Tidal Backfilling

[DuckEngineer]

I have a situation where I have a pond outletting into the ocean. A portion of the tidal influence will be above the normal water surface of the pond. I am interested in determining the effects on the pond due to ocean water, independent of rain events. My current model is a detention pond with applicable storage and the outlet set as primary. This is routed into a catch basin with two identical copies of the first pond outlet, one primary, one secondary. The primary is routed back into the upstream pond (double arrow) and the secondary is routed into a link with tidal settings for the elevation. Settings are Sim-Route, dt=0.05, no initial elevations. The elevation for the tide shows what I expected to see, but there's no flow. Does the elevation in a link only serve as notice to the program of backflow conditions? I'm curious as to some way to model this. Thanks.

 

[psmart]

A link can be used to provide a tidal tailwater elevation that can reduce the discharge from an incoming pond. However, it will not produce a flow in the reverse direction. HydroCAD will behave as if a one-way (flap) valve is present, allowing flow in only one direction.

A reverse outlet can be used to simulate reversing flows between two ponds. But the ponds must have some storage, so you cannot model a reverse flow from a catch basin (zero-storage pond). So adding the dummy CB to your model doesn't really accomplish anything. It will not "trick" the model into creating a reverse tidal flow.



Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[DuckEngineer]

So, I can create a backfill situation by looping two pond nodes (assigning storage values to both), but it's going to route from the starting elevation (and any rain events) only - i.e. no cyclical components. The other option is to route a pond into a tide link, which will allow for cyclical tailwater effects, but no direct backflow. Correct?

 

[psmart]

That's right. The tidal link can be used to create a tailwater that will reduce the discharge from inflowing ponds, but it will not create a reverse tidal flow.


Peter Smart
HydroCAD Software

http://www.hydrocad.net