Mostly river water level and flood forecasting methods are based on gauging stations measurements at discrete locations, which limits their capability to provide accurate and timely data over large extent, also limited or no data available on remote locations. So here an idea to use high resolution satellite images for real time mapping of river water level is presented. In this research, a Web based GIS system is developed for mapping river water level, early warning and for flood disasters . To improve flood forecasting / warning, a decision support system (DSS) for flood monitoring and prediction is setup that integrates GIS, satellite image processing and hydrological modelling. A methodology is presented for data integration, floodplain delineation, and online map interfaces. Web based GIS system can dynamically display observed and predicted water levels for decision makers and the general public.The users can access a Web-based GIS system which models current flood events and displays satellite imagery and 3D visualization integrated with the flood plain area.The output from the hydrological modeling be used for flood prediction within next 24-48 hours.