measure of the reliability of the method. This was the actual reason, 

 aside from its basic research value, for selecting this particular 

 area for measurement and study. The general trend of the curves 

 (Figure 12) could obviously be predicted for uniform sand ripples. 

 This however, made it nonetheless gratifying to have the data from the 

 actual samples collected confirm the prediction that had been made. 

 There was not sufficient data for conclusive proof but the test results 

 indicated considerably higher concentration values in the vicinity of 

 sand ripple crests with lower values nearer the trough. The variability 

 of concentration was more sharply defined at sampling elevations below 

 0.75D (where D was the water depth) and where most of the material in 

 suspension was concentrated. The water depths used were 1 to 1.2 feet. 



The maximum sediment concentration found to exist above the sand 

 ripple crest was greater than the minimum concentration above the sand 

 ripple trough by a factor of four. This was for a constant sampling 

 elevation of 0.1 foot above the bottom (Figure 12). This ratio of 

 maximum to minimum concentration value decreases sharply for higher 

 sampling elevations above the bottom. At elevations of 0.4 to 0.5 

 foot above the bottom in a water depth of 1.0 foot there was a very 

 minor difference between the concentration values above sand ripple 

 crest and trough. 



The principal conclusion we can draw from the explanation is that 

 the relative position of sampling nozzle and local bottom irregularities 

 can greatly influence the sampling results and should be taken into 

 account in the collection of suspended sediment data. 



Most of the samples were collected in water at about 20 centigrade, 

 however, in order to investigate experimentally the effect of temperature 

 on suspended sediment, some twenty samples were collected at temperatures 

 of 8 to 9 centigrade (46 to 48 F). Correlation of the suspended 

 sediment data relative to temperature" change indicated a general increase 

 in sediment concentration for those samples collected at the lower 

 temperature (Figure 11). 



REFERENCES 



(1) Report No. 5, Laboratory Investigation of Suspended Sediment 



Samplers, St. Paul, U. S. Engineer District Sub-Office, 

 Hydraulic Laboratory, University of Iowa, Iowa City Iowa. 



(2) Watts, G. M., Development and Field Test of a Sampler for Suspended 



Sediment in Wave Action, Beach Erosion Board Technical 

 Memorandum No. 34, March 1953. 



(3) Lane, E. W. , E. J. Carlson, and 0. S. Hanson, Low Temperature In- 



creases Sediment Transportation in Colorado River, Civil 

 Engineering, September 1949. 



59 



