350 



fry. SEDIMENTATION IN RESERVOIRS 



[Ch. 20 



shed with respect to cultivation or other factors that influence erosion, 

 intensity of rainfall, and other hydrologic factors that alter the sedi- 

 ment load with the discharge. 



The samplers developed by the cooperative federal project utilize 

 a pint bottle for obtaining the sediment samples (Iowa Institute of 

 Hydraulic Research, Nos. 5, 8). The samples taken on any stream are 

 analyzed in a laboratory to determine the amount of sediment carried 



Fig. 1. Modern sediment sampler used in open streams. The sample flows 



through the calibrated nozzle into a pint bottle inside the body. Sampler is 



hinged to permit removal of bottle. 



by each sample (Iowa Institute of Hydraulic Research, No. 4). On 

 the basis of the quantity determined by the laboratory analysis, the 

 amount of silt carried by the stream can be computed. 



In addition to the amount, the size of the particles of the sediment is 

 important (Iowa Institute of Hydraulic Research, No. 7). The size 

 of the sediment particles influences the location in the stream cross sec- 

 tion where the sediment is carried and is an important factor in the 

 deposition of the sediment in a reservoir. Fine-grained material, for 

 example, will be carried farther into a reservoir and deposited nearer 

 the dam than coarse-grained material, which tends to deposit near the 

 upper end of the streams that bring it into the reservoir. Research has 

 developed the bottom withdrawal tube for determining the size of 

 particles (Howard, 1948). 



