Impacts Of River Bank Morphology And Time Of Day On Drift And Stranding Of European Grayling (Thymallus Thymallus L.) Caused By Hydropeaking

We analysed the effects of hydropeaking in terms of drift and stranding of juvenile graylings ( Thymallus thymallus L.) with an average length of 53.3 mm. Single peak experiments were investigated in 2 outdoor flumes each of 20 m length with the main focus on time of day and gravel bank morphology ( absence or presence of dewatering potholes). By daytime we observed low median drift rates of 15 % and median stranding rates below 5 % in dewatering potholes and on homogenous gravel bank during decreasing water level. Although, in the presence of dewatering potholes, the nighttime drift rates were about three times and stranding rates around seven times higher than on the homogenous gravel bank.