عنوان مقاله [English]
نویسندگان [English]چکیده [English]
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. s R/ K , Froude number, r F , and channel shape factor, y 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.