Defining a Control Structure in a Conduit

In Bentley SewerGEMS , you can attach a control structure, such as a weir or orifice, at either the upstream end or the downstream end of a conduit, or at both ends of the conduit. A control can also have a flap gate which allows flow to travel in only one direction. You define control structures for conduits in the Conduit Control Structures dialog box, which is accessible from the Property Editor for a conduit.

Note: For more information about control structures in Bentley SewerGEMS , see "Flow Control Structures"-357.

To define a control structure in a conduit:

Click a conduit in your model to display the Property Editor, or right-click a conduit and select Properties from the shortcut menu.
If the conduit has a start control structure, do the following:
In the Physical: Control Structure section of the Property Editor for the conduit, select the type of start control structure by selecting Side or Inline from the Start Control Structure Type submenu.
If the conduit contains a start control structure, set the Has Start Control Structure? field to True.
If the control structure contains a flap gate, set the Flap Gate field to True.
If the conduit contains a stop control structure, set the Has Stop Control Structure? field to True.
To define a control structure, click the Ellipses (...) button next to the Start Control Structure field and/or the Stop Control Structure, then perform the following steps:
In the Conduit Control Structure dialog box, click the New button, then select the type of control structure you want to create from the submenu (Functional, Orifice, Depth-Flow Curve, or Weir).
For a Functional control structure, specify whether the structure has a flap gate or not, then enter values for Crest Elevation, Coefficient, and Exponent.
For an Orifice control structure, specify whether the structure has a flap gate or not, enter values for Crest Elevation and Orifice Coefficient, select the Orifice Type (Bottom Outlet or Side Outlet) and Orifice Shape (Circular or Rectangular), then enter values for Diameter for a Circular orifice or Height and Width for a Rectangular orifice.
For a Depth-Flow Curve orifice, specify whether the structure has a flap gate or not, enter a value for Crest Elevation, then enter Depth and Flow values in the Depth-Flow table.
For a Weir control structure, specify whether the structure has a flap gate or not, enter values for Crest Elevation, Weir Coefficient, and Structure Top Elevation, then select the Weir Type (Inline, Side, V-Notch, or Trapezoidal) and enter values for the selected Weir Type.
Repeat Steps a - e for each additional component you want to add to the control structure, then click Close.
Perform the following optional steps:
To delete a component from the control structure, select the item in the list pane then click Delete.
To rename a control structure, select the control structure you want to rename, click Rename, then type the new name.
To view a report on the control structure, click Report.
To view a graph of a Depth-Flow curve, click Graph above the Depth-Flow curve table.

Conduit Control Structure Dialog Box

The Conduit Control Structure dialog box lets you add and edit control components to the control structure of a conduit.

Note: Only one control structure can be assigned to a conduit.


	New	Lets you create a new component for your control structure. These attributes are Functional , Orifice , Depth-Flow Curve , and Weir .
	Delete	Lets you delete the selected attribute.
	Rename	Lets you rename the control structure. By default, the structure is given a unique name, but you can set any other unique name that you prefer.
	Duplicate	This button allows you to create a copy of the currently highlighted control structure.
	Expand All	Expands all of the branches in the hierarchy displayed in the list pane.
	Collapse All	Collapses all of the branches in the hierarchy displayed in the list pane.
	Report	Lets you create and view a report of the control structure.

Depending on the type of control structure you select, the Conduit Control Structure dialog box contains the following controls:

Functional
Has Flap Gate?	Select this check box if the component includes a flap gate, clear it if not. When checked, reverse flow is not allowed through the structure.
Crest Elevation	The structure elevation at which flow starts to occur.
Depth or Head?	Define flow as a function of either freeboard depth or head across the outlet.
Coefficient	Set the coefficient.
Exponent	Set the exponent.
Orifice
Crest Elevation	Set the orifice crest elevation.
Has Flap Gate?	Select this check box if the component includes a flap gate, clear it if not. When checked, reverse flow is not allowed through the structure.
Orifice Coefficient	Set the coefficient.
Time to Open/Close	The time to open a closed (or to close an open) gated orifice. If 0 then time is not applied to the simulation.
Orifice Type	Select the type of orifice from the drop-down list: Side Outlet or Bottom Outlet . A Bottom Outlet type refers to a drop orifice (flow drops through it). A Side Outlet type refers to a normal flow-by orifice
Orifice Shape	Choose a circular or rectangular orifice.
Orifice Diameter	Set the diameter of a circular orifice.
Orifice Height	Set the height for a rectangular orifice.
Orifice Width	Set the width for a rectangular orifice.
Depth-Flow Curve
Has Flap Gate?	Select this check box if the component includes a flap gate, clear it if not. When checked, reverse flow is not allowed through the structure.
Depth or Head?	Define flow as a function of either freeboard depth or head across the outlet.
Depth-Flow Curve	Set the depth and flow values that define the depth-flow curve. The depth-flow curve consists of a table of the depth and pairs that define the depth-flow curve. Depth in this case refers to the water depth above the invert on the upstream side of the control structure and flow is the flow through/over the control structure.
New	Click this button to add new rows to the depth-flow table.
Delete	Click this button to remove selected rows from the depth-flow table. You can only remove one row at a time, if you have selected more than one row, only the last row you selected is removed
Graph	Click this button to view a graph of the Depth-Flow curve.
Weir
Has Flap Gate?	Select this check box if the component includes a flap gate, clear it if does not. When checked, reverse flow is not allowed through the structure.
Side Slope	Set the side slope of the weir.
Weir Coefficient	Set the weir coefficient, which is also known as the coefficient of flow. This value is used to account for variables that are not otherwise directly accounted for in the weir equation (e.g., vena contracta). The weir coefficient is unitless for V-Notch weirs, with a standard value around 0.58. The weir coefficient is unitized for the other weir types.
Structure Top Elevation	Set the structure top elevation for the weir.
Weir Type	Select the type of weir from the drop-down list: inline, side, V-notch, or trapezoidal.
Number of Contractions	Set the number of contractions for an inline weir. This field is available only when you select Inline Weir as the Weir Type.
Weir Length	Set the length of the weir.
Weir Angle	Set the weir angle for a V-notch weir. This field is available only when you select V-Notch Weir as the Weir Type.
Weir End Coefficient	Discharge coefficient for flow through the triangular ends of a trapezoidal weir. Typical values are 2.4 - 2.8 US (1.35 - 1.55 SI). This field is available only when you select Trapezoidal Weir as the Weir Type.
Weir Side Slope	Set the slope of the side of a trapezoidal weir. This field is available only when you select Trapezoidal Weir as the Weir Type.
SWMM Label	This is the weir link label used in the SWMM solver.
Can Surcharge	This option specifies how the calculation is performed if the weir opening is surcharged (submerged). If "True" is selected the solver switches the flow calculation from the weir equation to orifice equation when the weir opening is submerged and the weir equation is always used if the "False" is selected. This option does not apply to a weir that is part of a pond outlet structure since in that case a group of EQT (Pond Elevation - Outlet flow - Tail water elevation) curves are pre-generated and used in the pond calculations.

Note: The implicit solver may not be able to handle a structure when its crest elevation is higher than the pipes' crown elevation.

A note on the V-Notch weir coefficient with SWMM:

In Bentley SewerGEMS the weir coefficient (Cv) is Unitless and has a typical value around 0.58. However, in SWMM the v-notch weir coefficient (C) is unitized. In order to account for this the unitless value is converted to the unitized value upon export using the following equation.

C = (8/15)*Sqrt(2*g) * Cv

Alternativly, on import from SWMM C is converted to Cv:

Cv = (15/8) * C/(Sqrt(2*g))