SPATIAL VARIATION AT THE SURINAME COAST: Deriving alongshore and cross-shore patterns in tidal channel geometry, elevation and vegetation from UAV imagery
Creators: name: Deggeller, Tessa
name: Nijland, Wiebe
name: De Vries, Job
name: De Jong, Steven
Publisher: name: figshare
Year: 2021
Subjects: subject: 49999 Earth Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences

description: Globally, 40% of the population lives in coastal areas, m, often using satellite data. However, little<br>efforts have been undertaken to study detailed observations of channel morphology on the Amazon<br>coast, and its interplay with erosion and accretion is therefore not well understood.<br>Unmanned aerial vehicles (UAV’s) combined with photogrammetric procedures have proven to be a<br>valuable method for observing small-scale (changes in) coastal morphology, as it provides high<br>resolution imagery and elevation data. However, research into the application of this technique in<br>observing coastal elevation is scarce. This thesis focusses specifically on the application of UAV photogrammetry<br>in analysis of changes and spatial patterns in coastal erosion and accretion, and channel<br>geometry. This research comprises a case study on coastal change and spatial variations in<br>morphological features at Weg naar Zee, a coastal area in Paramaribo, Suriname, through the use of<br>UAV imagery. The objectives were as follows. The potential of using UAV imagery for the assessment<br>of coastal morphology is examined (1). Then, spatial patterns (2) and temporal changes (3) in channel<br>geometry, vegetation cover and elevation were analysed.<br>Orthophotos and DEM’s were created from the UAV imagery for two locations that were 2 km apart,<br>and for one of these locations a second dataset was made for 8 months later in time. Morphological<br>units were mapped manually based on the orthophoto and DEM. For each site, channels width, depth,<br>W:D ratio, area and channel bed elevation and slope were derived from transects with the DEM<br>elevation data. These geometries were compared for alongshore and cross-shore patterns and<br>differences. Lastly, elevation differences between the 8-month period were derived from the DEM’s.<br><br>Significant differences were visible despite the small spatial scale and short time period. The site closestto the river is bounded by dikes on the coastal side and a cross-shore levee. It showed signs of erosion,<br>namely an immature parallel channel pattern, low elevations and a small range of elevations on the<br>mudflat, lower width-to-depth ratios, less vegetation and dying vegetation, and an average high-water<br>line that reached all the way to the dike. The site further west of the river is more stable, with growing<br>mangrove vegetation and a large buffer zone between the mainland dike and the average high-water<br>line. The channel network pattern was meandering dendritic. At this site, mangroves are planted to<br>regenerate the vegetation, and permeable dams are constructed in the intertidal area as sediment trapping<br>units. After the 8-month period, the elevation of the intertidal mudflat had increased with ±0.5 meters.<br><br>This research has sketched a wide variety of spatial variations in morphology and coastal behaviour thatcan occur on a small scale in cross-shore and alongshore direction. As this local variation is critical in<br>understanding how and where to implement erosion mitigation strategies, it is necessary to upscale this<br>research with longer time-series and larger along shore coverage to determine which processes are at<br>the base of this variation. Furthermore, UAV imagery has proven to be successful in determining both<br>medium-scale and small-scale morphologies and elevations. It provides a diversity of datatypes, and it<br>has the potential to facilitate direct erosion and accretion, and automated morphology classification.