Problem

What does the following user notification mean?

"Non-increasing value for 2/t + O...Elevation= A ft. Discharge= B ft³/s. Volume= C ac-ft. St2O= D ft³/s." Engine Fatal Error

Solution

PondPack uses the storage indication method when doing pond flow routing calculations. There is some good detail on this in the Help (see Hydraulics Theory > Routing Methods > Ponds).

These calculations rely on the value of this equation to be increasing as depth increases (see the Help for background on this equation):

2 x Storage Volume / calculation time step + Outflow

But in certain situations this doesn't happen, so you get the error in question. The solution may be different in each situation, but a good start would be to check the storage volume for your pond. If it's very small, you may need a smaller calculation time step (set in the calculation options). For further help, contact technical support.

Conduit

If the notification points to a conduit and there are no problems with the configuration (ie. They have reasonable lengths, slopes etc.) then set the conduits' property Conduit Type to User Defined Conduit. Then verify the conduit shape, diameter, material and roughness are correct.
 
Note:

1. If the user defined conduit properties have not been defined for a pipe, then the values will be retained from the catalog conduit after switching the conduit type.

2. If the conduit is defined as a "user defined conduit" already then reduce the output increment and change the conduit type to "catalog conduit". In the catalog create a new catalog channel / conduit and use the values defined for the "user defined" conduit to create it. Then assign it and compute.

No Volume Pond

If you are using a "No Volume" pond, ensure that the adjacent outlet structures are configured correctly. A user defined headwater range should be used in the downstream outlet and a user defined tailwater range (via interconnected ponds as the type) should be used for the upstream outlet.

Void Space

If you have the "use void space" set to "true", try setting it to "false", then adjust the pond elevation-area or elevation-volume curve to compensate for the void space (instead of using the void space option). For pond types like Pipe or trapezoidal, this can be done by first viewing the elevation area table via right click > pond volume results table, then noting the area (or volume) results. Next, switch the pond volume type to elevation-area or elevation-volume and enter the adjusted values to define the pond volume available for storage.