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.