Comparison of Experimental Hydraulic Coefficients on Fixed and Mobile Bed Materials in Open Channel Flow

The prediction of hydraulic coefficients, which varies for different materials, is an essential criterion for designing open channels and related hydraulic structures. The main objective of this research is to compare experimental hydraulic coefficients on fixed and mobile bed materials in open channel flow. The study considered three types of bed roughness; namely steel beds, 2 mm uniform beds, and 25 mm uniform grain-sized beds in a rectangular flume model with a 1:500 and 1:200 adjustable bed slope. Manning's roughness coefficient and Chezy's equations were used to model channel bed roughness concerning the variation of flow characteristics for different bed conditions. The results showed that Manning's roughness coefficient had an inverse relationship with the discharge, flow depth, hydraulic radius, flow conveyance, and Chezy’s coefficient, but it was directly proportional to grain size. The values of mean velocity in the mobile bed along the channel are comparatively less than that of the fixed bed. The percentage change of average n value due to changes in channel slope and bed condition is slightly increased by 144.95% and 150.23% under the channel slope of 1:200, and 143.02% and 148.04% under the channel slope of 1:500. Also, the percentage change of the average C value is slightly decreased by 59.97% and 59.98% under the channel slope of 1:200, and 58.75% and 59.42% under the channel slope of 1:500 when the bed changed from fixed to mobile 2 mm and 25 mm grain sizes, respectively.