Historical and recent environmental changes of the Ombrone Delta (Central Italy)

Reconstruction of shoreline variations in the area of the Ombrone delta apex has been achieved by comparing aerial photos acquired in 1995, 1998, 2004 and 2006. This reconstruction allowed to define the recent evolution of the Ombrone delta area in terms of erosional and progradation rates. Comparison with older erosional and progradation rates derived from Bellotti et al. (1999a) evidences increasing erosional rates along the delta apex during the investigated interval. Moreover, it has been possible to identify the importance of mouth bar growth as a recurrent mechanism for confining narrow sea stretches. These results have been used as reference for inferring the genesis of a set of four older beach ridges and a lake reported in historical maps. According to previous studies, the modern ponds (locally known as “chiari”) are remnants of the old lake observed in historical maps. Based on the morphological analysis and reconstruction herein proposed the origin of the modern Chiaro Grande pond and Chiaro del Porciatti ponds is independent from that of the old lake, and likely reflects the growth of bars offshore the Ombrone River delta. Lake avulsion during main flood events, however, may have represented an additional contribute to the sourcing of the ponds, as supported by the evidence of washover breaks that connect the ponds with the area at their back where the lake existed until the end of 19th century.