STUDY OF THE INCIPIENT MOTION 03 BED PARTICLES FOR GRAVEL BED CHANNELS | ||||
| ERJ. Engineering Research Journal | ||||
| Article 4, Volume 23, Issue 3, July 2000, Page 63-76 PDF (652.5 K) | ||||
| Document Type: Original Article | ||||
| DOI: 10.21608/erjm.2000.71306 | ||||
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| Author | ||||
| Kassem Salah Abd EL-Wahab El- Alfy | ||||
| Assistant Prof., Dept. of Irrigation and Hydraulics, Faculty uf Engineering, Mansoura Univ., Egypt. | ||||
| Abstract | ||||
| For rivers in flood, the shear stress at the top of the stationary gravel bed can set up a sheared layer of contact-load (bed-load). As is well known, movement of solid particles does not initiate until the shear stress exceeds some critical value ( Tc ) The main objective of this research is the laboratory prediction of the conditions at which the incipient motion occurs in the gravel bed channels through fifteen grading of gravel bed. The laboratory critical shear stress for every bed grading is computed and compared with that resulted from formulae used in calculating the critical shear stress on channel bed. The experimental analysis is used to obtain the relations describing the boundary of the initiation of motion of the gravel bed particles. Also the flow velocity adjacent to bed and the mean flow velocity are measured at the critical conditions (case of incipient motion). The influence of the value of the downward angle of the bed on the critical shear stress is also examined. From the laboratory experiments, it was concluded that the values of the critical shear stress are similar to the values from the existingformulae, especially Shields diagram, and Shulits and Hill formula. From the measurements of the bed velocity at the incipient motion conditions, a relationship between the dimensionless critical bed velocity (VbdV,,) and the ratio (Re/Fnd) is predicted. It is also noticed that there is aninverse proportionality between the downward bed angle and the critical shear stress required to initiate motion of the gravel bed | ||||
| Keywords | ||||
| shear stress; incipient motion; critical conditions: bed particles | ||||
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