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

Downstream passage of potamodromous fish at small hydropower plants in Austrian rivers (#152)

Pablo Rauch 1 , Günther Unfer 1
  1. University of natural Resources an Life Sciences Vienna, Vienna, AUSTRIA, Austria

The downstream passage of various fish species was assessed at small scale hydropower plants in Austrian rivers covering a variety of river types. Opposed to the downstream migration behavior of anadromous fish, knowledge is scarce regarding the biological, behavioral and technical requirements needed for future planning and development of management strategies for downstream migration of potamodromous species. The project tries to (1) quantify downstream fish passage at hydropower plants including turbine mortality, (2) investigate the efficiency of newly built bypass systems, (3) assess potential preferences for certain migrations routes and (4) define criteria for the minimization of harmful effects during downstream passage. Fish upstream of the hydropower facilities were tagged individually using PIT tags and fixed antenna sets at various migration corridors were set up to study the downstream passage. At a species rich potamal river, turbine mortality was quantified at <23% for fish <160 mm TL. Although about 80% of river runoff passes the hydropower turbine, only 44% of migrating fish use this corridor. The fish migration facility and a residual flow bypass both located at the beginning of the irrigation channel showed much higher efficiency for downstream migration. 54% of fish passed these corridors (using only 14% of total discharge). A downstream migration bypass next to the turbine was used by only 5% of migrating fish. The performance of the built bypass systems was generally poor for migrating fish. We conclude that efficient and harmless downstream migration may happen at any corridor with permanent discharge and that the location of the upstream entrances is crucial for the efficiency. The frequent use of migration facilities built for upstream migration indicates a high potential for future planning scenarios. Efficient protection from turbine passage seems to be the highest priority to minimize mortality related to downstream passage at hydropower plants.