COASTAL EROSION IN THE GULF OF FOLLONICA AND BARATTI AND COASTAL DEFENSE METHODS

From 1988 to the present the Institute of Marine Biology and Ecology of Piombino has studied the marine environmental situation of the Gulf of Follonica (Italy), in collaboration with the Universities of Siena, Pisa, Urbino, Sassari, Corte (FR) and the CNR of Pisa. A particular attention has been given to the study of biocenoses and to the Posidonia oceanica (Linnaeus) Delile, 1813 meadows. In the year 2000 a cartography of the meadows of the whole Gulf was made with the changes of the profile of the coast in front of it (fig. 1). In recent years erosion has drastically changed the sandy beaches mainly as a consequence of the constant retreat of the P. oceanica meadows whose possible causes have been studied. The increase of the beach was the method adopted to make the beaches usable but with temporary results. Also in the Gulf of Baratti the methods adopted for the defense of the beach have been inadequate. Figure 1 Cartography of the P. oceanica meadows (green patch) of the Gulf of Follonica. FUP Best Practice in Scholarly Publishing (DOI 10.36253/fup_best_practice) Roberto Bedini, Paolo Colantoni, Christine Pergent-Martini, Coastal erosion in the Gulf of Follonica and Baratti and coastal defense methods, pp. 379-384, © 2020 Author(s), CC BY 4.0 International, DOI 10.36253/978-885518-147-1.37


Introduction
To understand the origin of the erosive phenomena of the beaches of the Gulfs of Baratti and Follonica we used experienced researchers in the various areas of investigation necessary to understand the reasons of the backspace of the beaches. If you don't know what is causing the damage, you cannot repair it.
A survey of the coastal strip of the Gulf of Follonica was made by the Institute of Marine Ecology and Biology using the filming of a drone. The footage shows, if there was need for, that where the beach rocks exist the coast has endured the storms while where there are no rocks or there are breaks in the rocks erosion has changed the beach, causing it to decline ( fig. 2). Flat beach-rocks perform a function similar to that of P. oceanica meadows: they dampen the impact force of the waves that arrive at the beach and they keep the sand removed from the beach when the waves come back.

Materials and Methods
The underwater shooting to map the P. oceanica meadows of the Gulf of Follonica was carried out by the G.A.I.T. oceanography and marine geophysics company and developed by the Geodynamic and Sedimentology Institute of the University of Urbino. Ecological data and the distance of the upper limit of the meadow from the coast line were carried out by marine biologists using transepts 500 m long perpendicular to the coast line.
Attempts have been made for the dune reforestation to keep much more sand during sea storms using planting squares of fascines with plants inside to hold the sand with 381 the roots (fig. 3). On the beach, close to the dunes, sticks and piles of logs tied by a rope have been placed ( fig. 4).
In the Gulf of Baratti sacks of geotextile cloth containing sand have been used to defend beaches from erosion ( fig. 5).

Results
The results were negative for all the methodologies used in the Gulfs of Follonica ( fig. 6 and 7) and Baratti ( fig. 8).

Discussion
The problems of the coastal erosion, and the methods used for its defense, are usually faced by engineers and geologists without the contribution of marine biologists. The extent of beach erosion problems also depends on what the waves encounter before reaching the shore such as P. oceanica meadows, flat beach-rocks or other types of seabed. This is the marine biologist's field of study who can make an important contribution to establish the methods of intervention. If I put in defense of a beach sacks of geotextile cloth containing sand I should know that during the storms stones or wooden logs thrown against them will destroy them.

Conclusions
Coastal erosion is a growing phenomenon in our seas often linked to anthropic activities. To fight it you need skills on what to do both on the coast and in the sea in front of it. The impact force of the waves must be dampened before it reaches the sandy beaches. The continuous retreat of P. oceanica meadows in front of the beaches of Baratti and the Gulf of Follonica has caused their consequent great erosion. So if we want to imitate the function of the P. oceanica meadows and beach rocks it is necessary to operate in the sea in front of the beach and not on it.