0.6 
0.5 
0.4 
Kr 0.3 
0.2 
Ronge of Kr 
0 OSD 1.0 1.5 2.0 ; 2.5 3.0 3.5 
3 
Figure 8. Wave reflection coefficients from laboratory 
beaches (from Chesnutt, 1978). 
6. Rubble-Mound Breakwaters. 
An upper limit or conservative estimate of Ky for breakwaters armored 
with rock or dolos may be obtained using 
a ge 
kK, = — 
ro g2 +B 
s; a = 0.6, 8 = 6.6 (21) 
Ninety-five percent of all observed laboratory breakwater wave reflection 
coefficients fall below this prediction equation for data sets c, d, g, and h 
outlined in Table l. 
More reliable predictions of wave reflection coefficients for rubble-mound 
breakwaters may be made using the method of Madsen and White (1976) (also see 
Seelig, 1979). Equations (16) and (18) should be used with the Madsen and 
White (1976) method to estimate energy dissipation on the seaward face of the 
breakwater caused by the outer layer of armor units. Figure 9 shows sample 
laboratory measurements (Sollitt and Cross, 1976) and predicted reflection and 
transmission coefficients for a rubble-mound breakwater. Observed and predicted 
reflection coefficients have the best agreement for wave conditions in the tur- 
bulent zone, but deviate where the Reynolds number becomes less than 10+ due 
to laboratory scale effects. 
2| 
