http://www.jennessent.com/arcview/arcview_extensions.htm
<http://www.jennessent.com/arcview/arcview_extensions.htm>

Although not SWMM-specific, this site has some nice tools for computing
the watershed parameters you described.

Chris Perry, P.E.
christopher.a.perry@usace.army.mil
<mailto:christopher.a.perry@usace.army.mil>