Idrodinamica dei pesci nelle strutture idrauliche: simulazione accoppiata ecologia-idrodinamica del passaggio dei pesci controcorrente nelle scala a fessura verticale

Anthropogenic activities have accelerated biodiversity loss by a factor of 100 to 1000 times compared to pre-human levels, with freshwater ecosystems being particularly affected, experiencing a 54% decline in the population of freshwater vertebrates. Two thirds of the world’s largest rivers have lost their free-flowing condition. At least 1.2 million barriers in 36 countries in Europe impact river connectivity. To recover river connectivity, structural measures such as fishways at barriers are applied, being Vertical Slot Fishways (VSFs) are the most popular among them. However, averaged passage and attraction efficiency are around 45% and 63%, respectively. Thus, this manuscript presents extensive investigation of VSFs, encompassing both hydraulic and biological evaluations. First, a comparative numerical investigation was conducted to evaluate two distinct VSF geometries, steep and mild sloped, hydraulic performance, employing open - source toolboxes for three - dimensional simulations and two - dimensional depth-averaged flow simulations, respectively. The three-dimensional simulations yielded superior results, demonstrating more accurate representation of flow dynamics. Two - dimensional simulations highly overestimated turbulent kinetic energy and did not represent accurately flow topology. However, velocities were captured, and simulation times were significantly lower compared to three-dimensional. Second, a Eulerian Lagrangian Agent-Based Model (ELAM) aimed to simulate the upstream migration of bighead (\textit{Hypophthalmichthys nobilis}) and silver (Hypophthalmichthys molitrix) carps through VSFs is presented. The ELAM considered four behaviors: exploration, attraction, wall collision avoidance, and escaping responses. It successfully reproduced the averaged pathlines, and the inclusion of the escape response enhanced model’s accuracy with little impact in the energy cost. Results suggest that uniformity and turbulence play a significant role in the agent’s pathline selection. Finally, the ELAM was modified to address spatial preferences and ascent times of Iberian Barbel (Luciobarbus bocagei) by adding a resting behavior. Thus, the ELAM effectively replicated fish spatial distribution and, to a certain extent, passage efficiency. In conclusion, this study proves that a comprehensive model is capable of replicating both the hydraulics and fish movement in fishways, providing new insights on cyprinids' behavioral responses to turbulent flow.