138 LAND DRAINAGE 



does not lie in this plane, a mistake has been made some- 

 where, either in the computations or in the work. The 

 mistake should be found at once and corrected. (See 

 Figs. 50 and 54.) 



179. Begin the work at the outlet. The work of 

 digging the ditch should begin at the outlet and should 

 proceed toward the upper end. A careful observation of 



FIG. 54. Showing line of grade bars in place ready for digging to begin. 

 Observe also the tile lying in place. Those in the immediate fore- 

 ground are the tile for the main. 



certain details will undoubtedly make the work easier 

 for the beginner. 



180. Opening the ditch. A line should be stretched 

 about two inches out from the grade stakes to mark the 

 edge of the ditch, and along this line the surface should 

 be cut three inches deep with a sharp spade. The chief 

 purpose of the line is to insure a straight edge for the 

 ditch. This edge should be carefully worked to. 



Usually it is not necessary, except with beginners, to 

 stretch a line to locate the other edge of the ditch. The 

 spade should be used to establish it by cutting about three 

 inches into the surface. 



Care should be exercised not to open the ditch too wide. 



