Preliminary study on mountain slope partitioning addressing the hierarchy of slope unit using DEMs with different spatial resolution

This study proposed a procedure of mountain slope partitioning for landslide hazard assessments that addresses a slope unit hierarchy. This study was undertaken to validate the procedure of slope partitioning using DEMs with different spatial resolution by comparing the relation between the average slope angle and relative height of each slope unit in the Akaishi Mountains and the Shikoku Mountains, Japan. We used DEMs of three types with spatial resolutions of ca. 50 m, 30 m, and 10 m grid cells. In general, individual slope units are partitioned by drainage and divide lines. We therefore newly defined an order of divide lines and partitioned slope units. Divide lines were regarded as catchment boundaries. The order of divide lines was defined according to frequency of divide lines that were extracted as catchment boundaries from DEMs, with changing area conditions of catchment identifications. By partitioning slope units with these divide and drainage lines, slope units therefore showed a relative hierarchy corresponding to the order of divide lines. These procedures were validated and cross-checked using both different spatial resolution DEMs and the different study areas, considering the relation between slope angle and relative height of each unit. Partitioned slope unit maps revealed inclusive relations among the hierarchies: a slope unit consisted of units with a low-order hierarchy, and was included in a high-order hierarchy. A scatter diagram of slope angle and relative height of each slope unit revealed a concentrated distribution that corresponds well to previous studies. This distribution was confirmed in both different DEMs and the study areas. These results demonstrate that the procedure of slope partition is useful to identify the same slope unit using DEMs of different kinds, and in different areas.