Development of a coastal vulnerability assessment model : application in the pilot area of the Gulf of Patras, Greece
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Date
2024-05-14
Authors
Μπουμπούλης, Βασίλειος
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Abstract
In this Doctoral thesis, a thorough investigation was conducted to assess various coastal hazards affecting the Gulf of Patras coastal zone, extending from the city of Patras to the cape of Araxos in Western Greece. Within this framework, two hazards were identified: coastal erosion and soil liquefaction. For both hazards, calculations were performed using indices, specifically the Coastal Vulnerability Index (CVI) for coastal erosion and the Liquefaction Potential Index (LPI) for soil liquefaction. Among the two hazards, coastal erosion was considered more significant, necessitating an in-depth exploration of its impacts on the coastal zone of the investigation area.
The primary objective of this thesis was to develop a methodological approach for coastal vulnerability assessment that could be applied along the shoreline of the Gulf of Patras and more generally in similar areas at a local scale. Consequently, a new Coastal Vulnerability Index (CVI) was created adapted to the specific conditions of the area, using seven variables with different effectiveness in the investigation area. The new index was named Geotechnical Coastal Vulnerability Index (GCVI) due to the highest importance given to the geotechnical variable. At the end, the developed index and the overall methodology, is considered as an attempt for the creation of a holistic model for the calculation of vulnerability against coastal erosion at a local scale.
According to the GCVI results for both FAHP and PCA indicates that the greatest part of the study’s area shoreline is under the regime of high and very high vulnerability. Comparison between of the GCVIFAHP and GCVIPCA results indicates higher rates in the high and very high vulnerability classes for the GCVIFAHP, while the GCVIPCA shows lower rates in the same classes. The reason is that the GCVIPCA gives more importance on the wave height and tidal range parameters in comparison with GCVIFAHP. Furthermore, the GCVIFAHP and GCVIPCA exhibit similar vulnerability regimes in some parts of the investigation area, especially in the high vulnerability zones. In general, GCVIFAHP and GCVIPCA are identical in their vulnerability indications, with the exception of some parts along the shoreline area, upon which GCVIPCA is more conservative in terms of vulnerability.
Both analytical methods were used for the validation of the GCVI results and the comparison between them showed that the PCA was more efficient than the FAHP since it was coincided better with the rates of historical shoreline movement and bed level change. Furthermore, the sensitivity analysis of the GCVI results indicated small rates of change in the GCVIFAHP and GCVIPCA variables for each 4% change in weight, which exhibit stability in GCVI outcomes even with significant percentage changes (±20%).
Another key objective of this PhD Thesis was to explore the potential for soil liquefaction. For this reason, Geotechnical in-situ tests, including Standard Penetration Tests (SPT) and Cone Penetration Tests (CPT), were carried along the shoreline of the investigation to calculate the safety factor (FS) and the Liquefaction Potential Index (LPI) for three different earthquake scenarios. This resulted to the construction of LPI distribution maps for the entire area, that are very helpful for urban planners and engineers to design safely infrastructure and buildings along the shoreline and develop future touristic activities for its economic growth.
In conclusion, this thesis presents an innovative and comprehensive methodology for developing a Geotechnical Coastal Vulnerability Index, addressing uncertainties and validating results. The application in the Gulf of Patras showcases the potential of GCVI as a valuable tool for coastal hazard assessment and management.
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Keywords
Coastal erosion, Coastal vulnerability, Coastal Vulnerability Index (CVI), GIS, Geotechnics, Soil liquefaction