The effect of surface rock fragments deployment pattern on soil erosion processes under simulated conditions

Extended abstract 1- Introduction The Soil surface characteristics have significant effects on the erosion process. The wide areas of watershed soil surfaces are covered with considerable amounts of rocks and pebbles. Surface rock fragments, resulting in water connectivity, change during the erosion process. Rock fragments on the soil surface may increase the infiltration and reduce soil losses because they can act as protective covers. When rainfall and runoff occur, this coating can has an important effect on soil erosion, sediment production, and infiltration processes. Surface rock fragments can protect the soil surface from raindrop impact, which further decrease the overland flow and its transport capacity, thus reducing erosion. But the effect of deployment pattern for these impermeable surfaces on the soil erosion phenomenon is not well known. 2- Methodology In the present study, using a rainfall simulator and soil erosion plots, the effect of impermeable rock surfaces include control (zero), 10, 15 and 20 percent of plot surface coverage, in three surface, semi-embedded and embedded situations and in three replications (30 plots in total) were studied. The experiments were performed in the rainfall and erosion simulation laboratory of the university of Torbat-Heydarieh. The erosion plots were smiliar to a  rectangular with a length of 1 m and a width of 0.5 m. The plots with a constant gradient of 9% for 10 minutes were exposed to rainfall with an intensity of 1.4 mm/min and after each rainfall event, the runoff volume, sediment production, sediment concentration, runoff coefficient, and infiltration rate were sampled and calculated at the plotchr('39')s outlet. Also, the spatial variations of sediment at the surface of plots were measured and compared using Laser roughness meter in different sections before and after each simulation. 3- Results The results showed that by increasing the percentage of rocks in the surface situation, the amount of sediment production increases, the volume of produced runoff volume decreases, and the infiltration rate increases. However, if the rock fragments are embedded, the sediment load and volume of produced runoff increase but the infiltration rate decreases. However, the main and interactive effects of treatments on soil erosion processes were not significant. Finally, according to the results of the comparison between pre-and post-roughness data in each treatment, there was a significant difference between the two groups. That, the difference between the groups, were caused by two factors: plot-level drop or the sectional transportation of sediments at the plot area. 4- Discussion & Conclusions In the current simulation study, the runoff and sediment yields were measured in soils with the different surface rock fragments in the laboratory utilizing a rainfall simulator and erosion plots. The most commonly utilized method for studying the influence of rock fragment cover on hydrological processes is to simulate rainfall on disturbed soils under laboratory conditions. The results showed that the difference between soil erosion and sediment production at the erosion plotchr('39')s level is also very considerable. So, the sediment delivery ratio should be seriously considered in erosion studies. It should be noted that the evidence of such differences between sediment analysis results and spatial changes of sediment, presents a new challenge for the erosion modeling and all of these inter-relationships should be perceived well enough that it would be possible to make them into effective erosion models.