Research Paper

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

¹ ICEO − 220 Rue des Ailes, 85440 Talmont Saint Hilaire, France
² Office français de la biodiversité − Direction de la recherche et de l'appui scientifique, Pôle R&D Ecohydraulique OFB-IMFT-PPRIME, IMFT, 2 Allée du Professeur Camille Soula, 31400 Toulouse, France
³ EDF R&D LNHE - Laboratoire National d'Hydraulique et Environnement, 6 Quai Watier, 78401 Chatou Cedex, France
⁴ Office français de la biodiversité, Direction de la police et du permis de chasser, Service prévention appui prospective, Pôle R&D Ecohydraulique OFB-IMFT-PPRIME, IMFT, 2 Allée du Professeur Camille Soula, 31400 Toulouse, France
⁵ ECOGEA, 352 avenue Roger Tissandié, 31600 Muret, France
⁶ EDF CIH - EDF CIH, Pôle Énergies Renouvelables, 4 rue Claude Marie Perroud, bâtiment C, 31096 Toulouse, France

^* Corresponding author: stetard@iceo-environnement.fr

Received: 8 June 2023
Accepted: 19 September 2023

Abstract

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 m³.s⁻¹) retrofitted with a 20 mm rack associated to a surface bypass (2 m³.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.