Figure 9. 



Depth-averaged current vectors along each transect for 

 08 October 1997 



from the Detroit District 6.1-m- (20.0-ft-) long boat and hoisted with a hand- 

 operated winch. 



Grain-size distributions and sample statistics (including D50) were obtained 

 for each sample. Some of the samples were too small to provide statistically 

 accurate grain-size distributions because they contained large cobbles in excess of 

 20 mm (0.79 in.) in diameter. For demonstration purposes and to identify areas 

 consisting of "'large'" sediments versus "small'" sediments, all samples (and sample 

 statistics) were assumed statistically valid. Figure 13 is sediment-size distribution 

 plot showing where sand and cobbles predominate. 



Bottom-fype characteristics cannot be determined solely from sediment 

 samples, so it is possible that some of the "large" samples actually indicate glacial 

 till where a few of the larger particles were gathered by the sampler. Therefore, it 

 is difficult to know whether these larger particles are part of a glacial till that has 



Chapter 3 Field-Data Collection 



15 



