Unrestricted fish migration
Achieving connectivity of the waterways: making it easier for fish to migrate
Migrating fish: connecting the waterways
Of the federal waterways, both free-flowing and impounded rivers are important connecting waterbodies used by fish on their journey between their habitats. Fish which migrate over long distances are guided by the main flow. At impoundment weirs they basically are gathering in the underwater of a hydropowerplant or an overflown weir. At these points, there is no other possibility of migrating further upstream, unless there is a functioning fish migration facility close to the weir or hydropower plant outflow. Since locks for shipping do not create a continuous leading flow, they cannot always be found by fish species which migrate by following the main flow. Species which do not follow the main flow are sometimes able to migrate upstream or downstream if they find an open lock basin.
Downstream: protecting fish at power plants and guiding them past
At impoundment weirs without hydro-electric power stations, downstream migration across a weir does not normally cause any problems. The condition for this, however, is that the weir is in operation, the head is not more than 13 metres and the water depth in the stilling basin is at least 0.90 metres. On the contrary, injuries ranging from slight to fatal may be caused by the turbines of a power plant during downstream migration. This turbine-related mortality depends on the fish species, the body length of the fish, as well as on the type and dimensions of the turbine, the head and on the specific operating conditions. In order to ensure risk-free downstream passage for the fish, the German Water Resources Act (Wasserhaushaltsgesetz) obliges the operators of hydro-electric power stations to equip or adapt the hydro-electric plants with suitable construction measures to protect the fish population (for instance, with fine mesh fish screens and a bypass leading around the power plant to the tailwater).
Upstream: here fish migration facilities are the only solution
Various investigations of fish migration in the Rhine, Moselle, Main, Neckar, Weser, Elbe and Danube rivers have demonstrated that although most of the impoundment weirs along these rivers are equipped with fish ladders in the upstream direction, it is nonetheless difficult for fish migrating upstream to find or pass through these. In May 2009 the Federal Waterways Engineering and Research Institute (BAW) and the Federal Institute of Hydrology (BfG) jointly agreed with the Federal Ministry of Transport, Building and Urban Development (BMVBS) on the following framework concept for the necessary work:
- drawing up of technical principles, particularly regarding the urgency from the view of fish ecology
- technical/specialist advisory services for the Waterways and Shipping Administration (WSV) and training courses
- research and development projects for the drawing up of technical standards and regulations
- standardisation of requirements and design of fish ladders, fish protection measures and downstream fish passages
In order to meet the current advisory requirements of the BMVBS and WSV, the BAW and BfG at present draw on their own specialist knowledge, specialist consulting agencies and specialist literature. For the continuing development of the standard of knowledge regarding fish migration facilities on waterways, precise project studies and research and development projects are being planned. The aim is – beside the development of proposals for implementation – to prepare fundamental recommendations for the positioning, orientation, dimensioning, endowment, operating methods and inspection of fish migration facilities.
Studies for new fish ladders on the River Neckar
The comprehensive study of the new construction of a fish ladder at the Neckar impoundment weir at Lauffen has been started as a “pilot project”. Nine fish ladders in total are to be installed on the Neckar in the next few years in connection with the river development to handle ship lengths of up to 135 metres. A task group appointed by the WSD Southwest (regional Directorate of the German Federal Waterways and Shipping Administration) has calculated the requirements for this facility with regard to the indicator fish species and the constructional design and dimensions and prepared an initial design for the fish ladder at the Lauffen impoundment weir. Here, a vertical slot fishway is planned, bankside, at the left bank, directly adjacent to the hydro-electric plant.
Ministerium für Umwelt und Naturschutz, Landwirtschaft und Verbraucherschutz des Landes Nordrhein-Westfalen: Handbuch Querbauwerke, 2005, ISBN 3-981006-3-2-1.
DWA Deutsche Vereinigung für Wasserwirtschaft, Abwasser und Abfall (German Association for Water, Wastewater and Waste): Technical bulletin DWA-M 509: Fischaufstiegsanlagen und fischpassierbare Bauwerke – Gestaltung, Bemessung, Qualitätssicherung, yellow print 02/2010, ISBN 978-3-941897-04-5