LAND DRAINAGE 



39 



may be devised from a carpenter's level and a straight edged 

 board. 



A little assistance and advice from someone experienced in 

 land drainage to determine the layout of the drain and the size 

 of the tile may be the means of saving the entire investment 

 with the benefit that should occur. These details are funda- 

 mental to the system and one dare not slight them. 



Construction for particular conditions. — Having established 

 the grades available on any particular area, certain types of 

 soil condition may be considered 

 with reference to the arrange- 

 ment and depth of drains. A 

 series of drains either in par- 

 allel lines or in lines having 

 irregular arrangement may be 

 joined together in a system hav- 

 ing a single outlet just as the 

 rills and creeks unite to form 

 the larger rivers. There are 

 two general types of arrange- 

 ment namely, (1) the natural or 

 irregular system in which the 

 drains are placed in hollow^s or 

 at strategic places to catch the 

 drainage w^ater, but do not cover 

 the entire area at regular inter- 

 vals, (2) the regular or parallel 

 system in w^liich lines of tile at 

 regular intervals are arranged 

 parallel, in so far as the uni- 

 formity of the slope Avill per- 

 mit. 



On flat land of tight, clayey 

 texture, drains are likely to be 

 needed at fairly regular inter- 

 vals of from four to five rods for 

 mixed general farming, down to 

 two rods or less for the more 

 intensive special cropping, such as vegetable gardening. Then, 

 too, they should not be too deep. Two to tw^o and a half feet 

 is sufficient for laterals. If the subsoil has pronounced hard- 

 pan properties an even less depth may be advisable up to eigh- 

 teen inches. This is a very exceptional case. The point is that 



Fig. 16. — Sketch showing a systoin of 

 drainage in whicli the cost of in- 

 stalling is increased by too much 

 double draining. — TJ. S. Dept. of 

 Agriculture, 



