Author(s): Jochen Aberle; Katinka Koll; Andreas Dittrich
Linked Author(s): Jochen Aberle, Katinka Koll
Keywords: Rmour layer; Near bed flow field; Turbulence; Irregular bed topography
Abstract: Results of a laboratory study carried out to investigate the interaction between water worked gravel-bed roughness and the near-bed flow field are presented. The spatial heterogeneity of flow velocities and turbulence parameters in the near-bed region are discussed on the basis of form-induced stresses which follow from the double-averaged Navier-Stokes equations. The results show that spatial flow heterogeneity is negligible at greater distance to the roughness tops and increases with decreasing height above the bed. Maximum values of form induced stresses are observed within the roughness layer, i. e., below the roughness tops. Absolute values of form induced stresses are comparable to turbulent stresses in this flow region. The results also show that: (i) spatial flow heterogeneity is independent of discharge; (ii) the influence of roughness geometry is reflected by the distribution of form induced stresses; and (iii) the contribution of form induced stresses to the momentum budget is larger for shallow flows than for flows with large relative submergence. A characteristic height for the upper boundary of the roughness layer is proposed.