Assessing Natural and Mechanical Dune Performance in a Post-Hurricane Environment

Abstract

The purpose of this study is to document the geomorphic evolution of a mechanical dune over approximately one year following its installation and compare it to the recovery of a natural dune following the impact of Hurricane Matthew (2016). During the study period, the dunes’ integrity was tested by wave and wind events, including king tides, and a second hurricane (Irma, 2017), at the end of the study period. Prior to the impact of the second hurricane, the volumetric increase of the mechanical and natural dune was 32% and 75%, respectively, suggesting that scraping alone is not the optimal protection method. If scraping is employed, we advocate that the dune should be augmented by planting. Ideally, the storm-impacted dune should naturally recover. Post-storm vegetation regrowth was lower around the mechanical dune, which encouraged aeolian transport and dune deflation. Hurricane Irma, an extreme forcing event, substantially impacted the dunes. The natural dune was scarped and the mechanical dune was overtopped; the system was essentially left homogeneous following the hurricane. The results from this study question the current practice of sand scraping along the South Carolina coast, which occurs post-storm, emplacement along the former primary dune line, and does not include the planting of vegetation.

Application of the Saffir-Simpson Hurricane Wind Scale to Assess Sand Dune Response to Tropical Storms

“…The 2018 nourishment cost $13.5 million, spanned ~3.8 km, and comprised 1.282 million m 3 of sand [38]. Following hurricanes, it is common on this island to scrape the beach, which is moving sand from the foreshore to the pre-storm foredune line (c.f., [39]). Historically, the dunes on the SW end of the island had heights that nearly doubled those found in the NE, at approximately 1.5 and 0.7 m, respectively [35].…”

Using High-Spatial Resolution UAV-Derived Data to Evaluate Vegetation and Geomorphological Changes on a Dune Field Involved in a Restoration Endeavour

“…The natural morphology of this dune is also influenced on the seaward side by sand mounds ("winter dunes" or "artificial dunes") artificially built by beach scraping and sand nourishment, accumulating sand taken from adjacent zones [56,57], with the aim of protecting touristic structures (beach huts, also locally called "bagni") during the winter season. The dune presents a "barchanoidal" shape, influenced by the artificial dune accumulation that is carried out every winter [58]. Despite all these artificial constrictions, the dune ridge preserves its natural dynamics, exceeding in some parts an elevation of 5.80 m above m.s.l.…”

Importance of Protection Service Against Erosion and Storm Events Provided by Coastal Ecosystems Under Climate Change Scenarios

“…In addition, the high numbers of people that use the beaches increase the trampling damage to the dune system, promoting additional stresses to the dune system and the degradation of the dune vegetation, and increasing the risk of further dune erosion. Vegetation plays a key role in the maintenance of the different coastal ecosystems, with their role in the recovery process been demonstrated in studies based on post storm surveys (Ellis and Román-Rivera, 2019). Vegetated dune systems reduce water flow velocity, lessening the impacts of storm surge, and wave forces to coastal fronts.…”