4. Influence of Multiple Layers of Armor. 
As the number of layers, n, of armor on a revetment increases, the amount 
of wave energy dissipated increases and the reflection coefficient decreases. 
In addition, as the size of the stone increases relative to the wave height, 
the roughness becomes more effective and the reflection coefficient decreases. 
Table 2 gives selected values of a correction factor, a', where 
1.3 
Hy: 
a = a' exp [eedon - o.5( 2) ] (19) 
Table 2. Correction factor due to multiple 
layers of armor.! 
d/H, 
<0.75 0.78 
O75 tt 2.0 0.69 
22,0 0.49 | 
Teo) = 2.55 d/l, 2 O15, 0,004 « desu 
<A 0803): 
for multiple layers of armor. These coefficients were obtained by taking the 
average of the ratios of the measured reflection coefficients for two, three, 
and four layers of armor to predicted coefficients for a slope with one layer 
of armor. Only one slope, cot® = 2.5, and stone size-to-water depth ratio, 
d/d, = 0.15, was tested. 
5. Wave Reflection from Sand Beaches. 
Chesnutt (1978) has the most extensive data set of wave reflection coeffi- 
cients from laboratory sand beaches. Unfortunately, there are little prototype 
data available. Chesnutt and Galvin (1974) and Chesnutt (1978) found that many 
factors influence the magnitude of the reflection coefficient. Their data 
suggest that 
2 
eo oe aS SS (20) 
2 
Eo ap B 
can be used to estimate reflection coefficients with the beach slope at the 
stillwater level intercept used to determine &€. Use a = 1.0 for conservative 
estimates of K, and a = 0.5 to give predictions of the average reflection 
coefficient measured throughout a test (Fig. 8). 
20 
