476 Irrigation and Drainage 



are each a radius of a circle from the same center, 

 1-1, the fall along each will be the. same, namely, 2.4 

 inches per 100 feet ; hence, to drain this piece of 

 land, three mains may occupy the positions of these 

 three lines, meeting at station 1-1. But if laterals 

 are to be placed 100 feet apart, these could be given 

 about as great a fall if they were to connect with the 

 diagonal as a main, and take the positions indicated 

 by the two right -angle systems of lines in Fig, 155, 

 I, II, III, IV, V, representing laterals on the upper 

 side of the main, and 1, 2, 3, 4, 5 on the lower. If, 

 however, drains were to be placed 50 feet apart, then 

 the most rapid fall could be secured and the least 

 amount of tile would be required, by arranging the 

 laterals as shown in Fig. 156, where the same area 

 is represented with the contour lines drawn 100 feet 

 apart horizontally and .2 foot vertically, as they are 

 also in Fig. 155, and where the heavy ruling repre- 

 sents main drains and the light ones laterals. 



STAKING OUT DRAINS 



When the location of mains and laterals has been 

 determined, the next step in the practical work is 

 staking out the drains. There are various methods of 

 doing this, but one of the best is as follows : Short 

 stakes, about 8 to 10 inches long, called grade pegs, 

 are provided, and another set upon which records can 

 be made with lead pencil, longer than the others, and 

 called finders. With a tape line or chain and hatchet, 

 the work begins by laying off along the main, begin- 



