dual drainage model in swmm dual drainage model in swmm julsmed (Marine/Ocean) (OP) 10 Jun 18 02:54 what are the procedures to do a dual drainage model in swmm for flood zones using the sewer and drainage data for the area RE: dual drainage model in swmm pinkpig (Civil/Environmental) 14 Jun 18 15:49 Your question is too broad. What kind of dual drainage system you want to mode – for example, do you really want to model each inlet opening as a weir/orifice or just a simply manhole without flow restriction? Your budget and time? Modeling a dual drainage system in EPA SWMM is very time consuming (still doable). You may want to use SWMM commercial version instead if they have some built-in features to model street inlets and gutter.