Genesis, scenarios and features of flood prediction in the middle reach of the Amga River (Central Yakutia)

Abstract

Ice-related phenomena made a significant contribution, more than 0.5 m, into the formation of the maximal water level on the Amga River in the cross section near Amga settlement during 41 high water episodes out of 76 (1938–2018). The average value of the ice jamming input into the maximal water level was 1.6 m, during the years with floods – 2.4 m, and the maximal value exceeded 5 m. With respect to the genesis, floods on the Amga River belong mainly to discharge-jamming type – fourteen cases, or to discharge type – five cases during the years 1938 to 2018. The scenarios of the development of discharge and ice-jamming floods differ from each other. Ice-jamming floods occur four days earlier on average and involve lower moisture content in the snow than that in the case of discharge floods. During the years with late expanded springs, floods occur very rarely. Synoptical parameters may be used to make assumptions concerning the type of forthcoming floods, but it is necessary to develop more accurate quantitative methods to predict the probability of the floods and their expected levels. These methods should take into account the non-stationary nature of the main synoptical factors leading to waterfloods. The rate of flood repetition during the time of observation remains unchanged, which points to inefficiency of the measures against jamming that were carried out in the river basin during the two recent decades.