Assessment of hydropeaking-induced alterations of benthic communities in experimental flumes

The relationships between discharge alterations due to the intermittent discharge of turbinated water downstream of hydropower plants (hydropeaking) and drift of zoobenthos were investigated through the simulation of two different flow increases in artificial flumes, i.e. one similar to natural high-flow events (stepwise increase in discharge 2x), and one to hydropeaking (abrupt increase in discharge 7x). The effects on zoobenthos detected with the artificial flumes were compared with those of a field study of an hydropeaking wave in an alpine stream, in order to assess the validity of the artificial flumes to simulate natural streams in hydraulic manipulation experiments. The research was conducted in the Adige River catchment. The experimental structure of five steel channels with adjustable discharge and slope is located along the Fersina Stream. The hydropeaking wave was studied in natural conditions in the Noce Stream, 0.25 km downstream of Cogolo-Pont hydropower plant. Results showed a strong increase in drift in response to discharge increases; the temporal trend and absolute value of drift in the station downstream of the plant were similar to those of the artificial channels, especially of the channel with abrupt discharge. Taxa responded differently according to their levels of adaptation to flow increases. Differences in drift rates between artificial and natural conditions were probably due to the daily timing of hydropeaking in the Noce Stream, which reduce the consistence of the benthic community. The study also confirms the validity of the artificial flumes to manipulate discharge in order to develop guidelines for an eco-sustainable management of hydropeaking-impacted alpine streams