ON THE USE OF ROTATING HYDRAULIC MODELS

Two problems regarding the use of rotating hydraulic channel flow mode ls are addressed. The first concerns the difficulties encountered when trying to identify the ''potential'' depth for a flow of uniform (but nonzero) potential vorticity in a practical situation. Guidelines are given to check whether a chosen value of the potential depth is consi stent with the rotating hydraulic theory. The second problem deals wit h the applicability of the so-called zero potential vorticity approxim ation. It is shown that the accuracy of this, approximation depends on the ratio of the channel width to the Rossby radius of deformation (b ased on the potential depth) and the ratio of the fluid depth to the p otential depth. To establish when this simplified model yields an accu rate approximation of a flow of constant (but nonzero) potential vorti city, the two models are compared for a variety of channel geometries.