Particle residence time between porous obstacles: application to management strategies of invasive aquatic species.

Freshwaters transport a wide range of particulate matter, such as plant seeds, fish eggs, drifting invertebrates and plastic debris. Such particles experience complicated flow structures across a wide range of scales generated by in-stream obstacles and characterized by the obstacles’ pore sizes and densities. We analyze the residence time of particles in the gap between two porous obstacles focusing on the relevant flow scales that determine particle transport. Laboratory experiments were conducted on a closed-loop racetrack flume using six types of porous obstacles and two particle types analogous to aquatic invasive species in their early life stages: 1) neutrally buoyant with 1 mm diameter and 2) negatively buoyant with 4.8 mm diameter. We used particle tracking velocimetry (PTV) to identify particle trajectories and preferred locations relative to the obstructions with longer local residence time, and particle image velocimetry (PIV) to characterize mean and turbulent conditions driving particle retention and redirection within and past the gap. Analysis on the interaction between particles and flow structures of different scales provide guidelines for efficient management strategies of aquatic invasive species based on: 1) accurate prediction of accumulation zones; and 2) physics-based guidelines for effective design of in-stream traps.