The Oldest Danubian Island in Vienna - The Alberner Schotterbank

MAGYARUL

Let's start with a riddle: Which is the oldest natural island still in existence on the heavily regulated, straightened, and de-insulated section of the Danube in Vienna? If there is one at all. 

Of course there is; otherwise, the question would be pointless to begin with, and there would be no reason to even write this post. In any case, this is by no means obvious on the ground; in fact, given its morphology, it should rank among the youngest islands, and everything points to the fact that this riverbed was created by humans between 1972 and 1988, when the Danube regulation carried out between 1870 –1875 was revised in Vienna, creating the bleakest urban zone in the river’s history, known as the Überschwimmungsgebiet, where the natural riverbeds of the time lay on the banks for a long time, like dead fish after the cyanide pollution of the Tisza river. A hundred years later, these remains were dredged up and buried beneath a 21-kilometer-long artificial island called the Donauinsel, which has one positive aspect: it was ultimately not built up with office buildings and apartments, but instead developed into a city park, featuring varied topography and a diverse shoreline despite its straight, paved banks. 

Along the Donauinsel, bays, peninsulas, and quieter stretches of water bordered by rock embankments have been created—and even separate Danube islands—to replace the natural tributaries that have been eliminated and so to increase biodiversity. One such artificially created island is the Albern Gravel Bank (Alberner Schotterbank), which could easily be called an island due to the floodplain forest that has developed on it, interrupted at only one point by the highly spectacular pipeline system connecting the Schwechat oil refinery with the Lobau oil terminal. 

On Monday, May 11, 2026, in the early afternoon, during a low-water period of 150 centimeters—with the water level slightly receding—measured at Wildungsmauern, a significant overflow was observed in the approximately 20-meter-wide side channel next to the Alberner Schotterbank. The water flowed extremely rapidly in the deep channel between the extremely steep, eroded bank walls composed of massive pebbles. On both sides, tree roots hang in the air. There are two human-made reasons for this: one is the Freudenau Dam, downstream of which lies the Alberner Schotterbank; the other reason can be traced back to the same project, albeit somewhat indirectly. This is because beneath dams, the riverbed suddenly deepens, the original water level drops, and the islands are left dry. 

That’s what happened here as well; this gravel bar is very close to the dam, and it functioned as a gravel bar right up until the dam was built. As a result of the drop in water level downstream, it became an island, which is why the forest was able to grow there, and why the side channel began to dry up. In Austria, they typically don’t leave things like this alone and set about dredging. Between 2023 and 2024, with a brief interruption when the Boris flood deposited an astonishing amount of silty sediment and debris in the area, they dredged out the deep channel still visible today, despite protests from regular beachgoers [1]. The dredged gravel was used to counteract the deepening of the main channel and was spread out below the Freudenau dam. Some online maps still show the old situation of the river, so many visitors may be surprised to find that the island can no longer be reached on foot even at low water, a fact that beachgoers have resented ever since; conversely, the wildlife is quite grateful for the isolation. 

The Alberner Schotterbank in 1856.

The Alberner Schotterbank first appears on Pasetti’s 1856 nautical chart of the Danube. It was closer to Mannswörth than to Albern, and was located on the opposite bank. At that time, Albern was a small fishing village belonging to Kaiser Ebersdorf, which suffered greatly from the Danube’s floods. It was destroyed by the “Himmelfahrtsgieß” flood of 1501, and then by the “Allerheiligengieß” flood of 1787, when erosion by the Danube washed away 85 hectares of land, including the village itself [2]. It was then that the fishermen relocated to the site of the present-day settlement. In 1809, Napoleon, passing through here, dismantled the village to build a pontoon bridge using the beams from the houses in Albern.  

The Alberner Schotterbank in 1938.

The upsilted island before the dredging, 2023. 

The current situation

On Pasetti’s map, it appears that one of the islands in the vast Danube side channel—which was dammed off between 1836 and 1841 opposite the settlements of Albern and Mannswörth—was split in two by the dam, with the smaller, shoal-covered section remaining in the floodplain. We are most likely witnessing the very moment of the Alberner Schotterbank’s birth; in other words, this island in the Danube—now part of Vienna—will soon be blowing out two hundred candles on its birthday cake. The Albern gravel bar is a true relic. It is not so much its formation as its survival that is considered a miracle. Although it is inseparable from the history and territory of the Donauinsel today, it is very distinct from it.

Recommended and cited literature:

 

[1] https://www.krone.at/3157759

[2] Wasser | Stadt | Wien 

The Rise and Fall of the Vienna Archipelago (1529-2010)

Cutting the Gordian Danube, Vienna 1875. (source)

IN HUNGARIAN

My absolute favourite book of 2023 was Wasser | Stadt | Wien. 458 pages of solid hydrology about Vienna, much of it of course about the Danube. The volume also includes nine full-page pictures of the changes in the river meanders around the city of Vienna. Lovers of urbanism will certainly find things of interest in the previously published images, but it is the floodplain patterns, which are now mainly similar to those of the Danube at Gemenc, Hungary, that are worth observing. It is a little known fact in Hungary that the Danube has caused far more serious problems in Vienna than in Budapest throughout the city's history. In historical times, the Danube flowed through a floodplain up to seven kilometres wide in Vienna, creating and destroying countless islands along this river section. The Viennese had an ambivalent relationship with the river, fearing its difficult crossing between the two banks and the many flood damages, but it was an advantage for the city in terms of trade. Around 1565, the main branch of the Danube moved away from the city and efforts by locals to bring the main shipping route back close to the city failed, leading to a compromise solution of extending the Vienna branch of the Danube, which later became the Donaukanal. 

Ugyanakkor a folyókanyarulatok vándorlása mellett a rendkívül fonatos meder gyakran okozott jégtorlaszokat. A budapestinél sokkal kevésbé stabilabb mederben a zátonyokon és szigetcsúcsokon kialakuló jégdugók gyakran eredményezték azt, hogy a télen levonult jeges árvíz kártételeinek felszámolása után a bécsiek már teljesen máshol találták meg a folyót. Ez az állandóan változó ártéri világ egyre inkább akadályává vált a város terjeszkedésének, amelyre megoldást kellett találni. Végül egy meglehetősen drasztikus beavatkozás szüntette meg a bécsi szigetvilágot 1870-1875 között, amikor is egy új, nyílegyenes medret ástak a Dunának, meghagyva egy széles, hasonlóan egyenes elöntési területet az árvizek számára. Az utóbbi időszak módosításai ezt a területet érintették, amikor a széles, kopár parti sáv helyén létrehozták a Donauinsel-t, melyet a bécsiek már sokkal inkább birtokba vehettek. 1875 után a lefűzött, kiszáradó folyókanyarulatok két utat jártak be. Ahol városi zöldfelületek területére estek, ott javarészt fennmaradtak (Prater, Alte Donau, Lobau, stb.), ahol viszont a város szövete ugrásra készen várta a kiszáradást, ott esetleg csak az utcák nyomvonala emlékeztet a régi medrekre (pl. Schwarze Lacke), többségük több méter feltöltés és beton alatt húzódnak. 

However, in addition to the migration of river meanders, the extremely braided riverbed was often clogged by iceblocks. In a much less stable bed than Budapest's, ice jams on sandbanks and islands often meant that, after the damage caused by the winter ice flood had been cleared up, the Viennese found the river in a completely different place. This ever-changing floodplain world became an increasing obstacle to the expansion of the city, and a solution had to be found. Eventually, a rather drastic intervention eliminated the Danubian archipelago in Vienna between 1870 and 1875, when a new, straight-edged bed was dredged for the Danube, leaving a wide, equally straight floodplain for the floods. More recent modifications to this wide, barren flood area included the creation of the Donauinsel, that was more easily occupied by the Viennese people. After 1875, the story of the newly created oxbows and drying river meanders took two paths. Where they fell into urban green spaces, they were largely preserved (Prater, Alte Donau, Lobau, etc.), but where the urban developers eager for more territory, only the street network may be reminiscent of the old riverbeds (e.g. Schwarze Lacke), most of them beneath several metres of landfill and concrete. 

Half a thousand years of river bend changes in Vienna 1529-2010 (source)

The nine detailed landscape reconstructions created using geographic information methods were almost begging for a .gif version. This version was most certainly created by the authors, but unfortunately the format is not compatible with the capabilities of the Guttenberg Galaxy. So I quickly put together my own version. In varying time-intervals, nine dates in total (1529, 1570, 1662-1683, 1704, 1780, 1825, 1875, 1912 and 2010), we can see the immediate surroundings of Vienna, with the Praterstern roughly in the centre.