| Popis: |
Globally, 40% of the population lives in coastal areas, m, often using satellite data. However, littleefforts have been undertaken to study detailed observations of channel morphology on the Amazoncoast, and its interplay with erosion and accretion is therefore not well understood.Unmanned aerial vehicles (UAV’s) combined with photogrammetric procedures have proven to be avaluable method for observing small-scale (changes in) coastal morphology, as it provides highresolution imagery and elevation data. However, research into the application of this technique inobserving coastal elevation is scarce. This thesis focusses specifically on the application of UAV photogrammetryin analysis of changes and spatial patterns in coastal erosion and accretion, and channelgeometry. This research comprises a case study on coastal change and spatial variations inmorphological features at Weg naar Zee, a coastal area in Paramaribo, Suriname, through the use ofUAV imagery. The objectives were as follows. The potential of using UAV imagery for the assessmentof coastal morphology is examined (1). Then, spatial patterns (2) and temporal changes (3) in channelgeometry, vegetation cover and elevation were analysed.Orthophotos and DEM’s were created from the UAV imagery for two locations that were 2 km apart,and for one of these locations a second dataset was made for 8 months later in time. Morphologicalunits were mapped manually based on the orthophoto and DEM. For each site, channels width, depth,W:D ratio, area and channel bed elevation and slope were derived from transects with the DEMelevation data. These geometries were compared for alongshore and cross-shore patterns anddifferences. Lastly, elevation differences between the 8-month period were derived from the DEM’s.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,namely an immature parallel channel pattern, low elevations and a small range of elevations on themudflat, lower width-to-depth ratios, less vegetation and dying vegetation, and an average high-waterline that reached all the way to the dike. The site further west of the river is more stable, with growingmangrove vegetation and a large buffer zone between the mainland dike and the average high-waterline. The channel network pattern was meandering dendritic. At this site, mangroves are planted toregenerate the vegetation, and permeable dams are constructed in the intertidal area as sediment trappingunits. After the 8-month period, the elevation of the intertidal mudflat had increased with ±0.5 meters.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 inunderstanding how and where to implement erosion mitigation strategies, it is necessary to upscale thisresearch with longer time-series and larger along shore coverage to determine which processes are atthe base of this variation. Furthermore, UAV imagery has proven to be successful in determining bothmedium-scale and small-scale morphologies and elevations. It provides a diversity of datatypes, and ithas the potential to facilitate direct erosion and accretion, and automated morphology classification. |
