| Summary |
Croatan and Roanoke sounds in North Carolina (NC) are regions constantly undergoing geomorphic changes associated with sea-level rise, storm events, and anthropogenic modification. These estuaries are part of the larger Albemarle-Pamlico Estuarine System (APES), a composite of drowned coastal plain river valleys and large bar-built shallow sounds fronted by the Outer Banks barrier islands. Changes in shoreline morphology driven by erosion and accretion, associated with oceanographic/atmospheric drivers (e.g., wave energy, fetch), influence modern sedimentological patterns and sedimentation rates in the APES. This research focused on the dynamics and controls of modern sedimentary processes (e.g., accumulation) and shoreline change on an anthropogenic time-scale (~100 years) around Roanoke Island, NC. Sedimentological, geochemical, and geospatial analyses provided the necessary information for modern interpretation of the geological processes at work within the past century. Surficial sediment analyses revealed variable grain-size patterns and high loss on ignition (% LOI, organic content proxy) across the region. Sediment accumulation rates (0.12 ± 0.01 cm/y to 0.37 ± 0.04 cm/y) varied over the long-term, and one location (DH-S17) displayed rapid episodic deposition (2.3 ± 0.5 cm/month). Long-term shoreline change (1915-2012) indicated net erosion of the system (-0.68 ± 0.05 m/y), with temporal changes observed in the intermediate time-intervals, and more accretion was captured in the recent- and short-term (2007-2012: -0.24 ± 0.32 m/y). Long-term shoreline change rates (SCRs) provided insight into chronic changes (hydrodynamic and geomorphic changes), while short-term rates, due to events (e.g., hurricanes), revealed episodic variations in accretion and erosion that might not represent the long-term patterns in the system. Overall, the amount of sediment eroded from the shoreline over the 97-year interval (1915-2012) was calculated to be 8.32 x 10⁶ m³, with a mass of 4.16 x 10⁹-8.32 x 10⁹ kg (assuming a dry bulk density range of 0.5-1.0 g/cm³). A sediment accumulation budget of 9.32 x 10³ m³/y (7.24 x 10⁶ kg/y) was calculated for two regions (offshore UNC CSI, Shallowbag Bay), and modern accumulation accounts for ~11% (8.57 x 10⁴ m³/y) of the amount of annually eroded sediment. Data from this thesis indicate that the majority of eroded sediment is exported out of Croatan and Roanoke sounds. Spatial and temporal trends in shoreline change and accompanying sedimentary characteristics examined in this thesis provide insight to coastal managers and homeowners in systems similar to the Roanoke Island area. |
