Geomorphological and statistical analysis of the dune changes in Lido di Classe (Ravenna, Italy) based on remote sensing techniques

Coastal dunes are well-known for their significance in providing vital ecosystem services. However, its highly dynamic nature and its exposure to climatic and anthropogenic pressures make them one of the most vulnerable geologic features along the coastal zones worldwide. On a local perspective, the coast of Ravenna – a low-lying coastal zone located along the Northern Adriatic Sea in Italy, is among the areas that are subjected to increasing environmental risks such as coastal erosion, storm surge, groundwater and soil salinization. Restoration initiatives have been implemented in some of the protected dune areas to combat against impending risks. This thesis aimed to contribute to the assessment of the dune restoration project in the protected natural area of the Bevano River mouth in Ravenna using UAV monitoring surveys from 2016 to 2021. The restoration measure included two windbreak wooden fences that were installed in front of the dune foot and parallel to the coast to stop wind and facilitate sand deposition and accumulation. Primarily, the objective is to assess the impact of the 2016 restoration project in the dune development in terms of sand volume changes by utilizing the Structure from Motion (SfM) photogrammetry and the Geomorphic Change Detection (GCD) toolset. Next is to establish a systematic workflow for UAV data processing and elevation data analysis that is suitable for sediment volume calculations. Last is to explore the utility of orthomosaic images for vegetation change detection in order to determine other contributing factors to the overall geomorphology of the dune ridge. For the methodology, the UAV topographic survey, coupled with GPS ground survey using Real-time Kinematic (RTK) positioning, were carried out from 2016 to 2021 in order to assess the geomorphological evolution of the area over time. SfM photogrammetry was utilized to generate and classify the point cloud and orthomosaic images for each survey year using Agisoft Metashape Professional. The classified ground points were interpolated in ArcMap to create Digital Elevation Models (DEMs), while the orthomosaic images were utilized to confirm the possible sources of data noise in the model and assess vegetation changes. GPS points and profiles were used to validate the elevation models. The volumetric changes in sediment storage and error analysis were calculated using the DEM of Difference (DoD) approach under the Geomorphic Change Detection (GCD) extension toolbar in ArcMap. The results show that sand accumulation was observed along the dune foot where the wood fences were established. The following changes have also been observed - progradation of the front dune, development of insipient dunes, decrease in slope stoss, decrease of blowout features due to increase in vegetation colonization. There is also an increase in vegetation and debris cover within and near the wood fences. Overall, it can be concluded that the windbreak fence has proven to be an effective intervention to prevent dune erosion since significant geomorphological changes and vegetation colonization have occurred based on the comparison between the 2016 and 2021 data. This is despite numerous factors affecting the overall sediment budget dynamics in the study area. The GCD toolset can be an effective monitoring tool for coastal dunes provided that the sources of uncertainties are well accounted for. In a coastal management perspective, the results of this thesis can supplement in showcasing the importance of implementing sand trapping fences and limiting debris cleaning as nature-based solutions to combat dune degradation along the coastal zones of Ravenna. The proposed systematic workflow in this research can also be explored in creating transferable guidelines to relevant stakeholders in implementing its integrated coastal zone management (ICZM). The manuscript has a total of five (5) chapters. Chapter one includes a comprehensive literature review on the basic principles relevant to coastal dune geomorphology and the gaps that this study would like to fill in. It also includes the information about the scope and area of the research. Chapter two provides the in-depth details about the methodology of the study that includes the data acquisition and processes, the implemented workflow for SfM, DEM creation, quality check and assessment, and vegetation analysis using the high-resolution orthomosaic images. All the results are presented in Chapter three, while the detailed discussions are in Chapter four. Conclusions and recommendations are presented in Chapter five.would also like to thank the Water and Coastal Management (WACOMA) and the Erasmus Mundus Joint Master’s Degree (EMJMD) programs for giving me the opportunity to study in Europe and to widen my research career in the field of coastal management