34 



BULLETIN 502, U. S. DEPARTMENT OF AGRICULTURE. 



of both the relief and the intercepting principles of drainage as ordi- 

 narily understood when applied to shale lands — this notwithstanding 

 the fact that both of the tile lines were 6 feet deep and that a com- 

 plete system of relief wells was installed in conjmiction with lateral 

 A. Particular attention is called to the system of drainage as it 

 was worked out later. This embraces branch A-1 and laterals B 

 and C with their branches. Branch A-1 follows closely the lower 

 margins of a broad shale point, only one edge of which is shown on 

 the map. Branches B-1, B-2, and B-3 are located up the back- 



rWir 



S30' 



100 



Fig. 8. 



200' 300' 400 



-Typical profiles across tract shown in figure 7. 



^SZ(f 



bones of three very narrow points. Branches C-1 and C-2 are located 

 up the two sides of a broad shale point. Relief wells were installed 

 every 15 to 20 feet along the tile lines in the shale points. This 

 method of intercepting the seepage from the shale has been entirely 

 satisfactory and has afforded all the relief expected. The quality of 

 water developed by this drainage system has been above the average 

 in salt content and is represented by sample C in Table I. 



EXAMPLE VII. 



The project shown in figure 10 is of peculiar interest in that the 

 existence of the wet spot almost on the bank of the wash, 12 feet 



