Reactivation of oxbow lakes on the Brenz near Giengen an der Brenz

The Brenz was monotonously developed, straightened and deepened in the 1960s. Due to its consequently poor biotope characteristics, it was designated in the action plan of the European Water Framework Directive (EC-WRRL) as a program section for the improvement of the watercourse structure and for the establishment of passability.

The planning objective for the near-natural redesigned stretch of water is to achieve the good ecological status according to the requirements and the assessment criteria of the EC WFD and WHG. Furthermore, according to the Danube River Basin Management Plan and Programme of Measures, the measure should contribute to the achievement of the good ecological status of water body No. 65-03 within the framework of its stream and interaction with the other measures planned for the Brenz.

The aim of the project was to eliminate the structural deficits in the straightened course of the watercourse in accordance with the requirements of the EC WFD and to create passability by dismantling an old weir. For this purpose, a new curved watercourse was created and a separated old branch was de-silted and reconnected as the main channel between Herbrechtingen and Giengen. The former old arm has a high structural diversity and suitability as fish habitat due to its habitat equipment (riparian wood, deadwood, etc.). A second old arm (natural monument "Vogelinsel") was also partially reactivated by controlled inflow from the main channel. The old, straightened channel remained intact and was limited in sections by so-called diversion structures made of armourstone, which are only overflowed at higher water levels. From downstream, these sections are connected at the same level as the river bed; these flow-calmed areas (still water conditions) offer retreat areas and spawning habitats for fish in addition to numerous partial habitats in the main channel with the reconnected old arm. Valuable island structures were created between the former and the new main channel while preserving the existing woody banks. In the water meadow, a still water was created, which aims to promote the amphibian population, especially the tree frog.

In total, three measures were planned by the office to meet the objectives of the EC WFD on the Brenz. In addition, a lookout tower was built at one point in Sontheim to enable recreationists to see the redesigned water corridor of the Brenz.