Note on the analysis of plunging of density flows

This note is devoted to the correction of an error in a calculation contained in a classical published paper on the plunging of river flows as they enter lakes or reservoirs. The correction of the error provides a felicitous result, according to which not only the ratio of underflow thickness just after plunging to depth just before plunging, but also the densimetric Froude numbers both just before and just after plunging are all specified as a function of a single parameter. This single parameter characterizes the tendency of plunging to entrain ambient water into the density underflow.