  We studied low energy effects of impurities in several chiral 1D electron
systems that contain only excitations moving in one direction. We first
considered single-impurity scattering between two branches of 1D chiral
Luttinger liquids. The general form of impurity scattering matrix was found
which, some times, allow the chemical potentials on the outgoing branches to be
higher (or lower) then the maximum (or minimum) chemical potentials on the
incoming branches. We also studied the effects of many impurities (with finite
density) on two branches of 1D chiral Fermi liquids (that appear on the edge of
$\nu=2$ integral quantum Hall liquid). We found that the impurities drive the
system to a new fix point at low energies which has an SU(2) symmetry even when
the two branches originally have different velocities. (Note a clean system is
SU(2) symmetric only when the two branches have the same velocity.) The
probability distribution and correlation of scattering matrices at different
energies are described by universal functions which are calculated exactly for
this new fixed point.
