Sergey Fedorovich Krasnov

The paper considers the spatial heterogeneity of the flow of eroded soil material to the foot of the plowed slope and further to the side of the valley in the presence of a lyncahrt resulting fr om mechanical tillage on the lower border of arable land. A small catchment area in the area of intense Chernobyl pollution has been studied, wh ere the po- sition of the lower boundary of the arable land over the past few decades coincides with the upper boundary of the side of the valley. This made it possible to trace the spatial patterns of the distribution of eroded material with stable functioning of the lynchart as an important lithodynamic boundary accumulating and redistributing the slope runoff of sediments. The determination of the volume of material coming from arable slopes was carried out using mathematical modeling of erosion based on a high-precision digital terrain model, climate data, soil erodibility and crop rotations. To assess the intensity of accumulation, 137Cs of Chernobyl origin was used as a reliable tracer. The bulk of the eroded material enters the valley network through a system of slope hollows that concentrate the slope runoff and cut through the valleys. In the areas of the valleys sides outside the runoff concentration zones, the re- deposition of the material mainly depends on the morphology of the lyncahrt, occurs locally and is associated with episodic overflows as a result of the gradual filling of the depression before the lyncart. Under existing conditions, accumulation on the sides of the valley occupies a relatively small share in the total sediment balance of the studied catchment area. Significant changes may occur due to a gradual decrease in the barrier role of the soil as a result of sediment accumulation and climatic changes that contribute to an increase in erosion rates.

The study of erodibility of model soils using the methodology of washing out soil samples with a water stream in a hydrodynamic tube has been carried out. In comparison to the traditional method of vertical loading of cartridges, the new method of soil samples formation using horizontal loading allowed to obtain more homogeneous resistance of samples in the process of their erosion by water flow, to which the formed layers of soil aggregates are located perpendicularly. The use of the «Poseidon» measuring device made it possible to obtain washout intensities in dynamics, to evaluate the quality of sample preparation and to analyze the data in order to cull them, especially in the beginning and the end of the experiments. In addition, the use of the device allowed to skip some operations needed to clarify the data of experiments at their early termination (remainder accounting that requires drying to determine the mass of washed out soil by difference). The data files generated by the device at the end of experiments significantly simplified their processing and considerably reduced the time required for it. The coefficient of varia- tion of the washout intensity value decreased by 12% on average when using the new method of sample preparation compared to the previous one. The moisture ranges with minimum erodibility have been established for model soils. Dependences of soil washing intensity on water flow velocity in the range from 0.5 to 2.5 m∙s–1 were demonstrated. The results confirm the correlation of soil washout intensity with the cube of the flow velocity. Soil erodibility was determined as a coefficient of proportionality between the intensity of soil washout and the cube of flow velocity. The maximum erodibility coefficient typical for agrogray soil equals to 179×10–6, and the minimum value obtained for agrochernozem was 53.0×10–6 s2∙m–2. Agrosod-podzol soil features the intermediate value of erodibility coefficient: 80.3×10–6 s2∙m–2. The proposed methodological approaches and obtained experimental results can be further used to assess the erodibility of soil and soil monoliths and model samples of polyfractional composition close to natural.