A NUMERICAL MODEL TO SIMULATE SEDIMENT TRANSPORT 

 IN THE VICINITY OF COASTAL STRUCTURES 



by 

 Marc Perl in and Robert G. Dean 



I. INTRODUCTION 



1. General . 



The need for reliable predictions of shoreline response to man-made or 

 natural modifications is increasing due to environmental concerns and the 

 rising cost of remedial measures. The capability of numerical modeling in 

 addressing problems of shoreline response has advanced with improvements in 

 wave climatology, programs to better understand sediment transport 

 relationships, and improvements in numerical modeling. In-situ and remote 

 sensing technology for the measurement of directional wave characteristics 

 has been developed and applied, primarily within the last two decades. In 

 addition to providing the necessary climatology, the resulting measurements 

 have provided the basis for evaluation and refinement of directional wave 

 prediction procedures. Studies such as the Channel Islands Harbor Longshore 

 Sand Transport Study (Bruno, et al . , 1981) and the Nearshore Sediment 

 Transport Study (NSTS) (Gable, 1979) have yielded a better understanding of 

 surf zone dynamics and the resulting sediment transport. The increased 

 capacities of large computers and reduced computing costs combined with 

 improved numerical modeling algorithms have resulted in an extremely 

 promising potential for the numerical modeling of shoreline problems. 



Although it is doubtful that numerical modeling will ever replace 

 completely the use of movable-bed physical models, the former type offers 

 many advantages. The modeling of shoreline response is somewhat analogous to 

 the problem of simulating storm surges in the coastal zone in which the scale 

 effects and measurement difficulties essentially preclude physical modeling. 

 For shorelines, the scale effects inherent in modeling sediment are well 

 recognized and the costs of representing a substantial length of shoreline 

 may be prohibitive. The laboratory representation of a realistic wave 

 climate is at the forefront of technology. 



The investigation of shoreline response can best proceed by several 

 approaches, with each approach selected for the particular strengths which it 

 offers. Field programs are costly, usually because of the considerable 

 equipment and the extensive time required, but these programs are essential 

 for quantifying the values of constants or parameters, the forms of which may 

 be available from laboratory measurements or theoretical considerations. 

 Laboratory studies occupy a special niche by allowing the wave conditions and 

 independent variables to be controlled readily, experiments to be repeated, 

 and selected measurements to be conducted. Although, as noted before, scale 

 effects are present in laboratory measurements of sediment transport, the 

 physics governing the process should be the same. However, the relative 

 magnitudes of suspended versus bedload transport in the laboratory and field 

 may differ. Laboratory studies can also provide an excellent base for 

 evaluating certain aspects of a numerical model, including wave refraction 

 and diffraction and the resulting shoreline patterns due to, for example, the 

 placement of a littoral barrier. Numerical modeling offers the capability to 



