small. Most of the sand is so well sorted that the variation among samples 

 may be less than the error inherent in sampling and determining the size 

 data. 



3. Sample Position . 



Three of the independent variables in equation (1) describe the sample 

 position--S is the horizontal location with respect to the defined breaker 

 position, d is the local water depth, and E is the nozzle elevation 

 above the bottom. Figures 13, 14, and 15 show the measured distribution 

 of these variables in histogram form. 



Individual waves in a series of waves approaching shore may break at 

 different locations, rather than at a single point. For the Ventnor data, 

 stations defining either end of the range of breaker positions were deter- 

 mined and the midstation within the range was defined as the breaker posi- 

 tion. Figure 13 shows the distribution of samples relative to the breaker 

 position. These data indicate that about 67 percent of the Ventnor data 

 were collected within 25 feet of the breaker zero and only 11 percent were 

 more than 50 feet from the breaker zero. About 45 percent of the sample 

 locations were shoreward of the breaker zero and 55 percent were seaward. 

 Since the waves were often small, and consequently the surf zone was shallow, 

 there was a tendency to collect data from the seaward locations. 



Figure 14 indicates the range of water depths during sampling at the 

 two piers. By comparing the profiles shown on Figures 3 and 4, it was 

 possible to sample at greater depths from Jennette's Pier than from City 

 Pier. The profiles show depths of about 12 feet extended 150 feet along 

 Jennette's Pier, landward of the major longshore bar, but at Ventnor it was 

 necessary to get seaward of the major bar before reaching 12-foot depths. 

 Although the extreme depths were greater at Nags Head, the most commonly 

 sampled depths were greater at Ventnor (Fig. 14) . 



Figure 15 indicates the range of nozzle elevations. At both piers, 

 the most common nozzle elevation was in the range 0.3 to 0.6 foot off the 

 bottom, and nearly half of the samples were within 0.6 foot of the bottom. 

 Some of the extreme Nags Head elevations were more than 10 feet above 

 bottom. 



Distance from the breaker position, S, is very important. Lacking 

 any other information, it is assumed that sediment concentration will 

 increase at and shoreward of the breaker position, as compared to the con- 

 centration seaward of the breaker. Figure 16 supports this assumption, 

 using data from Appendix A. The increase in sediment concentration can be 

 up to two orders of magnitude, as shown by these data, and the concentration 

 increases significantly with closeness to the bottom. Data to be presented 

 later show that breaker type also affects concentration for given values 

 of S. 



Water depth is only incidentally related to suspended-sediment concen- 

 tration in that depth controls breaking wave height and maximum possible 



29 



