at the sites, even though contributions from storms, during which when most 

 of the transport occurs, have been omitted. If suspended- sediment transport 

 in storms could be included in the evaluation, the factor of 10 to 20 per- 

 cent noted may increase significantly. This suggests that suspended- 

 sediment transport is an important factor in total longshore transport rate, 

 but that the fractional proportion of Q, not including storms, may be 

 relatively small. 



3. Future Studies . 



This report identifies improvements needed in future field studies of 

 this type. It is important to be able to sample as close to the bottom 

 as possible, without disturbing the bottom. It is important to know more 

 precisely where the nozzle elevation is with relation to the bottom, both 

 with respect to elevation above the mean bottom and with respect to the 

 ripple crest. It would be useful to measure the variation in concentra- 

 tion in the longshore direction, possibly by simultaneously sampling from 

 two positions along the same ripple crest. More bottom samples are needed 

 at the time of sampling to better correlate the size differences between 

 suspended and bottom samples. The wave conditions, including height, period, 

 breaker type, and distance to breaker line, need to be measured at the same 

 station as the sample collection if wave conditions are to be better cor- 

 related with suspended- sediment concentration. Data collection under higher 

 wave conditions is needed. 



Finally, the data presented in this report, especially Appendix A, can 

 be further analyzed to yield a better understanding of suspended sediment 

 in the surf zone. A statistical analysis, aided by physical theory, of 

 dimensionless combinations of the independent variables in equation CI) 

 would be especially appropriate. 



V. CONCLUSIONS FROM FIELD STUDY 



1. Concentration decreases logarithmically with elevation above the 

 bottom, except very near the bottom where concentration may be higher 

 than a logarithmic extrapolation would predict (Figs. 19 and 20). 



2. Concentration increases as wave height increases relative to local 

 water depth. Concentration rises rapidly to maximum values as the wave 

 nears the height-to-depth ratio of 0.8 (Fig. 25). 



3. Plunging breakers appear to suspend the most sediment and spilling 

 breakers the least (Fig. 26). 



4. Median size of the suspended samples decreases gradually with 

 elevation above the bottom (Figs. 10 and 11). There is some suggestion 

 in the Ventnor data that the median size of suspended particles is larger 

 at the center of the breaker zone than immediately to either side of the 

 breaker zone (Fig. 12). Also, there was less variation of sand size with 

 nozzle height in the smaller size Ventnor sand than at Nags Head. 



47 



