Sustainability assessment of hydropower water wheels with downstream migrating fish and blade strike modelling

Abstract

Water wheels are low head hydropower converters considered fish friendly, although their ecological behavior has not been scientifically assessed. The results presented in the available reports are not generalized (thus hardly applicable in engineering applications), and they have not been performed at different hydraulic conditions or wheel characteristics. This work reviews available information on the ecological performance of water wheels to define the state of the art. To generalize and interpret results, a blade-strike theoretical model is developed and calibrated on field tests conducted in Germany on ten water wheels, that represent the most systematic and comprehensive series of tests. The dimensionless time T* (ratio between time needed for a fish of a certain size to access the bucket and the time for filling the bucket) and the geometric-hydraulic parameter α were identified as key parameters to estimate the ecological behavior of horizontal axis water wheels. The average injury likelihood induced by the blade strike on fish was 0.34% and 3.56% for T* < 1 and T* > 1, respectively, while the average mortality likelihood is 29% of the injury likelihood for T* < 1, and 26% for T* > 1, corresponding to a fish mortality rate of 0.10% and 0.94%, respectively. The concept of T* was applied to a dataset of water wheels in operation to estimate their compatibility with fish passage.