Urban ?ooding has become an increasingly important issue in many parts of the world. In this study, an integrated ?ood assessment model (IFAM) is presented for the coastal urban ?ood simulation. A web based GIS framework has been adopted to organize the spatial datasets for the study area considered and to run the model within this framework. The integrated ?ood model consists of a mass balance based 1-D overland ?ow model, 1-D ?nite element based channel ?ow model based on diffusion wave approximation and a quasi 2-D raster ?ood inundation model based on the continuity equation. The model code is written in MATLAB and the application is integrated within a web GIS server product viz: Web Gram Server™ (WGS), developed at IIT Bombay, using Java, JSP and JQuery technologies. Its user interface is developed using open layers and the attribute data are stored in MySQL open source DBMS. The model is integrated within WGS and is called via Java script. The application has been demonstrated for two coastal urban watersheds of Navi Mumbai, India. Simulated ?ood extents for extreme rainfall event of 26 July, 2005 in the two urban watersheds of Navi Mumbai city are presented and discussed. The study demonstrates the effectiveness of the ?ood simulation tool in a web GIS environment to facilitate data access and visualization of GIS datasets and simulation results.