A threefold research aimed at the reconstruction of an artificial dune (Migliarino-San Rossore-Massaciuccoli National Park, Pisa, Tuscany, Italy): preliminary data

This research has been carried aut through a collaboration between the Department of Earth Sciences of the University of Pisa and the Province of Pisa within the BeachMed project. lt has worked aut a better morpho-sedimentologic definition of a beach-ridge dune system primarily aimed at the reconstruction of an artificial dune in front of the Presidential House. The study area belongs to the Pisan coast and extends far about 23 km. lt nearly coincides with the boundaries of the Migliarino - San Rossore - Massaciuccoli National Park, and is exactly comprised between Torre del Lago Puccini (Lucca) to the north and Tirrenia (Pisa) to the south; the landward limit of the area corresponds to the last outcropping beach-dune alignment. This huge dune system has formed due to the progradation of the Arno River delta during the last 2000 years and at present is subjected to strong erosion processes. A multidisciplinary approach has been used in this work. A detailed morpho-sedimentologic survey (1 :2000) has allowed to group the dune systems into steady, semimobile and frontal dunes. Dunes which are no more subjected to processes that have previously led to their formation are called "steady'': they are fixed and characterized by arboreous vegetation. Dunes which can beat times subjected to erosion and accretion processes and are characterized by shrubbery are called "semimobile". "Frontal" dunes are active and covered with typical psammophile vegetation. Moreover, a series of sampling has been conducted far a more accurate sedimentologic definition of the area. Grain-size analyses have provided the granulometric range most suitable to the dynamics processes that affect this sector of the coast. First of ali, five transects have been traced and samples have been taken starting from the beachface to the oldest outcropping beachdune alignment. On the beach, the beachface, the berms and the backshore have been sampled; on the frontal dunes, the stoss-side, the crest and the lee-side; and on the steady and semimobile dunes, the crest and the interdune areas. The transects have been traced by significant locations, like updrift and downdrift of the Arno and Serchio rivers, and close to the Morto Vecchio River. Data processing has showed i) a decrease in grain-size moving towards the oldest dunes and ii) a slightly coarser grain-size of the crest dune sands in respect to the interdune deposits. These trends are further confirmed by sand vs silt plots. At last, provenance data derive from the petrographic analysis of a selected group of samples previously collected for the grain-size analysis and few more from Arno and Serchio rivers. The petrographic analysis has showed compositional variations within each transect, most notably the decrease in calcium carbonate moving towards the oldest outcropping beach-dune alignment. Preliminary data demonstrate that Arno River has represented the major source of sediments. In conclusion, this study has produced a better knowledge about this beach-dune system, and it has even provided useful data on how to improve and optimize any coastal protection structure local authorities might decide to set up