  We investigate the effect of peculiar velocities on the redshift space
distribution of z>~2 galaxies, and we focus in particular on Ly-alpha emitters.
We generate catalogues of dark matter (DM) halos and identify emitters with
halos of the same co-moving space density (M(Ly-alpha emitters) ~ 3x10^11
M_sun). We decompose the peculiar velocity field of halos into streaming,
gradient and random components, and compute and analyse these as a function of
scale. Streaming velocities are determined by fluctuations on very large
scales, strongly affected by sample variance, but have a modest impact on the
interpretation of observations. Gradient velocities are the most important as
they distort structures in redshift space, changing the thickness and
orientation of sheets and filaments. Random velocities are typically below or
of the same order as the typical observational uncertainty on the redshift. We
discuss the importance of these effects for the interpretation of data on the
large-scale structure as traced by Ly-alpha emitters (or similar kinds of
astrophysical high-redshift objects), focusing on the induced errors in the
viewing angles of filaments. We compare our predictions of velocity patterns
for Ly-alpha emitters to observations and find that redshift clumping of
Ly-alpha emitters, as reported for instance in the fields of high-redshift
radio galaxies, does not allow to infer whether an observed field is sampling
an early galaxy overdensity.
