# Aggregate and Particle Size Distribution of the Soil Sediment
## 1 Introduction
The studies where the sedimentation methods and laser diffraction were compared conclude that the volume representation of the clay fraction obtained by laser diffraction was generally lower than the mass representation of the clay fraction derived by the pipette or hydrometer method, while an opposite trend was determined for the silt fraction [21; 23; 27; 28; 29; 30; 31]. Conclusions from the study of comparison of laser diffractometer and sieving method are that the sieving method underestimates particles which contain non-equant grain types compared to the laser diffraction, because grains with a width to length ratio of 0.5 can pass through smaller mesh size of the sieve [31]. [PERSON] et al. [32] who presented an integral suspension pressure (ISP) method--this method is based on the temporal change of the pressure measured with high accuracy at a certain depth within the suspension to derive the particle size distribution--concluded that the results from the pipette method and the ISP method are in a very good agreement. In previous studies, the impact of slope to the erosion processes was investigated. [PERSON] et al. [33] found that if the slope is lower than 18\({}^{\circ}\), the intensity of erosion processes increases equally to the degree of the slope. For slopes from 18\({}^{\circ}\) to 25\({}^{\circ}\) the relationship between the erosion and the degree of the slope is exponential. On the other hand, the erosion processes decrease for slopes higher than 25\({}^{\circ}\). The higher the slope, the greater the influence of the rainfall intensity. The slopes of the experimental plots investigated by [PERSON] et al. [34] were 35\({}^{\circ}\), 40\({}^{\circ}\), and 45\({}^{\circ}\), and rainfall intensity was 102 mm/h. They concluded that with higher slope less water percolate to the soil which causes greater runoff and erosion effect. Erosion processes are influenced by the aggregate stability (AGS) and possibilities of their disintegration [35]. [PERSON] et al. [36] conclude the possibilities of the laser diffraction method in the studies of AGS. In most of the soil erosion studies, and in general, the size-selection of the sediment is recognized as a common natural process [37; 38; 39]. In another study, it was found that the fine particles were washed out during sheet flow and splash erosion, while the coarser particles were eroded during rill and interrill erosion [40]. The goal of this contribution was to achieve more detailed monitoring of the percentage representation of eroded aggregates and their distribution in individual soil fractions in relation to the slope gradient, precipitation duration, and the initial state. The research was focused on the bare soil on the steep slopes that are situated along linear engineering structures (road, railways, embankments). Many of recent studies have mainly been focused on soil erosion on cropland [33] where the slope is usually small. This study aims to investigate soil erosion processes on steep slope land, which has not been studied thoroughly before. Also, our study benefits from the large sizes of the experimental plots, which ensures good reliability of the results. In this study, three different methods to determine particle size distribution were compared to find the best suitable method for this research.