Geographic research in the Maremma Regional Park
Authors: Gabriele Ciampi, Michele De Silva (Partner 1)
It was conducted in the preparation phase of the work-together meeting at the Italian site, during the work-together and thereafter to accomplish the survey. The compartments of interest were the low plain of the Ombrone river and the coastline. The results were then crossed with the results of the other tasks and compared with those from the other study sites.
A study on the historical landscape of the Ombrone river plain was conducted, aiming at setting up a methodology for the study of the ancient landscape using different kinds of sources integrated in a GIS environment with special reference to historical cartography and aerial photo, and at applying this methodology for a better understanding of landscape transformation processes and the historical evolution of settlement patterns. Old maps of the inventories of the Catasto Leopoldino were used, corrected with a geographic grid, and thematic layers were interpreted, acquired and organised. Land-uses changes and coastline trends were mapped in time series. It was concluded that the landscape should be considered the result of a historical sedimentation process, where different natural events and human activities have all left their traces forming an interwoven and complex overall pattern. In order to understand, preserve and appreciate a Landscape it is therefore necessary to diachronically explore the natural and human processes which constitute its identity from a historical and environmental point of view.
The landscapes of the Ombrone river low catchment area, which include different environmental components, natural (geology, soils, morphology, vegetation) as well as man-made ones (water management structures, settlements, roads, etc.) was analysed. Each of them has been analysed as a single element and in connection to the others. The results of the observed interactions made it possible to draw lines which circumscribe relatively homogenous areas from the physionomic as well as functional point of view. Joint together they constitute the landscapes of the Ombrone river low catchment area (47,500 ha in size). Such area includes a flat share (75%) and a hill share (25%). The plain is that in which the low courses of Ombrone and Bruna rivers flow. As regards land-use, it is predominantly composed of farmland and partially urbanised; besides, it appears almost continually enclosed by a woods belts. South-westward, along the seaside there is a large pinewood planted on the sand-ridges; on the other sides, the plain is surrounded by hills and low mountains in some case completely covered by woods, in others covered only on their top belts. In the Ombrone river low catchment area, the historical long-term landscape changes have been huge in the human as well as in the natural aspects. Anyway almost all the changes have been caused (directly or indirectly, intentionally or unintentionally) by human activity. Opportunities and problems affecting the different landscape zones and subzones should be considered in land and town planning. Zones and subzones have been represented in a digital map.
Some new knowledge were inferred about Ombrone river delta dynamics through maps. According to a current opinion, the present phase of Ombrone river delta retrogradation began because of land reclamation by artificial aggradation (filling up) in the wetland of the Grosseto plain, carried out between 1828 and 1880. But a comparison between the maps of the early and those of the later 19th century shows almost no change of the delta apex protrusion: 30 m of retrogradation in the said period, compared with the 1250 m between 1883 and the present day. This observation allows one to reject the theory according to which the reclamation by artificial aggradation caused the beginning of retrogradation, because the latter happened when reclamation by aggradation was derelicted. In fact, generally, this technique takes off the sediment load only the suspended load, which has scarce importance in the sedimentary input at the mouth at the delta accretion, as it is spread widely and distributed far away by longshore transport and sea currents. On the other hand, bed load (sand in particular), stopped by the timber barriers built across the river in order to divert the water rich in sediment into the wetland settling ponds, always rose over the barrier during the floods. The most important cause are probably been the following: constructions of new large roads and railways along the valleys and across the slopes; construction of river embankments; watershed management structures in the inland tributary to the river; artificial afforestation (forest law of 1923); emigration of the rural population and the consequent reduction of cultivated areas; excavation of sand and gravel from the river belt for the building industry; glacioeustatic sea level increase and consequent major marine erosion capacity during storms; subsidence of the Grosseto plain. As regards the phases of the Ombrone river delta dynamics, various alternating progradation/retrogradation cycles evidence has been observed. A period of very accelerated progradation occurred in Italy during the period 13th-14th centuries; it was followed by an almost equal retrogradation. Differently from the opinion prevailing till now, the 14th century coastline was at least 500 m more advanced seawards than the one recognised hitherto. This datum has been obtained through an integrated study of historical maps and field work of the archaeological remnants concerning the more ancient of the two different “Torre della Trappola” built in 1283.