As part of the restoration of the 100-year flood protection on the Alb for the cities of Ettlingen and Karlsruhe, various solution variants were examined and compared from a water management and environmental perspective. The "Fish Ecological Report on the Alb" prepared by GefaÖ in 2017 and 2018 was used as a basis for the assessment of the comparison of variants.
As a result of an extensive site identification process with variant comparisons under environmental and economic aspects, a solution variant was determined. Part of this solution variant was the construction of the flood retention basin “HRB Spinnerei” in the Alb valley, structural adaptation measures along the Erlen- and Petergraben as well as the use of the intermediate reservoirs Weiherwald, Salmenwiesen and Oberwald, which were approved in 1983. This variant was also recommended in the fish ecological report prepared by GefaÖ in 2018.
Within the scope of the expert report prepared in 2022, the current status of the fish and lamprey fauna in the Alb, especially at the "Spinnerei" site and at the planned Weiherwald outlet structure, was to be presented and evaluated. The report deals in detail with the fish-ecological effects of the planned measures. Another objective from a fish-ecological point of view was the development of avoidance and mitigation measures with regard to the impacts caused by the construction, installation and operation of the flood protection measures.