DRAINAGE 



173 



the ditch and the depth of the ditch at these two points. 

 Where the line is long and there is a variation in the 

 slope of the surface of the ground, however, it is better 

 to take a level at each stake placed every 50 to 100 feet 

 alongside the line of the proposed drain. A line of levels 



Figure 76 Collared drain tiles or sewer pipes. 



thus taken and figured to express the height above datum, 

 as will be explained later on, will serve as a basis for 

 locating the exact line and depth of the proposed ditch. 

 From the first line of stakes where the levels were taken, 

 other levels may be taken at points on either side. A 

 new line with slight or considerable deviation from the 

 first line may be projected here or there, and by placing 

 stakes along the new line and taking several levels, its 

 practicability may be compared with the first location. 

 In this way the best place for the main drain may be 



Figure 77. Branched collared tiles. 



accurately determined in low areas where the problem is 

 a comparatively simple one. 



It is generally wise to have open ditches follow the 

 lowest levels. This is especially true in the northern 



