Drag of the water surface at limited fetch: laboratory measurements and modelling

Simultaneous measurements of the friction velocity of the air and the spectra of wind waves in and without presence of mechanically generated waves (a paddle wave) at different fetch and the wind speed are analysed with the help of the wind-over-waves coupled (WOWC) model. Wind waves in the laboratory conditions are characterized by higher values of the significant spectral peak steepness as compared to open waters conditions. Taken this fact into account the WOWC model is capable to reproduce the measured values of the friction velocity within 10% in the relative error, and in the whole range of fetch and wind parameters. A paddle wave being generated interacts with the airflow and wind waves changing the spectral properties of the latter. That leads to a peculiar distribution of the friction velocity depending on fetch and the wind speed. Accounting for these interactions the WOWC model is capable to reproduce those peculiar distributions of the friction velocity