PREDICTION OF NEARSHORE WAVE TRANSFORMATION 



by 

 Jon M. Huberts 



I. INTRODUCTION 



The U.S. Army Coastal Engineering Research Center (CERC) and the U.S. Army 

 Engineer Waterways Experiment Station (WES) entered into an exchange research 

 agreement with the Danish Hydaulic Institute (DHI) , Horsholm, Denmark, in 

 March 1980. One of the first benefits to the Corps of Engineers was the trans- 

 fer of the System 21 Mark 8 model to CERC and WES. The System 21 Mark 8 is a 

 proprietary research model used for computing water elevations and vertically 

 averaged currents. This model has been briefly described in the CERCular of 

 October 1980 and in U.S. Army, Corps of Engineers, Coastal Engineering Research 

 Center (1981a, 1981b) 1» 2^ 



The System 21 Mark 8 model can be used in two modes — the prediction of 

 coastal and estuarine long waves, such as tides or storm surges; and the pre- 

 diction of short waves, such as waves with periods of about 10 seconds. The 

 steps followed in applying the model are generally the same for both types of 

 application. 



This report discusses procedures for using the System 21 Mark 8 model to 

 predict nearshore short wave transformation and to make field personnel more 

 familiar with the type problems for which it can be used. The example discussed 

 illustrates the combined effects of refraction, shoaling, reflection, and dif- 

 fraction. The material discussed is intermediate in detail compared with that 

 discussed in the publications referenced above and the User's Guide, which would 

 be needed for an actual application. 



II. APPLICATION ANALYSIS 



1. System 21 Mark 8 Model Grid Setup . 



When applying the System 21 Mark 8 model the first step is to determine the 

 characteristics of the waves and the mean water depth in the region of interest. 

 By using these parameters and Figure 1, it can be determined whether the model 

 is applicable. Given the wave height, period, and mean water depth, the ratios 

 H/Lq and D/Lq (Lq = g/2Tr T^) can be plotted on Figure 1. The model applies 

 if the plotted point lies within the shaded region. 



The second step is to determine the size of the model area. This is gov- 

 erned primarily by two factors. The area should be large enough to include 

 any proposed structure and have boundaries far enough away from regions of 



^U.S. ARMY, CORPS OF ENGINEERS, COASTAL ENGINEERING RESEARCH CENTER, "Computer 

 Program: S21 Coastal Water Level Variations and Flows," CETN-I-4, Fort Belvoir, 

 Va., Jan. 1981a. 



^U.S. ARMY, CORPS OF ENGINEERS, COASTAL ENGINEERING RESEARCH CENTER, "Computer 

 Programs - Storm Surge," CETN-I-16, Fort Belvoir, Va., Dec. 1981b. 



