Analyzing leaping and movement potential at a migratory barrier.

Evaluating passage performance at migratory barriers is essential for managing connectivity within a watershed and is essential for improvements to fish passage and, in some cases, with invasive species control. To quantify upstream passage opportunities at barriers with complex geometry, a 3-D stochastic leaping model that couples species-specific behavior with hydraulics derived from Computational Fluid Dynamics simulations is developed. The model expands on traditional ballistic-trajectory models to evaluate attempts from any location downstream of a barrier and integrates stochastic variation in fish characteristics—including body length, launch speed, and leap origin—while maintaining computationally-derived local velocity and depth inputs in three dimensions. The revised model provides a spatially detailed assessment of conditions most conducive to successful leaping attempts, offering a more comprehensive evaluation of conditional passage probability at migratory barriers. Applied to two case studies (Union Street Dam—calibration; FishPass arc–labyrinth and low-flow weir—design), the model predicted conditional passage probabilities ranged from < 1% at base flow to ~ 10% at a 200-year flood. Results highlight how barrier geometry, tailwater depth, and flow cues shape leaping success, providing actionable guidance for either facilitating desirable passage or strengthening migration barriers.