Textural features of sand fraction grains as a source of information on the transfer of alluvial sediments in step-pool channels in small forested mountain catchments

Abstract

In small mountain catchments, hillslope and fluvial processes interact closely in both spatial and temporal dimensions. Understanding their interplay is essential for interpreting sediment supply, transport, and deposition in fluvial systems. This study analyzed the sand fraction of sediments collected from the channel of the Dupniański Stream. From these, 100 grains of each of three textural types were selected: Q – pure quartz, QW – „weathered” quartz, and S – sandstone. For each grain, shape parameters were measured: circular equivalent diameter (CE), HS circularity (HS), convexity (CON), aspect ratio (AR), solidity (SOL), and elongation (ELO). Relationships between grain features (above and below of log (LS) and boulder (BS) steps) and variables such as contributing catchment area (A), channel slope (SS), and height (H) and width (W) of the step were examined. Differentiation was based on grain type, deposition location, and the step type. The aim was to assess whether grain texture can indicate sediment processing and transfer in step-pool mountain streams. Three hypotheses were tested: (H:1) Various sand grain types provide insight into sediment sources and processing; (H:2) Grain shaping reflects catchment and channel morphometry; (H:3) Textural features can define a transition zone (TZ) between hillslope and fluvial systems.The study confirmed that using sand grains of varied textures is an effective method for analyzing sediment transfer in small mountain catchments. Grain features reflect their origin (e.g., hillslopes or eroded rock steps) and evolve as they move downstream. This analysis precisely identified the transition zone and revealed links between grain shape and channel morphology.