Sand supply from shoreface to foredunes: aeolian transport measurements and morphological evolution of a Tuscany beach stretch (Italy)

The coastal dunes are a highly dynamic sedimentary environment characterized by a continuous time-space readjustment in terms of morphology, shape and dimension. This is mainly due to the periodic fluctuation of the volume of sand available and by the force of the deflation processes, which are in turn driven by the interplay among pattern of vegetation cover, surface roughness and local-regional wind regime. The aim of our research is to quantify the deflation, transport and deposition of sands in a natural coastal field dune system located in the northern coast of Tuscany, Italy. The northern part of the investigated area is characterized by stable coastline condition while southwards strong erosive processes took place since 1800 year. Sedimentological data come from a series of sand collectors spaced along transects orthogonal to the coastline from the backshore to the semi stable dune field. The collectors were constructed of PVC pipe 100 x height 10 cm, with two openings 7 cm wide and 50 cm tall arranged on opposite sides of the tube. Opening willing to windward served for sand collection, and to leeward, covered with a metal wire 60μm opening. Collectors were buried along, until the base of the free window coincide with the surface of the ground about 1,5 m. The sand trapped within each collector was sampled every two hours for three consecutive times. In laboratory sand samples were weighed and subject to grain size analysis by means of mechanical sieves. The local winds parameters and their fluctuation with the time were acquired through a Meteorological mobile station. The station is equipped with three ammeters located to three different heights from ground surface: 40, 120 and 180 cm. A wireless sensor allows the constant output of data (each 5 sec) to a device. Temperature, and relative humidity value are furnished every 30 minutes. Analysis of data has evidenced the time-space fluctuation of sand volume in the two study area (stable area and under erosion). Basing on this methodological approach the time-space fluctuation of sand volume experienced by the two study areas (stable area and under erosion) has been estimated.