Low Water Stage Marks on Hunger Stones: Verification Elbe River in 1616-2015

14 The paper deals with the issue of documenting hydrological drought with the help of drought marks 15 (DMs) which have been preserved on dozens of hunger stones in the river channel of the Elbe in 16 Bohemia and Saxony. So far, the hunger stones have been regarded rather as an illustration of dry 17 seasons. Our aim was, among other issues, to draw attention to the much greater documentary value of 18 hunger stones and individual dry year marks inscribed on them. Therefore, we wanted to verify their 19 reliability and better understand the motivation of their authors. For this purpose, we used the current 20 extreme drought period of 2014-2019 which allowed detailed documentation of hunger stone in Děčín 21 with marks from 1536 to 2003. Thanks to the helpful position of the object near the water gauge, we 22 could compare the measured mark heights with the corresponding water levels. Simultaneously, we 23 have scanned the object into 3D format so that it is possible to perform a detailed inspection of all 24 marks, even those that were overlooked during field survey. A review of scientific and technical 25 literature from the 19 th century showed that marks of low water levels on stones and rock outcrops 26 were to some extent interconnected with other important points. They were linked to zero points of 27 water gauges, initially set up for navigation purposes, and also to flood marks. A particular situation in 28 Děčín is therefore a unique example of epigraphic indication of low and high water levels in the 29 enclosing profile of the upper part of the Elbe river basin. To verify the marks of low water levels we 30 used the then current scientific studies which in the past brought the identification of dry periods. 31 However, we also used the oldest series of daily water levels measured in Magdeburg, Dresden, and 32 Prague, available by 1851, i.e. by the beginning of measurements in Děčín. These series had to be 33 reconstructed or digitized from the CHMI archive sources. Since 1851 we have been able to accurately 34 identify the heights and sometimes even the specific days when the minima were marked. 35 After thorough examination of field and newly measured data, as well as data obtained from review of 36 older literature presenting the first surveys of marks on hunger stones already in 1842, older marks of 37 low water levels can be considered mostly as a reliable indication of annual water level minima. The 38 aim of the mark creators was not to make the commemorative inscription on drought, but to register 39 the exact position of the water mark of the annual minimum. The deviations of most of the marks from 40 the water gauge records did not exceed 4 cm, in worse cases 8 cm and only exceptionally the disparity 41 was greater. 42 From the material obtained so far, the overall slight downward trend of minima since the end of the 43 18 th century is noticeable. The view on minima of the 17 th and 16 th century is based on only a few data 44 and it is difficult to generalize so far. However, the minima obtained are comparable to or lower than 45 the data from the critical dry periods of 1842, and 1858 to 1874. Our verification and certain 46 rehabilitation of low water level marks should be an incentive to process all available epigraphic 47 1 https://doi.org/10.5194/cp-2019-113 Preprint. Discussion started: 7 November 2019 c © Author(s) 2019. CC BY 4.0 License.

could compare the measured mark heights with the corresponding water levels. Simultaneously, we 23 have scanned the object into 3D format so that it is possible to perform a detailed inspection of all 24 marks, even those that were overlooked during field survey. A review of scientific and technical 25 literature from the 19 th century showed that marks of low water levels on stones and rock outcrops 26 were to some extent interconnected with other important points. They were linked to zero points of 27 water gauges, initially set up for navigation purposes, and also to flood marks. A particular situation in 28 Děčín is therefore a unique example of epigraphic indication of low and high water levels in the 29 enclosing profile of the upper part of the Elbe river basin. To verify the marks of low water levels we 30 used the then current scientific studies which in the past brought the identification of dry periods. 31 However, we also used the oldest series of daily water levels measured in Magdeburg, Dresden,and 32 Prague, available by 1851, i.e. by the beginning of measurements in Děčín. These series had to be 33 reconstructed or digitized from the CHMI archive sources. Since 1851 we have been able to accurately 34 identify the heights and sometimes even the specific days when the minima were marked. 35 After thorough examination of field and newly measured data, as well as data obtained from review of 36 older literature presenting the first surveys of marks on hunger stones already in 1842, older marks of 37 low water levels can be considered mostly as a reliable indication of annual water level minima. The 38 aim of the mark creators was not to make the commemorative inscription on drought, but to register 39 the exact position of the water mark of the annual minimum. The deviations of most of the marks from 40 the water gauge records did not exceed 4 cm, in worse cases 8 cm and only exceptionally the disparity 41 was greater. 42 From the material obtained so far, the overall slight downward trend of minima since the end of the 43 18 th century is noticeable. The view on minima of the 17 th and 16 th century is based on only a few data 44 and it is difficult to generalize so far. However, the minima obtained are comparable to or lower than 45 the data from the critical dry periods of 1842, and 1858 to 1874. Our verification and certain 46 rehabilitation of low water level marks should be an incentive to process all available epigraphic 47

Introduction 51 52
In recent years, the phenomenon of drought has become the most prominent manifestation of climate 53 change in Central Europe. However, its objective evaluation and the evaluation of its extremity is 54 often a problem. The reason consists in difficult to grasp the phenomenon of drought or varying 55 impacts of it, respectively. Drought alongside the floods, though, rank among the most commonly 56 evaluated hydrological extremes. While the flood is caused by an unexpected and short-term excess of 57 water that causes damage, hydrological drought follows long-term deepening of water scarcity. 58 Our contribution is focused on hydrological drought, more precisely on minima of water stage of 59 surface water streams. The low water level and flow rate after long periods of deficit precipitation 60 represent particularly valuable information about the basin runoff. Therefore, they also report on the 61 base-flow, the groundwater accumulation, long-term depletion and hydrological drought propagation 62 (van Loon, 2015). The minimum water level or flow is, to a large extent, summary information on the 63 status of a given river basin. 64 Like floods, hydrological drought is difficult to study without examination of historical events. 65 However, what options do we have regarding low water levels? The available hydrological series 66 usually cover not more than 150 years. The longest hydrological series of measurements in Cairo 622-67 1933, representing 1311 years of Nile observation (Shanin, 1985), was used to assess drought and its 68 interrelations with phenomena such as El Nino. In Europe, the longest series comprising 69 measurements of water levels in Magdeburg started in 1726 (see the following text), and the 70 measurements in Paris that started in 1731 (Delametherie, 1800). However, it is not possible to 71 conceal another complication, namely the later beginning of systematic hydrometric measurements 72 which are mostly available only since the end of the 19 th century. This makes it difficult to estimate 73 flow rates somewhere. Therefore, stable profiles where we can assume the validity of the rating curve 74 as far back as possible are very valuable. Systematic series of water stages are therefore testimony on 75 runoff fluctuations but partly also on changes in the stream cross-section both natural and 76 anthropogenic. 1826, 1834,1842,1863,1868,1904,1911,1921,1934,1947,1953,1959  This article focuses on them wishing to clarify their purpose, origin and meaning. Traditionally, water 117 management experts and historians and perhaps ethnographers in Bohemia considered inscriptions and 118 year indication on hunger stones to be an interesting phenomenon symbolizing drought. At the same 119 time, however, the understanding prevailed that the marks of "dry years" were merely commemorative 120 records with no deeper meaning and that they were more or less randomly positioned. We believe that 121 it is in this area that we have taken a substantial step forward in the explanation and possible use of 122 these records. 123 We have therefore focused on the Děčín city located in the lower section of the Czech part of the Elbe 124 river basin. At the centre of our study is the Děčín city ( Fig. 1)  This gauge starts at 9 ells above the water level for full navigability (Bohemia daily, 1845). This depth 175 was traditionally referred to as the "Fünfspanner", i.e. "five-span", a sufficient navigational depth of 5 176 spans or 50 inches, or 125-130 cm for the full loading of the Elbe ships (Bohemia daily, n. 45, from 177 April 4 th , 1845). There was a rock block near the shore with a water gauge for low water levels in feet 178 [RG1] (1 to 5 feet), probably related to safe passage. In 1851, water levels in Děčín began to be 179 systematically monitored, initially at the old water gauge [OG] at the site of the navigation directorate. 180 Apparently, the water gauge served the navigation to efficient ship loading for the place of the second 181 water shallows area. It still bears the original German, now popular, name "Heger", or supervision. 182 Later, the observation was transferred to a new water gauge [G1851] (see chapters on methodology, 183 documentary sources). 184

Data and documentary sources 187
The first partial goal was to prove that the water level marks on the hunger stone in Děčín and other 188 stones were meant by their creators as signs of annual minima in the years attached to the line. The 189 simplest means is a comparison with concurrent water level measurements on a near water gauge 190 (accurate identification) and also use of other available measurements (approximate confirmation of 191 significant water level decline). We mainly used four series stored in CHMI (Czech 192 Hydrometeorological Institute). These are the systematic series at sites of Magdeburg (1726-1880), 193 Dresden (1801-1829), Prague (1825-1890) and Děčín (1851-2019). 194

A series of daily water levels in Magdeburg 1726-1880 195
Around 1880, this series was acquired by Prof. Harlacher (Elleder, 2012)   Elleder, 2016). The profile of the Old Town mills was related to the weir normal (i.e. to the weir crest) 221 so it was a profile that did not change. According to Novotný (1963)  He evaluated the significantly lower flow rate for the water stage at 113 cm only later on 19 August 254 1904, at 39 m 3 ·s -1 . This is a significant difference that would affect the flow rates at the extreme 255 minima of 1868 and 1904, and the question is whether to trust the 1876-1881 curve when it was not 256 possible to evaluate the lowest water levels because they did not occur. Hydrometry of small flow 257 rates on the Saxon side has been available since 1886, but extremes only since 1893. Therefore, in the 258 results, the flow rates at individual minima are accepted so far with caution.   3.6. Preliminary verification of the heights of assumed water level minima using regional press 263 and simultaneous measurements on the existing water gauge in Děčín 264 This study was preceded by about 10 years waiting (since 2005) for a suitable opportunity to 265 undertake a field survey of hunger stones that are totally or partially below the surface at normal 266 summer flow rates. There was no other possibility than to try to find an alternative solution. In 2009, 267 as part of a preliminary study, we tried to use rich iconographic material from the period 1894 to 1994 268 and reports of hunger stone in Děčín in contemporary newspapers. In the older press materials, reports 269 were looked up when the hunger stone was visible and an indication was given as well which year-270 marks were above the relevant water level. Then it was easy to classify the marks into height groups 271 with a water level higher than that of the day reported. Further specification of heights was possible 272 only on the basis of photographs by comparing which mark is higher or lower in the given group. The with annual water level minima. We have followed a partially similar approach with the hunger stone 276 in Pirna. 277

Field measurements 278
In 2011, it was possible to carry out a field verification of the estimated heights of the marks that were 279 located in the highest part of the stone. In 2014, the opportunity was not used as we believed that the 280 dry season will have a longer-term character which was confirmed in 2015 and 2018. In 2015, the 281 hunger stone in Děčín [HS3] and the stone in Těchlovice were surveyed. During the surveying of the 282 stone in Těchlovice located on the slip-off slope gravel deposits, it was not necessary to make any 283 ground adjustments. However, only relative heights recalculated to the minimum height of 1842 were 284 measured. 285 The surveying of the Děčín stone in 2015 required preparation representing sediment removal and 286 stone cleaning (manual work of 2 to 3 people for 3 hours or more). In 2015, the sediment layer 287 reached the sign of 1616, i.e. around 70 cm of height. In addition, it was necessary to make a pit 288 around the stone's very low marks. The use of a pump with a syringe to wash away sediment, blasting 289 stone and pumping water from the sump significantly accelerated the work. 290 The measured mark heights were linked to the nearby fixed geodetic point. All surveyed geodetic 291 levelling points were photographed. The measurement took place on 14 th August when water levels 292 dropped the lowest just before the expected rainfall episode which increased the Elbe water level 293 significantly. Participants of the measurements were: Ladislav Kašpárek and Jan Kašpárek from T. G.

294
M. WRI, Libor Elleder from CHMI and a land surveyor, Mr. Zvonimír Dragoun (presented on EGU 295 2016, Elleder, 2016b). 296 We basically did the same when scanning and creating a 3D model in 2018. The stone was prepared 297 by colleagues from CHMI: Martin Groušl, František Pěkný, Martin Hubený in advance on 27 th July. 298 The final adjustment was made on the day of measurement and was assisted by Daniel Kurka, Libor 299 Elleder and Martin Hubený. Martin Hubený also performed a hydrometric measurement in the hunger 300 stone profile ( Fig. 1 [HS3]) including the cross-section measurement using the ADCP (acoustic 301 Doppler current profiler). 3D scanning was performed by Libor Tělupil from the VR3D Company 302 (http://vr3d.cz) on 30 th July, lasting for about 3 to 4 hours. Similarly, the marks on the rock in the 303 [RG2] profile were scanned. Because scanning requires soft, shadow-free lighting, a temporary stand 304 was placed over the stone. The whole event was documented by the local press 305 (https://www.idnes.cz/usti/zpravy/decin-vodomer-hladovy-kamen-skenovani-3d-306 model.A180730_113803_usti-zpravy_mi) and the result is partially accessible on the CHMI website 307 (http://portal.chmi.cz/historicka-data/hydrologie/zaznamy-z-minulosti/hladovy-kamen). Both and 17 th century. 325 For the evaluation of the DM marks made after 1727 we used the above-mentioned series of 326 measurements in using the Magdeburg series rather for dating verification and the Prague and Dresden 327 series for assuming a very approximate estimate of the significance of the minimum. Concerning 328 newer cases after 1851, it is possible to confirm the correct or incorrect position of the mark (DM). 329 Regarding deviations from the measured water level for that day, we consider the precisely marked 330 height (HP) at a deviation of 0-4cm and approximately marked height (CP) at a deviation of 4-8 cm.

331
We consider larger deviations as a possible mistake when placing the measuring rod or a poor 332 understanding of the difficult-to-read position of the mark or line. If the DM mark does not have an 333 accurate dating, we can assume dating according to the minimum water level when there is the exact 334 (HP) identification with the minimum water level. chronological, so that the information is combined into a logical complex. 346

Complementing measurements according to other objects 347
Some marks (DM) are missing on the Děčín stone, but we find them elsewhere. If their heights were 348 measured during commission inspections of the Elbe River in 1842 (Protokoll, 1842)  organized to improve navigation conditions. The aim was a thorough description of all fixed points 382 (water stage gauges, flood marks and also marks on hunger stones), navigation conditions and 383 minimum navigation depths along the navigable section of the Elbe from Mělník town to Cuxhaven. 384 Stones and rocks in the river were of double importance for navigation. They were a dangerous 385 element, but at the same time they served the orientation for navigation. The commissioners travelled 386 by boat and the section Mělnik-Meissen was surveyed from 5 th to 11 th September 1842, 14 days after 387 reaching an absolute minimum water level. The water levels of the Vltava and Elbe were still very 388 low, but they were already 9 to 20 cm higher than the minimum in the previous August. In Děčín 389 town, measurements were made from 7 th to 8 th September (Protokoll, 1842) at a water level at about 390 3.5″ (9 cm) above the 1842 minimum. Three hunger stones in Děčín ( Fig. 1) and one in Dolní Žleb 391 were identified and surveyed. On the Czech side, a water gauge in Litoměřice and a water gauge for 392 navigation purposes in Děčín were noted in the section between Mělník and the state border (in both 393 cases there were no regular records available). On the Saxon side, water gauges in Bad Schandau, 394 Pirna, Dresden, Meissen and Riese were identified, managed by the Royal Navigation Directorate 395 (Königl. Wassebaudirection Dresden). The hunger stones were detected and partially surveyed in the 396 following locations: Schmilka and Pirna (see the text below), (Protokoll, 1842). to the minimum of 1842. The Commission was active in September when there was a significantly 407 higher water level than in 1842. Therefore, the marks on hunger stones were underwater and so 408 difficult to recognize. For the present stone [HS3], its top at 14½″ (37.7 cm) was below the then 409 current water level. Since, according to our measurement, the top is at the water level H = 176 cm, the 410 then current water level was about 214 cm and the flow rate was about 190 m 3 ·s -1 (according to 411 Harlacher's rating curve, 1883). The Commission had a new map of the Vltava River and the Czech 412 Elbe river which was created between 1843-1848 (Elbekarte, 1848) with already marked depths in 413 cross sections. In the following year on 1 st January 1851, the daily observation of water gauges on the 414 Czech Elbe River in the Mělník, Roudnice, Litoměřice, Ústí nad Labem, Děčín, and probably Dolní 415 Žleb cities begins. Zero points of the new gauges were established 6 inches above the minima in 1842 416 (Protokoll, 1858). At this stage, half-cargo navigation was possible (Wex, 1873). This drought also had a specific impact in the most industrial part of the Austrian monarchy, Bohemia. 446 In 1869, another Elbe Navigation Commission (Wex, 1873) was held. In 1871, Professor of the Prague 447 Technical University, A. R. Harlacher, established a temporary station for hydrometric observations 448 and calculating the amount of runoff from the Czech Elbe (1871-1872), (Harlacher, 1871, 1872). The 449 year 1873 brought, according to Cvrk (1994), the intensification of river regulation of the lower Elbe 450 (mostly digging and removing boulders) and finally deepening of the riverbed by approx. 20-30 cm.

451
The catastrophic drought in 1874 led, after a broad discussion, to the establishment of the   there is the so-called "Ara Bakchi", "Altarstein" or "Elfenstein" (Fig. 2, Fig. 3)) which is just one of 490 the sites that used to be accessible only during the low water stages of the Rhine.  visible during low water levels, and in 1746 the pillars of the old bridge in Mainz were visible (Fig. 3).  The term Hungerstein was not often used in the 19 th century. In the scientific literature we find the 520 heights of the low water levels as "Merkzeichen der Wasserstände" (Neue Schriften, 1845), in the 521 news reports the term millstones as "Malsteine" appeared. The commissions' reports in the Protocol 522 (1842) and Protokoll (1850) mention the stones as "Steine", and the remarkable ones as 523 "Merkwürdige Steine". The Elbe in the sandstone canyon used to be rich in local names: "Frog 524 Stones" or "Froschsteine" (Dolní Žleb) ( 1876). The Czech derived mutation " hladový kámen" ("hunger stone") was introduced by the regional 532 daily Jizeran (17 September 1892) during the drought in 1892. 533

Hunger stone in Těchlovice 534
The site is located above the sandstone canyon and the valley is formed by rocks of volcanic origin. 535 On the left bank of the Elbe River, approximately in the river km 85 (below Mělník), the Elbekarte 536 map (1848) shows the so-called "Mändelstein" in the riverbed, but actual stone is on a gravel bench 537 and the affinity of the objects is unlikely. The Protokoll (1842)  that the reason was the construction of the railway (Protokoll, 1850). Since the railway was on the left 569 bank, we tend to consider a possibility that the stone disappeared during terrain works for the Unfortunately, they only determined the difference of 5″ (12-13 cm) between the higher minimum of 576 1616 and the then lowest minimum of 1842 (difference of 11 cm was determined in 2015). 577 The stone was (see the metodology) divided into four height ranges and the following sides:  Table 4 is chronological so that the information is combined into a logical complex (detailed 596 information is included in the supplement). 597 Using the example of measurements in 1850, it is possible to clarify the system of rock gauges  In the river map (Elbekarte, 1848), a total of 7 to 8 stones are marked on the right bank of the Elbe 624 River upstream of Dolní Žleb, followed by another 6 downstream, as indicated in the Protokoll (1842). 625 At the former customs house (left bank), the Elbe river flow was narrowed by two rock outcrops: the

4.2.7.Hunger stone in Schmilka 654
On the right side upstream of Schmilka, the Commission (Protokoll, 1842) found a large stone with 655 the 1842 mark (4. 9.) which was 4″ (10 cm) below the then current water level. Further, the 1811 mark 656 was found that was placed higher by 3″ (7.5 cm). 657   It was located near a small gate at the navigation control point but the situation does not exist today. 680 Nearby, there was a transverse dam opposite to which a flat stone was to be with engraved marks. 681 According to the Protokoll (1842), the marks of 1616, 1706, 1707, 1746, 1834 and 1835 were 682 registered and surveyed (the other marks were illegible). Water level at that time was 6″ (0.13 m) 683 above the inscription " Waserbau Direction 1842", (Fig.8). information between CHMI and SLUG. We provided a sketch of the stone in Pirna which was used to 702 reconstruct the engraved signs that are exhibited today in the SLUG building in Dresden.

704
The second, newer stone in Pirna has the mark of 1904. 705 Tab Tolkewitz locality, there is a stone with the 2016 mark. In the Augustbrucke cross-section a low water 715 level of 1705 was indicated (Pötzsch, 1874), and now, there is also the mark of 2018.   There are always fewer records of low water levels (if any) than marks of high water stages, the only 736 exception is possibly the sandstone Elbe valley between Děčín and Pirna. It is more difficult to make a 737 mark of the minimum water level than making the flood mark. 738 (1) It is and it has always been difficult to estimate the correct instant of reaching the minimum level. 739 More demanding inscriptions were probably made in advance; the designated place was probably 740 enclosed beforehand by a small barrier so that the mark could be completed at a time when it was 741 clear that the minimum was reached, i.e. when the water was rising. Therefore, the logical 742 moment of making the minimum mark is after the minimum has subsided (in the reality 1-15 days 743 before annual minimum level were this DM levels engraved see tab. 4). However, it is not clear 744 whether this was a local or annual minimum. 745 (2) In some years, the level fell again lower, the exact date is given, or a range of water levels for a 746 given year is made, such as in Děčín for 1904Děčín for , 1921Děčín for , 1930Děčín for , 1934Děčín for , and 1957. A surprise can be 747 evoked also by marking the year 1707 in Pirna, as it concerns probably other year. The mark of 748 1842 seems to have a different meaning being the actual water stage in feet. 749 (3) The minimum markings are often made upside down (made from the upper side of the stone), 750 some were made while standing in water or at a lowered position (oriented normally). Therefore, 751 the engraved lines in such cases are not below the date (in the graphic sense) but above it, thus 752 closer to the water surface (in Děčín for instance DMs: 1536DMs: , 1707DMs: , 1892DMs: , 1893DMs: , 1904DMs: , 1911DMs: and 753 1934. 754 (4) The marks are completed by monograms (see Pažourek, 1998) According to Brázdil et al. (2013Brázdil et al. ( , 2015, the 1511-1520, 1531-1540, and 1631-1640 periods had a 773 higher decade frequency (n = 6 per decade) of drought reports. documented, with a recurrence period of 10 years or more (≥ Q 10 ) (Elleder, 2015). Although the dry 785 period does not exclude significant floods at all, in this case it concerned more frequent cases of floods 786 of approx. Q 20 . We can consider it a period with an average drought occurrence, where according to 787 monthly rainfall indices at least the index -2 (very dry month) occurred in two or more consecutive  Since 1726, we can identify the minima in the years highlighted in Fig. 6

811
The water level DM minima are plotted in the water level scale of the current water gauge in Děčín. A 812 coincidence regarding the water level (1746) is completely random (Fig. 6). However, there is a 813 noticeable difference in the trend of annual lows of both series. We also emphasized the effect of 814 overall minima, so the graph also separates the winter minima which show the downward trend, for 815 example, just before 1746.  In conclusion, we can state a good match of the minima detected which, moreover, are mostly 831 representative of the largest extremes. However, this is not true entirely, as some years such as 1540, 832 1590 or 1761 are missing. This is a great motivation for the next stage of future work. There is no need to doubt the credibility of the low water level marks in Děčín from 1868 to 1957. 845 When interpreting them, however, it is necessary to know the described changes, whether they are 846 changes in the channel or flow rate enhancement by the Vltava cascade. These are annual or local 847 minima marked with the greatest possible care. It is also obvious that older marks in the 19 th and 18 th 848 centuries were made in the same way and with the same intentions. Can this claim be extended to the 849 past, i.e. to the 17 th and 16 th centuries, and is this finding valid for other hunger stones both in Bohemia 850 and Saxony? 851 It would probably be appropriate to prove the connection of heights in Děčín, Dolní Žleb, Schmilka 852 and Pirna. However, when verifying the relationship between Pirna and Děčín, we can compare only 4 853 concurrent records. These are the years 1616, 1707, and 1842. Since we use the relative difference to 854 the water stage in 1842, we can only compare the three remaining heights of 1616, 1707, and 1746. 855 The relationships of 1616, 1707, and 1842 are linear, somewhat different is the water stage in 1746 856 where the difference from the expected value is greater than 10 cm. Perhaps only a local minimum 857 (LM not AM) was marked in Pirna. However, we only use the published data from 1842 and from 858 1843 and it is not entirely certain that the commissioners found and surveyed the lowest mark for a 859 given year. Verification is still difficult; we do not see this mark on the current stone in Pirna-860 Oberposta. 861 We can recommend further field survey in the future (next one especially in Dolní Žleb), levelling and 862 scanning of other objects, especially the stone in Pirna. For detailed analysis and search for relics of 863 older marks, it is not possible to rely solely on photographic documentation. Comparative older 864 photographic material (Fig.8) and detailed inspection of scanned 3D objects is required. Economic Society of the Czech Kingdom, respectively. They point to other low levels that we 876 expected and that could not be verified. This is, for example, the height of 1590. A report drawing 877 certainly from the results of the Commission in 1842 and therefore the Protokoll (1842)

903
If we take this source into account, and we combine this data with the data already presented, we get a 904 slight shift somewhere, but the overall picture and trend confirm information on the minima of water 905 levels from hunger stones in Bohemia. Another source is the report of the Patriotic Economic Society 906 (Neue Schriften, 1845) where the forester and observer of the Děčín-Podmokly station gives the exact 907 height of the marks (Tab 10). It is partly a compilation of the heights from Děčín and Dolní Žleb, the 908 data are very similar or the same (1616, 1707, 1746, 1811, 1835, and 1842). Differences over 8 cm 909 show only DM of 1766, minor differences are in the years 1782, 1790, and 1800. However, there are 910 also data for 1834, 1516, and 1517. To complement the Děčín data, the minima of 1516 and 1517 were 911 mainly used. We assume that, as a forester and a meteorological observer, A. Seidel could supplement 912 the report of the commissioners (who had only limited time to survey) from his own examination in 913 Dolní Žleb and Děčín, where he lived. The years 1516 and especially 1517 were really dry, as 914 evidenced by contemporary descriptions in the Old Czech Chronicles (SLČ), in particular, describing 915 rather meteorological and phonological parameters of drought (e.g. harvest already on 29 th June).