Flow Waters, Suspended Matter and Speed of Erosion of Karelian Coast

To determine the rate of decline in the drainage areas of the Karelian Coast, in the 2005–2017 period year-round observations of watercourses flowing into the Chupa, Medvezhya, Keret and Letnaya bays of the White Sea were carried out. In rivers and streams, seasonal and annual changes in water discharge and suspended matter concentrations were studied. It was revealed that the river water runoff does not exceed 2.5 km³, and the stream runoff does not exceed 45 mln m³ per year. The annual water runoff is distributed as follows: on average, 40 ± 2% is carried out during the spring flood, 33 ± 1% during the autumn flood, and 23 ± 1% during the summer low water. Despite the length of the winter period, the winter water runoff never exceeds 8% of the annual runoff. According to the suspended matter concentration, the watercourses of the Karelian Coast are classified as watercourses with a pure water mass, since the long-term average concentration of suspended matter in them is 3.30 ± 0.95 mg/L. It was revealed that the total river runoff of suspended matter is 6.5 thous. t per year; streams carry out less than 500 t of suspended matter per year. Based on the data obtained, an assessment was made of the module of suspended matter runoff and the rate of erosion of watersheds. The mean long-term modulus of suspended matter runoff averages 1.98 ± 0.31 t km^–2 per year, the erosion rate is 1.1 ± 0.17 µm per year (n = 382). The low runoff modulus and the slow rate of decline in the catchment areas are due to the geographical location and geological and geomorphologic structure of the Karelian Coast.