114. In summary, because of the many assumptions and approximations 

 that have gone into formulation of the shoreline response model, and to 

 account for the actual sand transport along a given coast, the coefficients 



Kj and K 2 are treated as calibration parameters in the model. Their values 

 are determined by reproducing measured shoreline change and order of magnitude 

 and direction of the longshore sand transport rate. 



Sources and sinks 



115. The quantity q in Equation 1 represents a line source or sink of 

 sand in the system. Typical sources are rivers and cliffs, whereas typical 

 sinks are inlets and entrance channels. Wind-blown sand at the shore can act 

 as either a source or sink on the landward boundary, depending on wind 

 direction. General predictive formulas cannot be given for the shoreward and 

 seaward rates q s and q , whose values depend on the particular situation. 

 These quantities typically vary with time and are a function of distance 

 alongshore. Kraus and Harikai (1983) modeled the effects of river discharge 

 and subsequent sand shoaling on the beach by means of a source term. The 

 capability to represent sources and sinks is not included in Version 2 of 

 GENESIS. As an alternative, a beach-fill volume (shoreline advance or 

 retreat) providing the same rate as a source or sink can be implemented. 



Direct change in shoreline position 



116. The position of the shoreline can also change directly, for 

 example, as a result of beach fill or dredging. In this case, the profile is 

 translated shoreward or seaward, as required, by a specified amount that can 

 be a function of time and distance alongshore. GENESIS allows specification 

 of a direct change in shoreline position, which may be positive (seaward), as 

 caused by beach fill", or negative (landward), as by sand mining. 



Empirical Parameters 



Depth of longshore transport 



117. The width of the profile over which longshore transport takes 

 place under a given set of wave conditions is needed to estimate the amount of 

 sand (percentage of total) bypassing occurring at groins and jetties. Since 

 the major portion of alongshore sand movement takes place in the surf zone, 



54 



