Blocking effects in flow over obstacles

A theoretical investigation is made of the flow of two fluids over an obstacle. Particular attention is given to the upstream disturbance that occurs when the obstacle is started up from rest in a long channel. This has importance as it relates to the blocking phenomenon that occurs when a stratified fluid like the atmosphere moves over barriers. The results of the analysis are borne out by the experiments in the special case of disturbances at a water-air interface. The blocking that occurs is accomplished by a bore moving up ahead of the obstacle raising the upstream depth. The phenomenon is unsteady; it is also non-linear as indicated by the fact that the upstream may be disturbed even when conditions permit no infinitesimal disturbance to progress upstream.