When I compute my model I get a user notification that states, "Downstream TW out of range. Looking for TW value that is less than lowest table value. Looking for TW: X.XX ft³. Lowest table value: XX ft. Used TW Elevation: XX ft. Results may be invalid. You need to add more TW rating points, starting at the lowest possible water surface elevation connected on downstream end."
This is an indication that there is something wrong with one or more of your outlet structures and if accompanied by another user notication that says, "The pond has a diversion with both interconnected and level pool outlet structures. It is recommended that you use either all interconnected or all level pool outlet structures with a diversion from a pond. " then you should follow the steps below. If it's not accompanied by this or a similar message please try to resolve all the user notifications and examine your composite outlet structures closely for mistakes.
Open the composite outlet structure manager (Components > Composite Outlet Structures).
3. In the composite outlet structure manager under the Tailwater section set the "Interconnected Pond Type" Property to "Use Pond/Outfall for Tailwater Range"
4. In the Pond/Outfall ID property click the drop down arrow in the input field and choose "Select from Drawing" then go out and carefully select the correct associated outfall so the Minimum(Tailwater) and Maximum(Tailwater) fields are populated.
5. Make sure to do this for each outlet structure and then re-compute your model
PondPack user notification: Mass balance for routing volumes vary by more than 0.5%
Calculation failure or bad results with a mix of ICPM and Level Pool ponds