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Geometry of fluvial channels
Published in Arved J. Raudkivi, Loose Boundary Hydraulics, 2020
In mountain streams the plan geometry of the stream is totally controlled by topographic features, i.e. in terms of the present time scale. The streams are at the bottom of steep sided valleys and changes of geometry are small. Photos in Figure 5.1a and b illustrate a mountain stream. Notice, the angularity of the rocks in Figure 5.1a. These rocks are rolled in flash floods. Figure 5.1b shows the same stream a few km downstream. Note the large variation in sediment size and the more rounded appearance of rocks. In the background is a residual bank of an eroded sediment wave. On its way down from the mountains the stream valleys widen and the river loses its lateral confinement. Wherever the river has any freedom to move laterally, it will attempt to attain a state of dynamic equilibrium, a regime, in response to the varying flow and sediment load by adjusting its channel pattern, cross-sectional shape, channel roughness and slope. The resulting river channel patterns are frequently subdivided into three limiting types: straight, meandering and braided channels, but many intermediate forms may exist. Straight river channels are rare. These occur only where the available potential energy gradient (slope) balances the energy loss of the flow. The river deals with its excess energy by developing a winding course that creates bend losses. Generally, the slope and sediment transport rate increase as the channel changes from straight to meandering and braiding. For detailed discussion of these aspects reference is made to Leopold et al. (1964), Schumm (1977) and Richards (1982).
Rivers
Published in Richard J. Chorley, Stanley A. Schumm, David E. Sugden, Geomorphology, 2019
Richard J. Chorley, Stanley A. Schumm, David E. Sugden
Although rivers are usually described as being straight, meandering, or braided, there is in fact a great range of channel patterns from straight through meandering to braided and anabranching or anastomosing (Figure 12.23). Straight and meandering channels are described by sinuosity P which is the ratio of channel length Lc to valley length Lv or the ratio of valley slope Sv to channel gradient Sc, as measured over the same length of valley: P=LcLv=SvSc.(12.18)
Scour in rivers and river constrictions
Published in H.N.C. Breusers, A.J. Raudkivi, Scouring, 2020
Where rivers are not confined by man-made bank protections, they tend to develop a number of characteristic shapes in planform. On emerging from the mountains, where topography controls the river geometry, a river develops into a pattern of multiple channels, called braided. In the lower reaches of the river, a single winding main channel pattern forms, called meandering.Leopold et al. (1964) related the slope, S, to the bank full discharge Qb, which separates the braiding and meandering regimes as: S=0.0125Qb−0.44
Fluvial morphology and reservoir sand-body architecture in lacustrine rift basins with axial and lateral sediment supplies: Oligocene fluvial–lacustrine succession in the Xihu sag, East China Sea Shelf Basin
Published in Australian Journal of Earth Sciences, 2020
L. Feng, Y-C. Lu, J. S. Wellner, J-S. Liu, X-F. Liu, X.-Q. Li, J-Y. Zhang
Overall, four major channel styles are identified in the Oligocene river channel system: (1) low-sinuosity braided channel, (2) high-sinuosity braided channel, (3) anastomosing channel, and (4) subaqueous distributary-channel patterns. The braided river system is characterised by the development of mid-channel bars (e.g. longitudinal bars, transverse bars, diagonal bars and compound bars). The styles of fluvial morphology are related to bed load or suspended load transport and the cross-section of channel geometry that shows the river width–depth ratio and the sinuosity (Schumm, 1968 in Miall, 2006; Galloway, 1981) (Figure 18). By reference to the fluvial–geomorphological classification of Galloway (1981) and Schumm (1963), a conceptual model depicting penetrated fluvial channel styles and component sand-body architecture in lacustrine rifted basins with axial and lateral sediment supplies is proposed and shown in Figure 18. Four depositional zones and channel styles are involved from proximal (upper-system) to distal zones (lower-system).
Modeling excess shear stress around tandem piers of the longitudinal bridge by computational fluid dynamics
Published in Journal of Applied Water Engineering and Research, 2021
Hongliang Qi, Junxing Zheng, Chenguang Zhang
The river characteristics include channel pattern, cross profile, and flow ratio (or water level). Channel pattern can be divided into straight, curved, forked, and wandering patterns. The cross profile of a river can be divided into the V-shaped valley and U-shaped valley, which are the most common cross-sections in mountainous rivers. The flow rate (or water level) of the river is also important.