Liu and Mei (1975, 1976a) studied examples of currents near offshore 

 and shore-connected breakwaters with their numerical model. Some observa- 

 tional evidences are cited, indicating similar qualitative trends but no 

 quantitative comparisons are attempted. 



In 1978, Allender, et al. (1978) measured the nearshore circulations 

 during two storms at a beach near Chicago on Lake Michigan. A towed sea 

 sled similar to that developed by Teleki, Musialowski, and Prins (1975) 

 monitored bidirectional currents measured at six locations across the surf 

 zone (see Fig. 81). Five-minute records were time-averaged to establish 

 the current vectors. Data sets were repeated every 3 hours over a 27- 

 hour storm period. The expressed purpose was to compare the field data 

 with results from the two-dimensional numerical model developed by 

 Berkemeier and Dalrymple (1975, 1976). This original version neglected 

 the convective acceleration and lateral mixing stress terms. 



•• PBfSSUBt C£Li 



DEPTH CONTOUR 



JOHNS HlMVILLt CRIB 



SEA SUO CieiE 



uTIUII POLES 



GENERATOR -' 

 lOON 



ACCESS ROAD -iJ- 



Figure 81. Plan view of experiment site and horizontal coordinate 

 system (after Allender, et al . , 1978). 



Model input included local bathymetry, offshore measured wave charac- 

 teristics, wind histories, and local water level changes. Comparisons 

 between model and observed v and Hj-ms fo'^ six different sled transits 

 (sled position fixed) are shown in Figure 82. In general, for all examples, 

 agreement is far from satisfactory for both currents and rms wave heights. 

 For example, in Figure 82(b), the peak measured currents are less than 30 

 percent of the peak currents predicted. And, in most ases, the model 

 energy levels in the surf zone are too high (e.g.. Fig. 82, d). The peaked- 

 ness of the model profile could be due to these wave height discrepancies 



206 



