تعيين ضريب زبري پوشش گياهي در سواحل رودخانه ها و دشت هاي سيلابي در حالت غير مستغرق

Determiation of friction factor in river banks and floodplains with non-submerged vegetation

Because of vegetation flexibility in flood plains and river banks, friction factors vary in these areas and are function of vegetation characteristics and flow conditions. Due to being of important structures such as water pumping stations, Roads, water treatment plans and wastewater, fish pools in the river banks and construction of structures such as bridges and diversion dams on them, study of river behavior especially effect of vegetation on flow capacity is very important. Purpose of this research was to obtain relationships and values suitable for vegetation roughness coefficients in the flood plains and river banks for Non- submerged conditions. To do research first identified and selected parameters effect on flow, including vegetation type, velocity, submerged ratio, density and absorption surface momentum and using dimensional analysis relations between roughness coefficient and dimensionless were obtained. Then 182 experiments were conducted on a laboratory flume and effect of parameters on the roughness coefficient was evaluated. By using of results, relations obtained from dimensional analysis were calibrated. Research results can be possible to calculate the friction factors with have above parameters. Roughness coefficients reduce with increasing of flow rate to be nonlinear and severely, for example increase velocity from 0.2 m/s to 2 m/s make Manningʹs coefficient reduces to one third of the first case. But reducing amount of coefficient with decrease of submergence ratio and density compared with the velocity is low and decreasing trend is linear trend, For example if density was reduced from greater category to lower category, value of manning coefficient reduce maximum by ten percent.