At Chausseestraße in Berlin-Mitte, the construction of an approximately 17,000 m3 underground stormwater overflow basin, designed by DAHLEM on behalf of Berliner Wasserbetriebe, has begun. The basin is intended to temporarily store stormwater during heavy rainfall in order to sustainably relieve the sewage system and the Spree River. It is part of Berlin's large-scale storage programme and "disappears" completely under the square on the banks of Süd-Panke. Apart from the operations building, which is architecturally adapted to the neighbouring wastewater pumping station, only a striking steel chimney rises 30 meters above the ground. If the basin is completely flooded within 30 minutes by heavy rain, the exhaust air escapes through this chimney high above the rooftops of Berlin. Currently, a circular diaphragm wall - double excavation pit, with a depth of around 30 m, is being built on the construction site in the immediate vicinity of the headquarters of the Federal Intelligence Service. The completion of the stormwater overflow basin, including the operations building, is scheduled for 2026.