Fish protection and guidance at water intakes with horizontal bar rack bypass systems

Fish move up- and downstream within rivers throughout their lives to find suitable habitats. During downstream movements, they can incur severe or even lethal injuries when passing through hydropower plant (HPP) turbines or when they are entrained at other water intakes. Horizontal bar rack bypass systems (HBR-BSs) are a state-of-the-art technology to protect and guide downstream moving fish through a safe corridor around water intakes. They are in operation at multiple HPPs for more than a decade, but technical knowledge about the velocity fields, the head losses, the fish guidance efficiency, and the clogging probability was so far missing. This doctoral thesis encompasses the state of knowledge of HBR-BSs and contributes with novel findings to this topic through hydraulic experiments and live fish tests. The velocity fields of HBR-BSs and hydraulic losses of horizontal bar racks (HBRs) were quantified for a wide parameter range. The fish guidance efficiency was assessed through live fish tests involving a diverse assemblage of riverine fish species, namely spirlin (Alburnoides bipunctatus), barbel (Barbus barbus), nase (Chondrostoma nasus), brown trout (Salmo trutta), Atlantic salmon parr (Salmo salar), and European eel (Anguilla anguilla). Systematic experiments with leaves of different tree species were carried out to determine the clogging probability at HBRs. The main findings of the present thesis include a detailed analysis of the effect of different parameters on the velocity fields up- and downstream of HBRs. Equations were proposed to predict the head losses at HBRs, which can be applied for a wide parameter range, including rectangular and foil-shaped bars, bottom and top overlays, and different HPP layouts. By applying foil-shaped instead of rectangular bars, the losses were reduced by more than 40%, depending on the rack configuration. The fish swimming behavior was analyzed in detail and equations were proposed to estimate the protection and guidance efficiency of HBR-BSs as a function of the clear bar spacing and the fish dimensions. The fish protection efficiency varied between the factors fish species, size, and clear bar spacing of the HBR. While the laboratory HBR-BS with a clear bar spacing of 20mm offered hardly any protection for juvenile nase, the average protection efficiency exceeded 90% for spirlin and European eel. The behavioral avoidance effect strongly increased with the application of a low-voltage electric field to the HBR-BS. High protection efficiencies were achieved for spirlin and eel, but their behavior strongly depended on their orientation in the electric field and spirlin often refused to enter the bypass. The probability that a leaf clogged at any bar of an HBR decreased linearly for larger clear bar spacings, while the probability of clogging over multiple bars decayed exponentially. The present work provides technical knowledge to design HBR-BSs, thereby accounting for fish protection, cost-efficiency, and sustainable operation. The weighting of these aspects has to be defined by involving all stakeholders. The findings of the present study contribute to a better understanding of the hydraulic processes and the fish behavior at HBR-BSs, but they cannot replace extensive monitoring campaigns at prototype sites, which are necessary to verify functional efficiency