The restoration of ecological patency is one of the central tasks of todays’ water management. By constructing weirs and locks, numerous waterways have been blocked over the centuries in order to be able to drive mill cycles or to operate shipping. Artificially built transverse structures lead to the fact that most of the German water bodies are hardly, or no longer, permeable to aquatic organisms. Fish migration within the widely ramified waterways becomes impossible. Since the amendment of the Federal Water Act in 2010, the Federal Waterways and Shipping Administration (WSV) has been obliged to maintain or restore the ecological patency of its weirs on federal waterways, as long it is necessary to achieve the objectives of the Water Framework Directive .
The WSV responds to this legal obligation at the Lahn river: Action A5 is designed to support all activities aimed at restoring the ecological patency of the Lahn by providing basic data and the contracting of preliminary studies and expert opinions. These preparatory measures will speed up the planning processes following later on and improve the communication between all stakeholders. The concrete planning and construction of new fish ladders at the Federal Waterway Lahn are supported by the LiLa project, but as well carried out at other weirs and locks of the WSV.
In addition, in 2016 a so-called "Fischschleusungsmanagement" (management of fish sluicing) for the lock Lahnstein has been developed. The weir Lahnstein (kilometer 135.960 roughly) is the biggest migration barrier from the Rhine to the Lahn river. Since 1957, the basin fish ladder at Lahnstein and the two eel pipes in the abutment piers have a very limited functionality, and the construction of a new fish-climbing system is a still ongoing process, which faces many problems due to difficult local conditions. As a first step, the LIFE project analysed and carries out a new way of fish migration management, using the locks to sluice fishes. The fish sluicing management was introduced in December by a pilot operation at the lock Lahnstein. By means of an adapted control of the sluice gates and contactors, migrating fish were directed into the sluice chamber and released to the upstream river or downstream into the Rhine. As a result, it was possible to create an additional option for migration of aquatic organisms which cannot find or pass through the existing fish ladder between the weir and the hydropower plant. This measure (Action C 1) serves as an interim solution for improving the ecological patency, but is not a substitute for the construction of a both a new upstream fish ladder and downstream fish migration facilities. In 2017, extensive monitoring and, if necessary, structural adjustments for the optimization of the fish migration through the sluice Lahnstein shall be carried out. If necessary, the fish sluicing management can also be transferred to other sections of the Lahn (or other rivers).
The aerial photo is taken from the hiking corridor over the sluiceway and the weir arm.