Impact Of Mozhaysk Dam On The Moscow River Sediment Transport

Abstract

Sediments are an essential part of the aquatic environment that define its transformation and development. The construction of dams results in severe changes in sediment fluxes. This study aims to assess how the sediment load of the upper Moskva River is affected by the Mozhaysk Dam flow regulation and to estimate its dynamics over the years of the reservoir’s existence. Our analysis of the 1968, 2012 and 2016 detailed field data shows a 20-40% decrease in the proportion of the spring flood in the annual sediment load into the reservoir, which is caused by changes in the streamflow regime of the inflowing rivers. The peak suspended sediment concentrations have decreased 5- to 10-fold, likely due to a significant decline in the watershed’s cultivated land area, which caused a decrease in the erosion rate. In the Moskva River below the dam, the seasonal dynamics of the suspended sediment concentration no longer corresponds to the natural regime. The annual suspended load of the Moskva River below the Mozhaysk Reservoir decreased up to 9-fold. The sediment retention in the reservoir has dropped from 90% to 70-85% and is to some extent restored by an outflow of the particulate organic matter produced in the reservoir. We also described the relationships between water turbidity and suspended sediment concentration of the reservoir’s tributaries, which allow for the first time to estimate the sediment load with higher accuracy than was previously possible.