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Добірка наукової літератури з теми "Sharp River Bends"

Автор: Grafiati

Опубліковано: 10 березня 2023

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Статті в журналах з теми "Sharp River Bends"

Ottevanger, W., K. Blanckaert, and W. S. J. Uijttewaal. "Processes governing the flow redistribution in sharp river bends." Geomorphology 163-164 (August 2012): 45–55. http://dx.doi.org/10.1016/j.geomorph.2011.04.049.

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Tritthart, M., and D. Gutknecht. "3-D computation of flood processes in sharp river bends." Proceedings of the Institution of Civil Engineers - Water Management 160, no. 4 (December 2007): 233–47. http://dx.doi.org/10.1680/wama.2007.160.4.233.

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Zhao, Shui-Xia, Wen-Jun Wang, Xiao-Hong Shi, Sheng-Nan Zhao, Ying-Jie Wu, Qiang Quan, Chao Li, Michal Szydlowski, Wei Li, and Tomasz Kolerski. "Freeze-Up Ice Jam Formation in the River Bend, a Case Study on the Inner Mongolia Reach of Yellow River." Crystals 11, no. 6 (June 1, 2021): 631. http://dx.doi.org/10.3390/cryst11060631.

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Concern has been expressed regarding the impacts of climate change on river ice and ice jam formation in cold regions. Ice jams are easily initiated in bends and narrow channels and cause disasters. In this study, observations and remote sensing monitoring are used to study the freeze-up ice jam formation of bends. Sediment transport and freezing process of the river interact, influencing bed changes profile and sedimentary budget. River ice processes, channel evolution, ice hydro-thermodynamics, and ice jam accumulation are explored. The results show that the channel topography determines the river thalweg, and that the channel elevation interacts with the river ice through sediment transport. The channel shrinkage increases the probability of ice jam, and the sharp bend is prone to ice jam formation. Under the effect of secondary circulation flow in the bend and in the outer bank, the juxtaposed freeze-up and the hummocky ice cover occur in the same location, and frazil ice accumulates under the junction of the main channel and the shoals. Affected by the increase of the hydraulic slope and the velocity downstream, open water reaches develops downstream of the ice accumulation. An open water section is emerged upstream of the bend, due to the ice deposition, and partly cut-off supply of the frazil.

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Kranenburg, Wouter M., W. Rockwell Geyer, Adrian Mikhail P. Garcia, and David K. Ralston. "Reversed Lateral Circulation in a Sharp Estuarine Bend with Weak Stratification." Journal of Physical Oceanography 49, no. 6 (June 2019): 1619–37. http://dx.doi.org/10.1175/jpo-d-18-0175.1.

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AbstractAlthough the hydrodynamics of river meanders are well studied, the influence of curvature on flow in estuaries, with alternating tidal flow and varying water levels and salinity gradients, is less well understood. This paper describes a field study on curvature effects in a narrow salt-marsh creek with sharp bends. The key observations, obtained during times of negligible stratification, are 1) distinct differences between secondary flow during ebb and flood, with helical circulation as in rivers during ebb and a reversed circulation during flood, and 2) maximum (ebb and flood) streamwise velocities near the inside of the bend, unlike typical river bend flow. The streamwise velocity structure is explained by the lack of a distinct point bar and the relatively deep cross section in the estuary, which means that curvature-induced inward momentum redistribution is not overcome by outward redistribution by frictional and topographic effects. Through differential advection of the along-estuary salinity gradient, the laterally sheared streamwise velocity generates lateral salinity differences, with the saltiest water near the inside during flood. The resulting lateral baroclinic pressure gradient force enhances the standard helical circulation during ebb but counteracts it during flood. This first leads to a reversed secondary circulation during flood in the outer part of the cross section, which triggers a positive feedback mechanism by bringing slower-moving water from the outside inward along the surface. This leads to a reversal of the vertical shear in the streamwise flow, and therefore in the centrifugal force, which further enhances the reversed secondary circulation.

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Vermeulen, B., A. J. F. Hoitink, S. W. van Berkum, and H. Hidayat. "Sharp bends associated with deep scours in a tropical river: The river Mahakam (East Kalimantan, Indonesia)." Journal of Geophysical Research: Earth Surface 119, no. 7 (July 2014): 1441–54. http://dx.doi.org/10.1002/2013jf002923.

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Xia, Junqiang, Qingrong Jiang, Shanshan Deng, Meirong Zhou, Yifei Cheng, Zhiwei Li, and Zenghui Wang. "Morphological characteristics and evolution processes of sharp bends in the Lower Yellow River." CATENA 210 (March 2022): 105936. http://dx.doi.org/10.1016/j.catena.2021.105936.

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Hamidifar, Hossein, Alireza Keshavarzi, and Paweł M. Rowiński. "Influence of Rigid Emerged Vegetation in a Channel Bend on Bed Topography and Flow Velocity Field: Laboratory Experiments." Water 12, no. 1 (December 30, 2019): 118. http://dx.doi.org/10.3390/w12010118.

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Trees have been used extensively by river managers for improving the river environment and ecology. The link between flow hydraulics, bed topography, habitat availability, and organic matters is influenced by vegetation. In this study, the effect of trees on the mean flow, bed topography, and bed shear stress were tested under different flow conditions. It was found that each configuration of trees produced particular flow characteristics and bed topography patterns. The SR (single row of trees) model appeared to deflect the maximum velocity downstream of the bend apex toward the inner bank, while leading the velocity to be more uniformly distributed throughout the bend. The entrainment of sediment particles occurred toward the area with higher values of turbulent kinetic energy (TKE). The results showed that both SR and DR (double rows of trees) models are effective in relieving bed erosion in sharp ingoing bends. The volume of the scoured bed was reduced up to 70.4% for tests with trees. This study shows the effectiveness of the SR model in reducing the maximum erosion depth.

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KANG, Taeun, Ichiro KIMURA, and Yasuyuki SHIMIZU. "STUDIES ON RIVER FLOWS AT SHARP BENDS WITH A WEAK SECONDARY FLOW USING 2D AND 3D CFD MODELS." Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 73, no. 4 (2017): I_613—I_618. http://dx.doi.org/10.2208/jscejhe.73.i_613.

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Spicer, Preston, and Kimberly Huguenard. "Observations of Near-Surface Mixing Behind a Headland." Journal of Marine Science and Engineering 8, no. 2 (January 22, 2020): 68. http://dx.doi.org/10.3390/jmse8020068.

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Field observations were collected near the mouth of the Bagaduce River, Maine, in order to understand how complex features affect the intratidal and lateral variability of turbulence and vertical mixing. The Bagaduce River is a low-inflow, macrotidal estuary that features tidal islands, tidal flats and sharp channel bends. Profiles of salinity, temperature, and turbulent kinetic energy dissipation (ε) were collected for a tidal cycle across the estuary with a microstructure profiler. Lateral distributions of current velocities were obtained with an acoustic doppler current profiler. Results showed intratidal asymmetries in bottom-generated vertical eddy diffusivity and viscosity, with larger values occurring on ebb (Kz: 10−2 m2; Az: 10−2 m2/s) compared to flood (Kz: 10−5 m2/s; Az: 10−4 m2/s). Bottom-generated mixing was moderated by the intrusion of stratified water on flood, which suppressed mixing. Elevated mixing (Kz: 10−3 m2; Az: 10−2.5 m2/s) occurred in the upper water column in the lee of a small island and was decoupled from the bottom layer. The near-surface mixing was a product of an eddy formed downstream of a headland, which tended to reinforce vertical shear by laterally straining streamwise velocities. These results are the first to show near-surface mixing caused by vertical vorticity induced by an eddy, rather than previously reported streamwise vorticity associated with lateral circulation.

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Mayomi, Ikusemoran, John Abdullahi, and Anthony Dami. "Terrain Analysis of Biu Plateau, for Road Transport Development, Borno State, Nigeria." Journal of Geography and Geology 6, no. 2 (April 1, 2014): 28. http://dx.doi.org/10.5539/jgg.v6n2p28.

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Among all the means of transportation, road has been described as the most important, probably because of its flexibility and its low cost in terms of construction, maintenance and usage. However, in Nigeria, road is considered to be the most dangerous means of transportation because of their bad nature such as sharp bends, narrow bridges, steep slopes and other related problems which are associated with the terrain where these roads are constructed. Road transportation therefore needs proper planning and development through the use of geo-information technologies that would ease accessibility reduces human energy and yet brings reliable and accurate information on the terrain. In this paper, Ilwis 3.5 was used to create Digital Elevation Modelling (DEM), Shadowing, 3-Dimentional View, Slope maps and river direction maps of Biu plateau to analyze the use of GIS on road planning and development on the plateau. It was revealed that the technique has great capabilities of terrain analysis as features which are deemed humanly impossible to assess are viewed as if one is at the scene which may enhance quick analysis on road transportation. It was therefore, recommended that all the stake holders in road transportation should employ the use of this geo-information techniques in terrain analysis to ease transport planning and development in the area.

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Дисертації з теми "Sharp River Bends"

Innocenti, Lorenzo. "Large Wood Dynamics in Sharp River Bends: Experimental and Numerical Investigations." Doctoral thesis, 2021. http://hdl.handle.net/2158/1255750.

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In last decades, the role of large wood (LW) in rivers was largely investigated due to the ecological importance for river habitats, and due to the associated potential hazards to humans and infrastructures, resulting an additional component of fluvial hydraulics. Despite recent research, knowledge of the dynamics of transported wood elements is still incomplete, particularly in modelling the effect of secondary currents on the LW dynamics. The present PhD research aims to enhance the knowledge on the transport of LW in sharp river bends by finding answers to the two main research questions: the identification of the main variables that influence the phenomenon, and assessing the capability of 2D depth-averaged models in reproducing effects of secondary currents on wood trajectories. A combined physical and numerical approach is used for this purpose. Physical model tests were performed in order to investigate the influence of (i) LW element dimensions, (ii) the approaching position of LW to the curve, and (iii) the initial orientation of LW, on the wood trajectories in a sharp bend. The analysis of experiments was conducted by considering the trajectories of wood pieces along the bend and providing statistical results. Moreover, experiments were analyzed by applying a mathematical model in order to provide the drag coefficient for floating LW subjected to a helical flow. For the simulation of secondary current effects, the 2D depth-averaged model “Iber-Wood” was enhanced and tested by simulating two experimental setups and a river-scale case study. The main results of the present work include the individuation of the main variables that influenced the LW trajectories in sharp river bends, the calculation of drag coefficients for a floating LW, and the improvement of the Iber-Wood model in simulating secondary current effects. In addition, two nondimensional coefficients are provided: the coefficient of variation for expressing the trajectory deviation along a bend, and the coefficient of similarity for expressing the similarity between two trajectories. Laboratory experiments particularly highlighted the influence of the wood length which is the main variable determining the trajectory of single wood pieces. Moreover, the approaching position of LW to the curve determined the impact of the wood against the outer bank towards which the wood pieces are pushed by the secondary current. The mathematical model defined for calculating the drag coefficient provides values ranging between 0.3 and 1.2 dependent on the orientation of the wood pieces with respect to the flow direction. Finally, the enhanced Iber-Wood model allowed to simulate the drift to which LW is subjected while transported along a river bend due to the presence of the helical flow.

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Частини книг з теми "Sharp River Bends"

Mehraein, M., M. Ghodsian, and S. Najibi. "Experimental investigation on the flow field around a spur dike in a 90° sharp bend." In River Flow 2014, 743–49. CRC Press, 2014. http://dx.doi.org/10.1201/b17133-101.

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West, Carla Van, and Timothy A. Kohler. "A Time to Rend, A Time to Sew: New Perspectives on Northern Anasazi Sociopolitical Development in Late Prehistory." In Anthropology, Space, and Geographic Information Systems. Oxford University Press, 1996. http://dx.doi.org/10.1093/oso/9780195085754.003.0010.

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Slightly before A.D. 1300, the Four Corners area of the North American Southwest was abandoned by prehistoric agriculturists. By that time, populations had undergone three major cycles of aggregation into large settlements, first constructing relatively large “public” facilities and then redispersing. The reasons for the final abandonment of this area, as well as for the earlier collapse of the Chacoan-related system of the mid-1100s, are classic areas of archaeological inquiry. Recently, the earliest cycle of village formation and dispersal, in the A.D. 800s, has come under increased scrutiny as well (Orcutt et al. 1990; Wilshusen 1991). In this paper we reexamine these phenomena by posing a simple but fundamental question: Under what conditions will farmers find it in their own best interest to share the food they produce? Whatever the particular features of these cycles of aggregation and dispersion, we suggest that periods of increasing complexity in the fabric of sociopolitical organization—which involve the growth of settlements, elaboration of social roles and networks, and heightened cooperation in building, hunting, and exchange—are constructed on top of reliable systems of food sharing beyond that expected among close kin. Such resource pooling has the effect of reducing the impact of variability in agricultural production in an area where great unpredictability surrounds the growing of food. Our thinking about how to approach these systems of food sharing has been influenced by recent analyses of sharing among hunter-foragers (e.g., Kaplan and Hill 1985; Smith 1988) and by current discussions of risk and uncertainty in behavioral ecology and microeconomics (Clark 1990; Stephens 1990). This study focuses on an area in southwestern Colorado about 3 5 km north of the New Mexico border and immediately east of the Utah state line. Notable landmarks include the northward bend of the Dolores River on the northeast, the escarpment of the Mesa Verde in the southeast, and the commanding presence of a volcanic laccolith—Sleeping Ute Mountain—on the south.

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Waitt*, Richard B., Brian F. Atwater, Karin Lehnigk, Isaac J. Larsen, Bruce N. Bjornstad, Michelle A. Hanson, and Jim E. O’Connor. "Upper Grand Coulee: New views of a channeled scabland megafloods enigma." In From Terranes to Terrains: Geologic Field Guides on the Construction and Destruction of the Pacific Northwest, 245–300. Geological Society of America, 2021. http://dx.doi.org/10.1130/2021.0062(07).

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ABSTRACT New findings about old puzzles occasion rethinking of the Grand Coulee, greatest of the scabland channels. Those puzzles begin with antecedents of current upper Grand Coulee. By a recent interpretation, the upper coulee exploited the former high-level valley of a preflood trunk stream that had drained to the southwest beside and across Coulee anticline or monocline. In any case, a constriction and sharp bend in nearby Columbia valley steered Missoula floods this direction. Completion of upper Grand Coulee by megaflood erosion captured flood drainage that would otherwise have continued to enlarge Moses Coulee. Upstream in the Sanpoil valley, deposits and shorelines of last-glacial Lake Columbia varied with the lake’s Grand Coulee outlet while also recording scores of Missoula floods. The Sanpoil evidence implies that upper Grand Coulee had approached its present intake depth early the last glaciation at latest, or more simply during a prior glaciation. An upper part of the Sanpoil section provides varve counts between the last tens of Missoula floods in a stratigraphic sequence that may now be linked to flood rhythmites of southern Washington by a set-S tephra from Mount St. Helens. On the floor of upper Grand Coulee itself, recently found striated rock and lodgement till confirm the long-held view, which Bretz and Flint had shared, that cutting of upper Grand Coulee preceded its last-glacial occupation by the Okanogan ice lobe. A dozen or more late Missoula floods registered as sand and silt in the lee of Steamboat Rock. Some of this field evidence about upper Grand Coulee may conflict with results of recent two-dimensional simulations for a maximum Lake Missoula. In these simulations only a barrier high above the present coulee intake enables floods to approach high-water marks near Wenatchee that predate stable blockage of Columbia valley by the Okanogan lobe. Above the walls of upper Grand Coulee, scabland limits provide high-water targets for two-dimensional simulations of watery floods. The recent models sharpen focus on water sources, prior coulee incision, and coulee’s occupation by the Okanogan ice lobe. Field reappraisal continues downstream from Grand Coulee on Ephrata fan. There, some of the floods exiting lower Grand Coulee had bulked up with fine sediment from glacial Lake Columbia, upper coulee till, and a lower coulee lake that the fan itself impounded. Floods thus of debris-flow consistency carried outsize boulders previously thought transported by watery floods. Below Ephrata fan, a backflooded reach of Columbia valley received Grand Coulee outflow of small, late Missoula floods. These late floods can—by varve counts in post-S-ash deposits of Sanpoil valley—be clocked now as a decade or less apart. Still farther downstream, Columbia River gorge choked the largest Missoula floods, passing peak discharge only one-third to one-half that released by the breached Lake Missoula ice dam.

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