Abstract
The beaches of the Cantabrian coast (northern Spain) are exposed to strong winter storms that cause the coastline to recede. In this article, the coastal retreat of the Gerra beach (Cantabria) is analyzed through a diachronic study using the following different geomatic techniques: orthophotography of the year 1956; photogrammetric flights from 2001, 2005, 2010, 2014, 2017; Light Detection and Ranging (LiDAR) survey from August 2012; Unmanned Aerial Vehicle (UAV) survey from November 2018; and terrestrial laser scanner (TLS) through two dates per year (spring and fall) from April 2012 to April 2020. With the 17 observations of TLS, differences in volume of the beach and the sea cliff are determined during the winter (November–April) and summer (May–October) periods, searching their relationship with the storms in this eight-year period (2012–2020). From the results of this investigation it can be concluded that the retreat of the base of the cliff is insignificant, but this is not the case for the top of the cliff and for the existing beaches in the Cantabrian Sea where the retreat is evident. The retreat of the cliff top line in Gerra beach, between 1956 and 2020 has shown values greater than 40 m. The retreat in other beaches of the Cantabrian Sea, in the same period, has been more than 200 m. With our measurements, investigations carried out on the retreat of the cliffs on the Atlantic coast have been reinforced, where the diversity of the cliff lithology and the aggressive action of the sea (storms) have been responsible for the active erosion on the face cliff. In addition, this research applied geomatic techniques that have appeared commercially during the period (1956–2020), such as aerial photogrammetry, TLS, LiDAR, and UAV and analyzed the results to determine the precision that could be obtained with each method for its application to similar geomorphological structures.
Highlights
Coastal changes, at a geological scale, are very slow and the morphology of beaches and cliffs retain features of earlier sea levels, but there are changes, at a human scale, that can be detected along the coastline
Two main findings from the study of sea cliff evolution highlight the temporal change in cliff top line recession mode, and the effect of beach sediment at the cliff toe on cliff erosion. [1,2] pointed out that our ability to quantify sea cliff retreat rates and their variability through time was the first step to understanding the sea cliff erosion processes and the responses to environmental and climate changes
The precisions of the different techniques for this purpose, and on the other hand, the receding rhythms of the cliff coast. This information can be applied to other sections of the Cantabrian coast for empiric and numerical models of cliff retreat, considering factors such as waves, currents, beach and cliff location, onshore morphology, intensity and frequency of storms, wind directions, rainfall, geological structure, sedimentary deposits, lithology, geomorphic inheritance and present day processes, and human use on the Cantabrian or Atlantic coast, both located in a temperate oceanic climate
Summary
At a geological scale, are very slow and the morphology of beaches and cliffs retain features of earlier sea levels, but there are changes, at a human scale, that can be detected along the coastline. [1,2] pointed out that our ability to quantify sea cliff retreat rates and their variability through time was the first step to understanding the sea cliff erosion processes and the responses to environmental and climate changes. Measures on sea cliff recession show distinct behaviors at different geographical locations and geological structures, and the spatial variations of the cliff retreat rates have been explained by changes in the geological structure, cliff collapses, or anthropogenic obstacles [3,4]. In the Atlantic coast, the retreat rates obtained from historical maps, aerial photographs, recent TLS and photogrammetry monitoring were −10 to −50 cm/yr [3]. The behavior of cliffs characterized by landslides on beaches are related to several factors, depending on climate, structural geology, lithology, and sea exposure. On European Atlantic coasts, they are under the dominant influence of precipitation and the evolution of the groundwater level [3]
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