DRAINAGE 75 



is now an easy matter to draw trial lines upon this profile, 

 locating the grade of the tile drain. The determination of 

 +he grade line usually resolves itself into the problem of 

 locating the outlet as low as possible, with the head deep 

 enough to secure good drainage and at the same time high 

 enough to provide sufficient fall for the line. 



Sometimes a thread is stretched across the profile as an 

 aid in deciding the proper location. After the grade has 

 been properly located, the elevation of the grade line at the 

 various stations may be read from the scale of the profile. 



Second Method. If the elevation of the grade line at the 

 various stations be subtracted from the elevation of the sta- 

 tion, the cut, which is the depth of the ditch at that point, 

 will be obtained. It is convenient to adjust the grade to 

 even hundredths of a foot per 100 feet, as, .02 or .25 foot per 

 100 feet. Two additional columns should now be utilized 

 in the field book. One should be marked G. L., which is to 

 contain the elevations of the grade line at the various sta- 

 tions; the other is marked "cuts," and contains the depth 

 of the ditch below the top of the grade stakes at the various 

 stations. It is possible to locate the grade line and deter- 

 mine all cuts at various stations along the line, without the 

 extra work in connection with the drawing of the profile, 

 but the profile is regarded more desirable. 



Uniform Grade Desirable. A uniform grade should be 

 used throughout the tile lines as far as possible, though it may 

 not be economical in all cases. For example, if the tile line 

 is to run through a ridge to an outlet, the grade will likely be 

 established by placing the tile at the minimum depth at the 

 head end of the tile drain to reduce the cut through the ridge 

 as much as possible and still secure a practical grade for the 

 tile line from the head end through the ridge. After passing 

 through the ridge the grade may be increased. It is always 



