^4 ENGINEERING FOR LAND DRAINAGE. 



main. All numbering and lettering of drains is done 

 from the outlet toward the upper ends. If this system 

 is not followed, some other equally clear one should 

 be used, so that the engineer may avoid the possibility 

 of applying the notes of one drain to some other to 

 which they do not belong. When the whole arrange- 

 ment is made clear, the contractor may take the work, 

 aad without any further explanation than that which 

 appears in the field and the schedules, he may follow 

 out the work in all its details. 



Levelling Drains and Keeping the Notes, 



The method of taking the levels after the drains are 

 staked out is the same as that previously described. 

 The rodman should hold the rod in a perpendicular 

 position upon each grade stake in order beginning, at 

 O stake, and after the * * all-right ' ' signal from the 

 levelman, he should at once pass to the next stake 

 and ** rod up ^* for another reading. He should call 

 off the station numbers of all intermediate stations, 

 branches, etc., as he approaches them that the level- 

 man may enter them correctly upon his book. It 

 should be remembered that in this kind of work each 

 level should be taken with the same care. Every stake 

 must be worked from in digging the ditch with equal 

 care. Sights of 400 feet in length should be regarded 

 as about the limit, though longer ones can be taken 

 with reasonable accuracy. The levelman should see 

 that his instrument is all right at the time he reads the 

 rod, and he should keep his mind closely upon the work 

 or he will take incorrect readings or enter them incor- 

 rectly upon his book. 



