the only one which rendered the nozzle intake completely independent 

 of the reversing flow. This statement seems sound, and were the sediment 

 concentration pattern reasonably uniform the orientation directed normal 

 to flow would probably reflect consistent results. However, the 

 restrictions of a non-uniform concentration pattern along the normal 

 to direction of wave travel indicates the compromise orientation along 

 the direction of wave travel may reflect more accurate sampling results. 



Sediment Concentration and Temperature Change. . Comparison of 

 the curves of sediment concentration versus depth (Figure 11 a and b) 

 for the water temperatures of 69 F and 47 F respectively, indicated 

 in general, a greater concentration over the range of sampling depths 

 for the lower temperature. This may result from the higher viscosity 

 accompanying the lower temperature. It would seem that the two curves 

 should diverge toward the water surface; that is the colder water or 

 higher viscosity would indicate a relatively greater amount of sus- 

 pended sediment for those samples nearest the water surface. The 

 higher sediment concentration of the colder water can be partially 

 attributed to a probable lower settling velocity of sediment particles. 

 The lower settling velocity acts to maintain a greater amount of 

 material in suspension. Consequently, for the same wave conditions, 

 there results a greater quantity of suspended load available for 

 transport by littoral forces. 



These temperature indications are of a preliminary nature only, 

 very little data having, been obtained. However, a similar temperature 

 effect has been previously observed with river flow^ 3 ', unidirectional 

 laboratory flume flow(4), and in a laboratory turbulence tank< 5 ). A 

 more intensive study of this indication is currently underway. 



Errors of Measurement 



In general the errors introduced through physical measurements are 

 not believed serious. The physical measurements refer primarily to 

 those of height of nozzle above bottom. As an example, take the values 

 of concentrations for the mean range of sampling elevations. The maxi- 

 mum probable error for a nozzle elevation displacement of 0.10 foot 

 was 2%, whereas the percent k change in concentration for this 0.1 foot 

 elevation displacement averaged from 200 to 500 percent. 



CONCLUSIONS 



The laboratory tests indicate that a vacuum pump sampler can be 

 adapted to the study of suspended sediment concentrations. The average 

 sediment concentration for a given elevation above the bottom as measured 

 by the sampling equipment and procedure developed appears to be related 

 to the distance between intake nozzle and sand ripple crests. 



The moderate success in using the equipment and procedure as 

 developed to obtain the graph (Figure 12) of horizontal distance from 

 crest to trough of a sand ripple versus concentration was in itself a 



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