Problem

A model with a mix of ICPM and Level Pool (free outfall) outlet structures between ponds results in invalid results (for example zero flow through some routes) or the following notification:

"One or more level pool ponds are connected to both upstream and downstream interconnected ponds"

Background

PondPack has some limitations with regard to a mix of ICPM and Level pool, as indicated in the below screenshots:

Solution

To overcome this problem, use the above illustrations as a guide as to how to configure your pond routes. Ensure that the headwater and tailwater range is correct for each one.

Another option is to convert all connected pond routes to ICPM (as the pond route tailwater type) If those ICPM routes end at an outfall node set as free outfall, set the outfall to the boundary condition type of "Time-Elevation Curve" and enter a time elevation curve as seen below. Note that using many ICPM routes can be difficult to solve and may yield large mass balance error, requiring adjustment to the timesteps, headwater/tailwater increments, and other settings as seen in the troubleshooting guide further below.

For the time-elevation table, use a constant elevation for the entire simulation duration, and have that elevation be below the bottom of the pond (so as to still act as free outfall)

Time              Elevation

0.0 hours            1 ft.

12 hours             1 ft.

100 hours           1 ft.

See Also

Troubleshooting Mass balance and instability with Interconnected Pond Modeling (ICPM)

User notification "Downstream TW out of range. Looking for TW value that is less than lowest table value."