Determination of Form Friction Factor of Armored Gravel-Beds Rivers
Author(s):
Article Type:
Research/Original Article (دارای رتبه معتبر)
Abstract:
Friction factor plays a substantial role in hydraulic computations. In coarse-bed rivers, friction factor depends on grain size and bed forms. A wide range of particle sizes and developing armor layer have great effects on friction factor. Therefore, determination of form friction factor of armored river beds has been investigated in this study and, a friction equation was developed based on computing grain friction factor of the total friction factor. Analysis of obtained equation showed that the friction factor is rather independent of grain-size distribution of the material forming the bed and the maximum grain size of this material. The major controlling parameter is the slope of the energy grade line. These results are explained by the coupling of the friction factor with the incipient motion problem and the rearrangement of the grains of the coarsest fraction in the armor coat. To verify the equation, Keulegan method was used which results 80% agreement between two methods. Also, including the major part of total friction factor to form friction factor (40%) shows the great effects of bed form on flow resistance. The results of the current study showed that making and development of armor layer increase bed roughness and friction factor and decrease average flow velocity causing a reduction in threshold Shields parameter and augmentation in bed stability. Field observations are employed to test the methods.
Keywords:
Language:
Persian
Published:
Journal of Hydraulics, Volume:13 Issue: 3, 2019
Pages:
1 to 16
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