Oleg Yermolaev

Geoinformation mapping of soil erosion in the Middle Volga region

The results of a medium-scale geoinformation mapping of soil erosion on an area of about 150000 km2 in the Middle Volga region are analyzed using the catchment-based approach. A quantitative index of the development of soil erosion on the agricultural lands is suggested. It reflects the intensity of soil erosion on slopes within the river catchments. A computer-based vector map of the boundaries of 3331 elementary catchments has been developed. It represents the territorial units for the analysis of soil erosion. Archive materials from the former institutes for land survey have been used to compile a series of the maps of soil erosion in river catchments on a scale of 1: 200000. The zoning of erosional processes has been performed, and the natural and anthropogenic levels of soil erosion in different basins have been estimated. The analysis of these materials shows that the topography and agricultural activity of humans are the major factors controlling the development of erosion. The maximum development of soil erosion in the studied region is typical of the subzone of broadleaved forests.

Evaluation of Erosion Intensity and Dynamics Using Terrestrial Laser Scanning

A new method of instrumental measurement of the intensity of rill and linear erosion on slopes by the method of terrestrial laser scanning is proposed. This method was tested on four plots in 2012–2016 with the use of Trimble™ GX, Trimble™ VX, and Trimble™ TX8 laser scanners. The terrestrial laser scanning is characterized by a high precision and rapidity, which could not be previously achieved by other devices. It has a number of advantages: registration of various types of erosion of temporary water streams; measurements from a distance without the disturbance of the studied surface and providing the safety of works; and calculations of morphometric parameters of slope using a high-precision digital model of topography. The given examples show that this approach may be applied to assess the denudation-accumulative balance of the moved soil material on slopes, to determine the dynamics of amount of deposits on different parts of a slope as a result of different kinds of surface runoff, and to identify spatial regularities of the formation of the network of rills and gullies. In addition, laser scanning makes it possible to perform an integral assessment of the combined impact of the entire combination of exogenous processes developed on slopes and affecting the soil cover. The observations on test plots showed a rather great role of autumn rains in the total soil loss from erosion. The data obtained were used as the basis for the elaboration of practical recommendations concerning the survey organization and monitoring of erosion with the use of laser scanning.

Mapping and spatial-temporal assessment of gully density in the Middle Volga region, Russia: Spatial-temporal assessment of gully density in the Volga region

A large-scale mapping of gully density was carried out for the Middle Volga region of the Russian Plain (188 000 km) based on the interpretation of aerial photographs (scale 1:17 000; surveys undertaken during 1956–1970). In addition, spatialtemporal dynamic of gully density were assessed for some parts of the study area (the Udmurt Republic and the Mesha and Ulema River basins of Tatarstan), based on the interpretation of aerial photographs (survey 1986–1991) and high resolution satellite images (2012–2015). Information on factors potentially controlling gully formation and development were collected and a geographic information system (GIS) analysis was conducted. Results show the strong development of gullies in the study area over the 1956–1970 period with an average gully density of 0.21 kmkm . For the Udmurt region, we found that gully densities varied little in the period 1956–1986, during which the total active gully length reduced with only 2%. This period was characterized by low variable climatic conditions and a stable fraction of arable land with a relatively continuous crop rotation system. However, gully dynamics seems to have changed more strongly during recent decades. We found a strong (order of magnitude) reduction in active gully density for the period 2010–2015 as compared to 1986–1991. The main reason for this is likely the increasing winter air temperatures. This leads to a significant reduction in surface runoff during spring as a result of snowmelt. Nonetheless, in some regions (i.e. the Udmurt Republic in the taiga zone), the abandonment of arable land after 1991 likely plays a significant role. Likewise, a decline in the frequency of extreme rainfall events (> 50mm) may have played a role. All of these factors contribute to a reduction of surface runoff to the gullies and their subsequent stabilization.