Calculating age and residence time in the tidal York River using three-dimensional model experiments

The age concept is applied to an estuary to estimate time scales quantifying transport processes of dissolved substance for a spatially varying case. A real-time three-dimensional numerical model was applied to the tidal York River estuary, a western branch of the Chesapeake Bay, to calculate the age distribution for a substance released from the headwaters of tributaries of the estuary under different hydrological conditions. The mean age, residence time, and turnover time were computed through a series of numerical model experiments. Both mean age and residence time are functions of freshwater discharge. The model results show that substantial time is required for a substance discharged into the system at the headwaters of the tributaries to be transported to the downstream estuary. It takes about 2 months and 3 months for the substance discharged into the headwaters to be transported to the mouth of the estuary under high flow and mean flow conditions, respectively. The results provide useful information for understanding the transport processes in the estuary and can be used to estimate dissimilative capacity of the estuary for environmental assessment.