Based on QGIS a database structure and a set of plugins have been developed to improve the workflow for the hydraulic design of urban drainage systems for consulting engineers. The main goal is pre- and postprocessing in combination with various commercial hydraulic simulation software packages. The plugins provide import and export functionalities, simulation result viewing and generation of longitudinal cross sections in a CAD program. All modules make intensive use of SQL based spatial functions instead of functions implemented in QGIS, because of their stability, higher flexibility and speed due to the indexing functionality. On the other hand the database structure is kept simple to make it possible for engineers as a typical user to work directly with the data in the database.