Abstract

Ecological problems related to fresh water resources are of significant scientific and practical interest. Special attention is paid to the rivers located in the areas where industrial and agricultural activities require ecological expertise as regards their impact on river condition. Special attention of ecologists should be paid to the rivers used for water supply, navigation, recreation and other purposes. Economical activities in river basins influence runoff formation and suspended sediment and bed load transport. Agricultural use of lands in river basins renders special affect on river runoff and sediment yield as well. But human activities directly in river channels should not be underestimated. Among this kind of activities channel works are most common for improvement navigation conditions particularly dragging shoals for making channels deeper, straightening the bends for shortening the ways, etc. Withdrawal of bed sediments for various purposes influences river conditions considerably. In those cases when the volume of the bottom material withdrawn is more than the volume of bed load incoming to the river, the changes of the channel may become irreversible. As a result directional downward movement of the riverbed and accordingly the fall of the water level take place. It brings to the lowering of the longitudinal profile of the river.

Keywords: bed load, stage discharge relation, dragging, sediment withdrawal, fall of water level