Land unter – Archäologische Untersuchungen zum Flutereignis 2021

Yes, hello, dear guests here on site, dear viewers in the stream. First of all, I would like to thank you for allowing me to present our current project as part of this event and would like to give a summary of our findings and investigations of the damage to the ground monument substance in the government district of Arnsberg, triggered by the strong weather event 2021, in the following minutes. Well, 2002, the Elbe high tide, Hurricane Curil 2007, the storm Ela in summer 2014 or the Hurricane Frederike in January 2018, just a few examples of the numerous bad storms of the last 20 years. Between 12 and 15 July 2021, another catastrophic weather event came along, often referred to as a flood of the century. To put it more precisely, it was a devastating event, which, especially in Rhineland-Pfalz and North Rhine-Westphalia, cost more than 180 people their lives. Estimates of the resulting damage are in the billions range. Immediately after the storm, first investigations took place in the Iserlohn area through the Olpe outpost. It quickly became clear that further investigations would be necessary to capture the entire damage. To be able to make a first entry into the damage area, Olpe's first weather data was evaluated in the outpost. Here it was shown that, especially in the Hagen area and the Merkischer Kreis area, the strongest downpours of the entire event could be seen. As can be seen in the diagram, this applies not only to the 72-hour maximum, but also to the corresponding meridian, which Hagen is even at first place. But there were also 182 millilitres of rain in one hour in the nearby Nachroth, which corresponds to about 182 litres per square metre. Further pre-measures for the project were carried out in the form of evaluations of topographical, hydrological and hydrological maps. Here it was shown that in the Hagen area and the Merkischer Kreis area, steep and winding valleys can be seen, which you can perhaps see quite well here in the diagram. These are made up of small streams that feed over the slopes of the so-called siepens. In the flood-damaged area, these are mainly the side valleys of the rivers Lenne, Volme and the Ennepe. The geological conditions of these slopes ensure that the rainwater almost completely and directly flows off. As can be seen in the picture, the slopes there are in most cases calamity forests, which are affected by strong borken beetle infestation. In the middle heights seen here, these waters first accumulate into larger streams. At these points, we call them medium slopes, the flow rate is strongest in combination with the amount of water. In the model, this has a strong resemblance to a large house roof surface on which rain falls, which then flows down concentrated over a single ridge, as far as it can. In practice, the whole thing looks something like this. Similar to the mentioned roof surface, not only the rainwater flows off, but pretty much everything that stands in its way. This means eroded soil in the landscape, but also forest waste. The large amounts of water in many places promoted the drainage of the stream bed to the bare rock. A conglomerate of rubble and wood in many places went downhill. A clogging of the flow possibilities, was the logical consequence. This effect was also intensified by structural conditions, such as the placement of streams on underground sewage channels. It is also worth mentioning that almost all of the prospected sites are in areas with intensive forestry. The picture shown here shows a very good overview of the basic situation of these prospects. By the way, in the left part of the picture, you can still see the old remains of a forest path, which is still just as recognizable. In any case, in order to capture the damage to the soil monument, we first oriented ourselves to well-known sites near the water. Here, in particular, the local researcher Dr. Manfred Sönneken is to be mentioned, who already in the 1970s intensively prospected the survey landscape and found many sites in the area. But we quickly noticed that the departure of already well-known sites alone was not sufficient. So the flood cut off large areas, where new finds were also exposed in many places. We therefore very early on decided to cover every side, especially the Lenne and Volme, also because these two valleys were hit particularly hard by the flood. In a large part of this project, all the water bodies examined could thus be found to be slag. In almost all cases, these could be re-moistened by the targeted drainage of the stream to an already well-known or new find site. It is fortunate that we were able to document around 100 new find sites. But even today, some paths and areas are still impassable even by foot. At these sites, old paths have been washed away. In other places, storm damage or dense undergrowth are so massive that it would only be possible to get there using chainsaws or even climbing equipment. Thus, our access to around a dozen already well-known find sites was denied. When recording damage, we used a traffic light system, so we first divided the damage into these three designated classes. When a find site was completely destroyed or there were severe damage to the find site, the status was given red. For light to medium damage, the status was given yellow. And when there was no damage to be done, the status was given green. A preliminary summary of the collected data shows that more than half of all find sites examined in the examination room can be proven. Of course, this does not correspond to the total number of all find sites in the examination room, but we were only able to prospect in many sections for time reasons. A full-scale damage analysis would probably take years. Here is a map of the examination area. The map shows an overview of the examined find sites in the damage area. The evaluated data confirmed that especially in the triangle Hagen, Schalksmühle and Nachhort-Wiblingwerde, which you see circled there, the damage was the densest. Here, however, the find site density increases. Here, however, the severe damage increases significantly. The damage area to be prospected is mainly due to a large number of Montan archaeological find sites. For example, the combination of find sites in the category Schlackenhalde, Meilerplatz, Pinge or Stollmundloch is often typical, and they also give the region a certain super-regional scientific significance. In this context, smaller hammer works or old mills can also be mentioned, which were sometimes already under building monument protection and are often deep in the forest. For the operation of a waterwheel, necessary dams or canals can also be found to be sometimes massive damage, up to the complete destruction of the dam. Almost all examined dams show severe flood damage. The damage picture we are examining is divided into two essential types of damage. On the one hand, the actual heavy rain, a very punctual damage that was caused on areas where a lot of rain fell on very small areas in a very short time, for example because rain clouds could not move away, but were located locally. This effect is also similar to a watering can with which the same place is watered over a long period of time. Meteorological conditions play a role here. In terms of space, these places can also be located on an off-piste, but in any case in areas where the water can flow easily and cheaply. Once the water collects, the damage seems to be limited at such places. The second type of damage results from the heavy rain, which is the corresponding flood. Here, hydrodynamic, topographical and geological properties and mechanics play a role in the development of the examined damage. The damage is mainly expressed in the form of flushing, such as flushing over, flushing under, flushing off, or the formation of large-scale flushing pots, as well as erosion. Erosion in particular can continue even after the flood. These damages are mainly found in the non-continuous water-leading smallest waters. Here, hydrodynamics of river waters play a role. Floods obviously increase the water pressure and the flow rate of the water, which has apparently increased the damage. Most of the damage in the brook bed is where the water hits the shore. These places are also called prallhang. There, the water can reach the most intensively and accordingly flush large amounts of soil. We actually found minor damage, especially in the flood area, where there was sufficient area to distribute. This also led to large flood situations, but in these places, potential damage was actually limited. In addition, damage images of the flood correspond regularly with damage to the forest or the forestry industry. Common damage images here are forest waste due to deforestation and deforestation from bark beetle-infested wood that land in the brook bed. Such damage images have apparently also contributed to the destruction of numerous finds in the context of the flood and strong rain event of 2021. Tracks through harvesters are obviously also a problem, especially when they enter the soil very deeply. Obviously, these tracks also have a similar effect to a small canal, so water bundles and the earth erodes. Further damage is damage to trees, further damage is storm damage and drought damage. Here in the picture, that was a former reservoir, the damage accumulates again, actually all known damage that we have examined in the investigation area. It was actually filled with water and is now almost filled with sediment all the way to the upper edge. Finally, I would like to introduce you to one of the most impressive damage images. The picture shows an eroded wall, the eroded wall of a brook bed, which was washed away over a height of over 6 meters, a depth of at least 6 meters and a width of just under 40 meters. You can see on the right in the picture that trees were first washed away in the root bed and more or less sunk to the spot. The root bed here shows the probably former shoreline. Well, as a conclusion, it should be said that at the latest the repeated rainy showers from the beginning of this year unfortunately also confirmed our previous assumptions about future damage to already affected sites. This has shown that erosion continues on numerous already damaged sites. In particular, sites with red damage seem to be particularly affected. It is quite likely that some of these sites will disappear completely in the next few years. Yes, I would like to finish my lecture with the mention of my dear colleague Daniel Riemenschneider, who is sitting in the front, who, as a native of Isalona, knew every last corner of the investigation area and thus always led to the goal through many, sometimes hardly passable, forests, always armed with a flight stick and a camera. I would like to congratulate him on this point again very warmly on his future training site as an excavation technician in the Außenstelle Olpe. Thank you for your attention.