where K is an empirical "transport" coefficient, D is wave energy dissipa- 

 tion of broken waves, D eq is wave energy dissipation of a profile of equi- 

 librium shape for the existing waves, and e is an empirical coefficient 

 determining the strength of the bottom slope term. D is defined as: 



1 dF 



D =hd^ (5) 



where F is the wave energy flux, given by shallow water linear wave theory 

 as : 



1 

 F = - pgH^gh) 1 ' 2 (6) 



,2, , ,.1/2 



in which p is the density of water, and g is the acceleration of gravity. 



A formal expression for D eq was obtained by Dean (1977), and its 

 magnitude has been estimated with field and laboratory data by Moore (1982). 

 For application in numerical models of beach profile change, Moore (1982), 

 Kriebel (1982), and Kriebel and Dean (1985) argued that if D > D eq , there is 

 excess energy dissipation and transport is directed offshore, causing the 

 profile to erode. However, if D < D eq , direct application of Equation 4 

 predicts a reversal in transport (neglecting the slope-dependent term), 

 producing onshore transport. In this case, the magnitude of the onshore 

 transport rate increases with a decrease in D and reaches a maximum for 

 D = 0. This limit is not considered correct since a threshold energy dissipa- 

 tion must exist below which no significant net transport will take place. 

 Therefore, in the present model the criterion given by Equation 3 is used to 

 determine the transport direction, and Equation 4 is applied to calculate the 

 magnitude of q. 



Seaward of the break point, the transport rate is given by: 



'(X-X^ 



(7) 



96 



