give the "plunge length." Galvin (1969) estimated the plunge length i to 

 be about four times the breaking wave height, showing a dependence upon beach 

 slope tan^ , where a steeper beach implied a shorter plunge length for the 

 same breaking wave height. The equation given by Galvin (1969) is 



^4.0 - 9.25 tan/3 (37) 



Hb 



415. Equation 37 was tested for predicting the plunge length but gave 

 unrealistically short distances for steep bar face slopes. Therefore, in the 

 numerical model an overall value of three times the breaking wave height is 

 used to estimate the plunge distance (see Singamsetti and Wind 1980, Svendsen 

 1987). 



416. For the region seaward of the break point, the transport rate 

 distribution is well approximated by an exponential decay with distance 

 (Equation 21). For offshore transport the spatial decay coefficient is a 

 function of the breaking wave height and grain size (Equation 22), whereas for 

 onshore transport the decay coefficient is effectively constant. 



417 . For the relatively short region extending from the break point to 

 the plunge point, an exponentially decaying transport rate is also used but 

 with a smaller value of the spatial decay coefficient. Analysis of available 

 data from the LWT experiments indicated the value of the spatial decay coef- 

 ficient to be approximately 0.20-0.25 that of the spatial decay coefficient 

 applicable seaward of the break point. A multiplicative factor of 0.20 is 

 used in the numerical model to compute the spatial decay coefficient in the 

 zone between the break point and the plunge point. The magnitude of the 

 transport rate at the plunge point is determined from Equation 33, and seaward 

 from this point the transport rate is calculated from the exponential decay 

 functions . 



418. The transport rate distribution on the foreshore is approximated 

 by linear decay with distance from the end of the surf zone (Part V) . The 

 slope of the transport rate distribution on the foreshore decreases with time 

 as the profile approaches equilibrium shape in the surf zone. Profiles 

 generated in the LWT that either eroded or accreted exhibited this linear 



170 



