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Water Resources - The runoff of glacial melt water into the river system of the Volga and farther into the Caspian Sea is evaluated for the epoch of the last glaciation. Melt water entered the... 相似文献
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Water Resources - Linearized equations of two-dimensional hydraulics have been analyzed by the method of small perturbations within a wide range of alluvial features sizes at large values of Froude... 相似文献
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Water Resources - Large paleochannels, which are common in the floodplains and terraces of rivers in the Volga Basin, are indicators of an appreciable increase in river flow in the past and can be... 相似文献
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A. Y. Sidorchuk A. V. Panin O. K. Borisova S. A. Elias J. P. Syvistki 《International Journal of Earth Sciences》2000,89(3):541-549
The relicts of large meandering palaeochannels are found throughout the territory of the periglacial zone of the Last (Valdai=Weichselian) Glaciation on the Russian Plain. Channel widths of macromeanders can be 15 times larger than the recent meanders of the same rivers. Palaeolandscape and palaeohydrological reconstructions show that these periglacial river channels were formed under conditions of high spring water flow, up to eight times greater than the modern discharges, when the flow coefficient was close to 0.9-1.0 due to presence of permafrost, summers were dry and streams lacked ground water supply. Permafrost degradation increased soil permeability in spring and increased ground water flow in summer, causing a decrease of annual flow (due mainly to the flood flow decrease in spring). As a result, large periglacial channels were abandoned and transformed into lakes and bogs. Late Holocene channels have much smaller channel widths and meander lengths. These were formed under conditions of lower annual flows and much steadier flow regime. 相似文献
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Three stages were identified in the development of meandering rivers and the formation of floodplains with natural levees
in Northern Eurasia: the development of rivers with size larger than that of the modern ones; the development of rivers smaller
than the modern ones; and the development of rivers of the present-day morphodynamic type. Small oxbows of the second stage
are widespread in the floodplains of lowland rivers in Northern Eurasia. The largest amount of floodplain segments with such
oxbows can be seen in the forest zone, mostly in the coniferous forests of northeastern European Russia. The available radiocarbon
datings show that river channel were significantly decreasing in size and the steepness of meanders was increasing during
the Atlantic period of the Holocene. Data on changes in the size of river channels were used to evaluate the ratios between
paleo- and modern discharges and to construct a map of difference between runoff depths in the Holocene optimum and in the
present and assess changes in water runoff volume. The discharges in the basins of the Vyatka and middle Irtysh accounted
for as little as 40–50% of their current values. North, east, and west from those basins, the ratio of ancient and present-day
discharges increases. During the Holocene optimum, water runoff from the northern megaslope of the East European Plain was
∼180 km3/year, which is 30% less than the present runoff from the same drainage area. The annual runoff in Volga basin was ∼134 km3, which is almost half as large as the present value. The runoff in Don and Dnieper basins during the Holocene optimum was
40% less, and that in the Ob and Irtysh basin was 30% less than the present one. If we accept the hypothesis that the Holocene
optimum was a climate analogue of global anthropogenic warming of the mid-XXI century, the obtained estimates of the state
of water resources in Northern Eurasia acquire great prognostic importance. 相似文献
6.
Aleksey Sidorchuk 《地球表面变化过程与地形》2006,31(11):1329-1344
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Abandoned rivers (large paleochannels and meanders) are common on river floodplains and low terraces on the East European and West Siberian plains. They are 10–15 times greater in size than the present-day river channels. The large paleochannels are dated back to 11–15 thousand radiocarbon years B.P. (the Late Glacial period). Based on the hydraulic and morphometric relationships for present-day rivers and the method of paleogeographic analogs, the surface runoff during the Late Glacial period was quantitatively reconstructed by the morphometric parameters of large paleochannels. The reconstructed surface runoff exceeded the present values by 1.4 times on the northern mega-slope of the East European Plain (the Northern Dvina, Mezen, and Pechora river basins), by 2.3 times on its southern mega-slope (the Volga, Don, and Dnepr basins), and twofold in West Siberia (the Ob basin). The large surface runoff volumes can be explained by the landscape and climate conditions, including the high coefficients of runoff (due to the permafrost), the increased proportion (and, conceivably, the amount) of snowfall, and, hence, the respective increased intensity of spring floods. The transformation of large Late-Glacial paleorivers due to climate warming at the beginning of the Holocene is a likely scenario of the surface runoff development within the present-day permafrost zone at the ongoing human-induced climate warming. A general decrease in surface runoff and its more uniform intra-annual distribution would result in the reduced size of rivers in the middle Siberia, Yakutia, and northeastern Russia. 相似文献
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S.YA. Braude S.L. Rashkovsky K.M. Sidorchuk M.A. Sidorchuk K.P. Sokolov N.K. Sharykin S.M. Zakharenko 《Astrophysics and Space Science》2002,280(3):235-300
This paper presents results and describes the improved data processing algorithm of the low frequency sky survey of discrete
sources carried out with the UTR-2 radio telescope. The measurements were conducted within the frequency range 10 to25 MHz.
Coordinates and flux densities of the sources detected were obtained. Identification with sources from the 4C survey has been
done. The resulting catalogue contains parameter estimates for 483 sources on a set of frequencies within the UTR-2 range.
This revised version was published online in July 2006 with corrections to the Cover Date.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Empirical prediction equations of the form W = aQb have been reported for rills and rivers, but not for ephemeral gullies. In this study six experimental data sets are used to establish a relationship between channel width (W, m) and flow discharge (Q, m3 s?1) for ephemeral gullies formed on cropland. The resulting regression equation (W = 2·51 Q0·412; R2 = 0·72; n = 67) predicts observed channel width reasonably well. Owing to logistic limitations related to the respective experimental set ups, only relatively small runoff discharges (i.e. Q < 0·02 m3s?1) were covered. Using field data, where measured ephemeral gully channel width was attributed to a calculated peak runoff discharge on sealed cropland, the application field of the regression equation was extended towards larger discharges (i.e. 5 × 10?4m3s?1 < Q < 0·1 m3s?1). Comparing W–Q relationships for concentrated flow channels revealed that the discharge exponent (b) varies from 0·3 for rills over 0·4 for gullies to 0·5 for rivers. This shift in b may be the result of: (i) differences in flow shear stress distribution over the wetted perimeter between rills, gullies and rivers, (ii) a decrease in probability of a channel formed in soil material with uniform erosion resistance from rills over gullies to rivers and (iii) a decrease in average surface slope from rills over gullies to rivers. The proposed W–Q equation for ephemeral gullies is valid for (sealed) cropland with no significant change in erosion resistance with depth. Two examples illustrate limitations of the W–Q approach. In a first example, vertical erosion is hindered by a frozen subsoil. The second example relates to a typical summer situation where the soil moisture profile of an agricultural field makes the top 0·02 m five times more erodible than the underlying soil material. For both cases observed W values are larger than those predicted by the established channel width equation for concentrated flow on cropland. For the frozen soils the equation W = 3·17 Q0·368 (R2 = 0·78; n = 617) was established, but for the summer soils no equation could be established. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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