SBEACH: NUMERICAL MODEL FOR SIMULATING STORM- INDUCED BEACH CHANGE 

 EMPIRICAL FOUNDATION AND MODEL DEVELOPMENT 



PART I: INTRODUCTION 



Problem Statement and Objectives 



1. The study of beach profile change in the broad sense encompasses 

 nearshore processes that shape the beach on all spatial and temporal scales. 

 Beach profile change is a phenomenon of fundamental interest and, as such, has 

 been studied by geologists, oceanographers , and coastal engineers. 



2. In coastal engineering, quantitative understanding of beach profile 

 change is pursued mainly to allow prediction of beach evolution in the 

 vicinity of planned or existing engineering projects. Two types of coastal 

 engineering problems of particular importance for which predictive tools are 

 needed are beach and dune erosion that occurs under storm waves and high water 

 levels and adjustment of beach fill to long-term wave action. The time scale 

 associated with storm- induced beach erosion is on the order of 1 to 3 days and 

 depends on the level and duration of the storm surge as well as the wave 

 characteristics, whereas the time scale of beach fill adjustment is several 

 weeks to several months and depends on season of placement, fill material, and 

 wave climate at the coast. 



3. It is often convenient to separate nearshore sediment movement into 

 two components , longshore sediment transport and cross-shore sediment trans- 

 port , although this separation is not always valid in a strict sense because 

 it is implicitly based on the assumption of plane and parallel profile 

 contours. Longshore sediment transport figures prominently in situations 

 involving loss of sediment supply, such as damming of rivers, and in impound- 

 ment at structures such as groins and jetties. In these cases longshore 

 transport is the major process governing nearshore topography change and 

 cannot be neglected. 



4. For beaches located away from structures, inlets, and river mouths, 

 it may be appropriate to neglect longshore transport as a first approximation, 

 i.e., assume the gradient of the longshore transport rate is negligibly small 



