Special Conduits

Six special conduits are available for use in simulating real time control in a drainage network. 

The following are the special conduits available in XPSWMM and XPStorm. Up to seven may be defined for one reach, with each given a unique.

This page contains the following topics:

Regulator Link/Inflatable Weir

Use this option to control the flow through a conduit according to the depth in a given node. If this option is selected a conduit must also be selected within the same multi-link.

Node Name. Enter the name of the node which will control the flow in this conduit. The depth at this node will be used to control the flow according to the adjacent table. This node may be anywhere in the system.

Depth Vs Multiplier. This table is a look-up table to determine the multiplier to use for the flow in the link. The depth at the nominated node is used to look up this table to determine the appropriate multiplier to apply to this conduit.

Bendable Weir

Use this option to control the flow through a conduit according to the depth in a given node. If this option is selected a conduit must also be selected within the same multi-link.

Node Name. This is the name of the node whose depth controls the flow over the weir. If this name is left blank the upstream node is used by default.

Depth. This is the depth of flow in the "Node Name" above.

Bend Factor. This factor (0 or 1) determines whether or not the weir will bend at this depth. A value of 1 indicates flow over the weir. A value of 0 indicates no flow.

Rebound Factor. This factor (0 or 1) determines whether or not the weir will "bounce back" after being bent. A value of 1 indicates the weir stays down and does not rebound.

Special Pump (Pump Type 5) - Controlled by remote node depth

A Pump 5 pumping system (the Pump 5 name comes from CH2MHill in Portland) uses a dynamic head pump and a rule curve to modify the behaviour of the dynamic head pump based on the depth at either an adjacent or non-adjacent node. The flow through the pump will always be the minimum of the flow calculated by the dynamic head pump and the flow calculated using the special pump. If this option is selected a dynamic head pump must also be entered within the current multi-link.

Node Name. Enter the name of the node that will control the flow in this conduit. The depth at this node will be used to control the flow according to the adjacent table. This node may be anywhere in the system.

Depth Vs Flow. This table of depth at the nominated node versus flow in the special pump is used to determine the flow through this pump. The depth in the nominated node is used to look up the corresponding flow.

Omega. This is the weighting factor for the pump start-up and stop. It is used to dampen the start-up or shut down. Its range must be between 1 and 2 with 1.12 the recommended value.

User Defined Weir

A User Defined Weir can be specified by entering a weir length, exponent and discharge coefficient for a series of corresponding depths.

Depth. This is the depth of flow above invert of conduit.

Length. This is the length of weir sill at the adjacent depth.

Exponent. This is the weir exponent to use for the sill at the nominated depth.

Discharge Coefficient. This is the discharge coefficient to use at the nominated depth.

Internal Rating Curve

Select this item to define an internal rating curve for a diversion.

Depth Vs Flow. This table is used to look up the flow in this conduit for given depths in the upstream node or a driving head difference between the upstream and downstream nodes. During the simulation the upstream node depth is used when the downstream water surface elevation (HGL in d/s node) is less than the upstream node invert (i.e. no tailwater condition) to look up the corresponding flow in the conduit.  If during the simulation the downstream node HGL is higher than the upstream invert (i.e. a tailwater condition exists) then the difference between the node HGL upstream and downstream is used to index in to the curve for the corresponding flow rate.

By default the above depth or elevation difference is used by the internal rating curve.  To always use the depth in the upstream node for all conditions, use the Configuration Parameter USE_US_RC.  This would then behave a lot like a pump would.  However, see the note below:

Note: It is possible because of severe downstream conditions that the downstream as indicated by invert and the arrows on links has a higher water surface elevation than the upstream.  For a typical conduit this would result in a flow reversal.  Likewise for an internal rating curve the definition of upstream and downstream switches as the highest HGL at each time step will be the upstream.  This can mean that the flows will switch direction and may result in a hydrograph that can oscillate.  Consider adding flap gates to the connecting conduits to impose one flow direction or substitute a depth in node based pump to avoid these oscillations.

Other Special Diversion Types

This item is used to enter data for special diversion types that have not yet been made available explicitly in the interface. Examples of such diversions and how to input the diversion data into the Special Diversion dialog is shown below.

The data entered in the underlying dialog will depend on the type of diversion being entered. As no user error or warning notifications will be produced by the engine if inappropriate data is entered extra care must be taken when using this option.

Column #1 - Column #4. The meaning of these Columns will depend on the diversion type selected.

Factor #1 - Factor #3. The meaning of this factor will depend on the diversion type selected.

Type Number. When a new diversion type is added to the engine a four digit number will be allocated to that diversion type. This number must be entered in this field.

Other Special Diversion Examples

Seepage Losses: Modeling Seepage Losses from a Storage Node in the Hydraulics Layer

Factor #1 should be called “function”, and the type number must be 5000. The power function equation is entered on line 1 to activate the seepage conduit.

The equation for function conduits is:

Q=Column1* Zup^Column3- Column2* Zdn^Column4

Where:

Q = 0.1 * Zup²

where, Q is the flow

Zup = Upstream depth

Column1=0.1 and

Column3=2

As reported in the *.out file:

=====================================================

Input Information for functional channels seepage

=====================================================

Equation: 0.100 ** 2.000 - 0.000 ** 0.000

Point Data Data Data Data

No. Column Column Column Column

# 1 # 2 # 3 # 4

----- ------ ----- ------- ---------

1 0.100 0.000 0.000 2.000

Pump Discharge Pipes (Force Mains) 

Force mains can be typically simulated by a closed conduit that has the nodes sealed so there is no loss of water between the pump and the conduits representing the force main.  Since the conduits are modeled using a Priessmann slot it is possible in some cases to have some flow attenuation if large force mains under a lot of pressure.  Below see an alternative method to model the force main as a system curve with the pump.  In this case the force main effects are modeled and the pump and force main are simulated as a complete system.  This makes the typical assumption that the fluid is incompressible and the walls are rigid.

The Special Diversion: pump dialog contains all of the data needed to model the force main and pump combination.

• The first column in the first line is the pipe diameter in feet or meters.

• The second column in the first line is the pipe length in feet or meters

• The third column in the first line is the pipe roughness.

The second line has the minor losses for the pump discharge pipe. These losses are additive and are added together in the model. Column 1 to 4 represent the Entrance, Exit, Valve and Bend losses, respectively. These are “K” values in the minor loss equation.

The following table indicates the data entered in each cell:

The factors column completes this special control. The “all” in factor #1 means that this applies to all pumps connecting these two nodes in the multi-conduit. The type number of 4000 means that this is the data for a pump discharge pipe.

Factor #2 is the number of iterations used to calculate the pump discharge dynamic losses in the pump discharge pipe.

Factor #3 is the initial guess the program makes for the flow in the discharge pipe. A value of 0.50 means that 50 percent of the maximum pump flow is used by the program. This value may be between 0.0 and 1.0.

The data entered for the pump discharge pipe is echoed in the model output file under the name “Special Force Main Conduits”.  Browse the model output file to see this data echo.

The software calculates a Force Main Head that has the effects of the pump minor loses and the force main friction losses. This system curve is used between the upstream and downstream node of the pump link which will be typically drawn from the pump location to the downstream node of the force main.  It assumes that the flow in the force mains equal to the flow in the pump and that the downstream node of the pump is the termination point of the force main as entered in to the Special dialog.

The alternative to employing the Special conduit would be to seal a node between the pump and the force main. The force main would then be the next downstream link. In this situation, there will be some flow attenuation due to conduit storage, the Preissman slot and other factors.

Variable Speed Pumps

This Other Special Diversion configuration will make the pumps in a multi-link behave as a “variable” speed pump. The configuration of the Special Diversion must be as shown - has a first row of all zeroes; has a factor #1 name of “variable”; and a type number of 5000. All of these together will mean that any pumps in the same multi-link as the “variable” conduit will act like variable pumps.

Pump Check Valves

In order to simulation Pump Check valves the Special Diversion dialog must be configured as shown - Factor #1 should be named “check” for check valves; Factor #2 should be the name of a downstream pipe; The type number should always be 5000.

The number in the first row, first column is the minimum reported depth or pressure at the downstream node of the pump. The number in the second row, first column is the flow in cfs or cms that will trigger the usage of the minimum pressure.

Valves with Head Loss

Use the name “oneq” for the value in Factor #1 and the type number 5000. The flow through the valve should be entered in column 3 and the head loss in column 4 in units of ft or meters depending on the project units.