To guarantee the secure evacuation of burnable liquids from tunnel driving surface syphons with slotted pipes or shafts with grids are installed. The required capacity of these dewatering systems are proven by means of in situ tests, tests in the hydraulic laboratory and with the help of numerical methods during research projects. During these tests different system components are investigated as these are pipe friction of partially filled pipes, aeration or deaeration due to syphons. Additionally the increase of the flow capacity with the help of the installation of regulating hydraulic elements is achieved. Many different investigations are carried out, as these were done in the Oswaldiberg, the Plabutsch tunnel as well as several further tunnels on the Pyhrn-motorway.