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Staircases to reconnect the river Sihl to Zurich
Water depth of the Sihl during the last 20 years.
“Only forty centimeters deep, the clear water of the Sihl rushes northwards over a rocky river bed. Dog walkers and cyclists drift past the reeds, alders and beeches that line the lush banks of this natural idyll in the centre of the Zurich. Yet despite appearances, it is the Sihl, more than the Limmat that is the product of human design and construction. The path of the Sihl through the city has been made and remade many times over the centuries to suit differing human requirements and, perhaps most importantly, as a means of controlling the natural flooding caused by overflows of the river delta.”

Since a weir has been build at the upstream Sihl lake, the water depth in the urban Sihl delta can be controlled much better. A hydrological analysis of this part of the river Sihl results in a new risk distribution on high water‐ and flood‐risks. Concluded can be that: The river Delta now is designed for a high water risk that no longer exists. During the majority of the year the water level is very low.

The height-difference between water and city is bridged by a series of staircases that make the space, framed by city and river, accessible for the inhabitants of the surrounding city.
Instead of being read as an addition to the current situation, the staircases become part of the riverbed and form a transition from the smooth cityscape into the lush river, both in material and size. The design allows the riverbed to be used by normal water depth but can also resist occasional high water.

Solving an urban problem on a very detailed scale allows subtle interventions, which find their qualities as humble architectural elements that work as a catalyst to enhance the existing qualities of the existing situation.

The design should also be read as a criticism on the tendency to make the concept behind a design the single most important tool of an architect. Typically the materialization and detailing, which define an important part of the experience of the user, come in a late state of the design. In constrast, in this project, by looking at material and detail parallel to large‐scale concept I hope to improve the symbiotic relationship between urban planning and atmosphere.

The Gieshübel-Moraine, which dates from the last small ice age in the Alps, is one of the best kept moraines in Zürich. The Klopstockwiese park and Castle Sihlberg are now situated on the moraine. To the west side, the spine drops steeply to the riverbank of the Sihl and forms an important habitat for birds and bats that come out at dawn to hunt insects above the shallow water of the Sihl. The river makes a sharp turn at Gieshübel (as a result of canalization in the late 19th century). Because the water flows slower in the inner curve, sandbanks appear. The Klopstockwiese park is separated from the River by an elevated bike path, this results in little use by pedestrians.

The Sihlhochstrasse, the end of one of the main highways to Zürich, covers 1,5 km of the Sihl. It ends just before the curve of the Sihl. After a lot of political discussion in the late 60s, the city of Zurich decided to stop the “project Y”, which aimed to connect the west and east side of the city via highways that would have covered the rivers. The last scar of this era is, in its most dramatic form, visible at Gieshübel where the project was terminated. Leaving a clean-cut section of the highway profile which is still very visible. The lower surface of the amputated highway reflects the water and the green of the riverbanks. As such it frames a unique space in the city with an important political and historical background.

By creating order in this eclectic place the existing qualities are enhanced. The elevated bike path is removed to allow pedestrian to walk down to the river bank. The riverbank is connected over the sandbanks with the downstream Sihlhoelzli park to allow pedestrians, joggers or dog walkers to enjoy the riverside. The bike lane is placed at the other side of the water and connected by the Gieshübelbrücke and the Utobrücke. Both these bridges have staircases that lead toward the pedestrian path on the west bank. The staircase curves into the riverbed and seems to grow out of it. Water from a faucet runs directly into the river and allows passing people to drink something.

At the Sihlhölzli park the Sihl is aligned on both sides by magnificent old sycamore trees. The park itself has little to do with the water and houses an athletic club with a notable clubhouse (build by Swiss engineers: H. Herter and E Suter). The clubhouse is in use year around by different sport clubs. A train tunnel that crosses the water just under the surface creates a small perfect symmetrical waterfall that became a known feature of the Sihl. Because the river is rather small at this point a paved riverbed should decrease the risk of flooding. Because of the paving, this is one of the only places where one can easily see the river is man made.

To connect the river to the park and to make the great river space enjoyable, a series of staircases is placed on the shores. They land on big steps that seem to grow out of the existing pavement. The lower the steps go the bigger they get and the rougher their finish. This dramatizes the feeling of descending into the river and avoids slippery stones after high water.

The Kulturinsel (Culture Island) has a lot of direct exposure because of its central location in the city of Zurich and the of restaurants, bars and cultural institutions on the river banks. The river profile is very wide and the amount of overgrown sandbanks high. Kulturinsel is situated directly next to the main station which results in a good accessibility of this part of the Sihl. Although big parts of the riverbed are almost permanently dry, the amount and quality of the connections between the city and the river is low. The restaurants and bars directly situated on the river banks have no connection to the water and seem to be turned away from the river.

The accessibility to the existing promenades on the riverbanks is improved by a series of staircases. The steps do not only allow better water access but also connect the existing restaurants and bars on the river bank to the Sihl by providing different terrasses on the waterfront. The material on the city level is urban and small grained. As you walk down into the river profile - and the flooding risk increases - the grain gets bigger and finishes robust. This way the design integrates in the situation and dramatizes the experience of entering the “Sihlraum”.
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