Water-energy-ecosystem nexus: Balancing competing interests at a run-of-river hydropower plant coupling a hydrologic-ecohydraulic approach

The water-energy-ecosystem nexus represents a complex interlinkage that depends on the flow regime type. Inadequate environmental flows setting may adversely affect the riverine ecosystem and/or hydropower revenue. This issue was addressed quantitatively in this study by considering a run-of-river hydropower plant located in a river of the Tagus basin characterised by a pluvial winter flow regime. Three models: a hydropower, a hydrologic, and an ecohydraulic model were integrated to estimate the influence of nine hydrologically-based environmental flow methods on hydropower production, flow regime alteration and fish habitat conditions. The target fish species was a native cyprinid fish, the Iberian barbel (Luciobarbus bocagei), considering three life-stages. Results show that high environmental flow releases did not necessarily provide the highest habitat availability and suitability at all seasons and fish life-stages. The adult life-stage resulted in being more vulnerable to water diversion, particularly during Spring season. Shallow-water hydromorphological units suffered the highest habitat loss. Some of the environmental flow methods demonstrated inconsistent results over seasons and fish life-stages by either allowing for higher environmental flow releases whereas highly restricting hydropower production or vice versa. However, results also suggest that combined and dynamic environmental flow methods promoted reasonable hydropower production while inducing less than 50% habitat loss and flow regime alteration, regarding the three life-stages over all seasons. This study contributes to the identification of the relationship between conflicting objectives, such as hydropower production and riverine ecosystem conservation. Also, it provides strategic recommendations on energy-ecosystem regulation for sustainable hydropower operation. This study also highlights the importance of considering seasonal flow discharge variability when analysing the water-energy-ecosystem nexus.