65
DISTANCE FROM STILL-WATER LINE
IN BEACH, x CMS
3.0
2.5
2.0
1.5
CMS
1.0
IS?
0.5
0
-0.5
Figure 5.1: Comparison of the numerical solution of Vemulakonda et al. (1985) for set-up
with experimental data of Bowen (1968). Source: Vemulakonda et al. (1985)
a constant. For the numerical results the set-up starts at the breaking point, whereas in
the experimental results the water surface elevation is nearly constant for some distance
shoreward of the breaking point and then there is a change in the slope of the water surface
elevation. The numerical results follow the analytical solution. This is an area that needs
further investigation. The reason for the difference between the analytical and experimental
results is that the analytical formulation is predicated upon the radiation stress term being
a function of the wave height, so that as the wave height is reduced after the breaking point
so is the radiation stress term. As pointed out by Svendsen (1984) the radiation stress term
remains nearly constant after breaking for a distance roughly equal to five or six times the
breaking depth. This distance is termed by Svendsen as the outer or transition region in
which there is a rapid change of wave shape. In the inner region the wave shape according
to Svendsen remains nearly constant and is characterized by a surface roller or bore. By
incorporating the surface roller Svendsen is able to obtain close agreement for wave height
and set-up to the experimental results of Hansen and Svendsen (1979). However this close