Aleksey Sidorchuk
Moscow State University, Geographical faculty, Faculty Member
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The hierarchical classification of Lower Volga channel landforms is put forward. The classification consists of 8 complexes and 5 classes. The class of nanoforms includes riffles; microforms - dunes and zastrugas; mezoforms -sand waves... more
The hierarchical classification of Lower Volga channel landforms is put forward. The classification consists of 8 complexes and 5 classes. The class of nanoforms includes riffles; microforms - dunes and zastrugas; mezoforms -sand waves and alternate bars; macroforms - big meanders and large ramification junctions; megaforms - ramifica-tions with parallel arms or the river. The main channel of Volga and its branch - Akhtuba form a parallel-channel system. Empirical probability density of channel forms length (for each class) may be fitted well by Gamma distribu-tion; the height may by fitted by Weibull distribution.
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Fractal dimensions of the more than 200 large river networks of the former USSR were calculated. We use the term «fractal» as «a structure consisted of parts which are in some sense alike to the whole». River networks don’t possess the... more
Fractal dimensions of the more than 200 large river networks of the former USSR were calculated. We use the term «fractal» as «a structure consisted of parts which are in some sense alike to the whole». River networks don’t possess the complete self-likeness – fractal dimension changes with the change of measurer unit and the chosen length of the rivers. Therefore the calculations were fulfilled with the measurer length lying within the limits of 1–10 km. Fractal dimension of the river networks of the former USSR changes from 1.1 to 1.7, which corresponds to the aggregate length of the short rivers (1–10 km) consisting 20–80% of total river network length. Then all studied networks have fractal dimension more than Euclidian dimension of line (1) and less than Euclidian dimension of plane (2) as it should be accordingly to the fractal approach. There is a tendency for fractal dimension to grow with the height of the river basin and humidity of the territory. It is also strongly correlated with the network density. Fractal dimension as an index of the river length distribution has some advantages in comparison with the other morphometric indexes used. It augments significantly the possibility of the quantitative analysis of the drainage networks.
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Climate change is one of the main factors of the modern erosion. Much less investigated the influence of accelerated erosion on climate change due to greenhouse gases emission. Healthy modern soils are the sinks for atmospheric carbon.... more
Climate change is one of the main factors of the modern erosion. Much less investigated the influence of accelerated erosion on climate change due to greenhouse gases emission. Healthy modern soils are the sinks for atmospheric carbon. Washed-out and buried soils (stratozems) are the sources of atmospheric carbon. The modern emission of carbon dioxide from this formed by accelerated erosion pool of carbon is small and does not affect significantly the CO2 budget in the atmosphere.
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The empirical three-dimensional hydraulic gully erosion and thermo-erosion model GULTEM was used to calculate the surface runoff optimal to form ancient periglacial dry valleys on the East European plain.
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The modern fluvial system on the lowland East European Plain is of depositional type. Sediment transport to the seas is only a few percent of the total erosion, and the main part of eroded material is accumulated in the channels. The... more
The modern fluvial system on the lowland East European Plain is of depositional type. Sediment transport to the seas is only a few percent of the total erosion, and the main part of eroded material is accumulated in the channels. The recent deposition of suspended sediments is caused by accelerated soil erosion on the arable slopes, which led to a high rate of lateral sediment input and deposition at the river headwaters and on the floodplains. The process of accumulation is facilitated by the unfilled “negative” volume of the net of dry valleys formed during the Late Glacial catastrophic erosion event. Such events of catastrophic erosion of the sediments deposited in the lowland fluvial systems occur with a frequency of 100-120 thousand years. In the conditions of both scarce vegetation and extremal surface runoff, the entire fluvial systems become the area of intensive erosion, with the deep incision of gullies and of the river channels. Therefore, despite the modern intensive dep...
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Между параметрами структуры современных речных систем и их гидрологическими характеристиками существуют как косвенные, так и прямые связи. Такие связи используются для оценки гидрологических характеристик древних русловых систем по... more
Между параметрами структуры современных речных систем и их гидрологическими характеристиками существуют как косвенные, так и прямые связи. Такие связи используются для оценки гидрологических характеристик древних русловых систем по параметрам их структуры в случае совпадения ландшафтно-климатических и литолого-геоморфологических условий на современных и древних водосборах. Эрозионный рельеф Русской равнины сохраняет информацию о прошлых событиях максимального стока воды. Максимальный сток во время валдайского позднеледниковья оставил в рельефе фрагменты больших меандрирующих пале-орусел в речных долинах и сеть балок на водосборах. На склонах водосборов широко распространена и хорошо сохранилась сеть ложбин, многие из которых сформировались во время события максимального стока воды в период деградации московского покровного оледенения. Густота сети балок и ложбин является индикатором гидрологических условий их формирования, в первую очередь максимального стока. Применены два способа ...
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In a study conducted during the summers of August 1993 and August-September 1994, four independent techniques were used to evaluate soil redistribution in an arable field in the Stavropol Upland, Russia, with a semi-permanent ephemeral... more
In a study conducted during the summers of August 1993 and August-September 1994, four independent techniques were used to evaluate soil redistribution in an arable field in the Stavropol Upland, Russia, with a semi-permanent ephemeral gully network and a downslope buffer zone of grassed dry valley bank with depositional fans. The relative importance of each technique and its contribution to a sediment budget for the entire period of cultivation in the study area were evaluated. The 4 approaches used were: (1) soil survey; (2) ephemeral gully volume measurements; (3) tracing soil redistribution using caesium-137 (137Cs) measurements; and (4) a Universal Soil Loss Equation (USLE)-based model modified for Russian conditions. All the methods used suggest severe soil losses from the arable part of the study field. Severe erosion occurred at the rate of 5 kg m2/year. The contribution of sheet erosion by water (calculated with the USLE) was ∼1 kg m2/year, whereas mechanical translocation contributed ∼4 kg m2/year. Sediment deposition within the buffer zone was low, representing only 6% of the total eroded material. Best estimates of soil redistribution rates were obtained by integrating the soil survey and the 137Cs conversion model (combined with gully volume measurement) approaches.
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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 Volga only from the part of the basin that was covered by the... more
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 Volga only from the part of the basin that was covered by the Scandinavian ice sheet. During the maximal phase (19–20 thousand years ago) the glacier occupied the farthest upstream parts of the basin, i.e., the Mologa–Sheksna depression (60 thous. km2) and the area near the Volga source and Lake Seliger (5 thous. km2). The volume of melt water runoff was calculated for deglaciation time by three models of the ice sheet. The upper estimate yielded a value of 60–70 km3 per year, and the lower estimate was 15 km3 per year, or 5–25% of the present-day Volga runoff into the Caspian Sea, where the lower value appears more plausible. In that case, even the maximal estimate is not enough to initiate the Khvalynian level rise in the Caspian Sea. In addition, the major part of the time of meltwater inflow into the Volga (~21...~16.5 thous. years ago) corresponds to a regressive state of the Caspian basin. This also does not allow us to consider the glacial factor as the cause of the Khvalynian transgression, the rise of which ~17 thousand years ago fell into the period of a decline of the glacial runoff.
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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 used to evaluate the paleodischarges of water using... more
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 used to evaluate the paleodischarges of water using morphometric relationships. The study develops the procedure proposed earlier for evaluating the paleorunoff. An improved procedure is used to evaluate the runoff in the period when large paleochannels were forming (18–13 thousand years ago) for more than 120 small basins. Areal interpolation was used to map the annual paleorunoff depth in the Volga Basin. The reconstructed field of river runoff in the Late Glacial Period shows zonality similar to that one can see now: the maximal runoff depth (from 450–550 mm) was recorded in the Upper Volga and in the upper part of the Kama Basin, and the minimal runoff depth (100–200 mm), in the Lower Volga. In large parts of the Volga Basin, the runoff was 1.5–1.9 times greater than its present-day value. The annual runoff for the entire Volga Basin was evaluated at 420 km3. This volume is enough to keep the Caspian level at elevations of the maximum of Khvalynskaya transgression (~+48 m abs.), provided that the effective evaporation (evaporation less precipitation) in the water area was one quarter less than its present-day level (~550 mm with the possible glacier runoff not taken into account and~600 mm with it).
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Текстура и структура аллювиальных отложений являются отражением динамики речного потока. Структура аллювия современных рек используется в качестве показателя поля скоростей в речном русле. Для этого применяются формулы для расчета... more
Текстура и структура аллювиальных отложений являются отражением динамики речного потока. Структура аллювия современных рек используется в качестве показателя поля скоростей в речном русле. Для этого применяются формулы для расчета критической скорости потока для условий начала движения или начала осаждения частиц различной крупности. Хорошая разработанность теории и экспериментальная проверка таких формул создала возможность реконструкции скоростей палеопотоков по измерениям крупности частиц наносов в аллювиальных отложениях. Этому также способствует нелинейность зависимости критических скоростей от диаметра частиц грунта, в результате чего широкому диапазону размеров перемещаемых частиц соответствует довольно узкий диапазон необходимых для этого перемещения скоростей потока. В результате при правильной оценке конкретной динамической обстановки формирования аллювиальной толщи и при правильном отборе образцов аллювия, возможно восстановить как среднюю скорость потока, так (иногда) и интенсивность его турбулентности. При этом следует иметь в виду, что методы расчета критических скоростей дают некий диапазон значений, обычно ±20-30% от среднего. Существенной ограниченностью этого метода является отсутствие возможности по крупности аллювия определить другие характеристики потока. Такая величина, как глубина потока, необходимая для правильного расчета скорости, оценивается по другим признакам, таким как текстура аллювия, морфометрия палеорусел и т.п. Так что оценка скорости потока по крупности аллювия обычно дополняет и уточняет палеогеоморфологические и палеогидрологические построения, выполняемые другими методами.
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... with wave-lengths several times greater than that of the present river, assumed a dramatic increase in river dis-charge at some ... I) The region where macromeanders are virtually absent from the river valleys corresponds to the... more
... with wave-lengths several times greater than that of the present river, assumed a dramatic increase in river dis-charge at some ... I) The region where macromeanders are virtually absent from the river valleys corresponds to the territory that was under the Late Valdai ice-sheet. ...
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Research Interests: Geology and Terra nostra
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Networks of dry valleys (or balkas) and hollows in the upper reaches of fluvial basins in extraglacial areas in the Penultimate Glaciation (Marine Isotope Stage 6—MIS 6) regions of the East European Plain demonstrate clear... more
Networks of dry valleys (or balkas) and hollows in the upper reaches of fluvial basins in extraglacial areas in the Penultimate Glaciation (Marine Isotope Stage 6—MIS 6) regions of the East European Plain demonstrate clear incision/aggradation rhythms corresponding to global glacial/interglacial climate cycles. The first phase of each incision/aggradation rhythm began after the global glacial maximum and was characterized by a cool and humid climate, permafrost and sparse vegetation, when high surface runoff and active linear erosion formed a dense network of gullies. The second phase occurred at the glacial–interglacial transition and the subsequent interglacial period with its warm and humid climate and dense vegetation. This phase was distinguished by the partial filling of fluvial forms with slopewash deposits, the transformation of gullies into dry valleys (balkas) and the subsequent stabilization of fluvial forms marked by the formation of mature soils on the sides and bottoms...
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The estimates of water flow in the paleorivers with known paleochannel morphometry was compared with basic hydrological and climatic indicators found by paleogeographic analogy in the regions-analogues, determined by fossil flora analysis... more
The estimates of water flow in the paleorivers with known paleochannel morphometry was compared with basic hydrological and climatic indicators found by paleogeographic analogy in the regions-analogues, determined by fossil flora analysis from the Holocene (from the present to 10 thousand years ago), the Late Valday (17–18 thousand years ago) and before the Eemian (~140 thousand years ago) deposits. Comparison of annual runoff depth obtained by regime equations and equations of hydraulics and taken from the hydrological maps in the regions-analogues, showed quite satisfactory compliance. Relative error of comparison for the different objects is in the range of ±11–23%, which does not exceed the average error of water flow estimation by each of these techniques separately. However, the error of ±20% is significant and geomorphological approaches can be applied only for the cases of sufficient changes in the water flow of ancient rivers (twice or more) and for long-term periods. Never...
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248 Aleksey Sidorchuk et al. The basin is densely forested (up to 98%), and its northeastern part is dominated by swamps. Swamps occupy up to 5 to 10% of the basin area. Interfluve areas are covered by spruce forest together with some... more
248 Aleksey Sidorchuk et al. The basin is densely forested (up to 98%), and its northeastern part is dominated by swamps. Swamps occupy up to 5 to 10% of the basin area. Interfluve areas are covered by spruce forest together with some birch and pine forests occupy sandy river ...
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The present research aims at estimating chronology of high-amplitude hydrological changes in the southern half of the East-European Plain through a study of palaeochannels preserved on river floodplains and low terraces. The research... more
The present research aims at estimating chronology of high-amplitude hydrological changes in the southern half of the East-European Plain through a study of palaeochannels preserved on river floodplains and low terraces. The research schedule includes (1) identification of palaeochannels on topographic maps (1:25000 1:100000) and aerial photoes, measuring palaeochannel parameters (width, meander wavelength and curvative) and grouping them into separate age generations; (2) studying palaeichannel geological composition and establishing their depth and active section area by making boreholes and examination of natural exposures; (3) establishing absolute age of palaeochannels through radiocarbon dating of organic matter from different alluvial facies (active channel alluvium, base of palaeochannel infill); (4) estimation of river discharge changes in the past from the transformation of palaeochannel parameters with time. Detailed investigations were completed at two key sites located ...