New Insights on Coastal Foredune Growth: The Relative Contributions of Marine and Aeolian Processes

Abstract

Coastal foredune growth is typically associated with aeolian sediment transport processes, while foredune erosion is associated with destructive marine processes. New data sets collected at a high energy, dissipative beach suggest that total water levels in the collision regime can cause dunes to accrete—requiring a paradigm shift away from considering collisional wave impacts as unconditionally erosional. From morphologic change data sets, it is estimated that marine processes explain between 9% and 38% of annual dune growth with aeolian processes accounting for the remaining 62% to 91%. The largest wind‐driven dune growth occurs during the winter, in response to high wind velocities, but out of phase with summertime beach growth via intertidal sandbar welding. The lack of synchronization between maximum beach sediment supply and wind‐driven dune growth indicates that aeolian transport at this site is primarily transport, rather than supply, limited, likely due to a lack of fetch limitations.

Coastal ridge constructive processes at a multi‐decadal scale in Barreta Island (southern Portugal)

“…Dougherty, 2014;Oliver et al, 2017;Fruergaard et al, 2019). In Barreta, moderate wave conditions are noted during the formation of Units 3 and 5, conditions that could have promoted the welding of submerged sand bars to the coast, as observed in many other coastal areas in the world (Aagaard et al, 2004;Bendixen et al, 2013;Cohn et al, 2018). The augmented progradation of these periods could be, partly, related to such events.…”

“…Winds, assisted by vegetation as trapping agents, and sediment availability, are major drivers of ridge aggradation. Moreover, aeolian events may coincide with wave storms, which translates to a reduction of the potential for sediment transport due to a reduction of the width of the emerged beach (Davidson-Arnottt and Lawt, 1996;Bauer and Davidson-Arnott, 2003;de Vries et al, 2014;Cohn et al, 2018). For the particular case of the barrier islands within the western flank of the Ria Formosa, the mean grain size corresponds to rather coarse sands (Pilkey et al, 1989;Costas et al, 2018), thereby limiting the potential contribution of local winds.…”

“…Initially, these landforms are believed to undergo a phase of construction by purely marine processes (Davies, 1957;Bird, 1960;Psuty, 1965), but as they grow above a certain threshold height and distance from the sea, vegetation is able to develop and survive for longer time periods and therefore, aeolian accumulation processes begin to dominate (Hesp, 1984;Costas et al, 2019). This suggests a rather complex genesis, resulting from different processes that work at different elevations and at distinct timescales, but with a transitional area where both building mechanisms act and imprint their signal (Bristow et al, 2000;Costas et al, 2016;Cohn et al, 2018). In fact, Cohn et al (2018) seasonally monitored cross-shore coastal barrier profiles and showed that, although winter winds assisted ridge growth within the transitional dune-beach region, waves also had a significant contribution to the vertical growth of this area, by transferring sand up to the maximum extent of the swash, even under collision regimes.…”

“…This suggests a rather complex genesis, resulting from different processes that work at different elevations and at distinct timescales, but with a transitional area where both building mechanisms act and imprint their signal (Bristow et al, 2000;Costas et al, 2016;Cohn et al, 2018). In fact, Cohn et al (2018) seasonally monitored cross-shore coastal barrier profiles and showed that, although winter winds assisted ridge growth within the transitional dune-beach region, waves also had a significant contribution to the vertical growth of this area, by transferring sand up to the maximum extent of the swash, even under collision regimes. The ambiguity of the relative importance of the processes involved on the generation and growth of ridges has opened a discussion regarding the adequacy of the used terminology (Hesp, 1984;Taylor and Stone, 1996;Otvos, 2000;Hesp et al, 2005).…”

Terrestrial LiDAR monitoring of coastal foredune evolution in managed and unmanaged systems

“…To quantify hydrodynamic forcing during the study, H s and T were used to compute total wave power (kW m −1 ) for each survey interval ( P I ) with the following equation: Wave power was used as a proxy for offshore wave energy, where calm periods are generally associated with accretional conditions and higher wave power intervals are associated with erosive conditions (e.g. Yates et al ., ; Davidson et al ., ; Cohn et al ., ).…”