  We study the effect of surface scattering on transport properties in
many-mode conducting channels (electron waveguides). Assuming a strong
roughness of the surface profiles, we show that there are two independent
control parameters that determine statistical properties of the scattering. The
first parameter is the ratio of the amplitude of the roughness to the
transverse width of the waveguide. The second one, which is typically omitted,
is determined by the mean value of the derivative of the profile. This
parameter may be large, thus leading to specific properties of scattering. Our
results may be used in experimental realizations of the surface scattering of
electron waves, as well as for other applications (e.g., for optical and
microwave waveguides)
