Traditional versus modern settlement on torrential alluvial fans considering the danger of debris flows: a case study of the Upper Sava Valley (NW Slovenia)

Abstract

Abstract We analysed spatial development of traditional and modern settlements on active alluvial fans in the Upper Sava Valley (NW Slovenia), by using old cadastral data from the beginning of the 19th century, time series of aerial photographs from the middle of the 20th century and recent building cadastre. The valley is surrounded by the mountainous Julian Alps in the south and the Karavanke Mountains in the north where there is a lack of space for settlements due to steep slopes that are increasing the danger of slope processes, torrential processes and floods. By using a very high-resolution 1m LiDAR digital elevation model, we defined the morphometry of alluvial fans and the characteristics of the drainage system of contributing tributaries. We classified the areas according to the threat posed by the modelled torrents and debris flows. We analysed the resilience of settlement in different periods from this perspective and evaluated the integration of natural processes effects in modern spatial planning projects. We found that geomorphic processes threaten a relatively large proportion of some new and old settlements on alluvial fans and that safe planning of areas of settlement has been successful neither in the past nor in recent decades.