  We present experimental results on simultaneous space-time measurements for
the gravity wave turbulence in a large laboratory flume. We compare these
results with predictions of the weak turbulence theory (WTT) based on random
waves, as well as with predictions based on the coherent singular wave crests.
We see that both wavenumber and the frequency spectra are not universal and
dependent on the wave strength, with some evidence in favor of WTT at larger
wave intensities when the finite flume effects are minimal. We present further
theoretical analysis of the role of the random and coherent waves in the wave
probability density function (PDF) and the structure functions (SFs). Analyzing
our experimental data we found that the random waves and the coherent
structures/breaks coexist: the former show themselves in a quasi-gaussian PDF
core and in the low-order SFs, and the latter - in the PDF tails and the
high-order SF's. It appears that the x-space signal is more intermittent than
the t-space signal, and the x-space SFs capture more singular coherent
structures than do the t-space SFs. We outline an approach treating the
interactions of these random and coherent components as a turbulence cycle
characterized by the turbulence fluxes in both the wavenumber and the amplitude
spaces.
