LAYING OUT A DRAIN OR SYSTEM 115 



the tile is laid in the bottom of the ditch. It is not so 

 convenient, and it is more expensive, to distribute the 

 tile after the digging of the ditch has begun. 



159. Leveling for the drain. If there is a system of 

 drains to install, the work of leveling begins with the 

 main. If there is only a single drain, the work of leveling 

 will proceed in much the same manner. The object of 

 the leveling is to determine the elevation above datum 

 of the surface of the field at each stake along the proposed 

 drain,, or at each stake in the proposed system, as the 

 case may be. The reasons for this will appear later. The 

 manner of doing the work of leveling will be the same as 

 was described in paragraphs 128-140. 



160. Steps in the procedure. The work of leveling 

 will begin at the stake driven at, or nearest to, the pro- 

 posed outlet. This stake is numbered 1. 



a. If the level to be used is a high class instrument, 

 and the drain is not over 60 rods long, it may be set up 

 at about the middle of the length of the drain. The 

 elevation of stake 1 will be assumed to be 10 feet above 

 datum and recorded as such in the proper column, after 

 stake 1 in the notes. 



The first reading will be a back-sight reading taken at 

 stake 1 and will be recorded in the proper column, after 

 stake 1 in the notes. This back-sight reading, added to 

 the recorded height of stake 1, gives the height of the 

 instrument. A fore-sight reading should now be taken at 

 every other stake within the range of the level along the 

 proposed drain. Each fore-sight reading should be 

 recorded in the notes after the number of the stake at 

 which it is taken. If all the stakes of the drain do not 

 fall within range of the instrument, one or more re- 

 settings will be necessary. 



