Anthropogenic morphological modifications in Turin along the Po, Sangone and Dora Riparia rivers (NW Italy)

Geomorphological mapping in urban areas must address the wide distribution of anthropogenic landforms and deposits in addition to the natural ones. Consequently, an integrated scientific approach, by combining field surveys and subsoil data with the use of historical documents, is necessary to recognize the main anthropogenic modifications of the natural landscape over time. Recent field research concerning the morphology and shallow subsoil stratigraphy of Turin, especially through the study of several boreholes, has led to the recognition of various anthropogenic modifications of the Turin natural landscape that have occurred in the last four centuries. Moreover, the examination of ancient papers and historical maps, with reported sectors in which the morphology of Turin appears different from the current one, indicated some evident, partly anthropogenic, modifications. Anthropogenic changes deduced essentially from ancient topographic maps have addressed the path of riverbeds, e.g. the stabilisation of the Sangone R. meander near the Mirafiori Castle, the setting and artificial cut of the Nichelino meander, the shift of the confluence between Po and Sangone rivers and the artificial cut of the wide meanders of the Dora Riparia R. near its confluence with the Po R., to allow the expansion of the monumental cemetery. Other significant anthropogenic river modifications that have been difficult to identify concern the filling of several ancient tributary incisions on the left of the Po R., which have now completely disappeared. Ancient quarries associated with brick-kilns lowered the surface through the removal of the clayey silt overbank cover of the Turin unit in wide sectors of southern Turin, Rivalta and Beinasco, as observed by field survey. Areas in which the landfill has substantial thickness and extension such as to simulate natural river terraces, e.g. the long stretch between the Palazzo del Lavoro and the Balbis Bridge, were also recognized by observing geognostic cores coupled with the radiocarbon dating of the underlying fluvial deposits. Surface surveys alone are sufficient to recognize the areas involved by substantial anthropic interventions when they are characterized by hummocky morphology such as in the Valentino Park and the Cavour Garden. Finally, anthropogenic modifications deduced essentially from historical reports consist of the construction and filling of the Michelotti Canal along the Po right riverside. The progressive extension of Turin was closely related to the natural evolution caused by geomorphic agents (above all erosional and/or depositional processes carried out by watercourses) but also by anthropogenic modifications of the topographic surface (excavations and/or fillings). The investigated anthropogenic modifications of the Turin landscape are therefore useful to both the scientific approach and the use of urban subsoil.