A project that uses a real-time web-based visualization approach for environmental modeling by integrating a geographic information system (GIS) with virtual reality modeling language and Java was explored. A new technique, the server push approach, is developed to “push” only up-to-date data from the remote server to the client and consequently reduce network traffic across the Internet. A fat client model is adopted to host the GIS environmental data model on the Internet. Online data hosting boosts interactivity, swift and transparent communication, user access, and cost-efficiency. These data can be analyzed online by using a GIS and the numerical functions embedded in Web3D-based Java applets. The spatially distributed GIS-based model used to generate data on catchment hydrology and runoff (the topography-based hydrological model; TOPMODEL) accepts incoming information and facilitates real-time simulation.