The Disjointed Double Channel of Chincoteague Inlet and Implications for Sediment Transport

Abstract:

The Chincoteague-Assateague-Wallops inlet system (Virginia, USA) is an extremely dynamic system characterized by duplexed (overlapping) barriers, an island-parallel inlet mouth, and a fronting island elongating by 40 m/yr. In such dynamic systems, it is often difficult to collect hydrodynamic and bathymetric data at a rate required to capture the rapid morphologic changes. Yet, these data are necessary to protect life, infrastructure, and natural resources by managing coastal erosion, maintaining navigation channels, and mitigating climate change.

To address these needs, repeat high-resolution bathymetric surveys and hydrodynamic data were collected in 2019 and 2020. Bathymetric data revealed the presence of two disjointed sections of channel. The sections are oriented north-south, but are offset east-west by 1000 m. The southwestern channel, which reaches depths of 8 m, hugs the western side of the inlet and is the section closest to the mouth, while the northeastern channel, which reaches depths of 12 m, hugs the eastern side of the inlet and is the section closest to the back barrier. Sidescan sonar data exposed sand waves in the channels up to 1.18 m in height with strong flood- and ebb-oriented asymmetry, highlighting potential sediment transport pathways in the channels. Hydrodynamic data were collected via moored instruments over periods of four to eight weeks, capturing both fair weather and storm conditions. Coincident with these, a moored rotary sonar conducted sector scans to record bedform migration in the inlet.

Preliminary results suggest that currents in Chincoteague Inlet transport sand in the form of sand waves into the inlet through the southwestern channel. This sediment appears to be circulated through the inlet system in a manner similar to tidal flow bypassing; however, the sand is likely stored one of the large, permanent, inlet-parallel shoals found inside the inlet. Morphologic surveys suggest that this sand is exported out of the inlet along the eastern (updrift) side of the channel, indicating that the shoals serve as a source of sediment for the rapid growth of southern Assateague Island. Further analysis will explore the relationship between the hydrodynamic data, the complex channel morphology, and their implications for sediment transport in this dynamic and unusual inlet system.