Effects of Boundaries

The previous discussion has focused on the manner in which momentum is exchanged across the sea surface assuming either that there are no boundaries nearby or that the wind is blowing from a long straight coastline. The ocean has been thought of as an infinite half space in the second case with a boundary perpendicular to the wind direction. What is the influence of other shore lines? What if the wind is parallel to a long straight coast? Let us restrict the problem in this chapter to where the wind is spatially uniform.

Since wind-waves have a broad spread of propagation directions, the sea surface roughness at a point is influenced by the fetch from each upstream portion of land. In this situation the wave development is not only a function of fetch in the wind direction but depends also on the cross-wind dimension of the water body. In the case of a lake or bay this will be the width. The other boundary that influences waves is the sea floor. It is through the changes in the surface roughness that we can speculate about the influence of boundaries on the drag coefficient. We will not consider effects such as wave shoaling, or the spatial changes in wind speed that result from variations in surface roughness between land and sea, as this is discussed in Chapter 11.