Sediment Runoff and Water Turbidity of the Main Tributaries of the Lake Ladoga

The vast catchment area of the Lake Ladoga is characterized by variety of underlying surface types and a complex hydrographic network. The processes of eutrophication of the southern littoral areas of the Lake Ladoga determine the relevance of assessing the removal of solid matter from the river flow to the estuaries of the tributaries of the Ladoga. Observations of sediment runoff of the main tributaries the Lake Ladoga were not carried out. In this regard, for each tributary were selected rivers-analogues the main criteria in the selection was the slope, the grain size of sediments and the catchment area (water availability). The modeling of annual solid runoff and turbidity of the Ladoga tributaries is based on an analytical formula for sediment flow by M.V. Shmakova and a stochastic model of annual solid runoff (M.V. Shmakova). According to the calculations, the annual flow of sediment entering the Ladoga water area is about 432 thousand t/year. The main sources of sediment are three major tributaries of the Lake Ladoga – the Svir, Volkhov and Vuoksa rivers, which account for 253 thousand t/year or 59 % of the total amount of sediment received in the lake. However, these watercourses have the smallest annual module solid flow, due to retention of sediment of backwater areas before hydroelectric dams on these rivers and as a consequence, a decrease in the overall sediment discharge. At the same time, the average annual solid runoff modulus for the Ladoga lake catchment area is 1.53 t/(km2·year), which corresponds well to the previous estimate of this value for the territory under consideration. The analysis of the annual module of solid runoff showed a good correspondence between the obtained values of this value and the conditions for the formation of solid runoff in the catchment, the characteristics of its soils.