This research presents recent advances on morphodynamic modeling over gravel dunes. Boundary-layer separation over gravel fixed dunes is investigated by Acoustic Doppler Velocimetry (ADV). Using the measurements of flow over dunes at laboratory scale, examined the influence of dune lee sides on the separation of flow. Experiments were conducted in a horizontal flume. A train of 2D fixed dunes were installed on the bottom of the flume starting just downstream of the entrance on the flume. Experiments were carried out using 2 types of dunes with different lee slopes, (38 and 8 degree). The results of quadrant analyses base on the stress fraction SHf versus the hole size at two elevations near the bed and near water surface for two angles of lee side, ,at the central axis of the flume also investigated. Both experimental observations and quadrant results were in agreement about the influence of dune characteristics on the flow separation in different dune lee angles.

Investigating the creation of bed forms due to sediment transport and flow structure in the presence of bed forms in alluvial channels is a constant challenge for engineers and researchers, because of its complex nature. In this research, turbulent flow structure and turbulence anisotropy in the presence of two- and three-dimensional laboratory dunes were investigated. The results showed that, at the reattachment point, the turbulence anisotropy at the centerline of a three-dimensional dune was the largest. On the stoss slope, the turbulence anisotropy for two-dimensional dunes was at its highest at the bed form’s trough and below the crest. The results also demonstrated a tendency at the crest line toward the plane–strain limit for two-dimensional dunes and the centerline of three-dimensional dunes. However, at a 20 cm distance, turbulence anisotropy at the crest line tended toward asymmetric contraction to an oblate spheroid.