Hydraulic and fish-biological performance of fish guidance structures with curved bars

Abstract

Run-of-river hydropower plants pose a particular threat for downstream migrating fish because of high injury and mortality rates during turbine and spillway passages leading to a decline in fish populations worldwide. Fish guidance structures with vertical bars such as angled bar racks combined with a bypass can protect fish and ensure their safe downstream migration. The optimal hydraulic performance of these structures is essential for a sustainable power plant operation and efficient fish guidance. Previous studies indicated that the hydraulic performance of the current angled bar rack designs is insufficient because of high head losses and asymmetric turbine admission flow. To mitigate these issues, a new bar shape of curved cross section was developed. Angled bar racks with novel curved bars, so-called Curved-Bar Racks (CBRs), show an improved hydraulic performance compared to fish guidance structures with straight bars. CBRs reduce the hydraulic head losses on average by a factor of 4.2 as compared to the equivalent angled bar rack configurations with straight bars. Moreover, they promote a flow straightening effect leading to flow conditions favorable for both fish guidance and turbine operation. This research reports the findings of the ethohydraulic experiments on an optimum CBR configuration with two European fish species, namely, the barbel (Barbus barbus), and the spirlin (Alburnoides bipunctatus). The fish swimming behavior at the CBR-bypass system was analyzed with heat maps generated with a 3D fish-tracking software. Since fish react sensitively to spatial velocity gradients, the bypass operation is optimized to maximize the fish guidance efficiency.