The frequency and dimension of severe floods has been documented with flood marks on buildings, whereas low water marks had been made on low-lying rocks in rivers and lakes to memorize extremely low water levels.
One of the most eye-catching assemblages of flood marks is inscribed on the wall of the "Gartenhaus" situated in Wertheim (Baden-Württemberg) on the bank of the Tauber River that is a tributary of Main River. The assemblage of 24 flood marks provides a survey of the dimension and frequency of floods and can be read as visual expressions of institutional risk memory in the sense of the insurance industry, which defines risk as the likelihood that a loss of a certain magnitude will occur.
In case of a very low water level of the Rhine River a low-lying rock, the so called “Laufenstein” near Laufenburg (Canton Aargau/Baden-Württemberg), emerged from the water. People used to commemorate such events by chiselling the relative year into the rock. The “Laufenstein” was blown up in 1908 or 1909 in connection with the building of the nearby power station. Fortunately, the memory of former extreme low-stage events chiselled into the rock was preserved by the engineer Hermann Walter, who wrote his PhD on the "cataract" of Laufenburg, probably in view of the planned run-of-river power station (Pfister, Weingartner, Luterbacher 2006).