Tracer Simulation to Analyze Channel Effect on Particle Transport in the Chesapeake Estuary

A particulate tracer was simulated by the Chesapeake Bay Estuarine Model. The tracer was loaded daily at the fall-line of Potomac River (a middle Bay's tributary), with a settling rate at 0.1 m/day. After tracers reached the mouth of Potomac River, most of them were transported to the lower-Bay. The landward movement with saline water intrusion is the main force for tracer transport to the upper-Bay and the upstream of non-source rivers. In the main-stem Bay, there exist concentration gradients from the Potomac mouth to the opposite shore, to the lower-Bay, and to the upper-Bay. These gradients are disturbed across deep channels. The landward saline water is favored along the deep channel over their shallower sides. Depending on the layer (saline or fresh water) that the tracer resides in and the direction that the tracer is transported, the preferential in tracer transport/deposit along channel versus its shallower sides is different. Contrasting "channel effects" are observed between the source river and non-source rivers, and between the lower Bay and the upper upper-Bay. Generally, the channel at the source-river or down-Bay have less tracer than the shallower sides; whereas, the channels at non-source rivers or the up Bay have more tracer than the shallower sides. The phenomena of the channel effect are disturbed by local bathymetry and freshwater inputs. The tracer simulation shows how particles are transported by the estuarine circulation, providing information for strategic source controls to protect targeted waterways.