of Mizuguchi, Oshima, and Horikawa (1978) were performed in a 15- by 

 15-meter wave basin with a 9-meter beach section of slope 1:10.4. Table 

 7 summarizes the results for four separate test cases. Current measurement 

 was by propeller-type meter and values recorded represented averages taken 

 in the vertical direction. A test section with no systematic acceleration 

 in the longshore direction was found to exist and data reported for this 

 location. The intersection of the mean setup and setdown lines was used 

 to define the breaking point. The wave breaking ratio, y was described 

 as approximately linear in the surf zone. 



Results of the laboratory experiments when compared with the theory 

 (solid line) are presented in Figure 65. Velocities are normalized by 

 the maximum current v-^ and distance by X]^. By requiring the theoretical 

 location of the maximum velocity to match the experimental results, all 

 curves were fitted to the data in this regard. Agreement for profile shape 

 is excellent in the region shoreward of v^ in all four cases. The dotted 

 line is the original model of Longuet-Higgins (1970) which gives very 

 similar results in this region since small angles are present. The model 

 of Kraus and Sasaki (1979) gives better agreement beyond Vm and the breaker 

 line where large wave angles are present. In two cases (1 and 4) the 

 theoretical tail dropped off too rapidly to fit the data. 



In three of the four cases studied, P* values were less than 0.1. 

 The eddy viscosity coefficient, V ranged from 0.0062 to 0.037 with higher 

 values associated with large wave angles. The bed friction coefficient, 

 C£ was in the range between 0.011 and 0.024. All these values were com- 

 puted and were not initially specified since fitting the maximum velocity 

 was used in their determination. To do this, y ^nd a^ must also be 

 initially specified. Thus by adding the extra condition available through 

 Xju, all parameters of the theory not usually obtainable by measurement, 

 i.e., P*, r and C^, pan be obtained by fitting the theoretical and experi- 

 mental maximum velocities. The model is made predictive by inputting expec- 

 ted values of xm, y, tan 3> and a^,. 



Results of the plane beach theory compared with limited observations 

 in the field (near Niigata, Japan) on a step-type beach are presented in 

 Figure 66 which also shows the beach profile with average slope of 1 to 

 40. Each velocity is the average of five measurements for the same loca- 

 tion. Reasonable agreement is now found seaward of v^^ but the stepped 

 beach profile produced secondary breaking and a nonlinear y ratio to give 

 the disparity of results shown shoreward of v^. Kraus and Sasaki stated 

 that a refined wave height description (requiring numerical solution) in 

 this shoreward region should produce better agreement. For this one field 

 observation, P* = 0.072, V = 0.015 and C^ = 0.0061. Other field data also 

 give P* < 0.1 and such low values are in agreement with observed rapid 

 decrease in longshore current profile tails outside the breaker zone. 

 Kraus and Sasaki (1979) also use this as evidence in support for their 

 weak current model. 



^%IZUGUCHI, M. , OSHIMA, Y., and HORIKAWA, K. , "Laboratory Experiments on 

 Longshore Currents," Proceedings of the 25th Conference on Coastal Engi- 

 neeving, Japan (in Japanese) (not in bibliography). 



179 



