12.1Introduction

The terracing of slopes is universally used to obtain cultivable land in steep areas since ancient times, today being one of the major morphological transformations implemented by humans in the world (Tarolli et al. 2014). The cultivable flat land is obtained by reducing the overall slope angle with the construction of soil reservoirs usually supported downstream by a dry-stone wall (terracing) or, in other cases, contained by clods (embankments). Building techniques are presented in detail in many texts (e.g. Brancucci et al. 2000; Rizzo 2008). The reduction of the slope has a positive feedback on the landscape regarding the reduction of the erosive power of the surface water flow and, consequently, of hydrogeological-related problems (Tarolli et al. 2014). Moreover, the decrease of the slope improves the pedogenetic processes. A necessary precondition to preserve such benefits is to guarantee the maintenance with the presence of farming. A terrace system can “resist” to erosive agents only thanks to the constant support of its components that include dry-stone walls and painstaking water regulation structures. Since the First World War, and definitely after the end of the Second World War, the development and promotion of the industrial activities accelerated the progressive abandonment of agriculture, especially in these highly demanding and poorly mechanised farming systems. The abandonment of terraced areas results in a new interference with the geomorphic system. As the lack of maintenance of a human-altered landscape persists the more, the geomorphic system gets the control causing erosion processes and land degradation. The final result is the increase of hazards with diffuse problems of instability and huge solid transport in the rivers (Brancucci and Paliaga 2006). In this chapter, we address the Liguria Region (Northern Italy) as a paramount example of the complex balance between the pristine morphology and the anthropic modifications. On these premises, we then highlight some potential hazards to propose, finally, key recommendations for designing suitable management strategies.

12.2Case Study

12.2.1Liguria: A Natural Laboratory for the Analysis of a Terraced Landscape

Liguria is a Northern Italian region that covers about 5400 km2, distributed in a thin strip of land ranging from East to West for about 250 km, bounded on the South by the Ligurian Sea, to the North by the Alpine and Apennine chains. Altogether, Liguria presents a very complex geology (Fig. 12.1).

The region is crossed by valleys, inherited from the local tectonic events, with East–West and North–South direction across the Tyrrhenian side and Po Valley. The climate is Mediterranean, characterised by heavy rainfall events occurring

Fig. 12.1 Simplified geological map of Liguria (Brancucci and Ghersi 2018). Base map from http://www.openstreetmap.org/copyright

mainly in late summer and during the autumn. The rainfall events are becoming more intense in recent years (cf. Vallebona et al. 2015). High steep slope and rainfall are the primary agents of the erosion processes. Such processes do not allow to generate top soils suitable for farming practice. In the last centuries, terracing agricultural practice has reshaped entirely the Liguria landscape. For several years, the presence of humans, who tenaciously maintained efficiently such land, has prevented any hydrogeological criticalities. However, the changed socio-economic conditions of the last century determined a progressive land abandonment that appears difficult to revert. People migrated from the mountains to the coastal areas where industrial and tourist activities could guarantee economic prosperity. Such land abandonment was related also to an increase in soil erosion processes and landslide events (Fig. 12.2).

In several situations, the lack of proper vegetation management (such as chestnut coppices) exacerbated such instability. The complex morphological context makes farming hard, by increasing the costs of production and consequently the prices of products. The consequence is that only a few traders are willing to invest in these areas. Terraces are perceived as part of the “identity” of the Ligurian landscape; in such area the Cinque Terre National Park is the most “representative image”. It is unlikely to recover the whole system, but it is imperative to break apart the problem into its various components to be able to provide adequate support to land planners and let them being constantly updated and updateable.

Fig. 12.4 Landsliding and terrace failures (white rounded arrows) within vineyards triggered by the intense rainfall event of 25 October 2011 (Liguria, Italy) (Agnoletti et al. 2012; after Tarolli et al. 2014)

This coincides with an increase in the occurrence of small landslides in the steps between terraces, which can evolve downslope as debris flows (Tarolli et al. 2014) (Fig. 12.4).

A similar mechanism occurred on 24 November 2000 in Ceriana (province of Imperia) where intense precipitation affected an entire terraced area triggering several mass movements and causing two fatalities. The mitigation of such phenomena demands tremendous efforts especially where the land tenure is fragmented. The ownership of terraced fields is frequently divided into small plots owned by multiple stakeholders in which the property is difficult to document. This situation leads to an obvious and additional difficulty of the system management.

12.2.3Ancient Terraces: A “Soil Reservoir” to Be Monitored

Figure 12.5 shows an ancient terrace system located in the inland of Liguria Region (Italy). This terrace has been built at the end of the eighteenth century for cultivating mainly potatoes and grapes. However, the very steep slope did not provide a suitable place. The structure is quite complex; it is characterised by a dry-stone wall of 7 m in height, complemented by an underground hydraulic system to drain water