Free outlet into open system

[ncst8pe]

It seems that the only way to model a pipe outlet into an open system is to provide a junction. However, the junction assumes a shape, therefore providing storage that isn't really there. Suggestions on how to accurately represent this situation?

[b22smith]

If I understand your question correctly, you are providing an outfall pipe to a wetlands, ditch, or other open system? When I encountered this I discussed with StormNET tech support and was told to provide a junction at the outlet end of the pipe (as you noted) and then provide a link from that junction to the outfall node. This last link the tech support had me create it as an arbitrary channel 20 feet wide and 40 feet long from the outlet pipe junction node to the outfall node. This channel is does not really exist.

I originally had the link modeled with the "Direct" option checked in the link properties, but was direct to use the overly wide channel (not sure why). I'm not answering your question for you, but that's how their tech support had me do it, so I'm interested in the StormNET response on this as well.

Brad Smith, PE
NCSU 1993

[Chris Maeder]

Note that I am not certain what you mean by "open system" other than perhaps a lake or wetland.

If you are needing to represent storage at a node, you should use a "Detention Pond" node--which is actually just a storage node. If you do not need to represent storage, then it can be handled by a junction node.

If you are needing to discharge into a downstream storage area and you really do not care about modeling that storage area, then you can model the downstream outlet as an "Outfall" node. When defining the Outfall node, you can define what the downstream boundary condition type is.

With regard to Brad's comment, we were initially debugging his model and did not know what the downstream boundary conditions were--and were just trying to make certain that the downstream end of the model was not causing un-necessary backwater in the pond.

All of these elements are described in detail in the StormNET User Manual and Online Help. (Make certain you have downloaded and installed the new StormNET software--it has a new User Manual and Help System.)

If you are continuing to need technical assistance, please feel free to contact our technical support at 800-488-4775. We are here to assist.

[b22smith]

Can you provide an example for when you would use the "Direct" option in the channel/pipe link options?

[Chris Maeder]

Selecting DIRECT as the link type causes flow to be instantly routed from the upstream inlet to the downstream inlet without considering any losses in the routing. A direct link has no physical properties such a length and diameter. This link type is useful when needing to link two adjacent nodes without having to define how the flow gets routed from the upstream node to the downstream node. It has no hydraulic effect in the model other than define hydraulic connectivity and preserve continuity relationships.