I have been looking at the demo. I'm not sure it does what I need. I believe my needs are probably similar to mike's above. He must be from Florida. Here, we are tasked to evaluate the 1, 2, 4, 8 and 24 hour duration, 25 year events for the critical duration storm. The intesity of the storm should vary with the duration for both the pre and post developed storm. The critcal duration storm would be the one generating the largest pond volume while keeping postdevelopment flow to predevelopment rates for all the storm durations. With HydroCad it appears I would have to model each individual storm, pre and post conditions, and from reading other posts on this site, it appears the software may set a zero percolation at the pond bottom. Regulatory agencies here require a 24" minimum distance from bottom of pond to groundwater, so percoalation rate at the pond bottom would never be zero. I am still looking into this software as I have not been able to find anything yet that does what I need. We bought PondPak awhile back and it incorrectly models the percolation rate to zero at the pond bottom.
Still searching.