for Torrey Pines Beach. Consequently, inshore S^^ was computed from a ver- 

 sion of equation (10), i.e.. 



S - pu(f ,z)v(f ,z)dz = E(f,e)n(f) sina cosa da (163) 

 -d -n 



where n is given by equation (15);.f, frequency; and E, the energy density 

 per unit frequency and direction. Further details are beyond the intended 

 scope of this review. The method relies heavily upon the fact that linear wa 

 theory can be employed to relate velocity measured at a single elevation 

 to the energy density spectrijm for u (see Guza and Thornton, 1980) . 



The bed shear-stress coefficient, C* found in this fashion from 

 equation (162) is shown in Figure 71 for various locations in November 

 1978. Seventeen-minute averaging times were used for each point and eight 

 such values when averaged produced the solid line. The average of all such 

 calculations gave C* = 0.006. Considerable scatter occurs outside the 

 breakers due to the onshore velocity variability in space and time. In 

 the surf zone, less scatter was observed because the variability is related 

 to local water depth. Thornton (1980) also found that C* was consistently 

 less inside the surf zone when comparing the results of other days. It 

 should be noted that this single value of 0.006 is consistent with that 

 deduced by Kraus and Sasaki (1979) from Japanese field data and their model. 



Some negative C^ values are noted in Figure 72 outside the breaker 

 line. Thornton (1980) believes this means the currents are driven in the 

 wrong direction. However, Huntley (1976) states that C| can possibly 

 become negative beyond the surf zone due to neglect of the lateral turbu- 

 lent mixing stress gradient in equation (161) or (162). Electromagnetic 

 current meters with a gain response cutoff around 2 hertz (see Fig. 16) 

 behave as filters to distort all higher frequency turbulence signals. Their 

 use is limited for studying wave breaking turbulence and wave-turbulence 

 interactions. 



The methods described by Thornton (1980) and applied to additional 

 field data in the NSTS from Santa Barbara, California, will be of consider- 

 able interest in the near future. Estimates of the bed roughness patterns, 

 heights, etc., both beyond and within the surf zone, are needed to corre- 

 late the data for future applications. 



b. Eddy Viscosity Closure Coefficients . 'Even less is formally known 

 about magnitudes and variability of eddy viscosity closure coefficients. 

 As discussed in Chapter 3, eddy viscosity is normally calculated from the 

 expression (eq. 86) 



where considerable disagreement exists as to the proper expressions to' 



188 



