experimental study of the effect of sediment particles shape on manning's coefficient

abstract in all river engineering projects, determination of flow resistance is essential. most commonly, the manning roughness coefficient, , is used to describe the flow resistance or relative roughness of main channel or flood plane. over the past decades little or no study has been conducted to investigate the effects of particle shapes on manning roughness coefficient. therefore, it is the purpose of this study to see how and by what extend, the particle shape can affect the manning’s coefficient. to do so three different sediment shapes (angle rounded particles and crushed particles and spherical artificial particles); each in 11 different sizes were collected and tested under different flow conditions. tests conducted in a flume of 10 meter long, 25 cm wide, 50 cm height and constant bed slope of 0.0005. the results show that the effect of particle shape in larger particle size is less compare to the smaller particle size. as in sediments with size of 11 mm, values of manning roughness coefficient ( ) for sediment particles shows great difference and in 21mm and 27 mm sediment particles, the manning roughness coefficient ( ) in angle rounded and spherical artificial particles are equal nearly as the average difference between manning's coefficient ( ) of these particles are found to be in the order of +1.65 percent and values of manning roughness coefficient ( ) for crushed particles in 21mm and 27 mm sediment particles shows little difference with other sediment particles. the average difference between manning's coefficient ( ) of crushed particles with natural rounded particles are found to be in the order of -6.2 percent.