Topographic analysis for the understanding of the erosion processes in the Febbraro valley (Sondrio, Italy)

An example of a GIS topographic analysis is here presented, regarding the study of the erosion processes in the Febbraro valley (N of Valchiavenna, Sondrio, Northern Italy). During various surveys on the area, 88 earth flows, with a maximum dimension of ten meters, were spotted. The aim of the analysis is to describe the sites morphology in terms of: altitude, slope, exposure and curvature. The derived properties were subsequently determined: flow accumulation, Topographic Wetness Index, Erosion Index and Stream Power Index. The index determination required a preliminary hydrologic analysis through the application of both the D8 algorithm, the multidirectional and through a different algorithm (the MDD8) combining the preceding two. The flow accumulation map was used to classify the earth flow, as a function of the flow type: overland flow (83) and channel flow (5). The erosion processes are located in areas with a medium-high saturation and with high values of the erosion and stream power indexes; this defines a kind of processes with strong flow and erosive capacity and high solid transport. Slope and flow accumulation have a greater impact on the calculated indexes than altitude and exposure.