in which q b is the transport rate at the break point, and x b is the 

 location of the break point. The spatial decay coefficient, A , is found to 

 be approximately constant with a value of 0.11 m -1 for accretionary condi- 

 tions, but a function of the ratio of grain size and wave breaker height with 

 a representative value of 0.18 m" 1 for erosional conditions (Larson, 1988). 

 In Zone II, the transport rate is described by a function of the form of 

 Equation 7 from the plunge point to break point (by which q b is determined) , 

 but with a value of the decay coefficient of 0.20-0.25 times that for Zone I, 

 inferred from limited data. The transport rate at the plunge point is given 

 by matching with the value obtained from Equation 4 at the Zone II/III 

 interface. 



Larson (1988) inferred that the transport rate distribution on the 

 foreshore, from the shoreward side of the surf zone to the runup limit, was 

 approximately uniform for accretionary and erosional conditions in the large 

 wave tank experiments. A linearly varying transport rate was implemented in 

 the model in Zone IV, constrained by avalanching (Allen 1970). Avalanching is 

 initiated on the profile if the local slope exceeds 28 deg, and it continues 

 until a residual angle of shearing of 18 deg is reached. 

 Profile change calculation 



Changes in beach profile are calculated from the distribution of the 

 cross -shore sand transport rate and equation of mass conservation of sand: 



3h dq 

 dt ox 



in which t is the time. Equation 8 is numerically solved by an explicit 

 finite-difference scheme on a uniform grid. Larson (1988) presents 

 verification and sensitivity tests to examine model behavior under variations 

 in empirical model parameters (K, e, D eq ) and input data (grain size, wave 

 height and period, and water level). The value of K applicable to field 



97 



