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Characteristics of sediment movement and river-bed morphology at mountainous stream confluence region
Published in Silke Wieprecht, Stefan Haun, Karolin Weber, Markus Noack, Kristina Terheiden, River Sedimentation, 2016
X.K. Wang, E. Huang, X.N. Liu, X.F. Yan, H.F. Duan
In the natural confluence zone, due to the significant energy loss occurring at joint of mainstream and tributary, it is observed that for the prototype a point bar occurs at the downstream corner near tributary side as shown in Figure 1. In the dry season, the water level is low enough so that the point bar is emergent. The angle between the mainstream and tributary approaches 90°. The point bar is protected by the tributary from scouring of the mainstream. The point bar, therefore, is stable in the dry season. In the wet season, the water level increases to submerge the point bar as the water discharge increases so that the point bar is eroded due to the occurrence of flow velocity above bed. The morphology of the point bar due to erosion, therefore, plays roles in not only influencing the flow structure but also reshaping the bed topography at the confluence zone.
Groundwater Targeting Using Remote Sensing
Published in Prasad S. Thenkabail, Remote Sensing Handbook, 2015
Alluvial plains are built up by plastic material deposited by meandering or braided rivers. Of the large amount of sediments carried by streams, the coarsest and most permeable fractions are deposited along the stream channels, while the finer ones are deposited on the flood plains and backswamps. The coarsest-grained gravels and sand make up the traction load of present and ancient buried stream channels. On the inside of meander bends, coarse-grained “point bar” deposits are formed. “Natural levees” often flanking the channels are generally built up by fine sand and silt. During the high-water stages, a slowly moving sheet of water covers the flood plain and deposits silt and clay. Coarser material may reach the flood plain when the levees are pierced during floods.
River action and control
Published in F.G. Bell, Geological Hazards, 1999
Deposition occurs where turbulence is at a minimum or where the region of turbulence is near the surface of a river. For example, lateral accretion occurs with deposition of a point bar on the inside of a meander bend. A point bar grows as the meander moves downstream or new ones are built as the river changes course during or after floods. Old meander scars can often be seen on flood plains (Figure 6.5a). The combination of point bar and filled slough results in what is called ridge and swale topography. The ridges are composed of sand bars, and the swales are the depressions, which are subsequently filled with silt and clay.
Observations of momentum advection due to secondary circulation in a curved tidal channel
Published in Journal of the Royal Society of New Zealand, 2021
The study of secondary circulation in open channels intensified in post World War II Soviet Russia by trying to find a way to reduce the amount of sediment entering hydroelectric and irrigation canals (Rozovskii 1957). The helical flow pattern would release sediment on the inner-bank of a canal intake structure in a similar way to a natural meandering river bend with a point bar topography. A point bar is a depositional feature where material gets deposited on the inner-bank of a meandering river bend casing a shallow sand bar. Secondary circulation research has been applied to a range of topics associated with flow in curved open channels such as the erosion of river banks (Einstein and Harder 1954; Darby et al. 2002; Constantinescu et al. 2013); the migration of meander bends in rivers (Hickin and Nanson 1984; Furbish 1988; Blanckaert 2011); and the transport of sediment (Dietrich et al. 1979; Blanckaert and De Vriend 2003; Zeng et al. 2008). Secondary circulation has also been studied in other geophysical environments such as tidal estuaries, Vennell and Old (2007), Russell and Vennell (2014) and coastal headlands where the helical flow pattern causes upwelling at the headland (Garrett and Loucks 1976; Geyer 1993; Russell and Vennell 2017).
A simple diagnostic model for the cross-channel distribution of the depth average velocity in curved open channels
Published in Journal of the Royal Society of New Zealand, 2021
More realistic of natural streams and rivers is a point-bar topography, see Figure 11. A point bar is a depositional feature of a meandering river bend where material gets deposited on the inner bank of the bend casing a shallow sand bar and the outer bank becomes steep and eroded. The helical motion of the secondary circulation will move sediment particles towards the centre of curvature away from the outer bank creating a point-bar topography (Engelund 1974). The point bar is a feature of curved flow in natural rivers and streams particularly in meandering and braided rivers.