  By analyzing hot-wire velocity data taken in an open channel flow, an
unambiguous definition of surface-layer thickness is here provided in terms of
the cross-over scale between backward and forward energy fluxes. It is shown
that the turbulence in the surface layer does not conform to the classical
description of two-dimensional turbulence, since the direct energy cascade
persists at scales smaller than the cross-over scale, comparable with the
distance from the free-surface.
  The multifractal analysis of the one-dimensional surrogate of the turbulent
kinetic energy dissipation rate in terms of generalized dimensions and
singularity spectrum indicates that intermittency is strongly depleted in the
surface layer, as shown by the singularity spectrum contracted to a single
point.
  The combination of intermittency indicators and energy fluxes allowed to
identify the specific nature of the surface layer as alternative to classical
paradigms of three- and two-dimensional turbulence which cannot fully capture
the global behavior of turbulence near a free-surface.
