Low water stage marks on hunger stones: verification for the Elbe from 1616 to 2015

Abstract

Abstract. This paper deals with the issue of documenting hydrological drought with the help of drought marks (DMs) which have been preserved on dozens of hunger stones (HSs) in the river channel of the Elbe in Bohemia and Saxony. So far, the hunger stones have been regarded rather as an illustration of dry seasons. Our aim was, among other issues, to draw attention to the much greater value of hunger stones and individual dry year marks inscribed on them. Therefore, we wanted to verify their reliability and better understand the motivation of their authors. For this purpose, we used the current extreme drought period of 2014–2019, which allowed detailed documentation of a hunger stone in Děčín, Czech Republic, with marks dating from 1536 to 2003. Thanks to the helpful position of the stones relative to the water gauge, we could compare the measured mark heights to the corresponding water levels. Simultaneously, we have scanned the objects into 3D format so that it is possible to perform a detailed inspection of all the marks, even those that were overlooked during the field survey. A review of scientific and technical literature from the 19th century showed that the marks of low water levels on stones and rock outcrops were to some extent interconnected with other important points. They were linked to zero points of water gauges, initially set up for navigation purposes, and to flood marks. The particular situation in Děčín is therefore a unique example of the epigraphic indication of low and high water levels in the enclosing profile of the upper part of the Elbe River basin. To verify the low water level marks or drought marks, we used the then current scientific studies focussing on dry periods. However, we also used the oldest series of daily water levels measured in Magdeburg, Dresden and Prague, available from 1851, i.e. the beginning of measurements in Děčín. These series had to be reconstructed or digitised from Czech Hydrometeorological Institute (CHMI) archive sources. Since 1851 we have been able to accurately identify the heights and sometimes even the specific days when the minima were marked. After a thorough field examination and newly measured data, coupled with data obtained from a review of older literature presenting the first surveys of marks on hunger stones as presented in 1842, older marks of low water levels can be considered a reliable indication of the annual water level minima. The aim of the mark creators was not to make commemorative inscriptions of drought but to register the exact minimum water level. Deviations between the marks and the water gauge records did not exceed 4 cm, and only exceptionally was the disparity greater. From the material obtained so far, an overall slightly decreasing trend of water level minima since the end of the 18th century is noticeable. The view on minima of the 16th and 17th centuries is based on only a few items of data, and it is difficult to generalise. However, the minima obtained are comparable to or lower than the data from the critical dry periods of 1842 and 1858 to 1874. Our verification of low water level marks should be an incentive to process all available epigraphic documents of this kind in the near future in closer cooperation with colleagues from Saxony. The potential of these objects offers a deeper knowledge of periods of hydrological drought and possibly of morphological changes in the Elbe riverbed.