Intra- and Inter-site variability of the beach dune profile and vegetation line: Is there a scale-invariant profile?

The response and recovery of foredunes to storms is an important control on barrier response to sea level rise. While field studies suggest that dune height is site-specific and dependent to varying degrees on sediment supply and transport potential, the process-based Coastal Dune Model (CDM) predicts that dune height depends on the distance of the vegetation line to the shoreline (Lveg) and that the beach-dune profile is scale-invariant. This study examines the intra- and inter-site variability of the beach-dune profile in relation to Lveg along the north shore of Prince Edward Island (PEI), Canada. A combination of LiDAR and UAV surveys of >19,000 beach-dune profiles suggest that the ratio of dune crest elevation (Cy) and distance from the shoreline above AMSL (Sx) to the Crest (Cx), is inversely related to cross-shore distance of Lveg. The tallest dunes have the steepest seaward slopes (Cy/(Cx-Sx)→0.45) and small Lveg distances controlled by the variability of the beach-dune envelope, while the shortest dunes are associated with beaches with relatively gentle slopes (Cy/(Cx-Sx)→0.01) and large Lveg distances controlled by tide and storm inundation. Comparison to previously published beach-dune profiles reveals a similar relationship between the profile and Lveg, suggesting that the morphology of the beach-dune system along the north shore of PEI and at other sites globally are reflective of their respective histories of storm activity, and do not trend towards the scale-invariant form assumed in the CDM. Further study of the contingent (or local) controls on coastal dune development and morphology are necessary to predict the evolution of coastal barriers to sea level rise and changes in storm activity.