Ponds in StormCAD are treated similarly to a manhole node, however there are calculation differences based on how the pond is set up as follows:

1. If the pond outlet has no control structure(s):
2. For this pond data type, the pond is treated the same as a manhole node in the flow calculation; all fixed and rational flow elements pass through the pond without any change and downstream all related flow is calculated as normal, i.e. you would expect the same flow results if the pond is replaced by a manhole node.
3. For the profile calculation, when the backwater calculated hydraulic grade line at the pond is lower than the user specified initial pond elevation, the initial pond elevation is used as the pond hydraulic grade line and for backwater calculation of the upstream elements.
4. If the pond has control structure(s):

The control structures are normally used to reduce the peak flow, so StormCAD calculations on such pond settings consider the flow reduction through the pond control structures.

You can use the pond initial elevation to control the outflow reduction; the solver uses the specified pond initial elevation and performs hydraulic calculations for the outlet control structures to determine the pond outflow. Once the pond outflow is determined it becomes a fixed flow (system additional flow) and all other fixed and rational flow elements are terminated at the pond outlet and the new fixed outlet flow will carry on to the downstream calculations.

The user-specified pond initial elevation will be the calculated pond hydraulic grade line and is used for upstream profile calculations, regardless what the downstream backwater profile gives at the pond.