A Numerical Model Study of Hypoxia in the Tidal Rappahannock River of Chesapeake Bay

Hypoxia, even anoxia, has persisted during summer in the bottom water of the lower portion of the tidal Rappahannock River, a western shore tributary of Chesapeake Bay. A laterally integrated, two-dimensional, real-time model consisting of linked hydrodynamic and water quality models was developed and applied to the tidal Rappahannock River. The model was calibrated and verified using field data collected in 1987 and 1990. The model reproduced the observed hypoxia very well. The model was used to study the effects on hypoxia of the physical processes (gravitational circulation and vertical mixing), oxygen demand (both in sediment and water column), and the quality of incoming bay water. Sensitivity analysis using the model provided further insight to the understanding of the processes contributing to hypoxia. This paper presents the model application with emphasis on the sensitivity analysis for hypoxia.