380 



THE FARiMER'S MAGAZINE. 



Where several undulations of surface occur, a separate 

 system of the directiou of the collecting drains must be 

 applied to every alteration in the plane of the surface, 

 so that the direction of the drains in each may be that 

 inculcated in the above-directed mode of laying out col- 

 lecting drains. 



On ground having a considerable declivity, or on 

 which the declivity has several gradients, or even in 

 large fields requiring great continuous length of collect- 

 ing drains, it will be proper in the first and last men- 

 tioned cases to have oue or more sub-main drains across 

 the direction of the collecting drains, and having such 

 obliquity of direction across the declivity of the surface 

 as to afford fall for a tolerably rapid current of water; 

 and in the second-mentioned there should be a sub- 

 main at the bottom of each gradient. The sub-mains 

 are required to prevent the wash likely to take place in 

 heavy summer showers after long-continued drought on 

 clay soils, or to relieve the small drains and prevent 

 their being blown from being overcharged from any 

 cause whatever. 



The most vexed question relating to thorough drain- 

 ing is the depth at which the drains should be laid. In 

 regard to this, it may be remarked, that no specific rule 

 can apply, as circumstances may render a dift'erence, 

 not only in contiguous fields, but even in the same field, 

 necessary ; and hence arises the discrepancy in opinion 

 that exists on this point. It may, however, be remarked 

 that failure in efficiency in draining never arises from 

 drains being too deep, but frequently from their being 

 too near the surface. Thus the ducts may be laid above 

 the principal water-feeders in the subsoil, in which case 

 the drains will obviously be of no use. A drain, how- 

 ever, may be deeper than necessary, and, therefore, 

 improper on the score of economy. 



Now, since drains may be too near the surface to be 

 efficient, and, if deeper than necessary, needless expense 

 will be incurred, the proper depth of drains in any par- 

 ticular case can only be determined by trial pits being 

 sunk. In making such trials, the pits should be sunk 

 to different depths, noting which draws most efficiently, 

 and adopting the least depth producing the greatest 

 effect. 



As the subsoil may vary greatly in its nature in 

 the same field, so the depths of the drains may be 

 required to be varied to produce the best effect at the 

 least cost. As a general rule in regard to the depth of 

 drains, the more compact the subsoil in which the 

 drains are to be laid, the deeper should be the drains ; 

 since water-feeders in a compact subsoil being smaller 

 than in that of a more open nature, it will require a 

 greater number of feeders to be in action in the former 

 case than in the latter, to discharge the same quantity of 

 water in an equal period of time. 



It is scarcely necessary to remark that, whenever the 

 collecting drains are at different depths, the receiving or 

 main drain into which they are discharged should be 

 sufficiently deep to receive the water from the deepest of 

 the small or collecting drains. 



The proper depth of drains being determined by the 

 means pointed out, their proper distance apart may be 



determined by their depth and nature of the subsoil in 

 which they are to be laid. 



Collecting drains, not exceeding six feet in depth, 

 will draw water from two to three times their depth, on 

 eauh side, in the purest and most compact clay ; from 

 three to four times their depth in clay containing no- 

 dules of gravel ; from four to five times their depth in 

 clay with seams of sand or gravel ; and six times their 

 depth in the most open subsoils. 



The distances apart at which drains should be laid, 

 in terms of their depths, according to different kinds of 

 subsoil, are as follow, viz. : — 



Nature of Subsoil. Distance apart of Drains. 



Strongest claya 4 to 6 times depth of drain. 



Clay mixed with nodules of 

 gravel 6 to 8 „ „ „ „ 



Clay, with seams of gravel or 

 sand, acccrding to the thick- 

 ness of such seams 8 to 10 „ „ „ „ 



Saudy or gravelly subsoils ., 10 to 12 „ „ „ „ 



In drains not exceeding six feet in depth, the fore- 

 going rule will be found to agree pretty accurately with 

 the most successful practice; but at greater depths, 

 which, however, are seldom required in ordinary field 

 draining, the distance apart of the drains under different 

 circumstances as to subsoil must be determined by the 

 experience of the engineer or drainer designing or con- 

 ducting the work. 



Common clay tile is the best material for the ducts of 

 drains, and the best form for the purpose is a plain 

 hollow cylinder. Such tile pipes are made by the tile 

 pipe machines in great perfection, and where fuel can 

 be had at a reasonable price they may be produced at a 

 very cheap rate. Drain pipes are usually made by 

 manufacturers of from one to nine inches bore, and they 

 may be obtained of even a larger size when required. 

 The usual, and indeed, the most convenient lengths of 

 tile pipes are from twelve to fifteen inches for those of 

 from one to six inches bore, and twelve inches in length 

 for those above six inches in diameter. 



Tiles that have not been thoroughly air-dried pre. 

 viously to being fired , those made from clay with too 

 large a mixture of sand, or having nodules of lime or 

 chalk in it, and those that have been made during frosty 

 weather, should be rejected. Tiles of good quality are 

 heavy, and emit a ringing sound when struck; but they 

 should not be so hard burnt as to be vitrified in the fire. 

 The quality of drain pipe tiles should be that of the best 

 garden-pots ; and the best mode of testing their quality 

 is to steep them for three or four hours in water, and 

 then to place them before a fire ; and should they re- 

 main hard and whole after such an ordeal, they may be 

 safely used. 



The size of pipe is a matter of much importance, and 

 should have consideration both for the collecting or 

 small drains, and for the leading or main drains. 

 For collecting drains, unless the drains are short, 

 are not far apart, and the current brisk, one inch 

 bore is too small. A much more useful size is two 

 inches, and then the length of the drains should not ex- 

 ceed ten chains, the distance apart thirty feet, and the 

 fall at least one-and-a-quarter inch per chain of twenty- 



