174 



FARM DEVELOPMENT 



states, where snow and ice accumulate in open ditches, 

 often clogging them when the surface water begins 

 to run in the early spring. At the points where 

 the open ditch passes through slight elevations of land, 

 the snow accumulates by drifting and serves as a dam 

 to prevent the early movement of water, whereas, if the 



drain follows 

 the lowest 

 level, even if 

 the ditch is full 

 of snow and 

 ice, this soon 

 melts or is 

 worn away by 

 the water from 

 the higher sur- 

 faces which 

 runs over it. 



A cross sec- 

 tion or contour 

 survey is some- 

 times necessary 

 on a nearly 



Figure 78. Elevations on a flat 40-acre field used in locating 

 an open ditch and branch tile drains. The outlet of the open level area, 

 drain, which is 3.2 feet belo.vv the general surface at A, 

 was taken as 100 feet above datum, and all figures show the 11 rp 78 

 elevation of the respective points above that datum plane. / 



sents a 4O-acre 



tract. Here, in a large area nearly level and difficult 

 to drain, cross-sectioning was found necessary, that the 

 main drain might be placed to the best advantage and 

 that the least expensive method of laying lateral tile 

 drains, to drain the low spots, might be devised. This 

 level area is shown, with the levels taken every 132 feet 

 each way. 



To map out the drains, the contour map may be used 

 to great advantage. In many cases, the drains can be 

 laid out on this map by studying the map alone ; in other 



A 



