DRAINAGE OF IRRIGATED LAND. 
19 
the slope and connected with an outlet din in. One of the com- 
mon est locations of seeped lands is this belt of comparatively level 
land at the foot of a steeper portion, and there is no place where 
drainage may be more economically applied. A single drain line, will 
usually intercept the flow from outside sources, and tho pervious 
stratum, being relieved of its water, serves as a drainage system to 
take care of the water applied to the tract itself. The pervious 
stratum may well be consid- 
/320- 
ered a great sheet drain. 
INTERCEPTION OF 
SEEPAGE. 
VERTICAL 
A special case, involving 
the same principles as the 
one just mentioned but in- 
troducing a peculiar condi- 
tion and a unique method of 
solution, is shown in cross 
section in figure 13. No map 
Section 
Fig. 12. — Plan and section showing typical case of water-logging due to seepage from higher land. 
is given, as the surface topography is similar to that shown in figure 12, 
and the drains have the same location and depth. The water moves 
down the slope from higher lands through a very deep pervious stratum. 
At the change of slope the pressure forces the water to the surface. 
Owing to the considerable depth from which the water must rise, it 
is spread over a large area and there is little in the appearance of 
the ground surface to indicate its source. The condition may be 
relieved by a single drain, located as shown in figure 12, and connected 
by means of relief wells to the pervious substratum. The water rises 
in the relief wells, owing to its pressure, and flows out of the drains. 
This situation is not infrequently met with, and until subsurface 
conditions are thoroughly explored the problem appears baffling. 
