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The
role of extreme floods in the formation of river beds
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)
ancondratyev@peterlink.ru http://bedload.boom.ru
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