StormCAD is a comprehensive modeling software program for the design and analysis of storm sewer systems. StormCAD provides calculations for catchment runoff, inlet capacity, and gutters and pipe network flow. StormCAD determines intercepted flow at network inlets, and routes bypass flow to selected bypass targets. Inlets can be computed using the U.S. Federal Highway Administration (FHWA) HEC-22 methodology and users can choose from grate, curb, slot, ditch, and combination inlet types. Engineers can use a variety of methods to compute headloss, including HEC-22 Energy and AASHTO. StormCAD uses the Rational Method to calculate peak flows in the storm sewer design, or accepts direct input of known flows for inlet inflows. StormCAD allows users to specify Intensity-Duration-Frequency data using equations or tables. Modelers can then plot the IDF curves, and reuse their data for other projects in that region. Engineers can work with an unlimited number of sub-watershed areas and C coefficients for each inlet watershed. The constraint-based design features in StormCAD allow modelers to automatically design gravity piping and structures. The design is flexible enough to allow users to specify the elements to be designed, from a single pipe size to the entire system, by simply entering the appropriate design conditions: minimum/maximum velocities, covers, and slopes; pipe elevation offsets (including whether or not to allow drop structures), maximum spread and depth for inlets in sag; and minimum efficiency for inlets on grade.