Capacity increases of Limmat bridges in the city of Zurich

If the Sihl has high tide, the city of Zurich is at risk of flooding. As a long-term solution, the canton of Zurich is planning a flood relief tunnel for the Sihl (Langnau am Albis) into the Lake Zurich near Thalwil. In case of a flood, the high water peaks can thus be directed into the Lake Zurich [1]. Without appropriate countermeasures, the water level at Lake Zurich would increase. As part of investigations in 2014, it was found out that the Rathausbrücke and then the Münsterbrücke limit the discharge capacities of the Limmat [2]. To compensate an increase of the water level of Lake Zurich, the discharge capacity of the Limmat is increased by targeted measures on the Limmat bridges (Munster- and Rathausbrucke).

To evaluate the influence of the planned measures on the discharge capacities of the Limmat bridges, the measures are integrated in the current 2D model and the discharges for certain high water levels of Lake Zurich are defined. Measures to increase the capacity are especially lowering of the bed and the optimization of the bridge piers on the Rathausbrucke, which is part of the project "Replacement Rathausbrucke" of the city of Zurich.