Water-surface slopes due to wind waves have been measured in a laboratory windwave tunnel. In all measurements, nonlinear effects are important for highfrequency wind waves; nonlinear effects noted are: increase of phase velocity due to finite amplitude of gravity waves, trapping of ripples on the leading slope of gravity wavelets, and limitation of slopes after the explosive growth of waves beyond a critical fetch....
Cox, Charles S.. 1958. "Measurements of slopes of high-frequency wind waves; Comments on Dr. Cox's paper." Journal of Marine Research 16, (3). https://elischolar.library.yale.edu/journal_of_marine_research/894