Beach–dune sediment budgets and dune morphodynamics following coastal dune restoration, Wickaninnish Dunes, Canada

Coastal dunes provide essential protection for infrastructure in developed regions, acting as the first line of defence against ocean‐side flooding. Quantifying dune erosion, growth and recovery from storms is critical from management, resiliency and engineering with nature perspectives. This study utilizes 22 months of high‐resolution terrestrial LiDAR (Riegl VZ‐2000) observations to investigate the impact of management, anthropogenic modifications and four named storms on dune morphological evolution along ~100 m of an open‐coast, recently nourished beach in Nags Head, NC. The influences of specific management strategies – such as fencing and plantings – were evaluated by comparing these to the morphologic response at an unmanaged control site at the USACE Field Research Facility (FRF) in Duck, NC (33 km to the north), which experienced similar environmental forcings. Various beach‐dune morphological parameters were extracted (e.g. backshore‐dune volume) and compared with aeolian and hydrodynamic forcing metrics between each survey interval. The results show that LiDAR is a useful tool for quantifying complex dune evolution over fine spatial and temporal scales. Under similar forcings, the managed dune grew 1.7 times faster than the unmanaged dune, due to a larger sediment supply and enhanced capture through fencing, plantings and walkovers. These factors at the managed site contributed to the welding of the incipient dune to the primary foredune over a short period of less than a year, which has been observed to take up to decades in natural systems. Storm events caused alongshore variable dune erosion primarily to the incipient dune, yet also caused significant accretion, particularly along the crest at the managed site, resulting in net dune growth. Traditional empirical Bagnold equations correlated with observed trends of backshore‐dune growth but overpredicted magnitudes. This is likely because these formulations do not encompass supply‐limiting factors and erosional processes. © 2019 John Wiley & Sons, Ltd.

Section: Introductionmentioning

confidence: 98%

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

Conery

Brodie

Spore

et al. 2020

“…While sediment budget approaches are conceptually simple, it has long been recognized that the actual controls on sediment supply to and from the foredune are numerous and complex (de Vries et al ., ; Walker et al ., ). Conceptual models of foredune evolution have sought to relate morphological response to gradients in specific controls such as sediment supply and littoral drift (Psuty, , ; Davidson‐Arnott and Law, ; Miot da Silva and Hesp, ; Heathfield and Walker, ), beach morphodynamics (Short and Hesp, ; Sherman and Lyons, ; Hesp and Smyth, ), storm frequency and magnitude (Sallenger, ; Houser and Hamilton, ; Splinter and Palmsten, ), vegetation type and cover (Hesp, , ; Hilton et al ., ; Baas and Nield, ; Darke et al ., ), and changes in sea level (Olson, ; Sherman and Bauer, ; Davidson‐Arnott, ). An increasing number of computer simulation models have been proposed that incorporate some of these controls, but typically they focus on equilibrium transport systems and the feedback that the evolving morphology exerts on the wind and transport dynamics (e.g.…”

Section: Introductionmentioning

confidence: 99%

Sediment budget controls on foredune height: Comparing simulation model results with field data

Davidson‐Arnott

Hesp

Ollerhead

et al. 2018

The form, height and volume of coastal foredunes reflects the long‐term interaction of a suite of nearshore and aeolian processes that control the amount of sand delivered to the foredune from the beach versus the amount removed or carried inland. In this paper, the morphological evolution of more than six decades is used to inform the development of a simple computer model that simulates foredune growth. The suggestion by others that increased steepness of the seaward slope will retard sediment supply from the beach to the foredune due to development of a flow stagnation zone in front of the foredune, hence limiting foredune growth, was examined. Our long‐term data demonstrate that sediment can be transferred from the beach to the foredune, even with a steep foredune stoss slope, primarily because much of the sediment transfer takes place under oblique rather than onshore winds. During such conditions, the apparent aspect ratio of the dune to the oncoming flow is less steep and conditions are not as favourable for the formation of a stagnation zone. The model shows that the rate of growth in foredune height varies as a function of sediment input from the beach and erosion due to storm events, as expected, but it also demonstrates that the rate of growth in foredune height per unit volume increase will decrease over time, which gives the perception of an equilibrium height having been reached asymptotically. As the foredune grows in size, an increasing volume of sediment is needed to yield a unit increase in height, therefore the apparent growth rate appears to slow. Copyright © 2018 John Wiley & Sons, Ltd.

“…Sediment is lost from the dune through access gaps due to the absence of vegetation and flatter slopes, but this can be limited by restricting access, creating elevated walkovers or planting of vegetation. The type of vegetation can also influence the shape and mobility of a dune, while the absence or purposeful removal of invasive vegetation can significantly increase sediment transport and dune mobility (Darke et al ., , this issue). In addition to demonstrating the potential for high‐resolution surveying to monitor the beach–dune sediment budget, the study provides important insight on treating invasive species to improve ecological function without compromising the protection afforded by the dune.…”

Section: Introductionmentioning

confidence: 93%

Barrier response to sea level rise and storms

Houser

2018

This commentary brings together, as a Virtual Special Issue, several recent papers in Earth Surface Processes and Landforms that improve our understanding of coastal barrier response to relative sea level rise and a change in the frequency and/or magnitude of storm events. The ability to predict barrier response depends on the ability to quantify the spatial and temporal scales of sediment exchange amongst the nearshore, beach and dune. This exchange controls the height of the dune, which in turn determines the transfer of sediment to the backbarrier through washover and/or blowouts. The papers in this issue provide new insight on beach–dune interaction and the importance of this interaction to long‐term barrier evolution across a range of sites and scales, and how active management can influence this interaction and alter barrier response. Copyright © 2018 John Wiley & Sons, Ltd.