  We investigate the clustering properties of 13 QSO lines of sight in flat
space, with average redshifts from z~2 to 4. We estimate the 1-D power spectrum
and the integral density of neighbours, and discuss their variation with
respect to redshift and column density. We compare the results with standard
CDM models, and estimate the power spectrum of Lyman-alpha clustering as a
function both of redshift and column density. We find that a) there is no
significant periodicity or characteristic scale; b) the clustering depends both
on column density and redshift; c) the clustering increases linearly only if at
the same time the HI column density decreases strongly with redshift. The
results remain qualitatively the same assuming an open cosmological model.
