EXTRAN ICONTER

I am wondering if anyone has had experiences or observations on the SWMM44 variable BC (1) - iconter, which prints out a continuity summary every iconter time steps.

In a case at hand I am getting 50-70% error an hour after startup; then this declines to essentially zero until an open channel fills up and dumps the standard "...using full flow parameters"; the error shoots up to 25% right after this and then drops to around zero and stays there through the system peak.

In these two cases the continuity error seemed to be correlated with a possible explanatory factor - startup dry conduits in the first case and the open channel full flow condition in the second case.

This was a 24 hour run based on the early-peak SCS Type I hyetograph.

A couple hours after the system peak the error gradually built up again over a few hours to about 20% and then dropped back down to essentially zero for remainder of run. The only thing of interest going on in this interval was the gradual decline in the level of an end-of-the line detention basin.

At the end of the run the overall run continuity balanced with negligible error. Since the errors did not occur at the time of the system peak they appeared to be innocuous in this case. Has anyone developed a list of the types of errors this output may indicate and why they occur? Aside from startup and full flow parameter cases, is there anything the user do to lower this error?

Ron Kilmartin