SLOPE OF SIDES OF DRAINS. 37 



By cutting the minor drains against the slope the 

 drain becomes active on each side i.e., it drains to its 

 full extent on each side ; whereas if laid obliquely, it 

 can only drain the upper side, and therefore more 

 drains will be required. There is, however, a limit to 

 this ; if the slope is too great there must be a slight 

 deviation from the right line, or a sub-main must be 

 cut obliquely, so shortening the minor drains. The 

 width of these open drains at bottom should be from 

 8 inches to I foot ; the former representing the minor, 

 the latter the sub-main drain. If less than this they 

 are difficult to keep clear. At the top they should be 

 such a width as to secure a correct slope ; and this 

 slope will increase with the friability of the soil. The 

 natural angle of repose will follow in due time by the 

 wear and tear of the elements, so that it need not be 

 too closely studied in the first instance. The " batter " 

 or slope of the sides will depend on the nature of the 

 soil, but it will range from i in I to I in i J, i.e., if the 

 drain is cut in a clay soil, and is 3 feet deep and I foot 

 wide at the bottom, the sides may slope i in i,and the 

 width of the top will consequently be 7 feet. On land 

 with little natural fall all minor drains should enter 

 the main at an angle of, say, 67 ; this assists materially 

 the uniform flow of water. One thing is obvious, and 

 will greatly assist the forester that is, the whole of 

 his operations being open, and the flow visible, he can 

 correct his work from time to time as it proceeds. 

 This, however, should not lead to hap-hazard and 

 inferior work. The previous plan and arrangement 

 should be as carefully studied as if he were engaged 

 in covered pipe-drainage. 



