Coastal vulnerability to storms at different time scales: application to the Catalan coast

• Autores: Eva Bosom García
• Directores de la Tesis: José A. Jiménez (dir. tes.)
• Lectura: En la Universitat Politècnica de Catalunya (UPC) ( España ) en 2014
• Idioma: inglés
• Tribunal Calificador de la Tesis: Agustín Sánchez-Arcilla Conejo (presid.), Jorge Guillén Aranda (secret.), Paolo Ciavola (voc.)
• Materias:
  • Ciencias de la tierra y del espacio
    • Geología
      • Geomorfología
    • Oceanografía
      • Procesos litorales o sublitorales
• Enlaces
  • Tesis en acceso abierto en: TDX
• Resumen

  • Storm-induced impacts are known to cause important economic and environmental damages to coastal systems worldwide. Consequently, the relevance of including hazards and vulnerability assessments in coastal policies has been highlighted during the last years, so that coastal managers can make informed decision to apply mitigation and/or adaptation plans. The main purpose of this thesis is to develop a methodology to quantitatively assess coastal vulnerability to storms at different time scales, considering the two main storm-induced hazards separately (inundation and erosion). In this work, vulnerability is defined as the potential of a coastal system to be harmed by the impact of a storm. Thus, it has been quantified by comparing the magnitude of the hazards with the adaptation ability of the coast. The proposed methodology is based on a probabilistic approach where hazard time series are fitted to an extreme value distribution. Consequently, hazard magnitudes and vulnerability are related to a probability of occurrence instead of to a determined storm event. The coastal manager has to decide the probability of occurrence to be accepted in the analysis, which will determine the return period (Tr) to be considered. Vulnerability indicators that compare the magnitude of each hazard to the response capability of the beach are built for erosion and inundation independently. Final vulnerability is formulated in terms of these two intermediate variables by means of a linear function that ranges from a minimum value of 0 (optimum state) to a maximum of 1 (failure state), defining 5 qualitative categories. In this particular case, these thresholds have been defined for each hazard in terms of the protection function provided by the beach. In order to evaluate changes in vulnerability at different time scales, variations in the adaptation ability of the coast due to the effects of other medium and long-term processes have also been considered. Taking into account the characteristics of the study area, erosion due to longshore sediment transport (LST) gradients and erosion and inundation caused by relative sea-level rise (RSLR) have been selected as the main medium and long-term coastal processes, respectively, to be analysed. In this sense, shoreline evolution rates have been used as representative of accretion/erosion due to LST, whereas different combinations of sea-level and subsidence scenarios have been used to determine erosion and inundation due to RSLR. The developed methodology has been applied to most of the sedimentary coastline (219 km) of Catalonia (NW Mediterranean). The results obtained for a Tr=50-yr show similar percentages of high and very high vulnerable coastline for erosion and inundation. However, the increase in vulnerability due to the contribution of LST and RSLR is slightly higher in the case of erosion. Results also indicate that changes in vulnerability due to RSLR are generally lower than those obtained when only LST is accounted. RSLR contribution is detected at longer time scales and is significantly higher in the southern part of the Catalan coast. This is mainly due to the presence of dissipative beaches with very mild slope together with the potentially significant subsidence of the Ebre delta. On the opposite, LST contribution does not seem to target any specific beach type. To conclude, the proposed method permits to identify the most vulnerable spots of a coastal area considering the dynamic response of the system at different time scales. This information is relevant for coastal managers when it comes to efficiently allocate the available resources. Moreover, the versatility of this method allows, not only to update the results according to the available information on hazards magnitude and beach geomorphology, but also to easily apply it to other coastal zones.