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.

We assessed the effect of a hydropeaking diversion mitigation measure that allows for additional hydropower production, which markedly reduced hydropeaking on a 10-km stream reach in the north-eastern Italian Alps. Hydropeaking, caused by a storage hydropower plant, affected the study reach from the 1920s to 2015, when a cascade of three small run-of-the-river plants was installed to divert the hydropeaks from the plant outlet directly into the intake of the RoRs plants, and hydropeaking was released downstream the confluence with a major free-flowing tributary. The flow regime in the mitigated reach shifted from a hydropeaking-dominated to a baseflow-dominated regime in winter, with flow variability represented only by snowmelt and rainfall in late spring and summer. The application of two recently proposed sets of hydropeaking indicators, the hydraulic analysis of the hydropeaking wave, together with the assessment of biotic changes, allowed quantifying the changes in ecohydraulic processes associated with hydropeaking mitigation. The flow regime in the mitigated reach changed to a residual flow type, with much less frequent residual hydropeaks; although an average two-fold increase in downramping rates were recorded downstream the junction with the tributary, these changes did not represent an ecological concern. The functional composition of the macrobenthic communities shifted slightly in response to flow mitigation, but the taxonomic composition did not recover to conditions typical of more natural flow regimes. This was likely due to the reduced dilution of pollutants and resulting slight worsening in water quality. Conversely, the hyporheic communities showed an increase in diversity and abundance of interstitial taxa, especially in the sites most affected by hydropeaking.This effect was likely due to changes in the interstitial space availability, brought by a reduction of fine sediments clogging. Besides illustrating a feasible hydropeaking mitigation option for Alpine streams, our work suggests the importance of monitoring both benthic and hyporheic communities, together with the flow and sediment supply regimes, and physico-chemical water quality parameters.

Application of mesoscale habitat models in gravel-bed rivers is increasingly common for a variety of purposes, from ecological flow design, impact assessment and conservation programmes. Integration with 2D hydraulic modelling offers the potential for broader applicability of mesoscale habitat models, extending applications to larger streams and nonwadable flow conditions, when on-the-ground and in-stream surveys are challenging or even prohibitive. In this work, a novel fully unsupervised procedure that allows the segmentation of the river channel area at a given flow condition at a scale that is consistent with the mesoscale is presented.

The flow regime of streams and rivers has been modified by human activities at a global scale (Grill et al., 2019;Tonkin et al., 2019). As the human population continues to grow, the increasing demand for water supply, flood protection, and energy production has prompted the widespread adoption of engineering solutions such as the construction of dams, levees, and other hydraulic infrastructures (Couto & Olden, 2018;Shumilova et al., 2018;Zarfl et al., 2015). As a result, streams and rivers are under increasing anthropogenic pressure and are among the most threatened ecosystems worldwide, with particularly high rates of species extinctions (Tickner et al., 2020). The ongoing global climate change is expected to further exacerbate this situation by increasing the frequency of extreme hydrologic events such as floods and droughts that act synergistically with other stressors affecting aquatic ecosystems (e.g. Navarro-Ortega et al., 2015). This is of particular concern since freshwater ecosystems support about 10% of all known species (Strayer & Dudgeon, 2010) and are essential for human well-being, providing a wealth of ecosystem services (Green et al., 2015). Understanding and limiting the ecological effects of flow alteration is therefore fundamental for sustainable use of water resources.The Natural Flow Regime Paradigm (Poff et al., 1997) is at the heart of the environmental flow definition and specifically acknowledges that river biota is adapted to seasonal and interannual variations of river flow. In order to mitigate the environmental impacts associated with infrastructures while maintaining their functioning, environmental flows (termed e-flows hereafter) should mimic the natural streamflow variability in terms of magnitude, frequency, duration, timing, and rate of change (Arthington et al., 2018). However, given the limits in the ability to mimic natural regimes in regulated rivers, e-flows policy must be informed by a clear understanding of the relation between river ecology and flow characteristics (i.e.,

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