Written by David Stäblein
The landscape en route from Munich to Deggendorf is dominated by the flat valley of the river Isar. The river has carried a lot of material from the Alps to the lower part of the river near Deggendorf. This is the reason the soil here consists of an eight-meter-thick layer of river sediment. The Isar valley is surrounded by hills, in a landscape where erodible brown soil has been heavily deposited. The colluvium from this landscape, combined with the river sediments, makes the area the perfect place for agriculture (primarily sugar beet and corn). The Mühlbogental is an area near Deggendorf which has become the focus of concentrated industry; here lies a paper mill, as well as a BMW production site that was built on subsidies to discourage migration out of the region.
To the south of Deggendorf the Isar flows into the Danube (Donau in German), which was, in former days, only constrained in its meandering by the Bavarian Forest (a cool, infertile, and mountainous range dominated by gneiss) in the north east. Today, many dikes bound the naturally wandering landscape of the Danube, and the ancient current is limited by a row of hydropower plants spanning the whole of the Danube’s course through Bavaria. Together, the hydropower plants in Bavaria produce around 15 percent of Germany’s electricity supply. All the best spots for these plants have been occupied, which means that the expansion of hydropower is only possible if the plants become more efficient (to reach the goal of 17 percent). The flood defenses around Deggendorf were first installed in the 18th century and have since been expanded and modernized. Throughout the year (especially around June and August) numerous small flood events (below HQ 30) hit the area, but the dikes and polders usually prevent severe damage to surrounding communities.
A few kilometers downstream from Deggendorf, there is a loop in the Danube known as the “Mühlhamer Schleife.” Here, the water is particularly shallow and the current strong, making it a problematic stretch for the shipping industry. Consequently, in 2013, the federal state of Bavaria planned to build a shipping channel with locks straight through the Mühlhamer Schleife. These locks would make it possible to ship on the Danube for more than 200 days of the year (the maximum number of shipping days in recent years). After big public protests that were spurred by the results of the forecasted impact of the channel and an inventory analysis by the ArGe Danubia, the project was put on hold. Thomas Liepold, hydraulic engineer, and Tobias Schiefer, ecologist, discussed the potential effects of the proposed canal on the ecology of the Danube.
The village Winzer has suffered severely from heavy flooding in the past. Because of this, a new dike is under construction to avoid catastrophic floods, like the notorious one of 2013. The new dike should protect the citizens of Winzer from 100-year floods (up to HQ 100). To do so, the dike is being reinforced with steel plates and will reach around eight meters in height. Pumps will be installed to pump water from the dike back into the Danube, should the dike ever break or the water accumulation behind it (caused by smaller inflows) become too high. The total cost of this project is estimated at €13 million. The land between the smaller dikes (which are close to the Danube) and the new, bigger dikes holds a high biological value because of the diversity of habitats and plants, including meadows and hardwood and softwood trees. Because of the Danube’s high nutrient content, the biodiversity between the first dike and the Danube itself is low. In contrast, the new dike hosts a high variety of herb layers due to the drier soil.
Next to Winzer is an area protected under the Flora-Fauna-Habitat (FFH) directive, the “Winzerer Letten.” Consisting of wetland meadows and reeds, it is home to many rare animals. The word “Letten” means that this area contains a lot of clay and experiences frequent changes in water level. The fluctuating water levels and the muddy water line that results make it a perfect place for riparian softwood trees, beavers, and the endangered freshwater pearl mussel.
Fischerdorf, situated on the other side of the Danube to Deggendorf, is part of the old city where fishermen traditionally lived. Today, Fischerdorf is a residential area that is separated from the river by a large dike built in the 1950s, and is connected to the rest of Deggendorf by numerous bridges. In 2013, when one of the highest local flood events of the last decades took place, a dike broke at Natternberg, some kilometers upstream from Deggendorf. Architect Mark Kammerbauer told us how some of the environmental problems that occurred during the flood were caused by architectural limitations. Water from both the Danube and the Isar inundated Fischerdorf, leaving the village standing in two meters of water for more than 10 days. Around a quarter of the population had to be evacuated on ships and it was lucky that nobody died. The severest impact of the flood was the contamination of homes and surroundings from leaked heating oil. Oil from poorly sealed tanks was rapidly absorbed into bricks along with the floodwater. Since the heating oil that was left in the house walls can cause cancer, many buildings have been demolished and rebuilt. Nearly half of the affected residents had taken out basic insurance against light damage but experienced difficulties claiming sufficient compensation, in contrast to those who had no insurance and received, without much trouble, a compensation package from the federal state of Bavaria.