For an upstream reservoir, the Okland model of self-similar flow is available including its generalized form with a superimposed upper pressure gradient. Along the lee side, more conventional hydraulic flow models require some sort of Bernoulli loss to enable the gap flow to reach the lee side lower pressure reservoir without excessive speeds.

Problems related to connecting the two types of hydraulic models near the Brenner pass in the central Alps will be discussed, as well as various mechanisms of Bernoulli loss (hydraulic jumps, surface friction, entrainment/detrainment at side valleys), and the role of the blocking mountain range at the exit of the valley. The idea is to identify and describe the key parameters governing the complete flow system.