Flow Structure in a River Bend in the Cryolithozone
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Vol. 54, No. 3, September, 2020
FLOW STRUCTURE IN A RIVER BEND IN THE CRYOLITHOZONE E. N. Dolgopolova1 Translated from Gidrotekhnicheskoe Stroitel’svo, No. 3, March 2020, pp. 32 – 35.
Rivers of the cryolithozone are under consideration. The structure of open-water and ice-covered flows in this zone is determined by moderate river falls, high sinuosity of rivers, especially delta branches, and long freeze up periods. The basic relationships describing the open-water and ice-covered flows in straight reaches of rivers are presented. Special attention is paid to modern studies of features of flow in a river bend. Keywords: river; river mouth; cryolithozone; ice-covered flow; flow structure in river bend.
curvature R ® ¥, then the channel is a series of bends with different radii of curvature. Let us consider the major features of the influence of ice on the flow in a straight reach and a bend of a river.
The channels of all rivers consist of more or less straight reaches connected by bends. Within some reaches, bends run into one another, forming a periodic function in plan, which is often used in mathematical descriptions of riverbed processes [1 – 3]. The degree of sinuosity of a river is estimated using the sinuosity coefficient k = L/l (L is the channel length; l is the straight-line distance from the source to the mouth, varying from 1.1 to 3 and more). Meandering is peculiar to the rivers of the cryolithozone, especially delta branches of the Arctic coastal zone, which form many bends. The slopes of mouth valleys are much less than medium river falls, which creates conditions for occurrence of meanders and ice jams after breakup of river ice. The coastal tundra in Russia is 50 to 80 m above the ocean level; therefore, river falls vary as follows: i = 2 – 5 × 10–4 from the Pechora to the Kolyma, 5 × 10–5 for the Mackenzie Delta, 10–4 for the Yukon Delta, and 7 × 10–5 for the Colville Delta (average i ~ 3.85 × 10–3) [4 – 10]. The ice in the rivers running into the Arctic seas starts to break upstream, and the ice-break wave, moving from south to north, meets rivers bends that are still under a thick ice cover, which creates conditions for occurrence of ice jam. In this case, either an ice jam forms or the flow moves over the ice-covered watercourse, entraining ice and sediments toward the sea edge of the delta, which is typical for the delta branches of the Yukon and Colville [5, 10]. Ice jams can also be promoted by the following features of river channel: sharp bend, abrupt narrowing, branching, flow divagation from bank to bank, and riverbed formations. Thus, open-water and ice-covered meandering flows cause the reconfiguration of river channels, and their structure is of great theoretical and applied interest. If straight reaches of a river are represented by bends with radius of 1
Flow in a Straight Reach of a River Open-water flow in a lowland river can be considered two-dimensional, and its structure is well-known and described mathematically [11 – 13]. A two-dimensional flow in a river covered by ice
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