PART VI: NUMERICAL MODEL OF BEACH PROFILE CHANGE 



377. Quantitative prediction of the response of the beach profile to 

 wave action and changes in water level is an important goal of coastal 

 engineering. The capability to quantitatively estimate dune erosion, beach 

 response to large storms, and the initial adjustment and long-term evolution 

 of a beach fill is necessary to design and make economic evaluations of shore 

 erosion and flood protection projects. A numerical model can be an efficient 

 tool to evaluate various design alternatives while easily incorporating 

 detailed process data, such as time series of waves and water level. 



378. Many attempts have been made to develop numerical models of beach 

 profile change. The authors are not aware of any existing model, however, 

 which can be applied to an arbitrary beach profile exposed to variable wave 

 and water level conditions to reproduce bar formation and movement in addition 

 to overall change in the profile. It was a major goal of this investigation 

 to model the growth and movement of bars as part of the beach profile 

 response, since these features constitute natural protection for a beach 

 exposed to severe erosional conditions. Furthermore, for long-term simula- 

 tions , a predictive model must necessarily incorporate events producing 

 onshore transport and berm buildup, which no known engineering model can 

 simulate. Development of such a model would allow simulation of seasonal 

 changes in the profile as produced by cross -shore sediment transport. 



379. This chapter describes the numerical model developed in this study 

 for simulating beach profile change. An important feature possessed by the 

 model is the capability to reproduce main morphologic features of the profile, 

 in particular, bars and berms . Many of the assumptions and relationships used 

 in development of the model were founded on observations presented in previous 

 chapters of this report. The numerical model is aimed at reproducing macro- 

 changes of the beach profile in a deterministic fashion, neglecting small- 

 scale features such as ripples and avoiding the extreme complexity associated 

 with detailed specification of the fluid flow and sediment concentration. 



380. The model is formally based on the equation of mass conservation, 

 for which mathematical expressions for the cross -shore transport rate are 

 required. Any type of theoretical or empirical transport rate formula can be 



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