Possible Laboratory Scale Effects Turbulent Zone 
Measurements 
Predictions 
Hy/L 
Figure 9. Predicted rubble-mound breakwater wave reflection 
and transmission coefficients (laboratory data 
from Sollitt and Cross, 1976). 
7. Spectral Resolution of Wave Reflection. 
The significant wave height and period of peak energy density are used to 
characterize irregular wave conditions in this report. However, a more detailed 
analysis shows that the reflection coefficient varies as a function of wave 
frequency for irregular waves. Figure 10 illustrates the decrease in reflection 
coefficient as a function of wave frequency that is typical of waves breaking 
on a smooth impermeable 1/2 slope (&€ < 2.3). Nonbreaking waves have a different 
characteristic shape of the reflection coefficient as a function of wave fre- 
quency. K,; increases as a function of f for frequencies higher than the 
frequency of peak energy density (Fig. 11). The shift to high frequencies seems 
to occur because wave energy is transferred from low to higher frequencies due 
to nonlinear effects when the waves interact with the structure. Note that this 
energy shift may produce a range of wave frequencies in which more wave energy 
is moving away from the structure than is incident to the structure, and the 
local reflection coefficient may be larger than 1.0 over this range of fre- 
quencies. Caution should be used when trying to obtain information from the 
highest frequency part of the spectrum above approximately the 95-percent cumu- 
lative energy density level because the signal-to-noise ratio is low and the 
wave speed is poorly known (Mansard and Funke, 1979). 
8. Reflection Coefficient Prediction Equations. 
Table 3 summarizes the equations recommended for estimating reflection 
coefficients for slopes, revetments, rubble-mound breakwaters, and beaches. 
22 
