The energy dissipation on a rough, imperjiieable slope was investi- 

 gated in Section III. The experimental investigation revealed the 

 need for an accurate method for the determination of reflection 

 coefficients from experimental data. The simple procedure of seeking 

 out the locations where the wave amplitudes are maximum and minimum, 

 respectively, may lead to reflection coefficients which are much too 

 low, unless the recorded surface elevation is analyzed and only the 

 amplitude of the first harmonic motion is used to determine the 

 reflection coefficient. Accurately determined reflection coefficients 

 for slopes with roughness elements consisting of gravel led to an 

 empirical determination of the friction factor (eqs. 124 and 125), 

 expressing the energy dissipation on a rough slope due to bottom 

 friction. Adopting this empirical relationship a procedure for 

 estimating the reflection coefficient of rough impermeable slopes was 

 developed. This procedure was quite accurate in reproducing the 

 experimentally obtained reflection coefficients in a separate set of 

 experiments. The procedure for the determination of the reflection 

 coefficient of rough impermeable slopes is limited to slopes having 

 roughness elements consisting of natural stones. To make the procedure 

 generally applicable, empirical relationships for the friction factor 

 should be determined for slopes whose roughness elements consist of 

 models of concrete armor units. 



The synthesis of the investigation is the development of an 

 approximate procedure for the prediction of the reflection and transmission 

 characteristics of trapezoidal, multilayered breakwaters. This procedure 

 is entirely self-contained and yields excellent results when compared 

 with the model scale experimental results obtained by Sollitt and Cross 

 (1972). 



It is emphasized that the analytical model for the reflection and 

 transmission characteristics of trapezoidal, multilayered breakwaters 

 developed here needs further verification before it can be used with 

 complete confidence. However, the good agreement between predictions 

 and observations exhibited in Figure 26 is encouraging and does indicate 

 that a simple analytical model which may be used for preliminary design 

 of rubble-mound breakwaters has been developed. 



101 



