Loss of connectivity in riverine systems due to construction of hydropower dams has resulted in a worldwide decline of anadromous salmonid species such as Atlantic salmon (Salmo salar L.) and sea trout (Salmo trutta L.). The future of these species depend on the presence of available spawning habitat in freshwater river systems. Modern research and mitigation efforts mainly focus on ensuring a successful upstream passage past dams e.g. fish ladders. Atlantic salmon and sea trout are iteroparous, and are thus able to spawn repeatedly during their lifetime. Individuals surviving upstream migration and spawning generally face a hazardous journey back to their marine feeding grounds. In this large scale natural field study I evaluate the possibility of using a bubble barrier as a non-physical structure to guide downstream migrating kelt past the turbines at a large hydropower station in northern Sweden. Results from this study clearly show that kelt effectively can be diverted using a bubble barrier in daylight conditions with a mean water velocity of 1.1 m s-1 (p=0,01). From a fishway managers perspective, increasing survival of salmonid kelt is a substantial step towards achieving a viable population with increased numbers of repeat spawners and large individuals. This study presents new results in a sparsely explored subject; the diversion of post-spawn salmonid migrants using non-physical barriers.

Les travaux présentés dans ce mémoire de thèse s’inscrivent dans le projet ANR BARPPRO réalisé dans le cadre de la réglementation française des PPRT pour les sites industriels classés SEVESO. L’objet est de proposer un outil pour le dimensionnement des barrières physiques de protection face à une déflagration de gaz. Une étude paramétrique à petite échelle est menée pour étudier l’effet protecteur d’une barrière physique. Un dispositif d’accélération de flamme a été conçu pour générer une vitesse de flamme sonique. Cela a permis de réaliser à petite échelle l’étude de l’impact de l’obstruction sur la vitesse de flamme et sur les paramètres de l’onde de pression. Ces résultats ont été confrontés aux modèles de la littérature. L’onde de pression incidente ainsi générée sert de donnée d’entrée et de référence dans l’étude de la barrière. Plusieurs paramètres de l’onde de pression sont étudiés : le temps d’arrivée, la surpression maximale et l’impulsion positive. L’influence de la hauteur du mur et de sa position par rapport à la source d’amorçage est traitée pour deux formes de barrière (droite et cylindrique) et pour deux mélanges hydrogène/air (stoechiométrique et de richesse 0.65). / This thesis is a part ANR BARPPRO project in the framework of the French regulation PPRTs for industrial Seveso sites. The goal of the present work is to provide a tool for the sizing of protective physical barriers against a gas explosion. A parametric study at small scale is conducted to investigate the protective effect of a physical barrier. For that purpose, a cylindrical device was developed to accelerate the flame gradually until reaching sonic flame speeds by increasing the obstruction inside the device. This has also led to the realization of a small-scale study about the impact of the obstruction on the flame speed and on the pressure wave’s characteristics. These results are compared with those obtained with models from the literature. The pressure wave generated by the acceleration device is used as input and reference in the barriers’ parametrical study. Several parameters of the pressure wave are considered: the arrival time, the maximum overpressure and the positive pulse. The influence of the wall height and position relative to the ignition source is processed for two barrier’s shapes (straight and cylindrical) and two hydrogen / air mixtures (stoichiometric and with an equivalence ratio of 0.65).