Identification of effective hydropeaking mitigation measures: are hydraulic habitat models sufficient in a global approach?

Downstream of hydroelectric plants, hydropeaking can cause frequent flow variations, resulting in habitat modifications (e.g. hydraulics, reach morphology, temperature, water quality), which can impact organisms (stranding, dewatering, forced drift, growth disturbances) and ultimately may have negative and lasting impacts on biological communities, reducing resilience. Nevertheless, the severity of habitat disturbances vary depending on other existing pressures and local site conditions, which need to be taken into account to achieve effective hydropeaking mitigation. Preserving hydropower flexibility is also a priority to ensure the stability of electric systems without recourse to more polluting alternatives. Given these apparently opposing objectives, we propose a consensual technico-economic framework to guarantee the feasibility and effectiveness of site-specific hydropeaking mitigation, based on our experience as a hydropower operator and a literature review. While existing tools (such as habitat models) can be used to predict expected local effects of proposed mitigation and compare scenarios, predicting biological community responses is not currently possible (lack of in-situ evaluations of mitigation efficacy). These uncertainties and complex socio-ecosystems necessitate a forward-looking global approach that accounts for climate change, multi-purpose water use and electric system requirements, combined with site-specific analyses of the relative importance of hydropeaking impacts with respect to other pressures.