Annual to decadal morphodynamics of the foredune system at Greenwich Dunes, Prince Edward Island, Canada

Abstract

The purpose of this study was to quantify relationships between season, sediment availability, sediment transport pathways, and beach/foredune morphology at Greenwich Dunes, PEI. This was done for periods ranging from a few days to multiple decades using erosion pins, bedframe measurements, annual surveys, and digital photogrammetry using historical aerial photographs. The relative significance of seasonal/annual processes versus response of the foredune system to broader geomorphic controls (e.g. relative sea level rise, storms, etc.) was also assessed.The data show that there are clear seasonal differences in the patterns of sand supply from the beach to the foredune at Greenwich and that there are differences in sediment supply to the foredune between the east and west reaches of the study area, resulting in ongoing differences in foredune morphology. They also demonstrate that models that incorporate wind climate alone, or even models that include other factors like beach moisture, would not be able to predict the amount of sediment movement from the beach to the foredune in this environment unless there were some way to parameterize system morphology, especially the presence or absence of a dune ramp.Finally, the data suggest that the foredune can migrate landward while maintaining its form via transfers of sediment from the stoss slope, over the crest, and onto the lee slope. Although the rate of foredune development or recovery after disturbance changes over time due to morphological feedback, the overall decadal evolution of the foredune system at Greenwich is consistent with, and supports, the Davidson-Arnott (2005) conceptual model of dune transgression under rising sea level.

Vegetation and sedimentation on coastal foredunes

“…Earlier measurements of sand deposition on incipient dunes (Hesp, 1983(Hesp, , 1988 and established dunes (Arens, 1996;Arens et al, 2001b;Ollerhead et al, 2013;Petersen et al, 2011;Sarre, 1989) on timescales of days to months showed how the vegetation limit and density influence sedimentation. In general, sedimentation across foredunes follows a distinct profile, where sedimentation increases rapidly past the vegetation line, reaches a maximum at some distance from this line and decreases again farther landward.…”

“…The turbulence induced by vegetation and the upward velocities caused by the dune slope may also initiate transport of grains in suspension (Arens, 1996;Arens et al, 2002). These grains may travel farther up the dune as they pass over the vegetation canopy, leading to deposition farther up the slope and near the crest (Arens, 1996;Arens et al, 1995;Hesp, 2002;Ollerhead et al, 2013;Petersen et al, 2011). Additionally, storm winds may bend the foliage into their streamlines, reducing roughness and creating a secondary surface for saltation, allowing sand grains to proceed considerable distances downwind ('modified saltation' of Hesp et al (2009) and Petersen et al (2011)).…”

“…General profiles of sedimentation have been obtained from measurements of daily to monthly elevation change on vegetated foredunes (e.g. Arens, 1996;Christiansen and DavidsonArnott, 2004;Ollerhead et al, 2013;Sarre, 1989). These show that maximum sand deposition occurs near the seaward edge of vegetation, decreasing with distance upslope.…”

Flow deflection over a foredune

“…Davidson-Arnott et al, 2003Walker et al, 2003Walker et al, , 2006Hesp et al, 2005Hesp et al, , 2009Hesp et al, , 2013Bauer et al, 2009Bauer et al, , 2012Delgado-Fernandez and Davidson-Arnott, 2009;Hesp and Walker, 2012;Chapman et al, 2012Chapman et al, , 2013DelgadoFernandez et al, 2013;Ollerhead et al, 2013). The foredune crest is ~10 m above mean water level with a steep stoss slope (20°-25°) and an ENE-WSW crestline orientation.…”

The Usumacinta–Grijalva beach-ridge plain in southern Mexico: a high-resolution archive of river discharge and precipitation

“…Rates are much higher than the average long-term aeolian accretion rates of 0.1-0.6 m 3 m −1 yr −1 for three beach-ridge plains in south-eastern Australia (Oliver, 2016) but are relative low compared to average long-term accretion rates for larger-scale foredunes, which roughly vary between 5 and 20 m 3 m −1 yr −1 (e.g. Aagaard et al, 2004;Ollerhead et al, 2013;Keijsers et al, 2014).…”