DEAINAGE OP lEEIGATED LAND. 



19 



the slope and connected with an outlet drain. One of the com- 

 monest 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 the pervious 

 stratum, being reheved 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- \\\\\\ \_\^ I ered a great sheet drain. 



INTERCEPTION OF VERTICAL 

 SEEPAGE. 



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 1 3 . 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 thc^ pressure forces the water to the surface. 

 Owing to the considerable depth from which the water must rise, it 

 is spread over a largo area and there is little in the appearance of 

 the groijiid 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 \\u\ pervious substratum. The water i-ises 

 in th(! ndjef W(^11h, owing to its pr(\ssurc, and fiows out of the di-aijis. 

 This situation is not infrequently met with, and until subsurface 

 C(Hi<lilions an; thoroughly exploic<l tlic ])n)l)l('ni appoai-s baffling. 



