Coastal resilience potential as a coefficient of the coastal erosion risk assessment, and the management of risk areas via nature-based solutions

Résumé

Climate change has now become a global problem since the level of awareness of civil society has grown. Even non-professionals have understood that this phenomenon is strongly influenced by human activities and by local or specific dynamics, which exacerbate its effects, especially in the case of coastal environment conservation. Coastal erosion is a natural process that is exacerbated by climate change and is considered a natural hazard since it threatens the safety of humans and their properties. As with other natural hazards, such as fire and hydraulic, the risk of coastal erosion is mainly driven by urban spreading and inadequate land management. There are numerous proposals in the scientific literature based on good practices, guidelines and studies on the assessment and management of coastal erosion to solve the problem. However, coasts around the world are still experiencing significant imbalances, and future forecasts on this issue are even more pessimistic. On a technical level, numerous solutions have been tested in recent decades. Unfortunately, these alternatives have been fundamentally oriented towards the construction of hard coastal engineering structures, which instead of solving the problem, on many occasions have created new phenomena of instability such as the generation of coastal narrowing and the translation of erosive phenomena along the coast. Solutions were proposed and tested considerably, during the last century; almost everywhere they comprised hard structures of coastal engineering that instead of solving the problem, created new instabilities, such as coastal squeezing and erosive shifting. These consequences, and the trends observable on the world's shores, have required the conversion of coastal engineering into a more sustainable discipline that strongly supports natural resilience. More generally, resilience represents the ability of natural systems, such as a coast, a community or an individual, to cope and respond to a traumatic event by drawing on their own resources. As for the loss of the beaches, this intrinsic character must allow the system to use the sedimentary stock, to rebalance the dynamics and feedbacks coming from each of its physical and biological components. This would allow the beach to "jump back" and reach the morpho-dynamic equilibrium it had in the phase preceding the erosive trauma. This work proposes an integrated method for calculating the resilience potential that can address both the assessment and management phases of coastal erosion risk. The proposed evaluation methodology comprises the use of innovative technologies, such as geographic information systems (GIS) for the mapping and spatial analysis of morphological trends, integrated in the analysis of economic and social dynamics. Such matrices differ greatly due to their different nature but must be considered as the product of vulnerability and exposure in risk assessment. Adopting an approach oriented to the use of multi-parametric indices, the resilience potential was calculated and integrated into the vulnerability assessment. This is essential as from a regulatory point of view areas exposed to natural hazards must be transformed into low risk levels to improve their natural stability before their use. In this regard, the coastal strip of the Municipality of San Vincenzo (Livorno, Italy) has been mapped and its potential use and regulation have been evaluated independently of purely economic or political approaches. However, this still represents a great challenge as the economy plays a strong role in valuation formulas, as well as management plans, which for these reasons are rarely decisive. The study was tested within the Interreg MAREGOT Project, of which the Department of Earth Sciences of the University of Florence is a partner. Initially a morphodynamic evaluation of the studied site was carried out, followed by the drafting of a morpho-sedimentological map. These activities were carried out at the Laboratory of Applied Geomorphology of the Center for Geotechnology (CGT) of the University of Siena. Subsequently, the morphological trends and the economic parameters examined were converted into diagnostic indicators of territorial change, at the Department of Civil Engineering of the Polytechnic University of Cartagena (Spain). The results highlight that an assessment of the resilience potential is not only necessary to address the effects of climate change, but it is mandatory to plan corrective actions that quantify the real capacity of coastal areas to cope with extreme events. Furthermore, in anthropized coastal environments the high density of concessions for recreational activities, the high price ranges of services, and the construction of buildings on the coastal area imply significant limitations that can be related to both social and morphological risks. The most important ones concern free access, the exercise of the right to swim, as well as the provision of a right of possession of the built works to the concessionaires, and subsequently the duty to protect them (by the administrations) through rigid works in emergency conditions. climatic. As already mentioned, these works are generally to be considered as the last alternative, as they can give rise to phenomena of contraction of the coastal strip at a local level, and sometimes cause the loss of some habitats. The European Commission's EU market regulation rules have sometimes highlighted the existence of shortcomings in the management of state-owned concessions in the maritime field. Indeed, in Italy they are generally automatically renewed to concessionaires for indefinite periods, without considering its implications on sedimentary dynamics of the coast. As already mentioned, this has influenced coastal engineering and urban planning on the territory of the entire Italian state. Hence, the Nature Based Solution tested in this study consists of a method that includes the potential for resilience in the management of areas subject to coastal erosion. This phenomenon is analyzed in terms of socio-morphological vulnerability on a local scale (beach), since it represents the administrative dimension within which this procedure is most applicable, and in which the concept of risk is linked to the loss of sedimentary stock. The approach adopted is oriented to the use of multi-parametric spatial indices through GIS tools, and shows the applicability of the method that allows to identify areas with different potential for relative resilience. Furthermore, it allows to generate territorial management strategies on a local scale consistent with the existence of morphological and social vulnerabilities.