Analysis of Impact of Urbanization Development on the Deterioration of Ecological State of Rivers

Abstract

Abstract The peculiarity of small rivers is the dependence of erosion-accumulative processes in their beds on the intensity of soil erosion in the catchment area: the smaller the river, the greater the contact with the catchment area of its channel, where mineral particles, washed off from its area, directly enter it. Soil erosion leads to the entry of an excessive amount of them into the channel of a small river, as a result of which sediment accumulation begins in it, siltation of the channel occurs. It leads to changes in the water regime of small rivers - a decrease in inter-soil runoff (up to the drying up of rivers), a sharp reduction in underground power supply. In the humid zone, due to the high water content, the siltation of small rivers is poorly expressed and has a local character. Siltation of small rivers is especially characteristic for the forest-steppe and steppe zones, as well as for the south of the forest zone. In the steppe zone of the European part of Russia, as a result of siltation, rivers of the first order completely disappeared, up to the fourth (up to 40-50 km long), leading to a total reduction of the river network by up to 30 %. In the forest zone, due to the disappearance of sources, the number of rivers of the first and second orders (up to 20 km long) decreased by 2.2 times. During the agricultural period (about 300 years), a layer of sediment with a thickness of 0.5 to 1 m accumulated in the beds and floodplains of small rivers in the southern half of the European part. The erosion of small riverbeds reaches on average only 20 % of washed off products, which is about 60 % of the total river sediment runoff. The rate of siltation of small rivers in the Don basin is 6-12 mm / year with a length of up to 25 km and about 1 mm/year with a length of 100 km and above. Siltation of small rivers is not typical for regions where the soil is washed away by meltwater, since the maximum flow of sediment into the rivers coincides with high water, when the channel-forming activity of water flows is most active.