In the past few weeks, the city of Munich has got a little taste of how fast it can go. With climate change, it is likely to rain heavily more frequently in the future. Such weather already existed in July and especially in June. And then not only did the level of the Isar temporarily rise from just under one and a half meters to more than double. The groundwater also pushed up, especially in the north-west of Munich. In Moosach and Feldmoching, in the Fasanerie and in parts of Aubing, the water has risen in places by up to 1.20 meters within a few days, according to the city. In some places, the highest water levels have been measured for 20 to 30 years.
The Isar is not everything that flows in Munich: the city is on water. It seeps through the earth, it flows through the gravel underground. It manages three to five meters a day, in a north-easterly direction. Sometimes it follows underground channels, sometimes it accumulates on obstacles made of stone or clay, in some places also a few centimeters in cellars, underground garages or subway shafts.
The people of Munich rarely see this water, but the city keeps an eye on it. Anyone digging a pit or drilling a well needs to know what to expect – and the best thing would be for the level of the groundwater to stay where it is. Not just for the sake of the plants. If the level rises too much, basements get wet and the water attacks the fabric of buildings. Conversely, if the water sinks too much, this can mean that wells can deliver less water and geothermal heating problems.
And so there are places like this one here, on the right bank of the Isar, at the height of Weideninsel. There is a concrete cylinder there, and a metal pipe protrudes from the top. The whole machine is 1.40 meters high, and when you do a small survey on site, nobody knows what the block is for. But if you look in above, you can see it glitter below.
It can happen that the level drops in the south while the water pushes up in the north
You need a key to look inside. Patrick Kotyla, a hydrogeologist in the Department for Climate and Environmental Protection (RKU) of the City of Munich, has one of them. When he lifts the lid from the pipe, it is a sunny morning. The city administration operates a total of 4,000 to 5,000 such measuring points in Munich, he says. Many were drilled during the construction of the subway, for example, to ensure that the groundwater did not accumulate. This measuring point as well: It is therefore called “U 8 400”.
The hydrogeologist Patrick Kotyla checks the groundwater level with a light probe.
(Photo: LEONHARD SIMON)
The level will continue to be measured regularly at around half of the measuring points, says Kotyla. Usually this is done by hand. And he shows how to do it. Kotyla puts a plumb bob into the pipe. When the tip becomes damp, a red lamp lights up. The groundwater is 2.2 meters below the surface, which is not an exceptional value. But it is relatively warm at 15.9 degrees Celsius. Eight to 13 degrees are common, says Kotyla. The heat comes from the nearby Isar, where the water seeps into the groundwater. “The Isar is infiltrating,” says Kotyla. The water is cooler at other measuring points.
It is actually complicated with Munich’s groundwater, because the subsurface is very different. There are several water-bearing layers, above and below the gravel plain from the Ice Age. Sometimes the layers are thicker, sometimes thinner. In the north, the uppermost layer of water flows in many places about two meters below the ground; in the south it is often closer to 40 meters. And a lot depends on the weather. It can happen that the water level in the south drops while the water in the north is pushing upwards.
It is also difficult to identify a clear trend for Munich. Unlike in the Free State: The dry one, recently warned Bavaria’s Environment Minister Thorsten Glauber (Free Voters). The climate is changing, too little groundwater is being formed, the levels are falling, the country is on the way to a “groundwater emergency”. This is already noticeable in northern Bavaria, according to the Munich water management office. Climate change means that it rains less often and persistently, but more often briefly and heavily. So the water cannot seep away, instead it increasingly flows off superficially. In Munich, however, the situation is different. The gravel plain is permeable to water and the land is rather flat. Both are good so that new groundwater can form.
In the area of the second main S-Bahn line, the groundwater level has tended to be high for some time, according to Deutsche Bahn, which currently operates two of the largest construction sites in Munich with the S-Bahn and the new main train station and extensively secures them against the groundwater got to. The levels have been measured for more than 15 years, says a spokesman. So far, however, “no significant changes” have been found there that would have made the precautions necessary.
The RKU has numbers for all of Munich. The level of the groundwater in Munich increased on average from 1980 to 2013, in places by more than a meter, according to the report. Recently, however, this trend has not been reflected in the majority of measuring points. In December 2019 and January 2020, the groundwater levels in the urban area were very low, especially in the southeast. Overall, the groundwater level has tended to fall at most of the measuring points in the last five years. In the long term, the city is preparing for the fact that the level will fluctuate. After heavy rain, it could rise quickly in several areas. Conversely, if the drought lasts for a long time, the level can drop.
The city reassures that the drinking water supply is guaranteed. The Munich tap water does not come from the soil of Munich anyway, but mostly from the Mangfall and Loisach valleys. Additional drinking water is only pumped in Trudering when there is a shortage of water. Only then will the people of Munich drink water from their own soil.
Whereby: That is not entirely correct, there is an exception. The people of Munich can certainly drink their own groundwater in everyday life, namely in beer. In order to be able to serve at the Oktoberfest, breweries have to specifically brew Munich beer, and for this they have to use groundwater from Munich. To do this, however, they do not tap into the near-surface groundwater, which will likely fluctuate in the future, but rather the deeper layers.