DISTANCE APART TO LAY LINES OF TILE 



119 



feet apart, one on either side of the proposed trench at the outlet, 

 and a lath (c) is nailed to them horizontally one foot from the 

 gromid (from top of lath), which would be five and one-half feet 

 from the proposed grade line (0, X), or the bottom of the trench. 

 Two other stakes {d, e) are driven in a similar manner at the upper 

 end, and a lath (/) is nailed to these two feet from the ground, 

 which would likewise be five and one-half feet from the grade hne. 

 Other pairs of stakes are driven in line with the first ones at inter- 

 vals of about 100 feet and to them lath are nailed horizontally 

 and in line of sight over the top of the laths ^' (c) '' and ^' (/) . " The 

 trench is now dug until the top of a stick five and one-half feet 

 long held vertically on the bottom of the trench is in line with the 

 top of the laths. In this way a perfect grade can be obtained, 



a S 



cy 



/ 



L/he 



^5j^2 feet 



-y 



y 



of sigh/- 



d e 



\ 



^'/e feef 



/ 



Fig 



Grade L/ne 



53 — The use of grade lath m lajang of tile D, outlet ditch, iV, proposed outlet for 

 tile, OXy proposed grade hne (See page 117.) 



because the line of sight over the laths is parallel to the proposed 

 grade line. 



On extended flat areas it is necessary to lay tile deep at the 

 outlet and shallow at the upper end, in order to secure sufficient fall 



On all large areas, especially if they are level or nearly so, it 

 is best to secure the services of a competent drainage engineer 

 to lay out the system of drainage and to supervise its construction. 



Covering the Tile. — ^As soon as the tile are laid, sufficient 

 amount of soil should be shoveled in to cover them, and to hold 

 them in place imtil the trench is filled. Covering and anchoring 

 the tile in this manner is called "blinding.'' 



Filling the trench may be done by hand, or by the use of a 

 plow or a scraper. 



Distance Apart to Lay Lines of Tile. — ^Frequently a single Hne 

 of tile is all that is necessary to drain a narrow wet strip. In 

 draining a narrow, wet depression (draw) between two areas of 

 high land, it is often best to lay two lines of tile, one at the foot 

 of each slope, or one on each side of the lowest center line. On all 



