The Virginia Department of Environmental Quality (VADEQ) under the direction of the United States Environmental Protection Agency (USEPA) has listed the lower Appomattox River as impaired because it violates current water quality standards for fecal coliforms. To advance the analytical process by which various scenarios for improving water quality within the estuary are examined, an array of computer-based hydrodynamic and water quality models were investigated. The Dynamic Estuary Model (DYNHYD5), developed by USEPA, was used to simulate hydrodynamics within the lower Appomattox River. The Water Quality Analysis Simulation Program (WASP6.1), also developed by USEPA, was employed to perform water quality simulations of fecal coliforms. Also, a detailed literature review examined DYNHYD5 and WASP6.1 model theory, computer-based model solution techniques, and background hydrodynamic theory.

DYNHYD5 sensitivity analysis showed that the model was most responsive to tidal heights (seaward boundary conditions) both upstream and downstream within the model network. Specific model parameters were varied during calibration until modeled water surface elevations converged on observed water surface elevations. A goodness-of-fit value of 0.749 was determined with linear regression analysis for model calibration. DYNHYD5 input parameter validation was performed with additional observations and a goodness-of-fit value of 0.829 was calculated.

Through sensitivity analysis, WASP6.1 proved to be most responsive to coliform loading rates in the downstream direction and boundary concentrations in the upstream direction. With these results, WASP6.1 input parameters were calibrated against observed fecal coliform concentrations. A goodness-of-fit value of 0.573 was determined with linear regression analysis for model calibration. WASP6.1 input parameter validation was performed with additional observations and a goodness-of-fit value of 0.0002 was calculated.

Model results suggest that hydrodynamic model calibration and validation can be improved with additional tidal height observations at the downstream seaward boundary. Similarly, water quality model calibration and validation can possibly be improved with the aid of detailed, time-variable coliform concentrations at the downstream seaward boundary. Therefore, it is recommended that a water quality sampling station and tidal stage recorder be installed at the confluence of the Appomattox and James Rivers to provide for further testing of estuary hydrodynamic and water quality models.