Coastal Management
Data subtraction to detect changes
in GMT, the position of each point is stored in 3 columns of x, y, and z respectively,as the Universal Transverse Mercator (UTM) coordinate is applied, so points are comparable. Thus, a simple mathematical subtraction between two dataset is adopted
DEM of 2015
Morphology Changes by cross-profile comparison
Comparisons of the profiles
DEM of 2016
DEM of subtraction data
There is an obvious pair of blue and red stripes at the location of dune. Blue means height is lower at this year at the same location, red means height is higher. The profiles cut at x=2000m are shown as references to investigate the morphology change and the height difference.As we know, dune crest is the relative highest peak, and it is worth to mention that even though the 40 degree is chosen as the rotation angle, but the along-shore direction is still not so parallel with X-axis,thus, when the y axis is fixed at 180m just as the left corner plot shows, the points it records are not all peaks as dune crest but still relatively heigh. However, it shows a general trend that the majority of points distributed at y=180m is lower than last year.
So, lower height of this year's data provides two possibilities of dune move directions: landward or seaward.From the DEMs of 2015,2016 and subtraction data under UTM coordinate system, it indicates that the majority of inner land and sea surface are stable with white color, so the main changes are convergent at the dune area.Assume there are only one fore dune (crest) and second dune (crest) in the each cross-shore direction. Here list two proofs about landward movement: 1. the individual DEM of each year gives visualized proof that the primary location of dune toe contour (bottom of green region ) is moving landward from about 120m to 140m in y direction at the delta position (the tilt shape of shore make it not corresponding with right up plot);2.if we assume the dune is moving seaward, then for this ~10m movement, while the second dune is moving seaward and probably site at the origin fore dune crest, this is corresponding with the left corner figure, but if it is true then the outer side of dune (close to sea, such as the y=120 to 140m in x=2000m profile) should have a tendency that the height of this year is higher than 2015's, however, the figure gives us reverse result. Finally, we can get the conclusion that the dune is retreating landward.