Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Hydraulic Approach for Dimensioning Fish Way Attraction Flow (#181)

Martin Henning 1 , Patrick Heneka 1 , Cornelia Schuetz 2
  1. Federal Waterways Engineering and Research Institute (BAW), Karlsruhe, Germany
  2. Federal Institute of Hydrology (BfG), Koblenz, Germany

The German Federal Institute of Hydrology (BfG) and the German Federal Waterways Engineering and Research Institute (BAW) are working to restore upstream connectivity for fish on German Federal Waterways by means of fish ways. In order for fish to find the entrance of a fish way, sufficient attraction flow is necessary. However, to this day, there is no generally accepted definition of sufficient attraction flow and how to evaluate it. Furthermore, according to the European Water Framework Directive fish of all species and sizes have to be considered for upstream migration. Thus, requirements for attraction flow are diverse.

Theoretically, attraction flow should be designed as large as possible. Practically, space for fish ways is often limited and large supply structures may lead to other restrictions, especially distract fish from their passage. In addition, in terms of operational discharge, fish ways often compete with hydropower and other interests. Thus attraction flow should be designed as large as necessary and as small as possible. It is common to design attraction flow rate as a proportion of competing flow, e.g. mean annual discharge or hydro power plant design discharge. However, these approaches do not consider site specific parameters such as geometric and hydraulic boundary conditions.

The framework presented characterizes requirements for attraction flow by a simple set of variables. Hydraulic jet theory is used in order to estimate attraction flow diffusion and to take into account tailrace characteristics. In doing so, site specifics such as water depths, river bed boundaries and influence of competing flow are considered. The straight forward approach aims at applicable dimensioning recommendations for attraction flow rates and fish way entrance design.