It is not often that a dam is demolished in the middle of one of Europe’s major cities but this is what happened in June 2018 in the centre of Zurich.
The Sihlpost Dam was situated in the River Sihl, a Swiss river that rises near the Drusberg mountain and eventually flows into the Limmat river in the centre of the city of Zürich. The river is 69km long and has a catchment area of 344 km2. The dam was a longitudinal concrete barrier fifty meters long and two meters high akin to a dividing wall down the middle of the river, just upstream from the city’s main railway station. The Sihl had been a very important route for twenty-five species of migratory fishes in the past, such as grayling, salmon and nase, and by removing the dam and carrying out related measures to restore the river, it was hoped that the potential for new and diverse fish habitats would be increased.
The dam was most probably built to stabilize the banks where the waters of the Sihl were met by those flowing from the Schanzengraben moat, one of the last remains of the Baroque fortifications of Zurich. But this had negative impacts on the river: the moat and river were separated by the wall, the banks were shut off from the main flow and the diversity of river habitats was diminished. At least fifty meters upstream and downstream of the barrier were affected.