Nizhnyaya Tunguska River - Hydrology

Hydrology

The value of average water discharge of Lower Tunguska gives it eleventh place amongst largest rivers of Russia. The annual water discharge of river's mouth is equal to 3,680 m³/s. The minimum value observed in 1967 was equal to 2,861 m³/s, the maximum one was 4,690 m³/s in 1974 or, respectively, for estuary of the river it corresponds to ~3,093 m³/s and ~5,070 m³/s. Water supply of the river is due to melting snow and summer rains. During winter season Lower Tunguska contains little water as its basin lies in the region of permafrost and it has not subterranean water sources. According hydrological observations during 52 years, the minimum average monthly discharge was equal to 27.8 m³/s in March 1969 — it was exceptionally dry winter — and the maximum value corresponds to June 1959 and is equal to 31,500 m³/s. The diagram below contains mean values of monthly average discharges calculated on the base of 52-year long period of observations at hydrological station "Bolshoy Porog".

The 73 per cent of entire annual water yield corresponds to the period of spring-summer season. The amplitude of water level variations in the lower stream of Nizhnyaya Tunguska is very high and is highest among all notable rivers of Russia. The narrow places of river channel jam ice during its seasonal drift creating temporal dams which blocks normal water flow and raises water level up to 30–35 m above mean value. The summer break-up and drifting of ice passes very violently, it leaves traces in the form of torned apart uprooted trees, polished rocks etc. During some days of spring freshets the river's discharge can peak at 74,000-112,000 m³/s and it supplies 50-60% of water volume to the lower stream of Yenisei river in the time of its seasonal inundation.