The first step when evaluating any HydroCAD model is to review the warning messages. In your case these are lots of [81] tailwater warnings. Clicking the message will give you details and recommended solutions:
[81] Warning: {node} Exceeded Pond x by x.x' @ x.x hrs
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At some point during the routing, the node's elevation has exceeded the elevation of an inflowing pond, indicating a possible tailwater dependency. The message shows the maximum amount of reverse head and the time at which it occurred.
Important: The pond routing is not altered by this situation, even though the higher tailwater may in reality cause a reduced discharge. To remedy the situation, select a pond routing method that is able to handle tailwater effects.
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In short, you need to switch from the default Storage-Indication method to the Dynamic SI procedures, which is able to respond to tailwater changes.
For the two "treatment systems", I would also use the "zero storage" option, which is more stable than attempting to do a storage routing of a 6CFS flow with only a few hundred CF of storage.
Next, I would incorporate the CB 655 pipe directly into the pond 1P outlet control. By placing the flow control directly on the storage volume you will get a more stable routing (in this case it eliminates the oscillations)
Finally, you need to review the peak elevation at each CB. If the peak exceeds the grate elevation, you need to model the overflow by including an appropriate overflow grate and/or above-grade storage. For details please see
After making all these changes you can begin to examine the results and start to draw conclusions.
Peter Smart
HydroCAD Software
