Cologne Water Gauge

Gauge-based water level measurements existed in Cologne from at least around 1771 – the senior building official Johann Esaias Silberschlag documented them in his book „Hydrotechnik“, published in 1772. Daily records from the Cologne gauge date back to 1782. A severe ice drift on 27/28 February 1784 destroyed this gauge; a replacement, in the form of a staff gauge, was not built until 1810 at a shallow spot on the Casselberg and began regular observations on 1 January 1813.

Older sources also record medieval water levels: the earliest known value comes from the Magdalene Flood of July 1342 at 11.53 metres, followed by 13.30 metres in January/February 1374. Until December 1816, Cologne measured using the local „Cologne foot“ unit; the Prussian ordinance on weights and measures of 10 May 1816 introduced a new measuring method from 1 January 1817. The gauge house on today's site received a recording gauge and went into operation on 25 June 1901. An air raid destroyed it on 29 June 1943; until 1 March 1948 the level in the Rheinauhafen at river kilometre 687.6 served as a substitute. The present gauge house has been in operation since 1 November 1951.

The highest level ever recorded was reached on 27/28 February 1784 at 13.84 metres – an ice flood. More recently, the Rhine rose to between 10.63 and 10.69 metres in 1926, 1993 and 1995. At 6.20 metres, flood mark I is reached, from which the first restrictions on shipping apply – a maximum of 20 km/h downstream, to prevent wave damage to the banks. At flood mark II of 8.30 metres, shipping is halted entirely, at 9.80 metres the Rhine bank tunnel closes, and at 10.70 metres the city's flood plan calls for a disaster alert. Thanks to new protective measures following the floods of 1993 and 1995, the old town is not flooded until 11.30 metres.

The opposite extreme has left its mark too: in October 2018 the Rhine reached a record low, equalling the previous low of 2003, and inland shipping was severely affected in the summer of 2018. On 18 October 2018 the gauge fell to 80 cm, and on 23 October to just 69 cm. On 20 August 2020, a cruise ship carrying more than 100 people had to be evacuated after running aground on a sandbank it could no longer free itself from.