OPEN DRAINS. 167 



proposed ditch, and if not, whether the grade and depth 

 can be so adjusted as to furnish the desired outlet. 

 These points can be determined by comparing the ele- 

 vations furnished by the topographical survey if one has 

 been made. If such a survey has not been made, lev- 

 els should be run out from the main line to all doubtful 

 points. At the time the survey of the center line is 

 made, ** bench-marks ** should be fixed at convenient 

 places not far from the line, to which reference can be 

 made in testing the ditch during and after construc- 

 tion. The most permanent are made on the brace 

 roots of trees into which a notch is cut. Usually, how- 

 ever, solid hub stakes driven firmly into the ground 

 at out-of-way points must be used. They should be 

 driven flush with the surface and described in the notes 

 after being marked by some guide-post or stake, by 

 which they may be located. 



Cross-sectioning. — Having established a grade, fig- 

 ured the center cut, and decided upon the size and form 

 of the ditch, proceed to set the slope stakes which will 

 define the top width of the ditch and to take such levels 

 as may be necessary to properly compute the required 

 excavation. 



Where ditches are made through level tracts and no 

 deductions are to be made for ditches already existing, 

 the distance out from the center may be measured di- 

 rect and a level taken at the side for a guide in con- 

 struction. In case the ground is more or less uneven, 

 the setting of slope stakes is a necessary part of the 

 work for both construction and computation purposes. 



The following is a convenient form for taking and 

 keeping all of the necessary notes. The center line is 



