Assessment of Long-Term Water Quality Impacts of the Craney Island Eastward Expansion, Elizabeth River, Virginia

The Craney Island Dredged Material Management Area (CIDMMA) is a 2400- acre, federally-owned and operated facility located in Hampton Roads, Virginia adjacent to the city of Portsmouth. A 520-acre designed expansion of the CIDMMA to the east was shown in a previous study to have the least impact to the hydrodynamic circulation of all evaluated land expansions. The 3D baroclinic hydrodynamic model HEM-3D coupled with the water quality model was applied over a domain spanning the James and Elizabeth Rivers. The model was calibrated, validated, and used to assess the long-term environmental impact of the terminal expansion, as well as the impact resulting from an intermediate construction phase. The study showed that a slight reduction in tidal prism was compensated for by an increase in the non-tidal residual flow during flood and ebb tide phases, thereby enhancing flushing. Dissolved oxygen (DO) levels due to the eastward expansion were mitigated by the enhanced exchange of Elizabeth River water with that from the oxygen-rich Lower James River. As a result, the increase of advective DO flux from the James River and local vertical mixing overcome the increase of low DO volumes. Overall, the impacts to DO levels due to both the south cell and the full expansion are minimal and are well within the range of detection limits.