Suspended sediment yield is one of the objective and sufficiently accurate measures of erosion intensity in river basins. In first approximation, it can be divided into the riverbed component –r(rb), the products of vertical and horizontal riverbed deformations), and basin component – r(bas), the products of soil and gully erosion. An attempt was made to distinguish this erosion structure in the USA river basins based on the partition of suspended sediments of 224 rivers (based on the data from the US Geological Service on the average monthly water discharges and suspended sediment yields) according to the method proposed by one of the authors of the paper, as well as an assessment of its factor dependence.
The average r(rb) value for the analyzed rivers of the USA is 7.9±1.1%: for lowland rivers – 10.6±1.7%, for low-mountain (including high uplands) rivers – 5.7±1.5%, for mid-mountain rivers – 4.3±1.5%. The geomorphic factor, landscape and climatic conditions within the river basins have a major impact on the suspended sediments flux ratio r(rb)/r(bas). Thus, in the USA plains, the largest average r(rb) portion is in the forest landscapes (taiga, mixed and broadleaf forests of the temperate zone, subtropical forests) – 10–15%. On the contrary, in the arid landscapes (semi-deserts) this value does not exceed 1%. Within these general trends, there are quite strong variations in the r(rb)/r(bas) ratios due to the changes in river basin areas, agricultural activities and lithologic composition of riverbed and floodplain sediments. There is an inverse hyperbolic relationship between the actual suspended sediment yield of the rivers and the riverbed sediment portion (r(rb)), which is most manifested in the plains and low-mountains of the USA. It is also shown that a composition of the river basin parent (surficial) rocks does not play a significant role in the variability of the r(rb)/r(bas) at this scale of the study. A comparison of the r(rb)/r(bas)-estimates and their factor dependence on the US rivers with the rivers of Northern Eurasia (the territory of the former Soviet Union) makes it possible to reveal good convergence of the results obtained in these parts of the Earth, and to suggest the universal nature of the revealed regularities (in total for 684 river basins) for the whole temperate (partly for subtropical and tropical) zone of the Northern hemisphere of our planet.
Scientific Research Methods
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The studied reach of the upper River Ob is quite complicated in the morphological aspect and characterized by very low channel stability and high discharge of sand load. Unconstrained conditions for lateral channel migration promotes active channel deformations not only at long-term scale, but also seasonally. Channel deformations contribute to the transformation of the channel and its morphodynamic type in time. The upper River Ob is intensively used as a water course, so any reorganization of the channel and river islands should be taken into account to support navigation.
Morphometric and morphodynamic analysis of the islands made it possible to develop their morphological classification. Morphometric parameters of islands, being associated with the characteristics of the channel itself, are one of the main classification features. Empirical relations were obtained that link the dimensions (Lo, Bo) and shape of islands (Lo/Bo) with the morphodynamic channel type and its stability, the degree of branching of the channel (number of islands no per 1 km of channel length x). The features of island dynamics are also determined by the morphodynamic type of the channel and are associated with the morphometric characteristics of the islands themselves and their position in the channel, which determines the transgressive, regressive and transverse shift or their stable position in time.
History of Science
Fifty years ago, in the autumn of 1968, experiments on interpretation of the first Soviet global space image made by 'Zond-5' automatic spacecraft and of American space images from Gemini III, IV, V piloted spacecrafts were carried out for the first time in the USSR. The aim of these experiments was the study of possibilities to use satellite images in geomorphology and geography.
The first results demonstrated high value of space images for geomorphological research for the studies of morphostructures and morphosculptures of various genesis, the discovery of a 2500 km long lineament in Sahara; real time-related transitive borders of latitudinal landscape zones in Africa were indicated for the first time. It was suggested that satellite images could be applied for the studies of various geological structures, seismicity, volcanic activity, global and regional zones of jointing as well as for thematic mapping. Thanks to these studies a new Department of Satellite-related Geography was established at the Institute of Geography of the USSR Academy of Sciences. Later on, studies were carried out at the Institute's Department of Satellite-related Geography in order to find application possibilities of TV multispectral scanned and photographic satellite images for thematic research and mapping. The first conclusions were confirmed in the course of further studies in the field of aerospace remote sensing in Russia and abroad; their results were summarized in two fundamental atlases published under the auspices of the Institute of Geography of the Russian Academy of Sciences (IGRAS): “Resources and Environment World Atlas” (1998) and “World Atlas of Snow and Ice Resources” (1997). Up to date, methods of aerospace remote sensing continue to be applied successfully at IGRAS for geomorphological studies and for resolving of environmental problems in physical and human geography.
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