  Empirical spectra for mechanical and wind waves measured in a large tank of
the First Institute of Oceanography of China are presented. Analysis for the
first and the second type of waves is done separately. It is shown that, in the
case of mechanical waves with a steepness more than 0.2, the frequency spectra
of waves evolve to ones with the tail decay S(f) ~ (f to power -4.2), whilst
the shape of spectra at large fetches is self-similar. Numerical solutions of
the four-wave kinetic equation, written in the fetch-limited version, result in
the same spectra. This allows treating the empirical observations for
mechanical waves as the natural evolution of free nonlinear surface waves. In
the case of wind waves, the wave spectra evolve to ones with the tail decay
S(f) ~ (f to power -4.0) at fetches X greater than 8 meters, under any applied
winds. The well-known Toba three-second relation, H ~ (T to power 3/2), between
the mean wave height, H, and the peak period, T, is well fulfilled. Though, the
intensities of spectra tails do not follow the Toba ratio, S(f) ~ (gu)(f to
power -4), rather they better correspond to the ratio , S(f) ~ ((u to power
2)/Xg)(to power p)(gu)(f to power -4) with p = 1/3. Moreover, the shape of the
wind-wave spectra is not self-similar. Discussion of the results is presented.
