Publication Date:
2014-08-30
Description:
This paper uses Particle Imaging Velocimetry (PIV) to provide the first measurements detailing the flow field over a porous bed in the presence of bedforms. The results demonstrate that flow downstream of coarse-grained bedforms on permeable beds is fundamentally different to that over impermeable beds. Most significantly, the leeside flow separation cell is greatly modified by jets of fluid emerging from the subsurface, such that reattachment of the separated flow does not occur and the Reynolds stresses bounding the separation zone are substantially lessened. These results shed new light on the underlying flow physics and advance our understanding of both ecological and geomorphological processes associated with permeable bedforms. Water fluxes at the bed interface are critically important for biogeochemical cycling in all rivers, yet mass and momentum exchange across the bed interface are not routinely incorporated into flow models. Our observations suggest that ignoring such exchange processes in coarse-grained rivers may overlook important implications. These new results also provide insight to explain the distinctive morphology of coarse-grained bedforms, the production of openwork textures in gravels and the absence of ripples in coarse sands, all of which have implications for modeling and prediction of sediment entrainment and flow resistance.
Print ISSN:
0094-8276
Electronic ISSN:
1944-8007
Topics:
Geosciences
,
Physics
