On the hydrological role of the relief in the southern part of the Russian plain

On the example of a southern part of the Russian Plain the surface slope runoff, the runoff from the hydrographic network and snow melt river runoff are considered. Based on the analysis of the data by water balance stations and the correlation of surface slope runoff values from different lands to the zonal river runoff value, the zonal values of the spring surface slope flow from separate lands located on loam and sandy loam soils are determined. Within agricultural lands there are fall plowed fields and non-plowed in autumn (stubble, layland, winter crops, perennial grasses). By the beginning of the spring flood, the soil at autumn-plowed fields is loosened and reduces the runoff, while on the fields that were not plowed in the autumn soil is compacted. In addition, the microtopography created by autumn plowing also contributes to the runoff reduction. The smallest surface slope runoff occurs under the forest. Differences in runoff increase in the direction from the southern part of the forest zone to the steppe areas. Taking into account the land composition and the mechanical composition of the soils, the weighted average values of the surface slope runoff were obtained for the period of the long-time average annual flow calculation (late 19th century and early 1960s). It is shown that subsequently there was a decrease in the spring surface slope runoff, initially as a result of the autumn plowing increase, and more recently, mainly as a result of changes in meteorological conditions, especially during the cold season (air temperature rising, frequent thaws, increased infiltration). In the overall structure of the spring river flood, along with a decrease in the share of surface slope runoff, the share of surface runoff formed in the hydrographic network increases, and especially the flow of infiltration origin (verhovodka and underground runoff). In the steppe zone the structure of river flow has changed most significantly.