DRAINAGE OF IRRIGATED SHALE LAND. 



29 



comer and extends to the center of the tract and thence south, where 

 it is well defined. Along these ridges the water table always was 

 nearest the surface. 



Several years prior to the draining of this tract a drainage system 

 was installed on the tract south and east. Four-inch tile were used 

 and branches were placed at frequent intervals, but the depth was 

 not much over 4 feet. While the surface of the ground is not wet, 



100' 200' 300' " 400 



Fig. 5. — Typical profiles across tract shown in figure 4. 



the trees are beginning to show the effect of a high water table and 

 a number of them are already dead. One of these 4-inch tile branches 

 was used as an outlet for the system under discussion in order to 

 cut down expenses, but it would have been better if an outlet of larger 

 tile had been constructed. 



The system was laid out as shown in figure 4, an attempt being 

 made to follow the shale ridges. The depth of the system ranges 

 from 6 to 7 feet. As nearly all of the trenches were in shale, very 

 little difficult construction was encountered. In some places the 

 banks of the shale trenches broke off in large pieces and it became 



