Measurements of rainsplash erosion and the formation of colluvium beneath deciduous woodland in the Luxembourg Ardennes

Abstract

AbstractIn wooded dry valleys in the Luxembourg Ardennes a gravelly and slightly organic colluvial deposit occurs. The depositionary nature of the material is ascertained by its micromorphological characteristics and its position on top of a truncated argillic horizon of an older soil. Pollen analysis revealed the colluvium to have been formed in the last 500 years, the lower 37 cm in the Haarts valley under non‐forest (presumably arable land) conditions and the upper 10 cm under today's oak woodland. A formation of the colluvium by Horton overland flow is ruled out by permeability and infiltration capacity measurements of the forest soil. The importance of rainsplash erosion for the formation of the upper part of the colluvium is demonstrated with simplified Ellison type splash boards. Two modes of transport, induced by raindrop impact, may be distinguished, one through the air (particles up to 6.3 mm) and one across the soil surface (particles up to and above 1 cm). The overall grain size distribution of the trapped soil strongly resembles that of the colluvium, and the gravel sized rock fragments in the colluvium certainly do not exclude an origin by rainsplash erosion.