Dynamics of the bed morphology around an obstacle in shallow flow. This paper reports the results of experiments conducted in a flume to observe the bed morphology around a spherical obstacle (diametre: 7.2 cm) half-buried in a non-cohesive sand bed (D50:0.56 mm). Flow depths varied from 0.45 cm to 1.4 cm; average velocities ranged from 0.25 m s-1 to 0.45 m s-1 and the Froude number from 0.8 to 1.6. Each run resulted in a typical current crescent surrounding the front and sides of the obstacle followed by a complex zone of furrows and elongated deposits. Maximum scour depth is highly variable but is sharply reduced as critical velocity for sediment transport is exceeded. The complexity of the sedimentary structure is controlled by the location and expansion of the vortices which develop in the vicinity of the obstacle. The set of vortices is governed by fluid velocity which determines the position and angle of the frontal wave created by the presence of the obstacle and consequently the bed geometry. At low velocity, the wave is bent around the obstacle but forms a wide angle leaving a large low pressure zone on the sides of the obstacle. This zone allows a secondary vortex to detach from the horseshoe vortex immediately surrounding the obstacle. The secondary vortex produces a zone of erosion marked by a furrow and zones of sedimentation in the shear layers. As velocity increases, the sedimentary structure becomes a simple current crescent with a small sand shadow tail in the lee of the obstacle. This is caused by the refraction angle of the wave which becomes more acute and gradually surrounds the obstacle thereby constraining the lateral expansion of the secondary vortex. This relation between sedimentary structure and flow dynamics is particular to shallow flow environments and it bears interesting implications for sedimentologists.