Directional measurements of wave growth in a short and narrow fetch geometry

The growth of young waves along a narrow bay and their directional spectra were studied. The fetch geometry was found to affect the shape of the spectrum already when the waves were young. When compared to the growth from a straight shoreline, the dimensionless energy was reduced, but the change in dimensionless peak frequency was smaller. The behaviour of the young waves was similar to that of the mature waves but the differences between narrow and broad fetch geometries were smaller, which suggests that due to a stronger nonlinear transfer the young waves are less sensitive to the fetch geometry. The directional spectrum of the young waves in the narrow fetch geometry was narrower at all energy containing frequencies than the spectra from broad fetch geometry, which further supports the conclusion that the shape of the spectrum is not independent of the fetch geometry.