Modeling an In-line flow split in PondPack

Product(s): PondPack
Version(s): CONNECT Edition,
Area: Modeling


How do I model an in-line hydraulic flow split? For example in a channel, junction structure, or inside a composite outlet structure (for example flow to a weir that splits into two separate pipes).



Insert a pond node at the diversion location and select the 'No volume' option for the pond node. Use any desired number pond routing links coming out of the pond node to represent diversion(s).

This configuration will allow the program to solve for the hydrograph diversion on the basis of structure hydraulics only. The storage effects are ignored. The diversion solution proceeds at each time step until the total structure outflow converges within tolerance to equal the sum of the flows discharged across all routing links, which share the same upstream pond volume node.


A composite outlet structure contains a weir which then directs flow into two culverts. The culverts have different invert elevations and diameters.

Typically, this would be done by setting the culvert to use multiple barrels. However, doing this requires the barrels to be the same size and at the same elevation.

This can be modeled with the following layout: Pond A > Weir > Pond B > 2 Culverts

NOTE: this example uses a single pond outlet structure and link for the two downstream pipes that split off from the weir. If you have a case where the flow splits off into two different directions and does not combine back together downstream, you may need to model two separate pond outlet elements and pond outlet structures.

Set  the Pond Outlet property "Has Control Structure?" to Yes, and assign a Composite Outlet Structure.

Pond Outlet A will use a composite outlet structure containing the weir.

Pond Outlet B will use a composite outlet structure containing the culverts.

Set Pond Type to No Volume for Pond B.

This will allow the conduits to be different diameters and at different elevations.

See Also

Modeling a flow split (diversion) in SewerGEMS or CivilStorm