Information about flood prevention, prediction and management is of high relevance nowadays. A good platform for presenting this highly spatial related information is the internet. Thus, research on online 2D and 3D visualization of flood issues is currently ongoing. As the data to be presented is coming from a huge diversity of proprietary hydro-numerical software systems, a proper data schema, respecting the needs of server side technology, is needed. We aim to demonstrate that CityGML is a good basic for providing this within three dimensions and embedded in a semantic model by presenting a concept for a CityGML Application Domain Extension for flood related data. In order to evaluate the schema a Java based implementation was coded, which is able to convert the hydro-numerical data in xml files conform to the developed “CityGML ADE Hydro”. During the evaluation phase, the schema was presented and discussed with hydrologic and CityGML experts. The current schema can map data provided by the hydraulic software tools HYDRO_AS-2D, MIKE21 and TUFLOW and is ready to be integrated in a Web 3D Service in order to provide the data for dynamic 3D flood visualization in interactive 3D scenes.