Detention Pond Drainage Simulation

[UDFCD]

I am trying to run simulation using EPA SWMM of the drainage of a detention pond. I am trying to simulate that the pond is already full and trying to determine how long it takes the pond to drain. I have the storage and rating curves defined, and I am successful in getting the simulation to run.

However, when I create a table of the volume in the storage unit, the volume steadily grows until it reaches its peak in about an hour and then begins to drain. I would like the volume to start at its peak and begin draining right away.

I would appreciate any suggestions that anyone has.

Thank you.