The artificial pulsed flows occurring downstream of hydropower plants due to electricity demand, i.e. hydropeaking, affect habitat selection by fish. This effect is particularly unknown for cyprinids, which are the most representative freshwater fish family in European rivers. This study aimed to evaluate the utility of two types of flow-refuge by Iberian barbel (Luciobarbus bocagei) at an indoor flume (6.5m x 0.7m x 0.8m) as a potential solution to mitigate the effects of pulsed flows associated to hydropower production. Based on previous comprehensive research conducted on cyprinids and with the results of this study, the best type of flow-refuge was selected, up-scaled and implemented downstream of small hydropower plants. Two different approach angles with the flume wall - 45⁰ and 70⁰ - were tested to assess the effectiveness of the created hydraulic conditions on attracting fish to the flow-refuge. For each type we tested a base flow event (7 l.s-1), simulating river natural conditions, and a peak flow event (60 l.s-1), simulating pulsed flows. For each setting, two flow-refuges (downstream and upstream) were installed in the flume and tested with a school of five Iberian barbels. The utility of the flow-refuges was assessed by the frequency and time of use by fish at two distinct flow-refuge locations i.e., downstream (area between the flume and the adjacent flow-refuge walls), and inside (the effective covered area of the flow-refuge). Blood glucose and lactate levels were quantified to identify potential physiological adjustments associated with the pulsed flows and the flow-refuge type. Preliminary results indicate that fish behavior differs according to flow event and the type of flow-refuge. The frequency of a single fish using the flow-refuge was higher in the 45⁰ refuge during pulsed flows than in the 70⁰. Overall, the average time spent inside the flow-refuges was higher during pulsed flows for both types and higher in the 45⁰ refuge.  After the 60 l.s-1 events, the blood glucose and lactate levels were higher than in the 7 l.s-1 events. In addition, lactate levels for the 45⁰ flow-refuge during the 60 l.s-1 events, were the highest when compared to 7 l.s-1 events. These results may be explained by the higher velocities created in the presence of the 45⁰ flow-refuge, shown by ADV results, that favoured individual use and rheotactic behaviour, setting off physiological adjustments, increasing residency time and the efficiency to use the flow-refuge.

Hydroelectricity demand is still growing due to its reduced carbon impact and strong dispatchability. Concurrently, the necessity to support self-sustainable fish populations in a cost-effective way and restore water-related ecosystems is urgent. The impacts of rapid and artificial flow fluctuations caused by peak electricity demand, i.e., hydropeaking, on fish fauna are still largely unknown, particularly for cyprinid species. Flow-refuges (e.g., lateral deflectors) are believed to help fish with rapidly changing flows and high currents. Nonetheless, most studies addressing hydropeaking and its impacts focus on salmonids. Recent studies have assessed the utility of flow-refuges for cyprinids in controlled experimental conditions. However, fish responses to hydropeaking and the use of flow-refuges in peaking rivers remain unknown. Rethinking the hydropower operation to improve fish habitat during key lifecycle stages (e.g., spawning) can be an option. However, these measures may affect the hydropower production profit. Including habitat use in models of hydropower plant (HPP) optimal management is usually achieved by adding restrictions regarding minimum flows. The feedback between the available habitat and profit has not been explicitly modelled. Including a description of how the available habitat changes with water flow can help estimate tradeoffs between profit maximization and habitat preservation and to inform the development of flow restrictions. EcoPeak4Fish intends to answer these questions in a multidisciplinary approach with the 4E’s: Ecology, Engineering and Economics in the profit of the Ecosystem protection. This project aims to assess the effects of hydropeaking in cyprinid species, propose a flow-refuge prototype and assess its cost-effectiveness, and develop a framework to adapt the HPP operation scheme to maximize profits and environmental benefits for a sustainable use of hydropower energy. The project intends to answer the following questions: How do fish react under hydropeaking conditions? Are flow-refuges an effective measure to mitigate impacts and contribute to the self-sustainability of fish populations? How can one find the HPP operation scheme that maximizes profit and power production while maximizing the suitable habitat for fish populations? This knowledge will be fundamental to implement new and redefine operational schemes, to recommend design criteria for flow-refuges, and to mobilize policy-makers to define legal instruments for hydropeaking.

To fight against global warming, we have to change our ways of consuming energy. Due to its low carbon impact and strong dispatchability, hydroelectric production will be one of the bases of this transition. However, peak electricity demand produces rapid and artificial flow fluctuations in tailwaters, i.e., hydropeaking, which has negative effects on fish biota. Thus, developing effective mitigation measures against hydropeaking is an urgent matter. The present study aims to limit the impact of this flow fluctuation on an Iberian cyprinid fish: the Iberian barbel (Luciobarbus bocagei). We experimentally tested different angles of flow refuge entrances (45° and 70°) in an indoor flume (6.5 m × 0.7 m × 0.8 m) to determine if this would affect the behavior of the fish. For each angle configuration, two refuges were installed and distanced 2.30 m from each other on the same side of the flume. Three possible resting locations were defined: downstream, inside, or upstream of each structure. Both angles were tested at 7 L/s (base flow), simulating the normal conditions of the river, and 60 L/s (peak flow), simulating a hydropeaking event. Each replicate comprised a group of five fish. For each, the frequency and residence time were quantified. The preliminary results indicated that the fish movement patterns changed when peak flow occurred. The downstream refuge was more frequently used in both configurations during peak flow. Additionally, the inside parts of the refuges were more frequently used, instead of the parts immediately downstream or upstream, and the time spent inside the refuge at peak flow was higher when compared to base flow. Additionally, hydraulic experiments were carried out at each configuration to determine the velocity field using ADV (Vectrino) technology. For the base flow, mean water depth and average velocity were 8 cm and 12 cm/s, respectively, increasing to 24 cm and 39 cm/s during peak flow. Measurements showed that velocity was equal to 74 cm/s in the narrowed area due to the refuge location, and velocity was null inside and directly downstream of the refuge. The results from this study will allow the development of guidelines for designing flow refuges for cyprinid fish, and hence mitigate the impact of hydropeaking.