Water Marks
High water marks on buildings were used to document the frequency and magnitude of severe flooding, while low water marks on low-lying stone blocks in rivers and lakes were used to document extremely low water levels. They generally occur after particularly extreme events, such as in 1342 in the Rhine catchment area or in 1501 in the Danube region in southern Germany and Austria. Sometimes they only consist of simple lines with the corresponding date, but sometimes some details are also specified in an accompanying inscription. As a rule, they were placed in publicly visible locations, for example on bridge piers, city gates or prominent houses in the city.
The illustration shows flood markers of the Tauber, a tributary of the Main, at the "Gartenhaus" in Wertheim (Baden-Württemberg). An ensemble of 24 flood markers such as the one at the Gartenhaus in Wertheim an der Tauber provides a visual overview of the size and frequency of floods and thus forms the basis for a risk assessment that corresponds to that of the insurance industry. This defines risk as the probability that damage of a certain magnitude will occur again.
However, the historical-hydrological evaluation of flood marks is not always unproblematic: Firstly, it must be asked whether the marked water levels actually represent the peak height of the flood or a somewhat lower level from the days before or after. Secondly, it needs to be clarified whether the high water marks are at all up-to-date and therefore also historically reliable. It is not uncommon for them to have been moved in the past (e.g. when a new house was built) and reattached at the same height. This also applies in particular to painted flood marks, as these were repeatedly destroyed during new floods With regard to the reconstructed flow rates, the question also arises as to how much the river has changed since the historical flood, for example due to the deepening of the riverbed or due to human influence, such as river straightening or changes to the retention area, i.e. the natural expansion areas in floodplain areas. In any case, flood marks are also important reminders of disasters, which in turn increased awareness of the possible recurrence of flood events.
While flood marks can be found in many places, low water marks, i.e. marks on large stones that only protruded from the riverbed or lake in years of extreme drought, are very rare. As they only become visible in a few years, they were not regularly renewed or maintained. Sometimes they also fell victim to river straightening or the construction of hydroelectric power stations. Such low-water marks are also known as "hunger stones" because such dry years usually brought very poor harvests.
The Laufenstein near Laufenburg (canton of Aargau/Baden-Württemberg) protruded out of the water when the water level of the Rhine was very low. Local residents recorded such events by chiselling the respective year into the stone. The Laufenstein was blown up during the construction of the Laufenburg power station in 1908 or 1909. Fortunately, the engineer Hermann Walter recorded the years with extremely low water levels in his dissertation of 1901, which was probably written with a view to the later construction of the power station (Pfister, Weingartner, Luterbacher 2006).
Perhaps the most famous example of such a hunger stone comes from Déčin on the Elbe (Czech Republic). Among other things, it documents the drought of the summer of 1616, for which data can also be found in Euro-Climhist. It led to a devastating failed harvest throughout Bohemia and the surrounding regions. A stone in the riverbed of the Elbe in Déčin near the German border reads: "If you see me, weep" (translated from German). In the long series of precipitation events in the Czech Republic, the drought of 1616 ranks second only to that of 1540.