Hydro-geotechnical monitoring in dry-stone wall terraces for the investigation of rainfall-induced landslides: preliminary results from the UNESCO World Heritage Site of the Cinque Terre

Dry-stone wall terraces are among the most ancient and widespread agricultural practices on hilly-mountainous landscapes. Their historical, architectural, and environmental value has been recognized worldwide. Recently, “the art of dry-stone walls” was inscribed on the UNESCO Representative List of the Intangible Cultural Heritage of Humanity. These anthropic landscape transformations have important effects on both the slope geomorphology, by reducing steepness, and hydrology, by increasing water infiltration and soil moisture and by mitigating runoff. Under optimal management, dry-stone wall terraces favour farming, providing pedological and ecological advantages. However, following farmland abandonment, dry-stone wall terraces may progressively lose their hydro-geomorphological functions due to lack of maintenance. Over time, these dynamics can be accompanied by the development of severe erosion processes and mass movements which can lead to slope degradation issues and risk scenarios.

A wide variety of factors can influence the hydro-geomorphological response of terraced systems after their abandonment. In this work, the effects of land use and of management practices are explored in a small terraced area (12.5 hectares) surrounding the Manarola hamlet (eastern Liguria Region, north-western Italy), within the UNESCO World Heritage Site of the Cinque Terre. The research purpose is to investigate the hydro-geotechnical behaviour of dry-stone wall terraces in different land use conditions and state of management. The research activities are in the framework of the project Stonewalls4life, a LIFE EU-project aimed at investigating the role of dry-stone walls in increasing the resilience of rural territories and in counteracting the impacts of climate change.

The engineering-geological characterization of the pilot site was developed through a multidisciplinary approach consisting of geological and geomorphological surveys, in situ and laboratory geotechnical soil tests, excavation of shallow test pits and non-invasive geophysical surveys. The stratigraphic and geotechnical modelling of the test site allowed to implement integrated hydro-geotechnical monitoring systems aimed at measuring over time: (i) meteorological data (e.g., rainfall intensity, air humidity, air pressure), (ii) soil hydrological properties (e.g., volumetric water content, matrix suction), and (iii) loads acting on retaining walls (e.g., soil pore pressure). Different monitoring scenarios based on land use conditions (e.g., cultivated and abandoned) and dry-stone wall management practices (e.g., existing not maintained wall and reconstructed wall) were established.

From the whole set of investigations, it is expected to improve the knowledge concerning the hydrological processes occurring in dry-stone wall terraces and to obtain useful information for modelling soil mass movements (e.g., shallow landslides), along with indications for the development of effective land management strategies.