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Effects of vegetation distribution along river transects on the morphology of a gravel bed braided river

Zhu Runye, Tsubaki Ryota, Toda Yuji

Acta Geophysica

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2024

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Vol. 72, no. 2

1097--1112

EN

The interaction between vegetation, sediment, and water flow creates various fluvial landscapes. Hydrological conditions and flood disturbances, as well as the habitat preference of vegetation, regulate its spatial distribution. To describe the spatial distribution of vegetation cover, here, we focus on vegetation distributions along river transverse transects that define vertical and horizontal distances from water areas during low flow periods. As one of the most dynamic river types, braided rivers can be significantly influenced by vegetation encroachment. However, the effects of vegetation distributions along river transects on braided river morphology remain unknown. To study the potential influence of vegetation distribution along river transects, a depth-averaged, hydro-morphodynamic model was employed. Using the model, we investigated a medium-sized, braided river with a gravel bed affected by riparian vegetation. The following scenarios of vegetation transect distributions were examined: (1) vegetation established near or covering the low water channel, and (2) vegetation established on bar tops and kept at a distance from the low water channel. The model successfully reproduced a reduction in the braiding index for a vegetated braided river. Depending on the transect distribution scenarios employed, significantly different effects for river morphology were obtained. For example, compared to vegetation on bar tops, vegetation located near the low water channel played a more critical role for changing river morphology, redirecting water flow, and changing the statistical characteristics of the riverbed elevation distribution. Vegetation near the low water channel not only concentrated water flow to low water channels but also redirected flow to the high elevation area by reducing low water channel flow capacity. The revealed effects of the vegetation transect distribution on river morphology development helped to determine effective management protocols for reducing the negative impact of vegetation encroachment.

2

Fluvial response to environmental conditions during MIS 4-3 : a sedimentary record at the Brześnica site, central-western Poland

Moskalewicz Damian, Tylmann Karol, Woźniak Piotr Paweł, Kopyść Natalia, Moska Piotr

Geological Quarterly

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2020

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Vol. 64, No. 4

915--930

EN

Fluvial deposits subjected to this study are exposed at the Brześnica site, in the south-western part of the Wielkopolska region in Poland, which was close to the ice-sheet limit during the Last Glacial Maximum (LGM). Sedimentological analyses, including lithofacies descriptions, palaeocurrent measurements, grain size and rounding analyses and heavy mineral compositions indicate that the fluvial deposits at Brześnica were deposited in braided river environment. The following fluvial sedimentary processes were inferred: (1) shallow, rapid flow alternating with waning flow, (2) infilling of erosional channels with fluvial sediments during flood events, (3) changes from supercritical to subcritical flows, and (4) shallow sheet floods. The results of OSL dating indicated sediment deposition ~65.2 ±1.5 ka, i.e. in MIS 4, that was here characterized by cold environmental conditions and a general shift from meandering to braided fluvial sedimentation style. This finding contrasts with accumulation/erosion phases interpreted previously in this region for that time interval; however, it is consistent with recent studies of fluvial systems functioning during MIS 5-2 and of factors responsible for sedimentation style.

3

The sedimentary environment of Devonian siliciclastics in the Babí lom locality (Brunovistulian Platform cover, Southern Moravia, Czech Republic)

Wojewoda J., Nehyba S., Gilíkova H., Burianek D

Geological Quarterly

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2015

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Vol. 59, No. 1

229--238

EN

Sandstones and conglomerates, which northwards of Brno agglomeration build a hill (ridge) named Babí lom are strongly diagenezed (anchi-metamorphozed) and tectonically deformed. Their regional distribution and stratigraphic position between the Cambrian(?) clastics and Upper Devonian limestones, as well as their appearance meant that they age is considering as Middle Devonian. They are distinguished as the so-called „Basal Devonian Clastics“. Almost all primary sedimentary features are well preserved and distinct. In the metasediments of the Babí lom hill were distinguished both the facies and structures typical of alluvial fans and rivers. Among others they are channel lags with imbricated grains, cross beddings and debrites. Within sedimentary association was established the way-up direction what clearly evidences a coarsening upwards sequence. Assuming the lack of rotation of series of sediments in the X-Y plane, the palaeotrasport was toward the north while major supply with material was from the east.

4

Sedimentary environment and palaeogeography of the ?Palaeocene-Middle Eocene Kashkan Formation, Zagros fold-thrust belt, SW Iran

Yeganeh Bizhan Yousefi, Feiznia Sadat, Loon A. J. (Tom)

Geologos

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2012

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Vol. 18, No. 1

13--36

EN

The Kashkan Formation (?Palaeocene to Middle Eocene) in the Zagros fold-thrust belt, SW Iran, which is intercalated between to marine limestone formations, consists of conglomerates, sandstones and siltstones. The sedimentology and the palaeogeography of the Kashkan Formation had not received any attention thus far, but have now been studied in seven sections, situated in the province of Lorestan. The sediments form twelve lithofacies, three ichnosubfacies and seven architectural elements, which are described, depicted and analysed. The analysis leads to the conclusion that most sediments accumulated in a low-sinuosity, low-gradient braided-river system (characterised by mainly unidirectional palaeocurrent directions, and by sheetfloods), that occasionally showed meandering characteristics (represented by overbank deposits and large bars). The deposits of this system closely resemble those of the South Saskatchewan River in Canada, which is considered as the classical example of a sand-bed braided river. The river flowed roughly from North to South, as deduced by palaeocurrent indicators such as imbrication and large- to medium-scale trough cross-stratification (direction measured in the trough axes). This current direction is supported by the southward to south-westward thinning of the formation and by the diminishing average grain size in the same direction. The trace fossils in the Kashban Formation fit all in the Skoyenia ichnofacies, which has here three ichnosubfacies which allow a more detailed palaeoenvironmental reconstruction, indicating that the braided stream passed into the low-energy shoreface zone of a tidally-influenced sea.

5

Braided-river and hyperconcentrated-flow deposits from the Carboniferous of the Lublin Basin (SE Poland) - a sedimentological study of core data

Waksmundzka Maria I.

Geologos

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2012

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Vol. 18, No. 3

135--161

EN

Fining-upwards cyclothems found in five boreholes in the Carboniferous (Lower Bashkirian) of the Lublin Basin were analysed sedimentologically. It was established that the cyclothems represent fluvial deposits, and the lithofacies were grouped into lithofacies associations. Most lithofacies associations represent three types of sand-bed braided rivers: (1) high-energy, (2) deep and (3) distal sheetflood-affected. Other associations represent hyperconcentrated flows. Both coarse-grained (type I) and fine-grained (types IIa and IIb) occur among the fining-upward cyclothems. The formation of most thick cyclothems was related mainly to allocyclic factors, i.e. a decrease in the river’s gradient. The thickest fining-upward cyclothems are characteristic of hyperconcentrated flows and braided-river channels. The aggradation ratios were commonly high. During the early Namurian C and early Westphalian A (Early Bashkirian), the eastern part of the Lublin Basin was located close to the source area. The sedimentary succession developed due to a transition from high-energy braided-rivers and hyperconcentrated flows to lower-energy braided rivers, controlled by a rise of the regional base level.

6

Environmental heterogeneity controls organic-matter dynamics in river-floodplain ecosystems

Langhans Simone D., Tiegs Scott D., Uehlinger Urs, Tockner Klement

Polish Journal of Ecology

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2006

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Vol. 54, nr 4

675-680

EN

Environmental heterogeneity is a key regulator of ecological processes. Riverine floodplains are particularly heterogeneous and dynamic systems and loss of their natural environmental heterogeneity and dynamism as a consequence of human impacts constitutes their most serious threat. On river floodplains, flow and flood pulses create a shifting mosaic of channels, ponds, bars, islands, and riparian forest patches. Composition and spatial arrangement of these habitat patches determine their degree of connectivity, which in turn controls the flux of matter and energy among adjacent patches. In light of these attributes, riverine floodplains are model ecosystems for studying the effect of heterogeneity on ecological processes. In this article we introduce a conceptual model for river-floodplain ecosystems that unifies leaf decomposition, organic-matter input, storage and quality, and stresses the importance of the flow and inundation regime. In combining these aspects of organic matter dynamics, which have been treated separately in the ecological literature, this model fosters a more holistic perspective of ecosystem processes on riverine floodplains. We conclude that the linkage between natural heterogeneity and ecosystem processes needs to be considered in future river-floodplain restoration projects.

7

Tectonically-controlled sedimentation of Cenozoic deposits from selected basins along the Vietnamese segment of the Red River Fault Zone

Wysocka A., Świerczewska A.

Acta Geologica Polonica

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2005

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Vol. 55, no. 2

131-145

EN

Small, narrow sedimentary basins occur along the main faults in the Vietnamese segment of the Red River Fault Zone (RRFZ), which is the major discontinuity separating the South China and Indochina microplates. The sedimentary basins of the RRFZ are grouped into three main sections: along the Red River Valley, the Chay River Valley and the Lo River Valley. The sedimentary basins are filled with thick series of Palaeogene and Neogene clastic deposits that differ in type and origin. In the lower part of the basin fill, coarse-grained deposits predominate. In the upper part, different types of sandstones, siltstones and brown coal occur. There are no sediments of Late Pliocene age. Quaternary deposits are represented by sands and gravels. Biostratigraphical data are very poor, therefore only lithostratigraphical subdivision is applied. Thus, it is possible that deposits from adjacent basins associated with the RRFZ represent strata of different ages.The investigations were focused on the Lo River Basin (associated with the Chay River fault), Yen Bai Basin (associated with the Red River fault) and Co Tiet Basin (associated with the southwesternmost branch of the Red River fault). Thirteen sedimentary facies were recognised in deposits filling the investigated basins. The facies were grouped into five facies associations representing five distinct depositional environments. These comprise alluvial fan, gravel-dominated fluvial channel, sand-dominated fluvial channel, alluvial plain and lacustrine environments. In addition, the basin fills show features characteristic of strike-slip basins.