No. 4.] HINTS ON LAND DRAINAGE. 381 



than in a lateral, and consequently such flat grades should 

 be permitted only in cases of actual necessity. 



Laying out and Construction of Drains. 



The laying out of drains, especially at flat grades, can be 

 properly done only with the aid of accurate levelling instru- 

 ments, which work can be done by an engineer or surveyor 

 of ordinary skill and capacity. The expense of such services 

 is trifling, compared with the facility, convenience and cer- 

 tainty of successful results thereby insured in the work. 



The following suggestions may aid in laying out and con- 

 structing the work. 



Having secured the proper outlet for the main drain, 

 mark the position of all mains and laterals by driving into 

 the ground at each end of each line, and also at every point 

 where there is a change either in grade or direction, a grade 

 peg or hub level with the surface. Beside it drive a refer- 

 ence stake, leaving one foot exposed, and mark thereon the 

 depth at which the drain is to be laid below the top of the 

 peg. 



Upon opposite sides of each peg, across the line of the 

 drain and far enough to clear the trench, drive two stakes 

 firmly into the ground, leaving two or three feet out, and at 

 some uniform height above the established grade of the 

 drain nail across each pair of stakes a batter board made 

 level from end to end, and mark thereon the centre line of 

 the trench by a nail or notch in the upper edge plumb over 

 the peg. Assume, for example, that all the batter boards 

 are to be set at the uniform height of six feet above grade. 

 If the cut or the depth of the trench marked on the refer- 

 ence stake at the lower end of any given drain is 4.25 feet, 

 then the batter board must be placed 1.75 feet above the 

 peg; and in like manner, if the cut at the next peg on the 

 same line is 3.8 feet, the batter board must be set 2.2 feet 

 above it. Thus the lines and grades of the entire system 

 are established and fixed safe from disturbance during the 

 execution of the work. 



In digging the trenches, begin at the outlet or lower end 

 of the main drain and work up grade, thus giving the water 



