Experimental Study of the Effects of Channel Bed Coarse Sediments on Flow Resistance Coefficient

Determination of flow resistance is an essential parameter for studying and hydraulic analyzing open channels. Flow resistance in channes with coarse materials on bed is mostly due to grain roughness. Over the past decades several studies have been conducted to correlate the flow resistance to the particle size; however the effects of particle shapes are not clear so far. Therefore, it is the purpose of this work to conduct experimental studies to see how important the type and size of coarse sediments are. In this study eight types of sediments; four rounded and four angular sediments have been tested under different flow conditions in a flume of 10 meter long, 25 cm wide and 50 cm height. Experiments were conducted under constant bed slope of 0.0005. Results show that parameters such as relative roughness., Froude number,, and channel shape factor, play important roles in accurate estimation of flow resistance. The results have also shown that in gravelbed rivers the flow resistance can be estimated by semi logarithmic and power equations with the same accuracy. In this study an equation was also proposed for prediction of flow resistance coefficient