Статьи

Key words: hydrological maxima, type of channel processes, forms of channel,channel-forming water discharges, channel forming factors

Disastrous river rearrangements caused by extremely infrequent hydrological maxima are seldom studied among known kinds of river channel formation.

There are 3 qualitatively distinguished types of channel rearrangements:

1. Quasicyclic recurrence of the forms of a channel within the framework of a definite type of channel processes at close to the average of the water regime (N. Kondratyev, 1982). These channel recurrences are the most studied, but existing results do not give the explanation of the causes of their formation.

2. Transformation from formation of a channel for definite type of channel processes to another type at the change of the main channel forming factors. The laws relating to type changes are less studied. One of the causes of change-type of channel processes is the relative conveying capacity of flow. The change of type follows a set pattern. Often it results from high discharge levels. Understanding the role of relative discharge explains the causes of formation of dynamically equilibrium type of channel processes (A.Kondratyev, 1999). Examples of a change of class are rivers Patuksent (USA), Zeya, Polomet, Amur (Russia), (Karasyov, 1975, Sidorchuk, 1992).

3. Catastrophic change of the river as a result of a flood. In this case, the new river appears instead former one. It has new morphometric and hydrodynamic parameters, which derives from the characteristics of a former channel. Such transformations are rare, but essential. New laws of beds formation are poorly known. N.S. Znamenskaya has elaborated the adequate scheme of formation of dynamically equilibrium type of channel processes, based on the disastrously caused initial straight-line beds. As example the river Issik (Uzbekistan) may be considered (Znamenskaya, 1992).

Channel-forming discharges lose sense in the event of the catastrophic flood (Makkaveev, 1988). In this case it is necessary to apply the method of computation of disastrous channel-forming water discharges offered by I.F. Karasev (Karasyov, 1975).

References:

1. Znamenskaya, N. S., Hydraulic modeling of channel processes. St Petersburg, Hydrometeorological Publishers, 1992, 240 pp. (in Russian)

2. Karasyov, I. Ph., Channel processes in runoff re-distribution. St Petersburg, Hydrometeorological Publishers, 1975, 288 pp. (in Russian)

3. Kondratyev, A. N., Correlation of streamflow transporting capacity and sediment runoff as condition of forming of various river channel types / Geomorphology, No 3, 1999, p. 14 – 18. (in Russian)

4. Kondratyev, N. E., Popov, I. V., Snischenko, B. F., Fundamentals of hydromorphological theory of channel process. St Petersburg, Hydrometeorological Publishers, 1982, 272 pp. (in Russian)

5. Sidorchuk, A. Yu., Structure of river channel relief. St Petersburg, Hydrometeorological Publishers, 1992, 126 pp. (in Russian)