Катастрофические скорости формирования флювиального рельефа

Аннотация

The Alabuga valley structure in the Central Tier-Shan indicates unusual downcutting rate, too high even for mountain streams. Usind various methods (historico-archeological, dendrochronological, cartographic, hydrological, dating by measuring the desert varnish thickness) the present-day rate of downcutting has been estimated, as well as its variations during the last 1300 years. The river channel cut through the Late Quaternary cemented gravel about 20 to 50 meters thick, the downcutting rate being about 0,5 cm per year. Having reached underlying lacustrine silts (Neogene) which are less resistant to erosion, the rate of deepening increased up to 9 in per year and more. Mean annual values of channel downcutting are about 0,4 to 0,9 cm near the river mouth and reach 32 cm near the Djergital water intake.

Such rapid deepening interferes considerably in normal operation of water intake stations and bridges. The authors come to the conclusion that in mountains the channel deepening reaches catastrophic rates under conditions of channel load deficiency and weak bedrocks. It morphological evidences of rapid downcutting are discerned, fluvial dynamics should be studied in detail before ehgineering works.