Analyses of recent geomorphic evolution of Gargathy Inlet, eastern shore of Virginia, U. S. A.

Abstract

Gargathy Inlet is a small natural tidal inlet in the northern region of the Virginia barrier island chain. It is 100 m wide with a throat cross-sectional area of 384 m2 and an average tidal prism of 6.47×106 m3. The inside drainage system is 7.8 km long and 2.2 km wide. The main channels comprise 5.8% of the area, shallow lagoons 19.8%, andSpartina marshes 74.4% in 1970. Over the period 1851–1989 the inlet narrowed and migrated northward while maintaining a weakening downdrift offset. The nearby barrier island coastline’s rapid retreat (average rate 4.78 m/a, 138 years retreat 660 m) was accompanied by back barrier channel and lagoon filling and a decrease in intertidal water volume which was probably the main reason for the entrance narrowing. The northward migration of the inlet was related to the dredging of the Inside Passage (before 1949) and the breaching of southern Metompkin Island (since 1957) connected with the inlet system. This altered the interior tidal circulation and likely shifted northward the divide between the drainage areas of Gargathy Inlet and Metompkin Inlet. Bypassing littoral sediment from north to south, downdrift local transport reversal, and onshore welding of swash bars formed a downdrift offset. Very strong coastal storms, particularly those of 1933 and 1962, played important roles in changing inlet geometry.