structure, to collect simultaneous wave records (incident and reflected waves 
superimposed), each containing 4,096 data points at a sampling interval of one- 
sixteenth of a second. A fast Fourier transform (FFT) analysis is made of each 
record, and each gage pair gives an estimate of the reflection coefficient sub- 
ject to the criteria discussed in Appendix B. The mean of the three estimates 
is taken as representative at each spectral line, and an energy-weighted aver- 
age is taken to characterize reflection for the entire spectrum of irregular 
waves. The significant incident wave height, H,, for irregular waves (Goda 
and Suzuki, 1976) is defined as 
4 Nrms 
18 Tl ape 3 (1) 
where bane is the average root-mean-square (rms) water surface displacement 
of the wave records at the three gages, and K;, the reflection coefficient. 
Data collection in this study emphasized obtaining additional data on wave 
reflection on smooth slopes and examining the influence of one or more layers 
of armor on reducing the reflection coefficient. Monochromatic and irregular 
waves were tested. 
For monochromatic wave conditions (sinusoidal wave generator blade motion), 
the wave reflection measurement technique was slightly modified. The wave- 
form for monochromatic waves is described by a Fourier series with the entire 
waveform moving at the speed of the primary wave (Dr. R. Dean, University of 
Delaware, personal communication, 1980). This allows the wave energy appearing 
in harmonics of the primary wave to be considered in determining the reflec- 
tion coefficient (App. B). 
IV. FACTORS INFLUENCING WAVE REFLECTION 
The conversion of wave energy concept is useful for defining the interre- 
lation between the wave reflection, dissipation, and transmission coefficients. 
Assuming that the water depth remains constant seaward and leeward of the struc- 
ture the partition of wave energy is given by 
l= Ki + K2 + Ke (2) 
where Kr is the reflection coefficient, Ka the ratio of wave energy lost 
through dissipation to the total incident wave energy, and K, a transmission 
coefficient including transmission through a permeable structure and trans- 
mission by overtopping for a low-crested structure. In an idealized monochro- 
matic wave situation where there are no transfers of wave energy to other wave 
frequencies, 
H 
Kr SS Tal (3) 
aL 
and 
H 
a (4) 
Hy 
where Hj, H,, and H, are the incident, reflected, and transmitted wave heights, 
respectively (see Fig. 1). 
