SURFACE RUNOFF TRANSFORMATION BY A FORTIFICATION RAMPART AND ITS APPLICATION TO ASSESS HISTORICAL AND MODERN SEDIMENT ACCUMULATION RATES

The article presents the assessment of modern and historical denudation rates in the fortification from the end of the 17th century – a section of the Karpov rampart of the Belgorod Line (Belgorod Oblast, Russia), and in a ravine that was formed in the same period as a result of the surface runoff transformation. The study object includes a ditch associated with a rampart (catchment area of 0.49 ha), which accumulated sediments over 344 years under natural sod cover, and a ravine of comparable age with a catchment area of 18.1 ha. The research methodology combined instrumental topographic survey, analysis of cartographic and satellite data, soil-genetic studies of vertical profiles of pedosediments in the ditch and ravine, as well as an assessment of modern accumulation rates using the chronomarker of the 137 Cs isotope. It was established that the average rate of pedosediments accumulation in the ditch was 0.26 cm per year, which corresponds to the average annual rate of erosion from slopes with high soil-protective efficiency of 2.5 t per ha. In general, since the second half of the 20th century (20% of the duration of the existence of the rampart), the maximum accumulation rates for the entire historical period have been observed: during this time, a third of the thickness of pedosediments was formed, and the rate was almost two times higher than the long-term average. Estimates of the modern rates of sediment accumulation in the ditch have shown a significant change in the accumulation rate over the past 70 years: before and after the Chernobyl accident in 1986, it decreased from 0.56 cm per year to 0.32 cm per year. The same tendency is characteristic for the rates of linear erosion. During the same periods, the growth of the ravine slowed down by 8 times (from 0.8 to 0.1 m per year), and its transformation into a dry valley occurred. The distribution of the percentage of particles less than 0.01 mm in size in the pedosediments profiles as an indicator of the variability of the water erosion intensity over the past 50 years shows the same nature of the formation of suspended sediment runoff both in the ditch and in the ravine, despite the significant differences in the area of the catchments. The features of a half-century period are shown, which was characterized by a sharp reduction in the snowmelt runoff layer from the 1970s against the background of an 8% reduction in rainstorm precipitation with a layer less than 10 mm.