A method, apparatus, and article of manufacture provide the ability to define a floodplain encroachment. River reach and station information are received into a geographic information system (GIS). Floodplain encroachment values are defined using a graphical user interface (GUI). The GUI provides a simultaneous view of station identifiers for each station for which the floodplain encroachment is to be defined, profiles defined for each of the station identifiers, a method identification corresponding to each of the defined profiles, and a target water surface elevation change for each profile. The values are provided to a HEC-RAS engine which outputs analysis results that are simultaneously displayed in the GUI with the other information. The analysis results include a water surface elevation change, a top width, and a velocity for each profile-station pair. Users can modify the values and dynamically view the results from HEC-RAS in the GUI.