Factors Affecting the Rates and Modes of Landslide Colluvium Removal in River Channels of Podhale (Western Carpathians)

Abstract

This paper presented some hydrological factors affecting the course and rate of fluvial erosion of landslide colluvium at its contact with river flow. Volumes of colluvium eroded by rivers in the period 2013–2019 were measured at Podhale (a part of Polish West Carpathians) on four landslides representing various geological settings. At each landslide, changes in shape and position of the contact zone between colluvium and river water were registered after episodes of high river stage. The obtained data on changes in relief of the landslide fronts and adjacent river channels were used to calculate volumes of colluvium removed during each episode. The course of erosion and volumes of colluvium eroded were compared with the water stage records for the studied period of time. Intensity of colluvium erosion was found to be strongly dependent on the water levels and cohesion of colluvium. Volumes of removed colluvium were the greatest during short-lived (1–2 days) and prolonged (7–10 days) periods of high river stages. The rate of erosional removal was the highest for colluvium consisting of poorly consolidated Quaternary matrix-supported massive gravel and overlying fine deposits stored within river terraces. Colluvium composed of Neogene mudstones and sandstones was removed at a lower rate and the rate of removal was lowest for large blocks and slices composed of solid layers of alternating sandstone and shales belonging to the Podhale Flysch series. Erosion of the landslide toes was more intense at those sites where the river flow approached the landslide front at a wider angle.

Landslide type inference based on statistical analysis of a high-resolution digital elevation model in Gorce National Park, Poland

“…Landslides that remain in contact with stream channels are constantly active, as they are under the influence of continuous fluvial erosion 44 . The intensity of colluvium erosion near the rivers in the Outer Carpathians was found to be strongly dependent on the water levels in the adjacent stream 45 . We also observed a similar phenomenon, with a significant number of landslides in the immediate vicinity of watercourses in the Gorce National Park study area.…”

Sediment sources and connectivity linked to hydrologic pathways and geomorphic processes: a conceptual model to specify sediment sources and pathways through space and time

“…On the falling limb, the river water continued to erode the colluvial layer as the pore water drained during a rapid fall of the flood wave when the river is mainly recharged through baseflow. Rise in the groundwater level through infiltration within landslides after a rainfall event also led to the reactivation of slope failure and increased the supply of colluvium to the channels (Kukulak et al, 2022). In another exampl e from a small stream in the Mid-Atlantic USA, Rose et al (2018) observed the combination of OW and US loading during an extreme climate event (ECE).…”