Thistle hole dam
The Distellochdamm is an artificially created dam near the Middle Franconian municipality of Burgthann in the district of Nürnberger Land in Bavaria .
location
The dam is part of the apex of the former Ludwig-Danube-Main Canal and lies at 417 m above sea level. NN . It is located about one kilometer southeast of Burgthann and is in the area of the Burgthann district of Oberferrieden . The dam is part of the Schwarzachtal landscape protection area with side valleys .
description
The earth dam spanning a deep valley cut completely, the eponymous thistle hole which also thistle Dobel is called. The dam is 319 meters long and 29 meters high. Together with the Gruberbach, Kettenbach, Schwarzenbach and Mühlbach dams, it is one of the largest of the 70 dams built on the Ludwig Canal. So-called towpaths lead along both sides of the dam crest on the canal itself . The northern path is gravel and marked as a cycle and hiking path. This path is part of the long-distance hiking trail Eppeleinsweg ( 
) and the national five-river cycle path . In the middle of the dam crown there is an information board with information about the history of the dam. The vegetation of the adjacent and steeply sloping northern dam shoulder is characterized by open meadows, fruit trees and some mighty deciduous and coniferous trees. The southern shoulder of the dam is completely forested and difficult to access due to dense bushes. The southern path on the crest of the dam is unpaved and deeply rooted.
history
Originally, instead of the dam, a bridge channel with five arches and a width of 14.5 meters was planned. For cost reasons and to avoid problems, a decision was made in favor of building a dam. Up to 9,000 workers were working at the same time to carry out the necessary work. In the "cut and fill" technique, material from the Guglhof incision and the Dörlbach incision in the west was used for filling. However, the material was unsuitable; together with adverse weather conditions, this led to massive landslides several times . Due to the impending contractual penalties, the work was continued even during long periods of rain and in winter with snow and frost due to lack of time. In the winter of 1841/42, during prolonged and uninterrupted rain, the filler soil got soaked and began to slide inexorably.
Attempts to stop the penetrating water by driving in wooden piles did not bring the desired result. In order to increase the durability of the dam, the original unsuitable shale was subsequently mixed with sand. The sand was brought in with great effort from a distance of seven kilometers over the already flooded section of the canal. In the further expansion, the dam was also widened and in some places reached four times the originally planned dam width. In addition, drainage tunnels and drains were created on the eastern slope of the valley of the thistle hole . These should prevent the dam from getting wet. Ultimately, only the combination of different and costly measures led to success and further landslides were permanently prevented. The package of measures was a widening of the dam base, the creation of drainage and drainage tunnels and an extension of the creek passage of the Tiefenbach. By widening the embankment base, the creek passage had to be lengthened accordingly and its course corrected by adding several steps near the outlet portal.
The dam has been designated as a building and soil monument by the Bavarian State Office for Monument Preservation (D-5-74-117-38, D-5-6634-0120).
Security gates
So-called safety gates were installed on both sides of the dam during the construction of the canal . Security gates of this kind were primarily installed on the apex posture or in the case of longer lock postures at critical points in the canal. In the event of an accident, the movably mounted gates should prevent complete leakage. The two oak doors were open during normal operation and installed in a slightly V-shape so that they could move against the direction of the possible damaged area. When an unusual current occurred, the two gates closed by themselves and blocked the canal like a lock gate. But they also served to drain the sewer in sections for necessary overhaul or maintenance. To do this, they were closed manually and the relevant sewer section was drained in a controlled manner.
The eastern security gate is designed twice and secures both the Distellochdamm and the Schwarzenbachdamm to the east. Today the two gates are always closed. The western security gate only secures the thistle-hole dam. In 2018 the northern gate was expanded for restoration.
Tiefenbach
The natural course of the Tiefenbach was interrupted by the construction of the dam. The approximately three-kilometer long stream rises near Oberferrieden and collects the water from other forest and meadow ditches in its course. The mean runoff is rather low, but can increase sharply with melt and flood waters. The Tiefenbach drains 500 meters north of the thistle hole into the Schwarzenbach which flows into the Schwarzach near Burgthann .
Tiefenbach passage
Due to the low-lying valley floor , the water from the Tiefenbach could not be drained into the canal. A generously dimensioned passage was built at the bottom of the valley for the passage . The course of the stream is directed through the dam base in a south-north direction over a length of about 180 meters. The U-shaped tunnel diameter measures about 2.30 by 2 meters on average. The portals are made of castle sandstone . The interior is completely and predominantly lined with castle sandstone blocks. On the right side, parallel to the brook, there is a one meter wide walkway that was laid out for revision work . Inside there is a chiselling with the year 1877. This seems to be more recent and was probably renewed during the restoration in the 1990s. On the ceiling and walls there are sometimes beautiful and colorful sinter and stalactite formations . They owe the reddish and brownish hues to the dissolved iron oxides from the surrounding Dogger .
The course of the stream through the dam is not in a straight line and has two kinks. The curves were created to drain the dam itself and the eastern slope of the valley and to reduce the speed of the flow. There are some stone steps about 30 meters in front of the outflow portal. These were added later when the dam base had to be widened.
In its further, open course, the creek bed is completely lined with sandstone over a length of about 100 meters and laid out remarkably flat. At the end of the route there is an approximately three meter high crash structure . The measures served to slow the water down, especially during floods. This prevents undesired indentations in the landscape, which would possibly endanger the dam again.
Drainage tunnel
In order to protect the dam from wetting by surface and spring water and momentous possible landslides prevent, the dam were drainage on the eastern flank stollen created.
Blind studs
There are two blind tunnels on the northern shoulder of the dam.
The portal of the higher and eastern tunnel is about five meters below the dam crest. The entrance portal is made of castle sandstone. The tunnel drains through this to the deeper Tiefenbach. It is about 80 meters long and designed as a blind tunnel. Inside, it is about 1.70 meters high, up to 85 centimeters wide and leads south into the dam. The cross-section is oval and it has the optimal shape to dissipate the pressure of the layers of earth weighing on it. The masonry inside, made of castle sandstone, has been preserved almost in its original form. Only damaged areas were repaired here. In the end, the tunnel was walled up. Due to vandalism and probably to check whether the tunnel continues, stones were broken out of the wall there.
The second blind tunnel is located near the western flank of the valley, about halfway up the dam. The portal is also edged from castle sandstone, but at a height of around 1.35 meters, it is significantly lower than the other drainage tunnels. An unpaved path leads directly past the outlet. The inside of the tunnel is in its original condition except for a few repairs. The drainage also takes place here in the Tiefenbach.
Continuous tunnel
The second tunnel is located about 20 meters to the east at about the same height as the creek passage. This stud has almost the same geometry as the blind stud. However, it runs completely through the dam. The second portal is on the south side about 10 meters east of the brook passage. Its course is not straight and with a length of about 230 meters it is significantly longer than the parallel stream passage. The course here is based on the eastern flank of the valley of the thistle hole. The drainage takes place in a south and north direction into the Tiefenbach. In the inner course, oval passages, straight walls, caverns and raw passages driven into the sandstone alternate. Colorful sinters and smaller stalactites can also be found here. In the 1990s, the tunnel was fundamentally renovated in its original style.
The tunnels and the creek passage are freely accessible all year round and at your own risk. They should not be entered between October and May for the protection of bats and in order to protect caves .
In the vicinity of the dam there are a few smaller sandstone quarries, which were probably used to provide local supplies of building material for culvert, tunnel and stream cladding.
Individual evidence
- ↑ Location of the dam in the Bayern Atlas (accessed on July 20, 2018)
- ↑ OpenStreetMap, location and extent of the dam (accessed on July 20, 2018)
- ↑ Schwarzachtal with side valleys at protectedplanet.net (accessed on July 22, 2018)
- ↑ The Ludwig Canal, A Brief Description of this Canal and its Execution, Heinrich Freiherr von Pechmann (Original) (accessed on July 20, 2018)
- ↑ The Ludwig Canal, A Brief Description of this Canal and the Execution of it, Heinrich Freiherr von Pechmann (copy with comments by M. Kimmig) (accessed on July 20, 2018)
- ↑ The Ludwig Canal - Its Origin and Significance as a Trade Route (Original, Friedrich Schultheis) (accessed on July 20, 2018)
- ↑ The Ludwig Canal - Its Origin and Significance as a Trade Route (transcription with comments by M. Kimmig) (accessed on July 20, 2018)
- ↑ BLfD's list of monuments for Burgthann (accessed on July 20, 2018)
- ↑ OpenStreetMap, course of the Tiefenbach (accessed on July 20, 2018)
- ↑ Plan of the Tiefenbach passage (accessed on July 20, 2018)
- ↑ Geological, hydrochemical and petrographic investigations on recent sintering and stalactites, Werner Kanz, GEOLOGISCHEN BLÄTTER FÜR NORDOSTBAYERN, 1981
Web links
- www.hansgruener.de, pictures from Distellochdamm
- www.hansgruener.de, older pictures from Distellochdamm
Coordinates: 49 ° 20 ′ 51.14 " N , 11 ° 19 ′ 40.08" E