the desired position. The simplicity of the sampler made 

 it popular from the mid- 1800 's to the 1940 's, but several 

 inherent problems have discouraged its use. Disadvantages 

 of such a sampler include excessive disturbance to the flow 

 caused by the cylinder and excessive intermixing of the 

 sample with water and sediment above the sampling point. 

 In addition, the samples are not sufficiently time-inte- 

 grated to give a representative mean of the sediment 

 concentration. An example of this type of sampler is the 

 Riesbol pipe sampler shown in Figure Al. It consists of a 

 2-in-diameter (5.1-cm) pipe with variable length (suggested 

 length is approximately equal to the river depth) . For use 

 of the sampler, the base plate is placed on the stream bed, 

 and the pipe is dropped from the surface, enclosing the 

 sample as it hits the base plate. The sampler was used 

 from 1874-79 on the Ganges Canal in India and was consi- 

 dered to give an average suspended sediment sample for the 

 depth of stream (Inter -Agency Committee on Water Resources 

 1940a) . 



2" PIPE 



SPONGE RUBBER 



id 



-1/2" STEEL 

 ROD FRAME 



Figure Al . Riesbol ordinary 

 vertical pipe suspended sampler 

 (from Inter-Agency Committee on 

 Water Resources 1940a) 



1/2- METAL PLATE -^ 



APPROXIMATELY TO SCALE 1:10 



(2) Instantaneous Capture Vertical Sampler 



An instantaneous capture vertical sampler is similar to an 

 ordinary vertical pipe sampler in that it consists of a 

 vertical cylinder that collects a sample when triggered. 

 However, the instantaneous capture vertical sampler 

 cylinder is shorter and operates by sealing the cylinder 



A5 



