Landslides and gully slope erosion on the banks of the Gauja River between the towns of Sigulda and Līgatne

This study examines contemporary and past slope erosion processes in the Gauja River valley and adjoining area between the towns of Sigulda and Līgatne. In the field survey landslides and gullies were mapped. Spatial landslide and gully data were correlated with the landslide- and gully-related features (local relief, slope lithology, slope form, slope angle and density of gullies). A novel approach was applied to establish the relationships between slope processes and factors influencing them. This approach uses correlation between raster values of landslide-related factors in specific slope sections and the number of slope processes in these sections to determine the areas prone to slope processes and their causes. As a result, the susceptibility index of the landslides and gullies was mapped and compared with landslides and gullies from field observations. The map of landslide susceptibility was more compatible with observations from field studies than the map of gully susceptibility. A more developed gully network in the northern part of the study area can be explained by smaller resistance of sediments to erosion, while in the southern part of the study area shallow dolomite deposits are limiting gully erosion. The distributed sediment volumes in separate zones were calculated to compare erosion rates on both banks of the Gauja River. Higher erosion rates were obtained for the left bank. Large cross sections of tributary valleys and large gullies, poorly developed erosional network, weak correlations with slope angle and lithology indicate that the erosion network was formed in a short time interval, possibly during the Late-Glacial period in paraglacial environments.