Estimation of linear and areal growth of gullyes using instrumental methods (on the territory of Udmurtia)
The main goal of this investigation is to establish the relationships between linear and areal expansion of gullyes based on their morphology, dimensions and hydrometeorological conditions. Instrumental methods for studying linear and areal growth of gullyes on agricultural land for the period from the early 2000s to 2017 are considered. The instrumental methods of the study included a planned geodetic survey of the top part of the gullyes, including the edges, talweg and transverse profiles using an electronic total station. Records from the three nearest meteostations and stream gages were used in the analysis. The objects of the study include 6 gullyes of various types (at the watershed, near-valley, top and bottom), developing within 6 key areas, where their catchment areas are arable land used for crops of legumes and forage crops. The main purpose of the research is to identify the relationship between the linear and areal growth of ravines, depending on their morphological and morphometric features and hydrometeorological conditions. For two of the gullyes under consideration, the maximum erosion was observed in 2001, when the linear headcuts retreat varied from 2.3–21.8 m, and the areal ones, respectively, from 23.1 to 436.7 m<sup>2</sup>. It is established that in most cases there is a clear relationship between the considered indicators, which is most typical for a bottom single-top gully and at the watershed growing with three headcuts (<i>r</i> = 0.832). A fairly high correlation was also found in the near-valley single-top gully on the right slope of the Vyatka river valley (<i>r</i> = 0.790), which erodes periglacial alluvium within the locality. The average relationship was observed in the single-top (<i>r</i> = 0.569) and technogenic three-top gullyes (<i>r</i> = 0.567) developing in different key areas of the right bank of the Kama river. No connection was found only in one top gully growing in the upper part of the Holocene gulch bottom with three headcuts (<i>r</i> = 0.269), which is explained by the technogenic redistribution of runoff in the plowed catchment of the gully. A smooth change in the area growth over the years and a rather sharp fluctuation in the values of the linear growth of the headcuts of gullyes, regardless of the type and their morphological and morphometric features, were revealed. The dependence of their annual growth on the conditions of land use in the catchment area and their morphological and morphometric features has not been revealed. The analysis of hydrometeorological indicators for 1998–2016 and the linear growth of the considered gullyes did not reveal a close relationship with any of the analyzed factors. A significant relationship between the area growth in 2000–2016 was found only in two gullyes with the intensity of snowmelt and the annual amount of precipitation, and, accordingly, a moderate relationship with the intensity of flood runoff in the line of the nearest small river. The research has shown that the spring flood runoff has ceased to play a dominant role in the linear and areal growth of gullyes during the period under review.