Lake Constance is one of the few unregulated Alpine lakes. Because there are different inflows and outflows, the water level fluctuates. He cannot be controlled. During floods, up to three times as much water flows into the lake than can flow out. This happened in 2005, when 1,450 m3 flowed into the lake from the Bregenzerach catchment area alone, although only 1,300 m/s can flow out at Konstanz. Within 24 hours the water level rose by 50 cm.
The mean summer peak level v. Lake Constance (approx. June 28th - July 4th) is 433 cm. The average winter rainfall level (2nd half of February) is 286 cm.
The last extreme flood in Bregenz occurred on June 11, 1999 and was 567 cm. The water level was only higher in 1890 and in the disaster year 1817. The lowest water level, only 231 cm, occurred on February 15, 2006. The water level zero point is 392.14 m above sea level. The water level in Bregenz can be several centimeters higher than in Konstanz if long-lasting westerly winds push the water towards Pfände.
The maximum inflow is reached in June and the minimum in January. As a rule, the water level fluctuates by around 1.5 m per year, and in extreme years by more than 3 m.
The water level has been measured in Bregenz since 1864. Today
The data from the measuring points at the port of Bregenz and on the Mili lands on the Internet via radio.
Worth knowing: You cannot see the Konstanz Minster with its 78m high tower from Bregenz. The curvature of the earth is 41.5m. The area of Lake Constance is 536 km, the length of the shore of Lake Constance is 273 km long and Lake Constance has 48 billion liters of water, enough to put the whole of Austria 60 cm under water!
(from the information board of the Vorarlberg State Government, Water Management Department)