2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 162-3
Presentation Time: 2:10 PM


SEMINACK, Christopher T., Department of Environmental Science & Policy, George Mason University, 4400 University Drive, Fairfax, VA 22030 and MCBRIDE, Randolph A., Department of Atmospheric, Oceanic, & Earth Sciences, George Mason University, 4400 University Drive, Fairfax, VA 22030, cseminac@gmu.edu

Assateague Island is a mixed-energy, wave-dominated barrier island located along the Delmarva Peninsula which has been subjected to at least 11 breaching events during the historical period. This study focuses on the two best preserved former tidal inlets along Assateague Island: Green Run and Sinepuxent Inlets. Life-cycle models of the two former inlets were developed using a multi-faceted dataset consisting of sediment cores, ground-penetrating radar profiles, historical maps, aerial imagery, and LIDAR data. Green Run Inlet was active from 1852 to 1880 and expresses well-preserved geomorphic features such as a relict flood-tidal delta, recurved spit ridges, and inlet-closure ridges. Ground-penetrating radar profiles captured the opening, lateral migration, and closure of the historical inlet and led to the development of a 5-stage life-cycle model. Green Run Inlet migrated 680 m and had a final channel 100 m wide by 3.5 m deep, resulting in a spring tidal prism of 2.79 X 106 m3. The former Sinepuxent Inlet was active from pre-1755 to 1831 and also depicts well-preserved geomorphic features, such as recurved spit ridges, inlet throat scarring, and subtle inlet-closure ridges. The inlet throat was impacted by overwash processes during the 1962 Ash Wednesday Storm, thus reworking inlet-closure ridges. This resulted in a less complex, three-stage life-cycle model for the inlet: the initial breach and formation of recurved spit ridges, development of inlet-closure ridges with subsequent closure, and progradation of beach ridges. While the extent of migration for the Sinepuxent Inlet is unclear, it likely had a final channel 660 m wide by 3.5 m deep, resulting in a spring tidal prism of 5.7 X 106 m3. Although Green Run and Sinepuxent Inlets had comparable tidal prisms and inlet throat dimensions, the geomorphic expression of features and their preservation differ. Green Run Inlet has a large, well-developed flood-tidal delta and numerous inlet-closure ridges preserved, whereas Sinepuxent Inlet has a poorly-developed flood-tidal delta and subtle inlet-closure ridges, but robust recurved spit ridges. The differences in these relict geomorphic features highlight the variability between tidal inlet systems of the same barrier island and stress the dynamic nature of the wave-dominated tidal inlet complex.