New Methods and Instruments for Coastal Monitoring

Nowadays, many European coasts are subject to erosive processes and the Italian coast is not an exception, indeed it has been suffering from severe erosion, one of the most visible consequences of a relentless depletion of the coastal environment, particularly alarming due to its crucial economic and social role. In this sense, a well-structured and continuous beach monitoring programme implemented within a farsighted management strategy is required to support coastal interventions, aimed at the coastline protection or the mitigation of the erosive tendencies. Under this perspective, video systems have become widely used all around the world in coastal monitoring strategies, allowing both high temporal and spatial sampling frequency, with low logistic and costs efforts. Main objective of this work is to contribute to the development of new instruments and methods able to be included in a wider coastal monitoring network for supporting regional planning and control activities. A new system for video monitoring and surveillance of Apulian coasts (South Italy) has been recently developed. In the present thesis, the implementation of the system, oriented at some key characteristics such as easy installation, robustness, low cost, efficiency of the acquisition and tasks scheduling, concerned with the installation at two different sites, is described. The system design aims at obtaining a tool able to work automatically. The tool is composed by several routines implemented also with a webapplication, addressed at images processing (e.g. shoreline extraction and geo-rectification), data analysis and sharing results about beach actual state and shore evolution, in quasi-real time. Within this context, a new specific model for shoreline detection, Shoreline Detection Model (SDM), has been developed. The present describes in details the algorithm, inspired by the global Probability of Boundary (gPb) concept and the seed-based segmentation, together with the image processing procedures used. It mainly allows extracting the sea/land boundary from automatic segmented Timex images. The SDM calibration and validation has been performed on coastal images derived from a video monitoring system installed back at Alimini (Lecce, IT) in 2005, by comparing automatic shoreline contours with manual detected ones, on several crossshore transects. The application of the SDM on images recorded by the new system has allowed testing the model feasibility at sites characterized by different morphological features and geographical exposition. In real time, processed images and shoreline contours are so, uploaded and make freely downloadable. Moreover, shoreline time variation analysis is available on user-selected transects. The reconstruction of intertidal bathymetry from video is reported and compared with topographical (d-RTK) field survey performed at Torre Lapilllo (Le), useful also in order to assess the system efficacy and accuracy in coastal area monitoring. The central side at the embayment of Torre Lapillo has been also involved in different coastal surveys. Among them, an innovative technique, by using Unmanned Aerial Vehicle (UAV) flight, is evaluated. A high vertical accuracy, in solving such a complex topographic system, is found by investigating the DSM and comparing it to traditional GPS surveys. The DSM has been reconstructed by processing the UAV imagery using the Structure from Motion (SfM) algorithm. All the processes involved, from acquisition phase to drawing results, are discussed. Besides, the new video system is employed on this study area for run-up measurements, performed over several cross-shore transects, by using time-stack images. A methodology useful in order to validate 2-d numerical predicted run-up values with such observations is presented. It is described a high resolution analysis of the interaction of irregular waves with natural beach leading to wave propagation beyond the coastline, swash and vertical run-up excursion, which are numerically predicted. The novel methodology proposed, combines a wide validated forecasting dataset, Mete- Ocean, with SWAN and SWASH models to achieve accurate and computationally feasible simulation of waves at different time and spatial scales, up to the total energy dissipation in the swash zone. A merging strategy between field surveys for properly resolving topographical input is employed and discussed. The subaerial surface, which is essential for accurate representation of the hydrodynamic interactions with the beach profile, is solved by employing the DSM UAV-derived. Results by employing such an approach show to be successful, while a proper calibration of the SWASH physical parameters, when the model is applied in 1-d has been necessary. The run-up observations used in this work has been compared with conventional empirical model data. Most of the empirical formulations led to a systematic overestimation, apart from two of them, which take into account transformation processes of the entire nearshore zone. It shall be mentioned that the work reported in this thesis has been done within the framework of scholarship founded by Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR).