movement, (3) representation of recovery processes (berm formation), and 

 (4) incorporation of major water motion and beach characteristics including 

 beach shape, grain size, and time variations of waves and water level. It was 

 considered necessary to simulate offshore bars because they are a natural 

 self -protective mechanism of the beach against erosion. 



Technical details of the model are given in Larson (1988) and Larson and 

 Kraus (1989). SBEACH operates by calculating the wave height at regularly 

 spaced intervals from deep water to the shoreline. Separate empirically-based 

 relations are then used to calculate the net cross -shore transport rate in 

 four distinct regions along the profile: pre -breaking, breaking, post-break- 

 ing, and the swash zone. The direction of transport is determined by an 

 empirical criterion involving the deepwater wave steepness and sediment fall 

 speed. Basic inputs are time series of wave height, wave period, and water 

 level; initial profile configuration; and grain size and water temperature. 

 A finite-difference numerical scheme solves the equation for conservation of 

 mass. The time step and discretization interval are on the order of 10 min 

 and 1-5 m. Overall, the model satisfactorily reproduces bar formation, 

 growth, and migration, but representation of foreshore recovery processes is 

 incomplete. Here, the model is used to examine the effects of generic, 

 commonly occurring storms on a beach nourishment project of two cross-sec- 

 tions. Kraus (1989) makes a comparison of the capabilities of various kinds 

 of beach change numerical models. 



PROCEDURE 

 Approach 



Major variables controlling storm-induced beach profile change are: 



(1) Offshore bathymetry and profile shape prior to the storm. 



(2) Grain size distribution of the native beach and fill. 



(3) Surge plus tide hydrograph. 



(4) Waves (wave height, period, setup, and runup). 



(5) Fill cross-section, if any. 



If long-term profile change is to be calculated, variables associated with 

 shore-parallel processes should be included. These are the longshore sediment 

 transport rate, fill length, and lateral boundary conditions. In the present 

 exercise, these processes are neglected. 



113 



