Controls on dune scarping

Abstract

The controls that affect the degree of spatio-temporal change to foredunes following scarping are reviewed herein. As sea-levels rises and climate changes, dune scarping will become more common. Thus, it is critical to understand what factors contribute to the magnitude of scarping, and what effect this has on dune systems to better manage coastal erosion into the future. Scarping occurs when foredunes are partially eroded by waves, generally during periods of high water level. The controls on the degree and magnitude of scarping examined include water level, foredune vegetation cover and species present, plant root mass, height and volume of the foredune, the original foredune morphology, surfzone–beach type, and compaction of sediment. Water-level height and duration of high water is the most significant control as it determines the elevation at which wave action can erode the dune and, therefore, the extent of scarping and dune volumetric loss. Higher plant density, greater rooting depth, high root mass, and greater compaction aid in reducing the degree of scaping. The presence of large woody debris and wrack may also influence the degree of scarping. The effects scarping has on the morphology of a foredune after the initial erosion event can range from small changes (e.g. minor, small scarps and slight slumping), to moderate changes such as the foredune translating landwards, to large change such as the transition of an entire dune system into a new transgressive dunefield phase. A new model summarising the key controls and their relationship/significance to the magnitude and extent of scarping is presented.

Sea level rise outpaced by vertical dune toe translation on prograding coasts

“…The dune toe is a key parameter to describe the dune profile and is part of the spatially and temporally varying beach-dune system typically moving seawards during accretionary periods, and landwards during storms and erosion events 10 – 13 . With SLR, the vertical extent of marine processes is altered, which influences the sediment budget of sandy beaches.…”

A Clustering Approach for Predicting Dune Morphodynamic Response to Storms Using Typological Coastal Profiles: A Case Study at the Dutch Coast

“…Conventionally, forecasts and assessments are performed on individual profiles because the intensity of large-scale erosion is not only associated with the offshore characteristics of a storm event such as the maximum storm surge, maximum wave height and duration, but also on pre-storm dune and foreshore morphology and their interactions with the forcing (Houser et al, 2008;Masselink et al, 2016;Athanasiou et al, 2018;Davidson et al, 2020). Exploration and understanding of these dependencies require the availability of high-quality observations of coastal change with pre-and post-storm surveys over large coastal areas, which are quite challenging to obtain.…”

The relative influence of dune aspect ratio and beach width on dune erosion as a function of storm duration and surge level

“…In a study on the geomorphic effects of sand fencing, Itzkin et al (2020a) demonstrated that foredunes are lower in elevation in areas where sand fences are constructed but that the dune system overall is substantially wider than foredunes in areas without sand fences. Other management actions, such as allowing vehicles to drive on beaches and beach raking, can also generate trade-offs between dune growth and coastal protection (Defeo et al, 2009). In a study on the effects of dune grass removal to restore Western snowy plover habitats in the PNW, Biel et al (2017) used XBeach (Roelvink et al, 2009) to explore dune erosion and found that where beachgrasses were removed, dunes maintained a lower elevation and were predicted to be more vulnerable to erosion compared to foredunes where beachgrasses were not removed and grew to a stable elevation.…”