The iconic Potsdamer Plaza bridges the scar left by the wall between East and West Berlin. A veil of shallow flow-steps create a rhythmic surface of shimmering waves, providing multiple opportunities for people to cross and interact with the water. This urban waterscape has contributed to make Potsdamer Plaza one of the most visited places in Berlin, which achieved 2011 DGNB Silver Sustainable Urban District Award after more than 10 years of its completion.
Expectations of the completed Potsdamer Platz were immense, and the problems on what was once Europe’s largest building site were highly complicated. Two demands: people were not just supposed to work here, they were supposed to spend their leisure time here as well. A vibrant urban construct was to be created, which is difficult in the shadow of towering company headquarters. And the intention of setting high ecological standards for the project had caught on as well. There were the following problems: very little space was available for leisure provision, and it was subject to all sorts of demands and wishes. What devices for planning open space, what themes can be used to do justice to a lot of people and the urban design at the same time, and finally to come close to meeting ecological aims?
Herbert Dreiseitl had already worked on Potsdamer Platz immediately after the Wall came down, with an Anglo-German planning team. The theme of water as a defining element in the open space had convinced both the Senate and the investors from the outset. First of all the design possibilities caught their imagination, and secondly they were fired by the chance of meeting the ecological challenges. The suggestion that rainwater should be used for flushing toilets and watering green areas was met with interest. The same was true of the idea of using the rainwater that collected in the underground tanks to feed a water system that would include a narrow pool on the northern side, one in the piazza, the large main area of water and the southern area of water. Additionally, this offered the opportunity not to lower the groundwater during the building phase and to make an intermediate collection of all the rainwater that fell on the buildings and slowly feed it into the Landwehrkanal.
A complex computer simulation was used to predict that the Landwehrkanal would only be compelled to absorb heavily increased amounts of precipitation three times in ten years; this is based on the approximate drainage figures for an unsealed plot. To guarantee this, the system must carry sufficient buffer capacity. This is provided in the first place by five underground tanks with a total volume of 2,600 cubic metres, of which 900 cubic metres are left free in their turn for cases of heavy precipitation. In addition to this, the main area of water can still offer a reserve of 15 centimetres between the normal and the maximum water level, which provides a storage buffer of 1,300 cubic metres. A key feature was the water resources that were discovered above the turbidity level of the main area of water. Solids can start to settle in the underground tanks before the water flows out of source vessels on the banks of the south and main areas of water, through planted purification biotopes, where it is cleaned biologically and chemically.
If necessary, technical filters can also be used, which will remove any floating algae in the summer months. In Marlene-Dietrich-Platz water flows in intricate patterns to the lowest point in the piazza. The water glides of flowsteps from the main expanse of water, and here rhythmic wave structures are formed. A detail that is accurate to a millimetre, worked out in 1:1 models. Then, immediately adjacent to the piazza, the water drifts from two sides over linear wave cascades, creating a clear link with the architecture. Finally water also emerges from a source in the northern area of water, then flows down a narrow channel. Given the extremely complex criteria that had to be met, DaimlerChrysler representative Karlheinz Bohn rightly pointed out after the opening that ‘as well as the fascination that this idea exercised over all of us, it soon became clear that an artificial expanse of water creates a number of problems if energy-intensive technology and chemical additives are not used.’ The results are convincing, as the quality of the water is good, the buffer capacity is adequate and the use of fresh water in the buildings has been reduced. In design terms, the ‘Urban Water Feature’ has given Potsdamer Platz a unique open space.
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