a uniform distribution was most common. Run 859060916 showed a clear peak in 

 the outer surf zone, and Run 859051528 showed a bimodal distribution with a 

 large peak in the outer surf zone and a small peak in the inner surf zone. It 

 is again noted that during DUCK85 the steep foreshore step was covered with 

 pebbles, and longshore transport was not observed there. Because of the 

 armoring and potential artificial suppression of transport on the foreshore, 

 the determined distributions cannot be considered as reflecting transport 

 behavior that might occur on a beach with a sandy foreshore. 



Total transport 



49. The eight cross-shore transport distributions shown in Figure 13 

 were integrated from the mean water shoreline to the most seaward trap or to 

 the break point (where the transport rate was assumed to be zero) to give the 

 total longshore sand transport rate. The measured total transport rates were 

 converted to an immersed weight transport rate, denoted by the symbol I , and 

 expressed in terms of a quantity called the "discharge parameter" (Kraus and 

 Dean 1987; Kraus, Ginger ich, and Rosati 1988) defined as: 



R = V Xb Hb (4) 



in which 



R = discharge parameter (m^/sec) 

 V = average longshore current speed (m/sec) 

 Xj, = average width of the surf zone (m) 

 Hb = average significant breaking wave height (m) 

 Values of these quantities are listed in Table 5. 



50. The total longshore transport rate is plotted as a function of the 

 discharge parameter in Figure 14. An approximate linear relation is found, 

 resulting in a least squares fit equation of I = 2.7 (R - R^) (correlation 

 coefficient r^ = 0.76), in which the intercept R^. = 3.9 m'^/sec is interpreted 

 as a threshold value for significant longshore transport to take place, and 



I is expressed in the units of N/sec. Reasonable visual agreement is seen. 



43 



