Hydrological hazards at the mouth of the Pechora River

Abstract

The paper presents the results of a comprehensive analysis of the situation with dangerous hydrological processes at the mouth reaches of the Pechora River (from the mouth of the Sula River to the Pechora Bay). The study used data from observations of water levels, discharges and ice phenomena at hydrological gauges (until 2022), information about inundations and adverse shallowing that occurred here, satellite images (since 1991). It was found that the main damage in the mouth of the Pechora River is caused by river inundations, one of the main factors of which is ice dams. It has also been established that the long-term repeatability of the icedam formation is actually greater than the gauge observation shows. During the spring flood, the floodplain is flooded almost annually, and in 25–50 and 10–14 % of years the water level exceeded the adverse and dangerous values. The city of Naryan-Mar often suffers from floods. Until the 1970s, these occurred almost every other year; more recently, there were major inundations in 1998, 2008, 2014 and 2017. The most dangerous season for the formation of ice dams and the occurrence of inundations has been determined. On a long-term scale, the frequency of flooding and ice-dam formation has remained practically unchanged, the duration of floodplain flooding has increased everywhere, whereas the time of the water level exceeding the adverse mark has increased in the river mouth segment upstream from the delta and decreased in the delta. The empirical dependencies between the water levels and the area of flooding, between maximum water levels and the duration of flooding are substantiated. There are four main scenarios of the channel of the Pechora River and delta branches opening from the ice cover in spring. The location of the main points of ice-dam formation has been specified. The third unfavorable hydrological process within the Pechora River mouth is adverse water runoff shallowing, which disrupts river navigation. In the vast majority of cases, it is associated not with low water levels in the delta, but with those in the middle and lower reaches of the Pechora River. This period lasts from August 11 to September 6. On a long-term scale, the situation with minimum levels in the summer and autumn season has improved. As regards other unfavorable hydrological phenomena — anomalous (by date) ice formation, sea-water intrusion into the delta branches, storm surges and wind-induced down-surges — it has been found that they do not cause damage either because of their low intensity and repeatability, or because they belong to other parts of the Pechora mouth region.