Integrating observational targets and instrumental data on rock coasts through snorkel surveys: A methodological approach

This work deals with recent advances in scientific snorkel surveying, starting from the results of several case studies in the Mediterranean between 2012 and 2018, for a total survey length of 531.4 km, with the aim of illustrating the pros and cons. The snorkel survey method, described here, also called 'Geoswim', allows rough-and-ready surveys of long sectors of rocky coasts. In particular, it is able to collect time-lapse images perpendicularly to the coastline and observe long sectors of rocky coastline, with particular reference to the tidal zone. In addition to the photographic survey along the coast, rough measures, lateral variations in geomorphological, geological, biological, and ecological parameters and the collection of hydrological data are usually performed during the work. The expeditions also provide the opportunity to produce large databases of coastal landforms such as coastal sea caves and tidal notches. The data collected can be improved by additional on-the-spot observations. The evaluation of the methodology here proposed was based on the results of SWOT analysis starting from the results and the experience of previous expeditions. Geoswim is the first snorkel approach that allows the collection of large amount of multidisciplinary data along wide sectors of rocky coastline. At the moment, this approach is the best and probably the only technique for characterizing the tidal and nearshore zone, but also to collect observational data of prominent objects along rocky coasts. However, snorkel observations are affected by limitations similar to those of terrestrial field surveys. The ability to observe specific forms or phenomena increases through the practice of field observation and are strongly observer-influenced. Sheltered sea basins are better suited than ocean basins, where tides and wave energy are generally higher. Data collection is also affected by weather and sea conditions. The quality of time-lapse images and videos may be reduced as a result of breakers at the cliffs, producing images that cannot be used for subsequent analysis. As for external factors, some sectors of the coast may be closed due to local restrictions on field activities.