The nomenclature for hydrogeological instability risks includes four main risks, which are distinguished according to the risk causes :
1) hydrogeological risk, that is slowly caused by natural factors (e.g. collapse landslides in a calcareous cliff in uninhabited areas and erosion along a marly-calcareous slope) in environments where human activities are minimal, i.e. woods, forests and mountain pastures;
2) hydraulic-pedological farming risk, that implies the occurrence of landslides in every winter and is caused by incorrect crop selection, not suitable for the soil and climate parameters (e.g. on a hilly slope with a clay vertisol type with a landslide having different fronts, when the arable land is cultivated with a cereal-legume crop rotation), or the presence of springs with missing drainage in clay soils with a high gradient;
3) hydraulic-infrastructural risk, that is caused by the building up of infrastructures not suitable for the surrounding environment, as they change the downflow of shallow water;
4) hydraulic-infrastructural-pedological-management risk, that is caused by crop operations not suitable for soil and crop parameters, where the selected cultivated plant species are suitable for the environment and field improvements change water downflow (e.g. in soils along hilly calcarenite slopes cultivated with olive orchards, where up-down soil tillage causes shallow water erosion).
Three case studies were selected in three sites of a hilly area of inland Western Sicily, located in the territory of Corleone (Palermo, Sicily, Italy). These case studies provided the input data needed for obtaining the work results, i.e. the hydrogeological instability risks observed during some surveys, on which the nomenclature proposed for these risks is based.
The excerpt of the Map of Instability n. 19 (Sicilian Region - Territory and Environment Department, Basin Shred Plan for Hydrogeological Layout, 2005) including the above area is shown in Figure 1.
Figure 1. Hydrographic basin of Belice river (057) - excerpt of the Map of Instability n. 19, including the surveyed area: the areas where soil erosion caused landslides are highlighted, i.e. those having active landslides are in red colour, while those having landslides at rest are in yellow colour (Sicilian Region - Territory and Environment Department, Basin Shred Plan for Hydrogeological Layout, 2005).
From March to September 2015, surveys were carried out in this area to identify the human activities that caused hydrogeological instability.
Thus, it was possible to focus on the unethical human activities that reduced the productivity of soils and caused damages to their infrastructures.
The above three case studies were selected for the surveys, as they are characterised by three different types of hydraulic instability risk:
- at the first site, a landslide was observed on a hilly slope (arable land) cultivated with a cereal and legume (Italian sainfoin) crop rotation;
- at the second site, an area degraded because of flooding, gully erosion and water stagnation was observed;
- at the third site, the damages caused by incorrect crop operations, implemented for an unsustainable field improvement (not suitable for the natural conditions of the hydrographic network), were observed.
The surveyed area is located at an altitude between 500 and 700 m a.s.l.
In this area, soils are mostly clay and calcareous, specifically Vertisols and Inceptisols. Entisols are slightly distributed where floods occur and on tender and hard rocks. The soils generally originate after a long pedogenesis and often have a high depth.
In the surveyed area, it is possible to observe dry arable lands cultivated with cereal and legume crop rotations on clay formations, as well as olive orchards, vineyards, small arable lands and pastures on the roughest soils.
This area is highly sensitive to hydrogeological instability, because of its soil and climate parameters. In fact, some areas subjected to landslides and damages caused by floods and water stagnation were identified during the surveys.
Risk Type | Risk Causes |
---|---|
Hydrogeological risk | Natural factors in woods, forests and mountain pastures. |
Hydraulic-pedological farming risk | Crop selection (e.g. cereal and legume crop rotations on arable lands) is not suitable for the within-field soil and climate parameters or the presence of springs (hydrological limit) with missing drainage (a surface levelling must be carried out by means of bulldozer in September) in clay soils with a high gradient (pedological limit). Landslides occur every winter. |
Hydraulic-infrastructural risk | Building up infrastructures not suitable for the surrounding environment, as they change the downflow of shallow water, for example:
|
Hydraulic-infrastructural-pedological-management risk | This risk occurs where crop operations are not suitable for the soil and climate parameters, e.g. up–down soil tillage along slopes, causing water erosion, are carried out, while the soil use is correct and field improvements change water downflow. |
This entry is adapted from the peer-reviewed paper 10.3390/land11010108