For better understanding structure of favorable pressure gradient (FPG) flow in cobble bed with submerged vegetation on turbulent characteristics, a laboratory set up and a cobble-bed river reach in the central Iran were considered in this study. The objective of this study is to understand the interaction of cobble bed and submerged vegetation under accelerating flow and expanding the result to Kaj River. This experiment was conducted in a flume of 8 m long, 0.4 m wide, 0.6 m height and maximum discharge of 46 l/s. The median sizes of grains in the flume and river were 52.5mm and 37.33 m and water depth of 200 mm and 280 mm, respectively. The measurements in the flume and river were carried out by ADV. Laboratory experiments were carried out in 5 series: - bed slope of -1.5% and presence of natural vegetation with 150(stem/m) density - bed slope of -1.5% and presence of artificial vegetation with 150(stem/m) density - bed slope of -1.5% and presence of natural vegetation with 100(stem/m) - bed slope of -1.5% and bare bank - Uniform flow with bare bank. The results were shown that velocity profiles in cobble-bed streams with vegetation strip under FPG flow were divided into three sub-zones. The maximum magnitude of Reynolds shear stress was in top of the vegetation where corresponded with inflection point in velocity profiles at mixing layer. Kelvin-Helmholtz instability create in the mixing layer due drag effects of vegetation. The anisotropy of turbulence or vorticity parameter was nearly constant in uniform flow while its decrease from bed to z/H=0.3 and became constant to water surface. The results of quadrant analysis shows the dominant events in all series from bed to z/H=0.4 was sweep, ejection, outward and inward, respectively. The contribution of outward and inward increased from z/H=0.4 to water surface and became nearly equal with sweep and ejection events. Keywords: river, accelerating flow, cobble bed, submerged vegetation, turbulent flow
