Exploring the contributions of vegetation and dune size to early dune development using unmanned aerial vehicle (UAV) imaging

Abstract

Abstract. Dune development along highly dynamic land-sea boundaries is the result of interaction between vegetation and dune size with sedimentation and erosion processes. Disentangling the contribution of vegetation characteristics from that of dune size would improve predictions of nebkha dune development under a changing climate, but has proven difficult due to the scarcity of spatially continuous monitoring data.This study explored the contributions of vegetation and dune size to dune development for locations differing in shelter from the sea. We monitored a natural nebkha dune field of 8 ha, along the coast of the island Texel, the Netherlands, for 1 year using an unmanned aerial vehicle (UAV) with camera. After constructing a digital surface model and orthomosaic we derived for each dune (1) vegetation characteristics (species composition, vegetation density, and maximum vegetation height), (2) dune size (dune volume, area, and maximum height), (3) degree of shelter (proximity to other nebkha dunes and the sheltering by the foredune). Changes in dune volume over summer and winter were related to vegetation, dune size and degree of shelter.We found that a positive change in dune volume (dune growth) was linearly related to initial dune volume over summer but not over winter. Big dunes accumulated more sand than small dunes due to their larger surface area. Exposed dunes increased more in volume (0.81 % per dune per week) than sheltered dunes (0.2 % per dune per week) over summer, while the opposite occurred over winter. Vegetation characteristics did not significantly affect dune growth in summer, but did significantly affect dune growth in winter. Over winter, dunes dominated by Ammophila arenaria, a grass species with high vegetation density throughout the year, increased more in volume than dunes dominated by Elytrigia juncea, a grass species with lower vegetation density (0.43 vs. 0.42 (m 3 m −3 ) week −1 ). The effect of species was irrespective of dune size or distance to the sea.Our results show that dune growth in summer is mainly determined by dune size, whereas in winter dune growth was determined by vegetation type. In our study area the growth of exposed dunes was likely restricted by storm erosion, whereas growth of sheltered dunes was restricted by sand supply. Our results can be used to improve models predicting coastal dune development.

Biogeomorphological responses of nebkhas to historical long-term land uses in an arid coastal aeolian sedimentary system

“…Crop cultivation ceased in the 1960s, and the period of time that has passed since then may have enabled the recovery of the corresponding plots. This recovery may also be due to the greater sand supply of the dunes, a fundamental factor in dune size (Davidson-Arnott and Law, 1990), and not to exposure as detected by van Puijenbroek et al (2017), because in this case the aerodrome and aggregate extraction areas are more exposed. Perhaps in the case of El Médano, exposure is not significant because there are no seasonal changes throughout the year (unlike temperate regions), and the main reason for recovery is sand supply because its origin is a mixture of inland sources (local ravines, with rainfall) and marine sources (practically all year).…”

“…This causes exposed nebkhas to present a higher overall growth compared to protected (i.e. inland) nebkhas (van Puijenbroek et al, 2017).…”

Accommodation space indicates dune development potential along an urbanized and frequently nourished coastline

“…6c suggests that the unnourished northern part of the Delfland coastline supports a higher potential for dune development compared to the nourished southern coastline. In part this may be due to the fact that the Delfland coast is characterized by a net northward sediment transport regime (Van Rijn, 1997), which is reflected in the sand-feeding budget of the Zandmotor. In the first 18 months after its completion, De Schipper et al (2016) for example show that up to 40 % more sand of Zandmotor was transported in a northward direction rather than southward towards Rotterdam harbor.…”

UAV Photogrammetry and Ground Surveys as a Mapping Tool for Quickly Monitoring Shoreline and Beach Changes

“…The geomatic surveying methods, such as aero photogrammetric surveys [7,8], unmanned aerial vehicle (UAV) [9][10][11][12][13][14][15], remote sensing with satellite images [12,16], airborne light detection and ranging (LiDAR) [17][18][19][20][21][22], synthetic aperture radar (SAR) [23,24], video systems [25][26][27][28][29] are widespread techniques to measure wide areas, generate digital terrain models (DTMs) and maps, and to quantify coastal changes by multi-temporal comparisons.…”