Abstract. We describe a new algorithm that automatically delineates
the cliff top and toe of a cliffed coastline from a digital elevation model
(DEM). The algorithm builds upon existing methods but is specifically
designed to resolve very irregular planform coastlines with many bays and
capes, such as parts of the coastline of Great Britain. The algorithm
automatically and sequentially delineates and smooths shoreline vectors,
generates orthogonal transects and elevation profiles with a minimum spacing
equal to the DEM resolution, and extracts the position and elevation of the
cliff top and toe. Outputs include the non-smoothed raster and
smoothed vector coastlines, normals to the coastline (as vector shape files),
xyz profiles (as comma-separated-value, CSV, files), and the cliff top and toe (as
point shape files). The algorithm also automatically assesses the quality of
the profile and omits low-quality profiles (i.e. extraction of cliff top and
toe is not possible). The performance of the proposed algorithm is compared
with an existing method, which was not specifically designed for very
irregular coastlines, and to manually digitized boundaries by numerous
professionals. Also, we assess the reproducibility of the results using
different DEM resolutions (5, 10 and 50 m), different user-defined
parameter sets related to the degree of coastline smoothing, and the
threshold used to identify the cliff top and toe. The model output
sensitivity is found to be smaller than the manually digitized uncertainty. The code and
a manual are publicly available on a GitHub repository.
A detailed study is presented of the tidal constituents for Livingston and Deception Islands (Antarctica) obtained at the LIVMAR and DECMAR tide gauge stations. Data were acquired with tide gauge pressure sensors, and calculated from a long time series of 798 days of data-logging, using the least-squares harmonic estimation method. The results show an improvement over previous results in the region. Seventy tidal constituents were obtained, of which 19 were the most representative with amplitudes greater than 1 cm and a contribution of 93% of the wave energy. In both stations, it was confirmed that the tides are mixed, with a semi-diurnal behavior. The tidal gauge benchmarks (TGBMs) were linked to vertical and horizontal Antarctic Geodetic Networks, which provides a very important contribution for geodetic, oceanographic and hydrographic studies in the area.
A methodology for monitoring the behaviour and size of sand after a beach nourishment process is presented herein. Four sampling campaigns (before and just after the nourishment, after six months and one year later) were performed on four beaches of the Gulf of Cadiz (Spain). D50 and sorting size parameters were analysed. Among the results, it should be noted that differences of up to 20% between native and nourished sand values disappear only one year after the nourishment.
Abstract. We describe a new algorithm that automatically delineates the cliff top and toe of a cliffed coastline from a Digital Elevation Model (DEM). The algorithm builds upon existing methods but is specifically designed to resolve very irregular 15 planform coastlines with many bays and capes, such as parts of the coastline of Great Britain. The algorithm automatically and sequentially delineates and smooth shoreline vectors, generates orthogonal transects and elevation profiles with a minimum spacing equal to the DEM resolution, and extracts the position and elevation of the cliff top and toe. Outputs include the nonsmoothed-raster and smoothed-vector coastline, normals to the coastline-(as vector shapefiles), xyz profiles (as commaseparated-value files), and the cliff top and toe (as point shape files). The algorithm also automatically assesses the quality of 20 the profile and omits low-quality profiles (i.e. extraction of cliff top and toe is not possible). The performance of the proposed algorithm is compared with an existing method, which was not specifically designed for very irregular coastlines, and to handdigitized boundaries by numerous professionals. Also we assess the reproducibility of the results using different DEM resolutions (5 m, 10 m and 50 m), different user defined parameter-sets related to the degree of coastline smoothing, and the threshold used to identify the cliff top and toe. The model output sensitivity is found to be smaller than hand-digitized 25 uncertainty. Code and a manual are publicly available on a github repository.
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