Picture a structure that tames the Isar’s flow. That structure is the Stauwehr Oberföhring. It stands as a testament to early 20th-century engineering. This is more than just a dam. It is a vital component of Munich’s water management system.
The Stauwehr Oberföhring you see before you connects the northern part of the Englischer Garten with Oberföhring. Oberföhring is a district east of the Isar. Its construction finished in 1924. The structure marks the beginning of the Mittlere-Isar-Kanal. The canal stretches 64 kilometers. It eventually flows back into the Isar near Landshut.
Interestingly, the Stauwehr Oberföhring does not generate power directly. However, a small, mostly underground power plant sits just below it. This plant redirects water from the canal back into the Isar. It uses a Kaplan turbine to generate one megawatt of power. The power plant is barely visible. Only a small machine house is visible on the Stauwehr’s northeast side.
The primary function of the Stauwehr Oberföhring is to raise the Isar’s water level by about six meters. This diverts much of the water into the Mittlere-Isar-Kanal. The canal powers a series of seven run-of-river power plants. These plants have a total head of approximately 109 meters. Uniper Wasserkraft operates plants accounting for 88 meters. The Uppenbornwerke, owned by Stadtwerke München, account for the remaining 21 meters.
Notice the bright, beige building spanning the Isar. The building with the weir system lies perpendicular to the river. An inlet structure is set at a 45-degree angle to it. The building spans 78.5 meters. It features four arches, each 17 meters wide and about 5.7 meters high. Three pillars support the structure. They extend far into the downstream water. These pillars provide small viewing platforms for pedestrians.
The Stauwehr Oberföhring’s building is simple. It features brick construction, plaster and a hipped roof. The structure rests on a concrete slab. A 14-meter-deep concrete wall extends below the upstream water. This wall consists of a caisson. Compressed air was used in its construction. It reaches down to the solid Flinz layer. The foundation plate extends 45 meters downstream from the gate wall. A nine-meter-deep iron sheet pile wall completes it.
The steel gate panels are 5.65 meters high. Motors or hand cranks lift them. These are housed in the superstructure. A crane inside the building operates the stop logs. These can also close off the Stauwehr Oberföhring.
The inlet structure has a clear width of 46.6 meters. It was built at a 45-degree angle to the river’s axis. This reduces the amount of gravel and sand entering the canal. Eight gates, each 5.5 meters wide, can close the inlet. Flushing canals are arranged at an angle towards the Isar below the canal inlet. Their water flows through a triangular settling basin. It then returns to the downstream water between the dam and the inlet.
Before the Stauwehr Oberföhring was built, a wire rope ferry operated here starting in 1896. Plans to use the Isar’s gradient for power generation between Munich and Moosburg existed before World War I. The Mittlere Isar GmbH began planning the canal in 1918. Theodor Rümelin led the project. In 1919, the Bavarian state took over planning. Construction started to combat unemployment. The Mittlere Isar AG took over the project in 1921. They completed the Stauwehr Oberföhring by 1924.
The four concrete arch bridges connecting Oberföhring to the Isarinsel were built at the same time. This island is formed by the canal. The Stauwehr Oberföhring and its bridges survived World War II. The planned demolition of Munich’s bridges was prevented.
In 2002, Bavaria and E.ON Wasserkraft agreed to increase the minimum water flow in the Isar. The flow increased to 15 cubic meters per second. A new power plant was built at the Stauwehr Oberföhring to use this water. This improved ecological conditions on the Isar between Oberföhring and Moosburg. The power plant went online in 2008. It generates 5.7 million kilowatt-hours of electricity per year. The power plants on the Mittlere-Isar-Kanal generate a total of approximately 430 million kilowatt-hours. A new fish ladder was added next to the power plant in 2012.
In 2022, artists Loomit, Lando, and Bert were commissioned to paint the Stauwehr Oberföhring.
Today, the Stauwehr Oberföhring is a popular spot. Pedestrians can cross the Isar. They can use a wide bridge on the building’s north side. This bridge also provides access to the Isarinsel Oberföhring. It is a recreation area between the Isar and the Mittlere-Isar-Kanal.