THE DRAINAGE OF FARM SOILS 217 



The mains should make sweeping curves, 

 not abrupt ones. The laterals also may join the 

 mains at any angle, depending entirely upon the 

 grade. If the main is in a marked depression it 

 may be necessary to run the laterals nearly parallel 

 with it for some distance, so as not to make their 

 fall too great, making a long acute angle; but 

 if the main is in a very slight depression 

 the laterals may be almost or quite at right 

 angles to it. In any case they should be 

 given a slight curve before they join the main, 

 so that the water may be carried into the main 

 with the current, not across it. 



When draining land that has a marked slope the 

 lines of the tile may be run up and down the slope, 

 across it, or obliquely. If there are springs on 

 the slope these will be cut off most effectively 

 by cross-slope drainage, otherwise it makes little 

 difference which method is chosen except for the 

 difference in fall. Most drainage, engineers prefer 

 to run the drain obliquely down the slope when- 

 ever it is expedient. 



There are thus many systems of laying out tile 

 drains, each of which has merits under certain 

 conditions. The contour of the land, the character 

 of the soil and the position of the outlet usually 

 decide this question. In fact, it is often necessary 

 to put in a combination of several systems on one 

 field, because of the variation in contour. In 

 planning any system of tile drains the aim should 

 be to use 3-inch tiles in preference to larger 

 sizes, wherever they can do the work, for the 

 larger size of tiles add greatly to the expense of 

 the system. Every fjeld is a new problem; no 

 one can tell how the drains ought to run without 

 studying the field. 



