A three dimensional numerical hydrodynamic model has been applied to the Upper Chesapeake Bay C & D Canal Delaware River and Bay system. The purpose of the study was to assess the impact of channel deepening in the Delaware River and Delaware Bay on salinity intrusion and circulation. To aid in the modeling study, a field data collection effort was conducted from October 1992 through September 1993. These data were used in the model validation phase of the study as well as to provide boundary conditions for some production runs. For assessing the impact of channel deepening during low flow periods, the drought of record that occurred during 1965 was selected to be simulated. Model results for the flow regulation plan of the Delaware River Basin showed that salinities would be slightly increased at Philadelphia with a 1.52 m increase in the depth of the navigation channel, but they would still be below what are considered critical values. Impacts of channel deepening on salt intrusion for both average and high flow conditions are also presented. In addition, the numerical model was used to assess the impact of sea level rise and of closing the C & D Canal.