Flow Over Gravel Dunes.

Aims: Flow over gravel dunes is investigated. Measured velocity and Reynolds stress distributions over gravel dunes are compared to those for sand bedforms under similar geometric and hydraulic conditions. Place and Duration of Study: Experiments were carried out at the hydraulics laboratory at Isfahan University of Technology, Iran, during the summer of 2012. Results: Results show that the dune surface roughness plays a significant role in the stream wise velocity near-bed region (z/H <0.3), but it has no influence on the velocity distribution in outer flow region (z/H>0.3). While flow separation is clear in the troughs of sand bedforms, it is not evident over gravel bedforms and this has important implications when considering drag and flow resistance. The convex shapes of the Reynolds shear stress distribution over the trough and stoss regions of gravel bedforms are comparable to those of sand bedforms for z/H>0.5, but significant differences are found for z/H<0.5. The greater surface roughness of gravel dunes increases peak values of Reynolds shear stresses over the trough, crest and stoss regions.