Sedimentary Characteristics of Flood Deposits in Coastal and Fluvial Environments: Examples from Washover Fans (North Carolina, USA) and Floodplain Deposits (Mississippi, USA)

Extreme flooding from severe and prolonged meteorological events and / or overbanking rivers are some of the most deadly and expensive disasters globally, impacting millions of lives, the environment, and property. People living in vulnerable areas, such as near coasts and rivers, are the first to be impacted with effects of these flood hazards. Scientific studies and their results can aid communities and officials in planning and preparing for those flood impacts. In this three-part study, flood impacts from coastal storms in North Carolina, and flooding along the Mississippi River (MSR) in the state of Mississippi, USA are assessed from the characteristics of sand these hazards typically leave behind. The first two studies are on the barrier island segment of Pea Island, North Carolina at three localized sites. In the first, washover volumes and deposition rates along the back barrier are investigated from the washover deposits of six storms (hurricanes and nor’easters) that impacted the island from 2003 to 2019. Results showed the six storms yielded ~90,000 m3 of deposition on the three sites, an increase of 40% over a previous period at two comparable island sites. The second study employed an inverse numerical model compared with hindcast data produced from hurricanes Isabel, Irene, and Sandy, two nor’easters (2006 and 2009), and one post-Isabel field survey to reconstruct overland inundation depths produced by these storms. The reconstructed inverse model results were within ±0.8 m of the hindcast data and within ±0.1 m of the post-storm field survey observation. Since the inverse model’s results were within 1 m of the hindcast and field survey results, it was deemed acceptable for application to nor’easters impacting Pea Island. Lastly, the deposits of major floods along the MSR at the Shipland Wildlife Management Area, MS were analyzed to assess whether flood control structures implemented during the 1930s had an impact on the local floodplain. Using similar methods as in the first study, three major floods (1927, 1929, and 1937) were interpreted to have left deposits ~11.1 m thick, creating a local elevation maximum at this site as accommodation was filled by flood deposits.