ABSTRACT
Traditionally, open channels have tended to be modelled assuming a difference in roughness between the bed and the walls of the channel. Whilst this is a reasonable starting point, the reality is much more complex with heterogeneous roughness elements (or roughness ‘patches’) regularly occurring on the bed of the channel. Given that the bed acts as a source of vorticity, a regular change in bed roughness causes varying levels of vorticity to be present at different cross sections. The ‘new’ vorticity, which occurs as a result of changes in bed roughness, interacts with the existing flow structures leading to a complex flow field which can either result in the manifestation of lateral or vertical shear layers depending on the magnitude of the relative roughness. This flow field has implications not only on the conveyance capacity of a channel but also on other parameters such as sediment transport. This paper presents results relating to a series of laboratory experiments investigating these phenomena. These results have been used to calibrate a numerical model. In the model f has been shown to have the most influence on the model followed by Γ, with λ being relatively unimportant and thus able to be modelled using the standard value without loss of accuracy.
