exactly the same, then only one gate group should be defined. If there are gate openings that are different in shape, size, elevation, have different coefficients, or other data, then an additional gate group must be added for each gate type.

Clicking on the [Add] button will create an additional gate group and automatically assign a name in the format of Gate # in the Gate group ID dropdown entry.

Clicking on the [Copy] button allows the user to copy the selected gate group (in order to change a dimensional parameter, etc.) and assign the Gate group ID in the format of Gate #.

Clicking on the [Delete] button allows the user to delete the selected gate group.

Clicking on the [Delete All] button allows the user to delete all defined gate groups.

Gate Definition

This section is used to define the gates at a roadway crossing.

Gate group ID
This dropdown combo box allows the user to select the gate group defined in the project. Clicking on the pencil icon allows the user to rename the selected gate group.
Type
This dropdown combo box allows the user to select the type of gate. Five options are available:
1. Sluice
2. Radial
3. Overflow (Closed Top)
4. Overflow (Open Air)
5. User Defined Curves

Based on the gate type selected, the contents of the Gates panel will be changed to show the required information for that gate type. Note that not all of the information is required for each gate type.

Gate Centerline Stationing

This section is used to define the centerline stationing of the gate openings. The user can manually enter a different centerline stationing for each gate opening that is part of the current gate group. All gate openings within the same gate group are identical in every way, with the exception of the centerline stationing. As a user adds new centerline stationing values, the number of identical gates in the group automatically increases and is displayed in the Gate Number column. A maximum of 25 gate openings can be defined in the table.

Gate Dimensions

This section sets the dimensions of the gate group being defined.
Gate Dimensions section

The following options are provided:

Height
This entry field is used to specify the maximum possible height that the gate can be opened. Alternatively, click the [Pick] button to measure gate height from the SA/2D connection plot.
Width
This entry field is used to specify the width of the gate. Alternatively, click the [Pick] button to measure gate width from the SA/2D connection plot.
Invert elevation
This entry field is used to specify the elevation of the gate invert. For overflow gates, this is the lowest elevation that the gate will open to. Alternatively, click the [Pick] button to select gate invert elevation from the SA/2D connection plot.

Sluice Gate Flow

This section defines the coefficients for the gate group being defined. Note that this section will be disabled if the Overflow (Open Air) and User-Defined Curves gate options are selected in the Type dropdown entry of the Gate Definition section.
Sluice Gate Flow section

The following options are provided:

Headwater reference
This dropdown option is used to select the reference point from which the upstream energy head will be computed. Two available options are: Sill (Invert) and Center of Opening.
1. Sill (Invert): This option is normally used when the flow through the gate goes out into a channel. By default, this option is selected.
2. Center of Opening: This option is used if the gate causes the flow to jet out freely into the atmosphere.
Discharge coefficient
This entry field is used to enter the coefficient of discharge for the gate opening. This coefficient ranges from 0.6 to 0.8 for Radial gates and 0.5 to 0.7 for Sluice gates.
Submerged orifice coefficient
This entry field is used to enter an orifice coefficient, which will be used for the gate opening when the gate becomes more than 80 percent submerged. Between 67 percent and 80 percent submerged, the software uses a transition between the fully submerged orifice equation and the free flow gate equations. When the flow is less than 67 percent submerged, the software uses the free flow gate equations.

In addition, the following options are available in the Radial Gate Flow section. Note that these options are only available when the user has selected a Radical gate option in the Type dropdown combo box of the Gate Definition section.
Radical gate flow section

Trunnion exponent
This entry field is used to enter the trunnion height exponent, which is used in the radial gate equation. By default, the software uses a value of 0 for this field.
Opening exponent
This entry field is used to enter the gate opening exponent, which is used in the radial gate equation. By default, the software uses a value of 1 for this field.
Head exponent
This entry field is used to enter the upstream energy head exponent, which is used in the radial gate equation. By default, the software uses a value of 0.5 for this field.
Trunnion height
This entry field is used to enter the height from the spillway crest to the trunnion pivot point. This data is only used for radial gates.

Weir Flow Over Gate Sill (Gate Out of Water)

If a gate is opened to the point where the top of the gate is no longer touching the water (or if an open-air overflow gate is being used), then the flow through the gate is modeled as weir flow. The software will automatically transition from gate flow to weir flow when the upstream head is between 1.0 to 1.1 times the height of the gate opening.
Weir Flow Over Gate Sill (Gate Out of Water) section

The following parameters are required to model the weir flow through the gate opening:

Weir Shape
This dropdown combo box allows the user to define the spillway shape at the overflow weir. The available options are: Broad Crested, Sharp Crested, and Ogee.

Based on the weir shape selected, the contents of the Weir Flow Over Gate Sill (Gate Out of Water) section will change to show the required information for that weir shape.
Weir coefficient
This entry field allows the user to specify the coefficient of discharge to be used in the weir flow equation for overflow. Note that different coefficients are used depending on units such as US Units or Metric (SI) Units. Clicking on the […] button will display a lookup dialog box containing weir coefficients.

If the user has selected the Ogee as weir shape, two additional parameters: Spillway approach height and Design energy head are displayed in the Weir Flow Over Gate Sill (Gate Out of Water) section.
Spillway approach height and Design energy head parameters

Note that the [Compute] button adjacent to the Weir coefficient entry field is used to compute the weir coefficient based on spillway approach height and design energy head.

Spillway approach height
This entry field is used to define the height, which is equal to the elevation of the spillway crest minus the mean elevation of the ground just upstream of the spillway. Alternatively, click the [Pick] button to measure the spillway approach height above the spillway crest from the SA/2D connection plot.
Design energy head
This entry field is used to define the height, which is equal to the energy grade line elevation minus the elevation of the spillway crest. Alternatively, click the [Pick] button to measure the design energy head above the gate sill from the SA/2D connection plot.

If the user has selected the Sharp Crested as weir shape, the following option will be displayed in the Weir Flow Over Gate Sill (Gate Out of Water) section.
Weir Shape-Sharp Crested shaped weir

Weir method
This dropdown combo box allows the user to define the weir coefficient from the following options: Weir Coefficient; Rehbock Equation; and Kindsvater-Carter Equation.

If the Weir Coefficient option is selected, the user simply enters a coefficient in the Weir coefficient entry field that will be used for weir flow through the gate, for all head ranges.

If the Kindsvater-Carter Equation is selected, the user must enter a spillway approach height in the Spillway approach height entry field. In addition, the user selects which form of the Kindsvater- Carter equation will be used from the Weir coefficient(L/b) dropdown entry to compute the coefficient. The form of the Kindsvater-Carter equation is based on selecting one of eleven equations that are based on varying L/b where L is the width of the gate opening, and b is the top width of the approaching water upstream of the gate. If more than one gate is defined at a particular opening, the user must figure out an average approach width for flow going to each gate.

If the Rehbock Equation is selected, the user is asked to enter a spillway approach height in the Spillway approach height entry field, and the weir coefficient is then computed with the Rehbock equation.

Outlet Rating Curve Panel

This panel allows the user to define and manage rating curves for the selected SA/2D connection structure.
Outlet Rating Curve Panel

Rating Curve Specifications

This section is used to define general information regarding the defined diversion rating curve. The following options are provided:

Rating curve ID
This entry field allows the user to specify a name for an outlet rating curve.
Outlet flow horizontal station
This entry field is used to define the specific horizontal position or stationing along the outlet structure where flow measurements or ratings are obtained. Alternatively, the user can click the [Pick] button to select the horizontal station from the connection weir on the Map View.
Outlet width (perpendicular to flow)
This entry field is used to define the width of the outlet structure perpendicular to the flow direction. Alternatively, the user can click the [Pick] button to measure the outlet width from the connection weir on the Map View.
Inlet location
This read-only field allows the user to select the inlet location where the water is coming from. Clicking on the [Pick] button allows the user to select the inlet location from the Map View. Clicking on the [Clear] button allows the user to delete the inlet location.
Outlet location
This read-only field allows the user to select the outlet location where the water exits. Clicking on the [Pick] button allows the user to select the outlet location from the Map View. Clicking on the [Clear] button allows the user to delete the outlet location.
Outlet flow based upon upstream
This dropdown combo box entry defines the type of diversion rating curve data that are to be defined. Two available options are:
1. Water Surface Elevation
2. Flow
  
  Note that based on the option selected, the contents of the table contained in a Diversion Rating Curve Data section will change.

Diversion Rating Curve Data

This section contains a table for entering and editing SA/2D connection structure diversion rating curve data.

Upstream Reference Water Surface Elev
This column of the table is used to specify the water surface elevation at a reference location upstream of a connection structure.
Outlet Flow
This column of the table is used to specify the flow values (discharge) for the corresponding diverted flow through the SA/2D connection structure.

Note that if the Flow option is selected in the Outlet flow based upon upstream dropdown entry of the Rating Curve Specifications section, the following table will be displayed:

Channel Flow
This column of the table is used to specify the flow values for the channel or outlet structure being analyzed.
Diverted Flow
This column of the table defines the corresponding diverted flow through the SA/2D connection structure for the diversion rating curve.

Outlet Rating Curve Plot

This section automatically plots the user-defined diversion rating curve. This visual representation allows the user to assess the behavior of the curve and make adjustments if necessary. Note that the rating curve axes change based upon the type of rating curve selected.

Outlet Time Series Panel

This panel allows the user to specify a name for an outlet time series to be used as an additional outlet through the SA/2D connection structure. Then a flow hydrograph can be specified for the SA/2D connection structure in the Unsteady Flow Data command. The flow time series will be labeled in the output based on the user-entered name for the outlet time series.
Outlet Time Series Panel

Refer to this article in our knowledge base to learn how to use the Unsteady Flow Data command.

Dam Breach Panel

This panel provides dam breach specifications for the selected SA/2D connection.
Dam Breach Panel

Note that the contents of this panel are the same as the Dam Breach panel contained in the Inline Structure Data command. Hence refer to this article in our knowledge base to learn more about this panel.

Linear Routing Panel

This panel provides linear routing specifications for the selected storage area. Note that this panel is only available when a Linear Routing option is selected in the Structure type dropdown entry of the Connection Structure section under the Connection Data panel. Otherwise, it is disabled (i.e., grayed out).
Linear Routing Panel

Note that the Linear Routing panel can only be used to connect two storage areas.

The following options are provided:

Positive flow direction routing coefficient
This entry field defines the linear routing coefficient for the positive flow direction (in the defined flow direction of the storage area connection).
Negative flow direction routing coefficient
This entry field defines the linear routing coefficient for the negative flow direction (opposite the defined flow direction of the storage area connection).
Overflow crest elevation
This entry field defines the minimum elevation of the spillway crest for flow to transfer from one storage area to the other. If both storage areas’ water surface elevations are below this crest elevation, then no flow is transferred between storage areas.

Geometry Adjustment Panel

This panel is used to adjust the geometry for the selected SA/2D connection.
Geometry Adjustment Panel

Adjust Storage Area Connection Geometry

This section defines the type of adjustment to be applied to the SA/2D connection geometry. The following radio button options are provided:

No change
On selecting this option, no change will be found for the SA/2D connection geometry. Note that this radio button option is selected by default when the dialog box is displayed.
Adjust elevations
On selecting this option, the entry field next to this option gets enabled, which allows the user to adjust the SA/2D connection geometry elevations by the defined amount.
Adjust stations
On selecting this option, the entry field next to this option gets enabled, which allows the user to adjust the SA/2D connection geometry stations by the defined amount.
Shift stationing
On selecting this option, the dropdown combo box and entry field next to this option gets enabled, which allows the user to shift the SA/2D connection geometry stationing using an existing reference point. The user can select the corresponding reference point from the dropdown combo box and then assign the station to be assigned to the reference point. The dropdown combo box contains the following options:
1. Leftmost Station
2. Thalweg
3. Rightmost Station

Perform Geometry Adjustment

This section shows the progress of the geometry adjustment with the help of a progress bar. Clicking the [Apply] button will apply the geometry adjustment to the selected SA/2D connection. Note that while performing the geometry adjustment, the [Apply] button changes to [Cancel] so that the user can abort the process if desired.

Geometry Point Reduction Panel

This panel allows the user to reduce the redundant geometry points so that the SA/2D connection can be analyzed by HEC-RAS.
Geometry Point Reduction Panel

Geometry Point Reduction

The Current number of weir geometry points is a read-only field that shows the total number of geometry points associated with the selected SA/2D connection.

The Reduce number of weir geometry points to entry field allows the user to enter the target numeric value (geometry points) for the SA/2D connection. By default, this entry will show 490. However, the user can enter a different value if desired.

Clicking on the [Preview] button causes the software to generate a preview of the defined geometry point reduction.

Select River Regions

The Apply reduction to dropdown combo box allows the user to specify the river regions for which the ground geometry point reduction should be applied. The user can choose from the following:

Current SA/2D Area Connection
All SA/2D Area Connection

Perform Geometry Point Reduction

This section shows the progress of the reduction of geometry points with the help of a progress bar. Clicking on the [Apply] button will apply the reduced geometry points to the specified SA/2D connection. Note that while performing the geometry adjustment, the [Apply] button changes to [Cancel] so that the user can abort the process if desired.