Effect of Flow Diversions on Contaminant Transport Modeling in the Niagara River

A numerical model is formulated to simulate one-dimensional transport of a conservative tracer through the Niagara River, from Fort Erie to Niagara-on-the-Lake. The model accounts for flow splits at Grand and Navy islands and, more significantly, incorporates the operations of the New York Power Authority and Ontario Hydropower. These involve large-scale diversions and temporary storage of water for power production, resulting in a dispersion-like effect on the breakthrough curves for the tracer at Niagara-on-the-Lake. In comparison with straight through-flow calculations, the model results indicate an increase in mean residence times by up to 25% and decreases in peak concentrations by up to 50%, depending on the time of day the contaminant release occurs. In addition, the model shows the distribution of tracer mass remaining in the system after a typical sampling program, as currently followed in the Niagara River Toxics Management Plan. This allows a determination of optimal timing for sampling in order to maximize mass recovery. The model provides a tool to help understand transport in this complex hydraulic system.