Adaptive Fishway Design : Designing a Bypass Channel to Fit Large Discharge Fluctuations

Abstract: Especially with regard to achieving the goals of the European Water Framework Directive, the construction of fishways is becoming more prominent in Sweden's hydraulic engineering sector. Particularly the importance of nature-like bypass channels is increasing, being the type of fishway that is currently implemented in most cases of small scale hydropower. However, to date there are no uniform guidelines for the design of these, which creates particular challenges with regard to their implementation and the evaluation of their functionality regarding fish migration beforehand. Furthermore, it is to be expected that higher requirements for the amplitude of permissible flows may arise in the future. Within the scope of this work, a method was developed, which serves to estimate the functionality of nature-like bypass channels regarding fish migration in advance. These design guidelines are then used to apply a parametric design to the cross sectional profile of the bypass channel. Three different profile types were tested: a trapezoid, a double trapezoid and a double channel. Both the trapezoidal profile and the double channel outperformed the simple trapezoid in terms of both magnitude and amplitude of the conveyed discharge. The double channel, on the other hand, had the further advantage of having a larger continuous interval of flow meeting the hydraulic criteria for fish passage. To further validate these results, further research should be conducted in the area of functionality verification, as well as various cross-section design options.