Identification and Mapping of Shallow Landslides in the City of Zagreb (Croatia) Using the LiDAR-Based Terrain Model

Landslides in the hilly zone of Medvednica Mt. were identified visually using LiDAR DTM with a spatial resolution of 15 x 15 cm. Acquisition of the LiDAR data was performed in December 2013, following an extreme precipitation period that resulted in numerous landslides. Topographic derivative datasets for interpreting landslide morphology were computed from the LiDAR DTM: hillshade maps, degree of slope, contour lines, curvature, and surface roughness. Visual interpretation of LiDAR DTM derivatives was taken for the pilot area of 21 km(2), which represents 12% of the hilly area in Zagreb City. This resulted in a landslide inventory map, indicating the contours of 676 landslides. Seventy-five percent of the landslide bodies showed a size between 159 and 2018 m(2). The area of the smallest identified landslide in the test area is 43 m(2). The majority of mapped landslides are located in a forested area. Each mapped landslide was assigned a level of confidence based on the LiDAR characteristics and it could be concluded that the LiDAR-based terrain model is a valuable tool for preparation of landslide inventories in heavily vegetated regions such as the hilly area of Medvednica Mt. The analysis of morphological properties of the landslides will be implemented to perform a semi-automated landslide mapping in the entire hilly area of the City of Zagreb (total area is 180 km(2)).