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

Abstract

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.

Spatial Variability of Coastal Foredune Evolution, Part A: Timescales of Months to Years

“…The high-resolution terrestrial lidar measurements collected in this study demonstrate the important role of dune grasses on trapping wind-blown sediment and its potential beneficial use in dune management. Consistent with numerous other works (e.g., [65,[88][89][90]), grass planting may be an effective measure in limiting aeolian transport to homes adjacent to the beach and enhancing coastal resilience to flooding by promoting natural dune growth (Figures 9, 10 and 12). However, morphological feedbacks similarly have an important role in influencing dune dynamics ( Figures 7, 8 and 13).…”

“…Except in the presence of very dense vegetation, lidar-based systems can obtain bed points through the vegetation canopy, and therefore do not suffer from the same challenges as UAS technologies. Thus, this work demonstrates that high-frequency terrestrial lidar scanning approaches, which can be collected in either stationary [52,53,55,56,65] or mobile [54,87] setups, provide data at resolutions suitable for advancing our understanding of coastal morphodynamics and for improving coastal management approaches.…”

“…Dune morphology was measured at the northern and southern dune sites at approximately monthly intervals (gray dashed lines, Figure 3) from December 2014 through December 2017 using a VZ-2000 terrestrial lidar scanner, manufactured by Riegl Laser Measurement Systems, Riedenburgstrasse, Austria. These data were collected and processed following the same methodology described by Conery et al [65]. The scanner was mounted on a tripod at five locations within each study site-three on the beach, and two behind the dune (as an example, colors in Step 1, Figure 4 show data from individual scans).…”

Dynamic restoration and the impact of native versus invasive vegetation on coastal foredune morphodynamics, Lanphere Dunes, California, USA

“…Repeat‐collection TLS surveys are often used to quantify and interpret coastal change (e.g. Conery et al, 2019; Feagin et al, 2014; Grilliot et al, 2019; Young et al, 2021). This study provides another example of the application of TLS for assessing coastal foredune change, while also assessing vegetation development.…”

Evaluating Collection Parameters for Mobile Lidar Surveys in Vegetated Beach-Dune Settings

“…Past research in coastal systems has used MTL to monitor beach nourishment performance (e.g., Pietro et al 2008), cliff erosion, and regional scale subaerial beach and dune morphology (Donker et al 2018;Spore et al 2019). Fixed station (tripod-based) terrestrial lidar scanning (FTL) has also widely been utilized for providing valuable new insights on coastal dune dynamics on sub-meter spatial scales and at time scales of months to years (Brodie et al 2019;Conery et al 2019;Danchenkov et al 2019). However, the ability to accurately quantify dune evolution at these same temporal scales utilizing MTL systems, which can cover much larger spatial extents than FTL scanning, would enable significant advancements in the ability to effectively monitor coastal dune evolution at sub-decimeter scale.…”