of these forces are averaged out, and a concentration value more re- 

 presentative of the average wave conditions measured is obtained. 



In general, the suspended sediment concentration resulting from 

 a given wave condition varies with distance from shore, usually being 

 a maximum in the zone of wave breaking. In developing the sampler, 

 it was judged expedient to limit the overall length of the sampling 

 area, thus obtaining somewhat limited total variability of sediment 

 concentration in order to have the data more sharply focused on 

 sampling procedure. The samples were actually collected in an area 

 one to two wave lengths seaward of the breaker zone. The breaker 

 zone was not included. 



Purpose . The primary purpose of the study was to investigate 

 by exploratory sampling in wave action those factors of sampling 

 equipment, procedure, and environment (local bottom irregularities) 

 tending to influence the accuracy of suspended sampling data. 



In particular it was desired to study the effect of pumping (or 

 sucking) sediment • laden water through an intake nozzle positioned at 

 some point above the sand bed. Visual observations of this operation 

 combined with repetitive samplings and analysis would provide the 

 basic sampling design criteria. This basic design criteria could then 

 be systematically improved by studying the inter-relations of nozzle 

 disturbance to f,low, flu id- sediment flow, and local bottom irregularities. 

 All these factors in greater or less degree affect the exactness of 

 agreement between a pumped sample and the actual suspension at the 

 sampling point. This type of study would provide the necessary data 

 to evaluate the test results in terms of the degree of sampling re- 

 producibility. Sound recommendations could then be made for improving 

 the reliability of the sampling procedure. 



Definite criteria for nozzle size, shape, orientation, filtration 

 technique, etc., were not decided before the testing began; but 

 rather the project actually began by collecting samples using a 

 relatively arbitrary setup of sampling apparatus and proceeded to study, 

 from test observations and analysis, the changes in test setup or 

 procedure which improved the accuracy of the sampling operation. The 

 ultimate objective was then* to select from the numerous sampling 

 setups the particular procedure found to produce the most satisfactory 

 results. 



EQUIPMENT AND PROCEDURE 



General Testing and Apparatus . The tests were -made in a concrete 

 wave tank 85 feet long, 14 feet wide and 4 feet deep (Figure 1). The 

 tank had been partitioned lengthwise into four sections for previous tests, 

 each of the separate sections containing sediment with a different dis- 

 tribution of grain sizes; the median grain diameters being 0.22 mm., 

 0.47 mm., 1.20mm., and 3.44 mm. respectively. Suspended sediment sampling 



42 



