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

Surface bypass as a means to protect downstream-migrating fish – lack of standardized evaluation criteria complicates evaluation of efficacy (#73)

Elena-Maria Klopries 1 2 , Zhiqun Daniel Deng 2 , Theresa Ursula Lachmann 1 , Holger Schüttrumpf 1 , Bradly A Trumbo 3
  1. RWTH Aachen University, Aachen, NRW, Germany
  2. Pacific Northwest National Laboratory, Richland, Washington, USA
  3. U.S. Army Corps of Engineers, Walla Walla, Washington, USA

Surface bypasses are downstream migration structures that can help reduce hydropower-induced damage to migrating fish. However, no comprehensive design concept that facilitates good surface bypass performance for a wide range of sites and species is available. This is why even efficiencies at recently built bypass structures vary widely between 0% and up to 97%. We reviewed surface performance studies and existing guidelines for salmonids, eels, and potamodromous species if available to identify crucial design criteria for surface bypasses. Two-tailed Pearson correlation of bypass efficiency and bypass design criteria shows that bypass entrance area (R=0.3300, p=0.0036) as well as proportion of inflow to the bypass (R=0.3741, p=0.0032) are the most influential parameters on bypass efficiency. However, other parameters like guiding structures and trash rack spacing though not statistically significant (Spearman correlation, ordinary t-test) have shown to have an effect on efficiency in some studies. The use of different performance criteria and efficiency definitions for bypass evaluation hampers direct comparison of studies and therefore deduction of design criteria. To enable meta-analyses and improve bypass design considerations we suggest a list of standardized performance parameters for bypasses that should be followed in future bypass performance studies.