3. Experimental Investigation . 



The theoretical analysis of the reflection coefficient of rough 

 impermeable slopes described in Section III. 2 suggests a rather simple^ 

 experimental procedure for the determination of the value of f^^. Imagine 

 that an experiment is performed in which the reflection coefficient, R, 

 is determined for given slope (d and £5) ^"<^ incident wave characteristics 

 (a^ and L) . With l^/L and R known. Figure 15 may be used to obtain the 

 the corresponding value of cf.. |a| = R^ la.^ and Fg may then be obtained 

 from Figures 16 and 17 and equation (109) written in the form: 



h 



f = tan3 TTT F- tan2<J) , (116) 



w s |A| F^ 



may be used to obtain the value of f . 



Performing a series of experiments for various slope and incident 

 wave characteristics and analyzing the results as outlined above will 

 produce a number of values of f^^ from which an empirical relationship 

 of the type suggested by equation (115) may be established. 



It should be pointed out that this procedure for the analysis of 

 experimental data relies heavily on the theoretical development 

 presented in Section III. 2. The resulting empirical relationship for 

 f^^ therefore incorporates not only the true physical dependency of f^^ 

 on the relative roughness, but reflects also inadequacies of the 

 theoretical development. This is important to keep in mind, since it 

 means that the resulting relationship for f^^ becomes an integral part 

 of the entire procedure for the determination of reflection coefficients 

 of rough impermeable slopes. 



From the preceding the aim of the experimental investigation is to 

 determine accurately the reflection coefficient of rough impermeable 

 slopes for a variety of slope and incident wave characteristics. 



a. Experimental Setup and Procedures . The experiments were 

 performed in a wave flume at the Ralph M. Parsons Laboratory at MIT. 

 This flume is glass walled and is 80 feet (24.4 meters) long, 15 inches 

 (0.38 meter) wide, and the constant water depth in front of the slope 

 was for the major part of the experiments kept at h =1 foot (0.305 

 meter). A piston-type wavemaker capable of producing periodic waves 

 of periods within the range of 0.6 second < T < 2.2 seconds is 

 located at one end of the flume. Experiments were performed for three 

 wave periods T = 2.0, 1.8, and 1.6 seconds which with h = 1 foot 

 correspond to depth to length ratios of the incident waves h /L=0.092, 

 0.105, and 0.12, respectively. 



A variable slope of rigid construction was installed approximately 

 60 feet (18 meters) from the generator. Care was taken to completely 



60 



