Experimental study for determine manning's coefficient with different slopes and channel bed materials

الملخص EN

Water resources and hydraulic engineering projects have been upward rapidly in all over the world, accordingly the prediction of roughness coefficient is essential criteria to design open channels, and related hydraulic structures.

The aims of this research are to find out the effect of changing beds materials and discharge on coefficient of roughness (n), the beds that used in the tests are smooth which represented by original channel bed (steel plate), rough bed material which is a gravel bed and waved bed .The experimental work was performed in a rectangular flume with dimension of (15 m* 0.3 m* 0.45 m) long, wide and deep, respectively with different value of slope (1:200 and 1:500) to analyze slope effect on coefficient of roughness in addition to the effect of channel bed material.

The experimental work showed that The coefficient of roughness reduced when the discharge increases for specified slope and channel bed, The slope of the channel and bed roughness is the main factors affected on determining coefficient of roughness and when the channel slope increases the coefficient of roughness increases, the coefficient of roughness is decreased when using smooth bed and it is increased when channel bed is waved.

The percentage change in the Manning coefficient due to changing in slope and channel bed is (112.6%) when slope equal to (1/200) and the channel bed changed from smooth to rough , (184%) when the bed changed from rough to waved, and (33.6%) when channel bed changed from rough to waved.

And for (1/500) slope, the percentage change in the Manning coefficient equal to (33.5%) when the bed changed from smooth to rough, (80%) when changed from smooth to waved, and (33.1%) when changed from rough to waved.