Evolution of an Urban Estuarine Harbor: Norfolk, Virginia
Keywords:Estuarine sediments, harbor, dredging and disposal, estuary hydrodynamics
The history of dredging and disposal has been compiled from historical charts and records to determine the course of harbor evolution at Norfolk, Virginia. Dredging activities between 1872 and 1982 have produced large geometric changes with important hydrographic and sedimentological consequences. The harbor once had a shallow irregular channel floor bordered by broad shoals, marshland and tributary creeks. Today after 100 years, dredging has deepened the channel 1.8 fold, smoothed the natural profile and increased sedimentation rates more than 90 times expected rates. Disposal as land fill has buried many creeks and marshes, moved the shore channelward and reduced the estuary area 26%. As a consequence these changes have reduced the tidal prism and entrance exchange. The dredge-fill-sedimentation cycle follows three stages of harbor evolution: (1) dredging entrance bars and the estuary head, (2) channel enlargement seaward with bordering landfill and open water disposal, and (3) contained disposal seaward of the early port, or ocean disposal. This case study shows that a series of small dredge and disposal projects in a small estuarine harbor can produce large cumulative effects that are the same order as natural geologic processes. Several other harbors follow similar stages of harbor evolution.