Anthropogenic influence on recent evolution of shorelines between the Conero Mt. and the Tronto R. mouth (southern Marche, Central Italy)

A study of the shoreline evolution during the last two centuries along the southern portion of the Marche region (between the promontory of the Conero Mountain and the Tronto River mouth) has been carried out on the basis of historical data and taking into account the effects of both natural events and anthropogenic interventions. The research started with searching, acquiring, georeferencing and digitizing all the available maps surveyed from 1835 to the present. The above data set has been used to implement a vector geodatabase containing the successive position and shape of shorelines, with particular attention to the neighboring river mouths. Since transitional and beach deposits have been almost completely eroded during the last decades, the adoption of traditional techniques of geomorphologic and sedimentological analyses has not been possible. The results of the above analyses have been correlated with the main natural events and human interventions occurring during the considered time span. The results of this comparison highlights that the evolution of river mouths and neighboring beaches mostly depends on deforestation carried out in their hydrographic basins. In the study area, the progradation of river mouths continued after the end of the Little Ice Age (ended around 1850). Namely, it has been observed that the retreat coincided with the start of reforestation and agricultural development (in the 20's of the last century). During the following decades, further interventions, such as construction of dams and check dams, extraction of sediments from thalwegs, fillings, modifications of stream paths, abandonment of agricultural practices etc., contributed to a severe reduction of river solid load with subsequent retreat of both river mouths and beaches, thus making it necessary to protect them with artifacts.