44 



diameter. The bed of the trench should be smooth, firm, and 

 even ; the inclination of no drain should be less than half an 

 inch or more than eight inches per chain. 



The direction of the main drain should first be settled, and the 

 minor drains are then mapped out in such a manner that the 

 undulations of the surface are taken due advantage of in the way 

 of securing a free and easy descent of the water. Great care must 

 be taken that, though the surface be undulating, the pipe-bed has 

 a uniform and even descent, and that there are no depressions in it 

 where the water could lodge, eventually decomposing the pipes and 

 filling up the drains with sediment. The depth of the main always 

 exceeds by a few inches the depth of the laterals, which should be 

 laid in a direction generally perpendicular to it, although where 

 they enter the main drain that direction should be at an easy angle. 

 These lateral drains, when laid fish-bone fashion on either side of 

 the main drain, should not enter it immediately opposite, but should 

 alternate to fit and adjust two pipes. The smaller one is chipped at 

 one end, flute-shape, whilst a hole is knocked out of the larger pipe 

 to receive it. The last pipe, at the outlet, is of iron, and its end is 

 well grated to guard against the intrusion of vermin, whilst each of 

 the minor pipes is also protected where it springs, to prevent earth 

 and silt finding its way inside the drain and blocking it. Should a 

 stoppage occur, an excavation is made and the cause, whatever be 

 its nature displacement of tile, accumulation of silt, or roots of 

 trees removed. A correct plan of the deep-drainage system is 

 in every case necessary for future use. 



The following table gives, for the character of the soil it is 

 intended to drain, the distance apart the drain is generally set, the 

 depth from the surface, and the number of 12-inch long tiles 

 required to the acre: 



In setting this table, it should be borne in mind that if the 

 drain is too shallow the water will run directly to it, without 

 benefiting the soil with its fertilising power ; if too deep, it won't 

 draw, and will not work. 



