Mitch,

Can you also tell me why into SWMM44h report the equivalent conduit, in witch the orifice is transformed, has the length 200 (metrics units!!??).

According to the SWMM4 manual (the blue book!) it say: 'the length of the equivalent pipe is computed as the maximum of 200 feet (61 m) or L=2*DELTA time*SQRT(gD), to ensure that the celerity (stability) criterion for pipe is not violated...'

I've set up the SI units and using a DELTA time of 1 second for a diameter of 0.3 m, the length should be about 3.4 m, thus The length used by the program should be 61 m (SI units), so why 200??

Furthermore, which discharge coefficients are typical for orifice?
Thanks!
Giovanni Di Conza