LAUSR

Abstract The study of sediment connectivity based on the geomorphic characteristics of the watershed has gained interest during the last decades. The calculation of connectivity indexes for a mountainous watershed that is normally susceptible to landslides allows the recognition of the unstable areas that have higher connection to any point such as the watershed outlet. Thus, the knowledge of spatial patterns of connectivity within the watershed is very useful in the sediment-related disaster management because the connectivity provides useful information on sediment pathways. The objective of the present study was to test four different global DTMs to compute the sediment connectivity index (IC) in the Mascarada river watershed (320 km2), southern Brazil. By analyzing the land use for each pixel, the Manning roughness was determined and used for the weighting factor in IC calculation. Field survey and satellite image analysis showed that 420 landslides occurred in this watershed on January 5th, 2017. The calculated IC value maps demonstrated that the hillslopes with landslide occurrences have higher values of IC. Among the tested DTMs, the one with the highest resolution (12.5-m resolution DTM) showed the best representation of the flow paths with high IC values. For all the resolutions, the IC mean values of the landslides scars were larger compared to the remaining area of the hillslopes, where the landslides occurred, which implies higher connectivity of the landslides to the watershed outlet. The results also showed that the 12.5-m resolution DTM generated the lowest mean and the largest amplitude of IC values, differentiating areas with high and low connectivity. It is concluded that the global DTM (12.5-m) is capable to provide important information on sediment connectivity and that together with a landslide inventory it can be an important tool for sediment management in mountainous watersheds.