Morphometric analysis of two calanchi areas in Sicily (Italy) by exploiting high resolution Digital Elevation Models

Abstract

In the Mediterranean areas, specifically in Sicily (Italy), irregular rainfalls, strong seasonal changes, scarce vegetation cover and, frequently, outcropping of clayey deposits favor water erosion phenomena. Badland landscapes are the result of severe erosion processes, characterized by steep slopes, sparse vegetation, high drainage density, rapid erosion rates and a shallow or non existing regolith profile. In this investigation we focused on the calanchi badland type, consisting of heavily dissected terrain with steep, unvegetated slopes and channels that rapidly incise and extend headwards. This research was carried out in two calanchi sites located in Sicily. The geometry of 25 badland channels was characterized in order to verify if relationships, already tested for minor linear erosion landforms (i.e. rills, ephemeral and permanent gullies), could also be verified for these bigger erosion channels. To this aim, two Digital Elevation Models (DEM) were processed in a Geographic Information System (GIS) environment: the first DEM obtained by a LIDAR survey, with 2 m and 0.1-0.2 m of horizontal and vertical resolution; the second DEM obtained by photogrammetry of 840 images captured by a drone, with 0.3 m and 0.05 m of horizontal and vertical resolution. Each channel was divided into segments delimited by transverse sections. Cumulative length and volume of all channels segments were plotted on scatter diagrams showing highly significant power relationships. Additionally, some morphometric attributes of channels segments (length, volume) and sections (depth, width), were combined into two dimensionless groups, already tested for minor erosion landforms, providing measured pairs also highly correlated by power relationships. The results of this experiment confirm that length of erosion channels is sufficient to predict volume of eroded material and evidence a morphological similarity between rill, ephemeral and permanent gullies and calanchi landforms.