Author(s): Kim V. I.; Makhinov А. N.
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Keywords: Debris dams; Riverbed transformations; Bank erosion; Surrounding vegetation; Russian Far East
Abstract: Debris dams on the rivers of the forest zone significantly affect river dynamics. They cause complicated channeling of the main stream, intensive riverbed transformations, local bank erosion and solid matter accumulations. Debris dams also cause problems for various engineering facilities like bridges, buildings and roads. In the taiga zone the number of dams and their structure depend on the river size, the specifics of riverbed and water regimes, the amount and composition of forests in the river floodplain. Debris dams are most common in mixed-forest regions of the Lower Amur. Much depends on the ratio between the size of trees and streams. The streams less 8 m wide have very specific conditions. Single big trees constitute a significant obstacle for the water flow there. Usually rather stable pools are formed behing the tree or in front of it. When the tree falls into the stream, it also causes changes of riverbed morphology. Such a tree acts like a dam, in front of which alluvial material accumulates and behind it pools of specific morphology are formed. Rivers up to 150 wide have much bigger debris dams of varied structure. They accelerate riverbed transformations and bank erosion and thus more and more wood falls into the rivers. This causes the formation of small sub-channels, where erosion is less evident. Riverbed processes on rivers over 150 m wide are less affected by the surrounding vegetation. The water flow easily carries even big tree, but sometimes they stop at the shallows. In this case local underwashing and accumulations of light alluvial materials take place. The described specifics of debris dams were used as criteria for zoning the southern part of the Russian Far East. The description of debris dam formation specifics, dam frequency and average size was provided for each selected zone. Special attention was given to the areas, where these river processes are most active and aversively affect economic activities and the state of natural landscape in the mountain river valleys.
Year: 2013