AbstractA geographic information system (ARC/INFO) is used to develop a model of the urban environment for storm drainage analysis. The drainage system is divided into surface terrain, stormwater intakes, and the drainage network. The intakes hydrologically connect surface and subsurface flow elements. The drainage network consists of both man‐made structures (pipes and channels) and overland flow paths that connect them. The land surface terrain is defined by a triangulated irregular network (TIN), which is used to determine necessary parameters for design flow calculations. Each of the three basic elements of the urban terrain representation, inlets‐defined as points, drainage network‐defined as lines, and surface terrain‐defined as TINs, has its own specific data structure. The three databases are fully integrated, and the stored information is used to determine whether inlets and pipes can convey 10‐and 25‐year design flows, using the rational method.An ‘intelligent network builder’, is developed using the Nexpert Object expert system shell, to test for completeness of databases and flow paths prior to hydrological computations. If necesssary, the intelligent network builder starts up ARC/INFO procedures that fill in missing links in the drainage network and missing flow properties of its components. An example application is made to the drainage system of a section of City of Asheville,