THE GROWTH-RATE OF FINITE DEPTH WIND-GENERATED WAVES

Fetch limited wind wave experiments traditionally investigate the grow th of wave energy with distance from shore. [Donelan, M., Skafel, M., Graber, H., Liu. P., Schwab, D., Venkatesh, S., 1992. On the growth ra te of wind-generated waves, Atmos.-Ocean 30, 457-478], have, however, shown that for deep water conditions it is advantageous to investigate the differential growth between points located along the fetch. Based on the extensive data set collected by [Young, I.R., Verhagen, L.A., 1996a. The growth of fetch limited waves in water of finite depth, Par t I: Total energy and peak frequency, Coastal Eng. 28, 47-78], this ap proach has been extended to finite depth conditions. The data clearly show that at short fetches the growth rate is comparable to deep water conditions. At longer fetches the finite depth influences increase an d the growth rate decreases compared to deep water. Finally the waves approach a depth limited state where the growth rate becomes zero. Bas ed on the observed differential growth between measurement stations, a relationship is developed which can be integrated to yield the develo pment of the total energy with fetch. This relationship is significant ly more flexible than previous finite depth growth relationships. Case s in which the water depth and/or wind speed vary with fetch can be in vestigated. In particular, it is shown that the development of the atm ospheric boundary layer with fetch has a significant influence on the observed wave growth. By the inclusion of a realistic relationship for the boundary layer development it is shown that apparently anomalous features of the [Young, I.R., Verhagen, L.A., 1996a. The growth of fet ch limited waves in water of finite depth, Part I: Total energy and pe ak frequency, Coastal Eng. 28, 47-78] data set can be explained. (C) 1 997 Elsevier Science B.V.