  We present a detailed study of the hydrodynamics of the matter reinserted by
massive stars via stellar winds and supernovae explosions in young assembling
galaxies. We show that the interplay between the thermalization of the kinetic
energy provided by massive stars, radiative cooling of the thermalized plasma
and the gravitational pull of the host galaxy, lead to three different
hydrodynamic regimes. These are: a) The quasi-adiabatic supergalactic winds. b)
The bimodal flows, with mass accumulation in the central zones and gas
expulsion from the outer zones of the assembling galaxy. c) The gravitationally
bound regime, for which all of the gas returned by massive stars remains bound
to the host galaxy and is likely to be reprocessed into futher generations of
stars. Which of the three possible solutions takes place, depends on the mass
of the star forming region its mechanical luminosity (or star formation rate)
and its size. The model predicts that massive assembling galaxies with large
star formation rates similar to those detected in SCUBA sources ($\sim 1000$
M$_\odot$ yr$^{-1}$) are likely to evolve in a positive star-formation feedback
condition, either in the bimodal, or in the gravitationally bound regime. This
implies that star formation in these sources may have little impact on the
intergalactic medium and result instead into a fast interstellar matter
enrichment, as observed in high redshift quasars.
