Evaluation of a fine-spaced angled rack with surface bypass in providing safe and timely downstream passage for salmon smolts and silver eels

• Published in: Knowledge & Management of Aquatic Ecosystems
• Main Authors: Tétard, Stéphane, Courret, Dominique, Tissot, Laurence, Richard, Sylvain, Lagarrigue, Thierry, Frey, Aurélien, Mataix, Vincent, Mercier, Olivier, Tomanova, Sylvie
• Other Authors: ICEO Environnement, Office français de la biodiversité - Pôle Ecohydraulique OFB - IMFT (Pôle écohydraulique OFB - IMFT ), Institut de mécanique des fluides de Toulouse (IMFT), Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Office français de la biodiversité (OFB), Laboratoire National d’Hydraulique et Environnement (EDF R&D LNHE), EDF R&D (EDF R&D), EDF (EDF)-EDF (EDF), Etudes et Conseils en Gestion de l'Environnement Aquatique - ECOGEA (FRANCE)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2023
• Subjects: Salmo salar; Anguilla Anguilla; Fish passage solution; Hydropower; Downstream migration; [SDV]Life Sciences [q-bio]; Anguilla anguilla; Atlantic salmon
• Online Access: https://edf.hal.science/hal-04326275; https://edf.hal.science/hal-04326275/document; https://edf.hal.science/hal-04326275/file/2023_Tetard%20et%20al_Efficacit%C3%A9GrillesFinesPebernat.pdf; https://doi.org/10.1051/kmae/2023020

International audience Hydropower production can cause migration delay and fish mortality, impeding the safe and timely downstream migration of diadromous fish, such as Atlantic salmon ( Salmo salar ) and silver eels ( Anguilla anguilla ). To date, only a few field performance tests, especially for eels, have evaluated the efficiency of fine-spaced angled racks associated to a surface bypass entrance to protect fish. Here, 115 salmon smolts and 65 silver eels were radio-tracked over a 2 yr period to assess passage efficiency and passage time at a hydropower intake (50 m 3 .s −1 ) retrofitted with a 20 mm rack associated to a surface bypass (2 m 3 .s −1 ). Results showed high impediment (89.6% and 96.9% for smolts and eels, respectively), and passage efficiency for the angled rack (89.1% and 93.3%), with short passage times (median, 3 and 7.5 min). However, our results highlighted a strong influence of hydrological conditions, in enhancing fish passage, especially through the bear-trap gate. We conclude that this fish passage solution, making use of existing spillways on the study site, is highly effective for both species. Special attention must, however, be paid to bar-rack design and its cleaning system to ensure fish guidance and prevent impingement or passage through the rack, especially for salmon smolts.