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Corresponding Author

Mahgoub, S.

Subject Area

Civil and Environmental Engineering

Article Type

Original Study

Abstract

The main objective of this study vis to investigate the effect of different flow parameters, mainly flow discharge and Froude number on bed configuration upstream and downstream of hydraulic jump. Bed regression was studied at different Froude numbers ranging from 2.0 to 19.6 upstream the hydraulic jump and ranging from 0.21 to 0.62 downstream the hydraulic jump. The sand used in the experiments was natural and sieving analysis was tested were grain size diameter was found to be 0.4 mm at 60% passing. This experimental study was conducted at the Hydraulics Research Institute (HRI), The National Water Research Center (NWRC), employing two different rectangular flumes with different capacities and dimensions. Therefore, different velocities; different depth and thus different Froude numbers were obtained. The two sides of the flumes are made of glass to facilitate visualizing and monitoring the bed configuration. Extensive field observations on sediment movements in movable bed flume have been carried out for estimating the bed roughness in river channels. Seventy-two runs were executed at different discharges started from 0.02 to 0.130 m3 /s with an increment of 0.01 m3 /s where each discharge has six different gate openings to get all characteristics of bed configuration. The experimental investigations showed that at low unidirectional velocities (≤0.50 m/s), increasing the flow caused the bed to evolve from small- scale symmetric ripples to large- scale symmetric ripples to dunes and later to plane bed. At higher velocities (≤0.50 m/s), a similar trend was observed, but ripples were more symmetric and moved to standing waves and then anti-dunes. Two phase diagrams are presented, the first diagram at Fr < 1 and the second at Fr > 1 to summarize the observed relationships of bed configurations to flow conditions. These diagrams assist in the interpretation of bed configuration characteristics.

Keywords

Sand- Bed Channel; Bed Regression; Ripples -Dunes; Configuration

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