Mean characteristics of asymmetric flows: application to flow below ice jams

Results are presented of a laboratory study on the effect of the introduction of a floating cover at the surface of a channel on the mean flow velocity distribution in the then “closed conduit” flow, and on the bed friction factor. It is pointed out that, contrary to common assumption, the location of the maximum velocity is not a point of zero shear stress when the bed and the cover have different roughness characteristics. Semi-empirical and graphical relationships between bed and cover friction factors, relative location of maximum velocity, and bed and cover roughness sizes are presented which are sufficient to estimate the mean flow characteristics below the cover for a given flow discharge and flow depth below the cover. The results may be of importance in the calculation of the characteristics of river ice jams in their initial stage of formation when their roughness is significantly greater than that of the river bed.