Stopping Tolerance in InfoSWMM, H2OMAP SWMM and SWMM5 Internal Units

InfoSWMM, H2OMAP SWMM and SWMM 5 share the same underlying dynamic engine code but one small difference is that InfoSWMM and H2OMAP SWMM allows the user to select the node stopping tolerance instead of always using the default SWMM 5 stopping tolerance of 0.0005 feet. SWMM 5 uses internal units of feet and shows the output in meters if you are using SI units, as does InfoSWMM and H2OMAP SWMM. The following table shows how the stopping tolerance translates to inches and millimeters in the engine of a US and SI model. The smaller the tolerance the larger the number of iterations used during the simulation but using a very small tolerance does not always mean a better simulation. If possible, for example, with pumps it is better to use a small time step and a medium level tolerance – for example 1 millimeter is a good starting value, but maybe 2 or 3 millimeters may help if you have a continuity error at a pump node.