FORMATION AND CLOSURE OF A WAVE-DOMINATED TIDAL INLET: IMPLICATIONS FOR A MULTIPLE-CHANNEL INLET SYSTEM ALONG ASSATEAGUE ISLAND, MARYLAND

A comparative analysis of 95 historical nautical charts, NOAA T- and H-Sheets, and maps dating from AD 1590 to present was performed to develop a detailed chronology of historical inlets along Assateague Island, MD/VA. Results reveal that Sinepuxent Inlet was open as early as 1755 and closed by 1840. Cherry Tree Inlet appeared to be open along with Sinepuxent from as early as 1755, but more detailed documents indicate that their coexistence may have been ephemeral from 1787 to 1839. No inlets were open along Assateague Island following the closure of Sinepuxent Inlet until Green Run Inlet was depicted open in 1852 and closed by 1882. A high-resolution 250 MHz ground-penetrating radar (GPR) survey of the former Sinepuxent Inlet area displayed evidence of three channel signatures within an 850 m swath, extending to a depth of at least 4 m. GPR images of the paleo-channels demonstrate sigmoidal-oblique radar facies and indicate prograded fill for two channels and a conformable fill pattern for the third. Tidal prism calculated using subsurface imagery, yields 2.8 x 10⁶ and 4.6 x 10⁶ m³ for the northernmost and middle channels, respectively. Tidal prism for the southernmost channel may have been as large as 20 x 10⁶ m³. The formation of Sinepuxent Inlet may be explained by the following multiple-working hypotheses. Hypothesis 1: the three channels formed in response to a single storm event and coexisted as a multiple-channel inlet system. This scenario would require shallow depths, because the tidal prism would be distributed among three channels. Present-day analogues of this hypothesis are observed along other wave-dominated settings, such as the Outer Banks, NC. Hypothesis 2: the inlet formed with three active channels; however, one of the channels pirated the tidal prism from the other two smaller channels, causing them to close. This hypothesis can be explained by an intense storm causing breaching over a wide section of the island. In this scenario, a single channel siphoned enough tidal prism to remain the only efficient active channel and, as a result, the remaining channels were subsequently filled. Hypothesis 3: the genesis of the three channels was a result of unrelated storm events. The three channels existed at separate times and were independent of each other. At this time, our data supports the second hypothesis.