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Uniform flow occurs only in long and prismatic channels. However, in real-life projects, channel cross sections and bottom slopes are not constant with distance in natural channels and these are varied in constructed channels to suit the existing topographical conditions for economic reasons. In addition, hydraulic structures are provided for flow control. These changes in the channel geometry produce nonuniform flows while changing from one uniform-flow condition to another.
If the rate of variation of depth with respect to distance is small, the flow is called gradually varied flow. On the other hand, if the rate of depth variation is large, the flow is called rapidly varied flow. Since the analysis of gradually varied flows is usually done for long channels, the friction losses due to boundary shear have to be included. These losses, however, may be neglected in the analysis of rapidly varied flows because the distances involved are short. In addition, the pressure distribution in gradually varied flow may be assumed hydrostatic because the streamlines are more or less straight and parallel. However, this is not the case in rapidly varied flows where significant acceleration normal to flow direction may be produced by sharp curvatures in the streamlines.
In this chapter, an equation for the spatial variation of flow depth in gradually varied flow is derived. The classification of various water surface profiles is then presented. This is followed by a presentation of procedures for sketching the water-surface profiles qualitatively and for determining the discharge from a reservoir. The properties of water surface profiles in a compound channel are then discussed.
Uniform flow occurs only in long and prismatic channels. However, in real-life projects, channel cross sections and bottom slopes are not constant with distance in natural channels and these are varied in constructed channels to suit the existing topographical conditions for economic reasons. In addition, hydraulic structures are provided for flow control. These changes in the channel geometry produce nonuniform flows while changing from one uniform-flow condition to another.
If the rate of variation of depth with respect to distance is small, the flow is called gradually varied flow. On the other hand, if the rate of depth variation is large, the flow is called rapidly varied flow. Since the analysis of gradually varied flows is usually done for long channels, the friction losses due to boundary shear have to be included. These losses, however, may be neglected in the analysis of rapidly varied flows because the distances involved are short. In addition, the pressure distribution in gradually varied flow may be assumed hydrostatic because the streamlines are more or less straight and parallel. However, this is not the case in rapidly varied flows where significant acceleration normal to flow direction may be produced by sharp curvatures in the streamlines.
In this chapter, an equation for the spatial variation of flow depth in gradually varied flow is derived. The classification of various water surface profiles is then presented. This is followed by a presentation of procedures for sketching the water-surface profiles qualitatively and for determining the discharge from a reservoir. The properties of water surface profiles in a compound channel are then discussed.
GRADUALLY VARIED FLOW
Chaudhry, M. Hanif (author)
Open-Channel Flow ; Chapter: 5 ; 125-153
2022-01-01
29 pages
Article/Chapter (Book)
Electronic Resource
English
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