Evaluation of a carbon dioxide fish barrier through numerical modelling

The Chicago Area Waterway System (CAWS) is a potential route for the migration of aquatic invasive species from the Mississippi River Basin into the Great Lakes. Electric dispersal barriers were installed in the Chicago Sanitary Ship Canal, within CAWS, to prevent invasive fish from reaching the Great Lakes. Despite the high efficiency of these barriers, occasional maintenance events create a vulnerability that fish can exploit to access the Great Lakes. This study aimed to assess the feasibility of a carbon dioxide (CO₂) infusion system to deter fish during the maintenance of the electric barriers. An algebraic slip mixture model was implemented in the OpenFOAM solver to represent the underwater CO₂ bubble plume and predict the concentration of dissolved CO₂ in the canal. Simulations under three canal flowrates and two sparger systems were conducted assuming a constant gas flowrate. Numerical results indicate that, for all simulated conditions, the CO₂ concentration is not fully mixed creating passageways that invasive fish could potentially use to migrate upstream. Injecting 4-mm bubbles induces two large-scale recirculations that are expected to synergistically improve fish avoidance. On the other hand, injection of 20  \(\upmu\) $\mathrm{\mu }$ m bubbles results on almost immediate dissolution with minimal effect on the flow pattern. To improve effectiveness, a gas pulse system was proposed and numerically evaluated. Based on the simulations, this system not only extends the operation of the CO₂ barrier but also increases efficiency creating CO₂ gradients that can promote a more responsive behaviour from fish. Moreover, the pulse concept mitigates potential effect of elevated CO₂ downstream from the treated area.