Location of Drains. 



317 



is therefore not uniform for all the laterals nor can it be- 

 when they are placed along parallel lines. 



If the field required drains every 50 feet then a greater 

 mean fall could be secured and less tile would be required 

 if a system like that of Fig. 136 were adopted. 



FIG. 136. Showing a second system ol drains laid out on the field of 

 Fig. 133. (From Irrigation and Drainage.) 



390. Laying Out Drains. When the positions of the 

 mains and laterals have been decided the next step is DO 

 mark them with "grade pegs" and "finders." The grade 

 pegs are short, driven securely into the ground just to one 

 side of the intended ditch, and are placed at regular inter- 

 vals apart. To one side of the grade pegs are placed longer 

 ones called "finders" upon which is to be recorded the 

 depth below the grade peg the ditch is to be dug. 



391. Determining the Grade and Depth of the Ditch. In 



doing this work the leveling begins at the outlet and the 



