Model of erosion–landslide interaction in the context of the reservoir water level variations (East Siberia, Russia): Factors, environment and mechanisms

A comprehensive investigation of landslide–erosion interactions has been carried out in the local shore geosystem of the Bykovo site located on the left shore of the Bratsk reservoir. The landslide process develops in the Mid-Quaternary grounds (aQ$_{\rm II}^{3})$ of the erosion-accumulative terrace’s fragment that comprises sand, sand with pebbles, sandy loams and loams. This study aims to assess the environmental factors of interacting landslide and gully erosion processes, to estimate their temporal dynamics by comparative analysis of cartographic models based on the data of repeated theodolite surveys, and to find out what level regime of the reservoir stimulates the activation of the landslide process. The authors propose two-stage descriptive model of erosion–landslide interaction and development mechanisms in the context of the reservoir water level variations in the Bratsk reservoir. The activation of landslide processes in the reservoir shores follows the periods of high water level stands. Shore slope stability is disturbed by abrasion of slope foot and inundation of the slide zone. The soils subject to landslide, erosion–landslide and erosion processes differ in their microstructure and properties. Largest erosion susceptibility is typical of soils with skeleton-aggregated microstructure, fine- and coarse-silt sandy loams and loams of high porosity, whose interstructural bonds are attributed to water-soluble salts (Sws = 0.4–0.5%) and high carbonate contents (Scr = 34–66%). High dispersion and aggregation of clay fractions is typical of the loams of the slide zone. The structure of soils subject to deformation slide is represented primarily by fine-sand particles and aggregates with smaller cohesion and strength properties.