SEISMIC METHODS 



923 



2700 



O 2600 



< 

 > 

 u 



w 2500 



'°-.c, ^-oi 7^'k"""' seismic 



"-OVERBURDENo— °-° "^ DEPTH POINTS 



./V BEDROCK 



1000 



2000 



3000 

 FEET 



4000 



5000 



Fig. 574. — Profile, Elkader Alternate No. 2 Dam Axis. (Courtesy 

 U. S. Department of Interior, Bureau of Reclamation.) 



Pyramids Dam Site. — The geophysical results at this site are 

 shown in Figure 575, which brings out that the average depth to bedrock 

 is considerably greater than at the Elkader site. The maximum depth found 

 was 72 feet. The most important difference between the Pyramids and the 

 Elkader sites is the 10-foot greater overburden thickness at the abutments 

 in the former. 



2600 



2500 



2400 



SMOKY HILL 



RIVER^ / ^0-97 



'-o^VERBURDEN. '<;" ||'h^%^ntS 



5000 



Fig. 575. — Profile, Pyramids Dam Axis. (Courtesy U. S. Depart- 

 ment of Interior, Bureau of Reclamation.) 



Differences in the depth to bedrock are the only basis of comparison 

 of the three sites derived from the geophysical survey. The Elkader site 

 therefore would be the most desirable, since the bedrock was at a minimum 

 depth. 



Exploration of a Buried Channel, Cedar Bluff Dam Site, 

 Ellis County, Kansas 



Geophysical investigations of a buried channel at the Cedar Bluff Dam 

 Site, Ellis County, Kansas were made in September, 1948, using the seismic 

 refraction method. The Cedar Bluff Dam on the Smoky Hill River is one 

 of the units of the Missouri Basin Project, U.S. Bureau of Reclamation. 



The purpose of the geophysical work was to trace the subsurface course 

 of an old buried channel which cut across the proposed axis of the dam on 



