Assessment of the physical vulnerability to erosion and flooding in a sheltered coastal sector: Florianópolis Bay, Brazil

Abstract

This study aims to characterize the physical vulnerability of the western coast of Santa Catarina Island by applying the Smartline methodology. Erosion and flooding processes can endanger the installed human infrastructure in the coastal zone, with the degree of vulnerability of a given site being dependent on its natural characteristics, or even due to changes induced by human action. The methodology applied in this research adopts a multiscale approach and considers, using coastline segmentation, the specificities of the analyzed coastal sectors. Each identified segment receives a classification regarding its physical vulnerability, resulting from the integration of several attributes, which must be selected according to the coastal hazard that one wishes to represent. In the analysis, three distinct levels of physical support and behavior of the coastal processes are considered. The first-order attributes are structural, and their characteristics are broad; the second-order ones are transitional between structural and dynamic and, the third-order attributes are dynamic, with specific characteristics. The methodology was applied on the west coast of Santa Catarina Island, a sector sheltered from oceanic waves, characterizing a low energy environment. Eight descriptors were selected for erosion and coastal flooding, these being: “geology” having two classes, distributed along 12 segments and “geomorphology”, three classes in eight segments, both of which were considered first-order variables. “Average astronomical tide current speed” (five classes in 15 segments), “average backshore height” (four classes in 20 segments), and “degree of exposure to wind waves” (five classes in 28 segments) compose the second order, while “backshore features” (seven classes in 28 segments), “grain size” (five classes in 26 segments) and “beach face slope” (three classes in 30 segments) describe third-order processes. By the integration of first-order attributes an Indicative Map of Vulnerability to Erosion and Flooding was generated, which classified the coast into “very Low”, “low”, “moderate”, and “high” vulnerability classes. As a final result of the analytical process the coastline, first-, second-, and third-order attributes were mathematically integrated by means of spatial analysis techniques, with the studied coastline represented as a segmented line according to the different classes of attributed physical vulnerability, highlighting the sectors with the most propensity to erosion and flooding. This Map of Physical Vulnerability to Erosion and Flood indicated that the west coast of Santa Catarina Island can be divided into sectors of low and moderate vulnerability in similar proportions, with occasional occurrences of high vulnerability in specific sectors.