Author(s): Dermisis C. Dimitrios; Papanicolaou N. Athanasios
Linked Author(s):
Keywords: Sand-bed; Gravel-bed; Critical shear stress; Clast; Sand ridge; Deposition
Abstract: The objective of this investigation is on the movement of sand over a flat, immobile gravel-bed with distinguishable isolated roughness elements (clasts) found atop the gravelbed, which are common ubiquitous features of natural gravel streams. For this case a flume experiment was conducted, under hydraulic conditions specified by the reference critical shear stress. The paper examines the hypothesis that isolated roughness allows the formation of distinguishable sand depositional patterns in the stoss region of clasts. Results confirm this hypothesis and show that the incoming sand particles were mainly deposited in the front region of the clasts, forming unique sediment depositional patches. A characteristic sand ridge was created at the sand-bed section along the center line of the flume, with a maximum height observed upstream of the clasts. The maximum depositional height of the ridge was attributed to the additional form roughness added by the presence of the clasts. Formation of the sand ridge in conjunction with the presence of clasts regulated the bedload rate. Future research will undertake additional experimental runs for the wake interference and skimming flow regimes. In addition, subsequent studies will investigate the role that clasts have, overall, in regulating sand movement in gravel bed streams. Thus, complementary experiments will be performed with the clasts being removed.
Year: 2007