Past hydraulics influence microhabitat selection by invertebrates and fish in hydropeaking rivers

Hydropeaking hydropower plants are the main source of renewable energy, meeting sub-daily peaks in electricity demand. They induce rapid artificial flow variations, highly variable velocities, drift, and stranding risks for aquatic organisms. In hydropeaking reaches, microhabitat selection likely depends on both present and past hydraulics (flow velocity and water depth); this study aims to assess their relative impact. For this purpose, we used observations of fish abundance in 1,180 microhabitats (507 sampled by electrofishing, 673 by snorkeling) and of invertebrate abundance in 36 microhabitats (hyporheic and benthic) in a medium-sized hydropeaking river. We described past hydraulics of microhabitats over the 15 days preceding sampling, using a 2D hydrodynamic model, by identifying microhabitats dewatering (drying during >10 hr) or with high-velocity conditions (>1.3 m s⁻¹ during >10 hr). Invertebrates guilds (defined based on their selection of present hydraulics in rivers without hydropeaking) responded significantly to past hydraulics, with abundances 3.5–15.3 times lower in dewatering habitats. Selection for present hydraulics by invertebrates was different from that observed in rivers without hydropeaking. For more mobile fish, responses were weaker and different, with a “bank” guild selecting dewatering microhabitats and, secondarily, a “midstream” guild avoiding them. Selection of present hydraulics by fish was similar to that observed in rivers without hydropeaking. Overall, past hydraulics influenced microhabitat selection, with stronger effects on invertebrates and stronger effects of dewatering than of high past velocities. However, high past velocities force fish to move and invertebrates to experience a large range of velocity.     

Introducing HyPeak: An international network on hydropeaking research,practice, and policy

An increase in the demand for renewable energy is driving hydropower development and its integration with variable renewable energy sources. When hydropower is produced flexibly from hydropower plants, it causes rapid and frequent artificial flow fluctuations in rivers, a phenomenon known as hydropeaking. Hydropeaking and associated hydrological alterations cause multiple impacts on riverine habitats with cascading effects on ecosystem functioning and structure. Given the significance of its ecological and socio-economic implications, mitigation of hydropeaking requires an inter- and transdisciplinary approach. An interdisciplinary network called HyPeak has been conceived to enrich international research initiatives and support hydropower planning and policy. HyPeak has been founded based on exchange and networking activities linking scientists from several countries where hydropeaking has been widespread for decades and numerous studies dedicated to the topic have been carried out. HyPeak aims to integrate members from other countries and continents in which hydropower production plays a relevant role, and grow to be a reference group that provides expert advice on the topic to policy-makers, as well as researchers, stakeholders, and practitioners in the field of hydropeaking.