54 



these data allows the modeling simulations to be evaluated in larger spatial and 

 temporal contexts. 



The project-level information includes shoreline position data (representing 

 at least three different times for model calibration and verification), offshore 

 waves, beach profiles and offshore bathymetry, and information on structures 

 and other engineering activities (both past and planned works). Beach profiles 

 are required to determine the average shape of the beach, and offshore 

 bathymetry is used to transform the offshore wave data to nearshore values. 

 The shoreline position data are required for calibration, verification, and 

 application of the model. Calibration requires that shoreline position data be 

 available for two different times, together with waves corresponding to that 

 time period. The model parameters Kj and K 2 , and in some cases with 

 detached breakwaters, the structure transmission to incoming wave energy, 

 Kj, are determined to reproduce known shoreline change. Model verification 

 refers to using the second shoreline position with the calibrated parameters to 

 predict a third shoreline. Once again, waves representative of conditions that 

 occurred to cause evolution of the shoreline from the second to third positions 

 should be used for model simulation. If model verification does not 

 adequately represent the known shoreline change, the modeler must iterate 

 through the calibration/ verification process until a reasonable model 

 agreement with measured shoreline position is obtained. The specifications 

 and date of engineering activities are required to properly set up the model 

 and, for planned work, evaluate future scenarios. 



Detailed discussions on the development of input data sets for use with 

 GENESIS are given by Hanson and Kraus (1989b) and Gravens (1991). 

 Gravens (1991, 1992) presents application of the Shoreline Modeling System, 

 which consists of a set of analysis programs that may be used separately or in 

 conjunction with GENESIS to streamline data preparation and analysis prior to 

 model implementation. Specific issues relating to input data required for 

 modeling of morphologic response to detached breakwaters are presented in a 

 subsequent section of this chapter. 



Previous GENESIS detached breakwater applications 



Sensitivity testing. Hanson and Kraus (1990) investigated the effects of 

 varying site and structure design parameters on beach response for a single 

 detached breakwater. Simulation results lend a general understanding to how 

 several of the controlling design variables affect beach response. The 

 discussion presented herein is summarized from Hanson and Kraus (1990). 



The structure used in the first set of GENESIS simulations was an 

 impermeable 300-m-long breakwater, placed 300 m offshore in the 3-m water 

 depth. The first case examined the effect of increasing offshore significant 

 wave height from 0.2 m to 1.0 m for normally incident wave crests, while 

 holding the wave period constant at 4 sec, for a 100-hr simulation (Fig- 

 ure 30). As offshore wave height increases, the transport potential of the 



Chapter 3 Tools for Prediction of Morphologic Response 



