A Eulerian-Lagrangian model for simulating fish pathline distributions in vertical slot fishways

Recovery of the river connectivity relies on the application of structural and non-structural solutions. Within the structural solutions, vertical slot fishways (VSF) are most popular, but achieving the desired efficiency remains a challenge. To this end, evaluation of both biological and hydraulic efficiency is imperative. A Eulerian Lagrangian Agent Based Model (ELAM) of fish upstream migration through VSFs is presented in this work that considers one passive and three active behaviors affecting fish swimming pathlines of bighead carps (Hypophthalmichthys nobilis) and silver carps (Hypophthalmichthys molitrix). The passive behavior consists in a 2-D random walk where no external stimuli are detected. The first active behavior represents fish attraction to a nearby flow region as a Gaussian distribution function of turbulent kinetic energy, velocity magnitude and velocity strain rate. The second active behavior represents wall collision avoidance, whereas the third considers the tendency of the fish to escape from high velocity zones. Stochasticity is considered in the model to represent the dispersion in the experimental pathlines. The ELAM is tested for two different VSF configurations and is found to well reproduce the experimental pathlines, particularly when the escaping response to high velocity zones is considered. Results show that the ELAM model can be used as an appropriate tool for modelers and designers to evaluate fish passage efficiency.