Влияние зарастания и заиления речного русла на водный режим рек (на примере р. Полометь)

Siltation and overgrowth of riverbeds occur on many small flat rivers as a result of natural causes and economic activities in the catchments. If the water runoff is generally stable over the long term, then the imbalance in the "water runoff – sediment runoff" system occurs due to changes in sediment runoff. The change of economic activity in the catchments, the extraction of building material from the riverbed, activate erosion processes and sediment flow into the water stream. As a result, long shoals are formed on the underlying river sections, where the slopes of the riverbeds decrease. Favorable conditions for overgrowth are created here. Overgrowth leads to an even greater decrease in sediment transport and siltation of riverbeds. The purpose of the article is to show the role of overgrowth and siltation in changing the water regime using the example of the Polomet River (Lake Ilmen basin). A comparative analysis of changes in river flow in an 8 km long section during the period of free and silted, overgrown riverbed has been carried out. It was established by the channel balance method that overgrowth with siltation led to a loss of 10–15 % of the annual runoff. Due to the decrease in the flow rate of the riverbed, some of the water began to spread over a vast swampy lowland. Most of this water evaporates in flooded and flooded areas, including overgrown and swampy hayfields and arable land in recent years. Runoff losses for evapotranspiration are comparable to evaporation. Siltation and overgrowth change flood conditions and their effect on the Polomet River is comparable to lake regulation. There is a decrease in the maximum water consumption, smoothing of the flood wave and an increase in the duration of standing high waters. Since clearing riverbeds is extremely expensive, in the context of current climate change trends and the ongoing reduction in the maximum water consumption of spring floods, a further increase in overgrowth and siltation of small riverbeds should be expected. This can have an even greater impact on the irretrievable loss of water resources by evaporation.