PART IV: CONCLUSIONS 



42. This report summarizes the results from 205 laboratory tests of 

 reef breakwaters conducted using irregular waves. Findings from this study 

 can be categorized as follows: (a) the stability of the structure to wave 

 attack, (b) wave transmission over and through the structure, (c) wave reflec- 

 tion from the structure, and (d) energy dissipation by the structure. These 

 findings are largely summarized through the use of equations fit to the data 

 which can be used to predict various breakwater characteristics with sur- 

 prisingly high accuracy. 



43. The important conclusions from this study are: 



a. A stability number was defined by Equation 2 and named the 

 spectral stability number which was found to be the single most 

 important variable influencing the stability of reef 

 breakwaters. 



b. There is very little stone movement or damage for spectral sta- 

 bility numbers less than six, but stone movement and damage can 

 be clearly seen for values greater than eight. 



£. For values of the spectral stability number above six, the in- 

 fluence of other variables on stability can be identified. 

 Other factors being equal, the stability of the reef increases 



the lower the relative crest height h /d ; as its size de- 



c s 



fined by Equation 3 increases; and as the slope of the struc- 

 ture, as defined either by Equation 4 or 5, gets flatter. 



d. Wave transmission over and through a reef is a very complex 

 process. Part of the complexity relates to the confusing in- 

 fluence of some variables; e.g., for breakwaters with positive 

 freeboards transmission over the reef is directly proportional 

 to wave height, while energy transmitting through the reef is 

 inversely proportional to the wave height. For conditions 

 where transmission is dominated by wave energy propagating 

 through the reef, a simple relation, Equation 12, was found to 

 predict the transmission coefficient very well. When the domi- 

 nant modes of transmission resulted from wave overtopping or 

 wave propagation over the crest of a submerged reef, a rather 

 complex relation, Equation 13, was required to make reasonable 

 estimates of transmission coefficients. 



e. Wave reflection is easier to predict than either stability or 

 wave transmission. A simple relation using only one variable, 

 Equation 14, was able to explain about 80 percent of the vari- 

 ance in the reflection coefficients. A more complex relation, 

 Equation 16, was developed which explained about 99 percent of 

 the variance in the reflection coefficient. Other factors 

 being equal, reflection coefficients increase with increasing 

 wave length and increasingly steeper reef slopes. Reflection 



43 



