254 ON THE DRAINING OF PLANTATIONS, 



secure will the sides of the drains be from falling in, for when cut 



straight down in loose and friable soil, and especially after frosts and 



heavy rains, when the ground is soft, and a strong run of water 



flowing, the risk of injury to the sides is very great. But when the 



soil is stiff or tenacious, less slope will be necessary. Open drains 



1£ feet deep are sometimes sufficient to dry the ground, where there 



is only surface water to contend with ; but as a general rule, drains 



less than 2 feet deep will not dry even the surface soil sufficiently 



for the reception of young plants. On the other hand, when over 



3 feet deep, they are not only inconvenient in the removal of 



thinnings or timber from the plantation, but they require great 



width at top, and take up more room than can be spared where 



close draining is necessary. It is however impossible to fix any 



definite depth for open drains, as 2 feet might answer the purpose 



on some soils, as well as 3 feet in others, but 2 J feet is a good average 



depth. In draining peat bog or other soft soils, containing a large 



quantity of organic substance, an additional depth should be allowed 



for subsidence as the water is removed, and if a stratum of gravel 



or clay occurs at no great depth, it is well to reach it so as to give 



the drains a solid bottom, as well as to dry the ground more 



thoroughly. In forming plantation drains, the soil taken therefrom 



should be spread between the drains, so as to make little weight on 



the sides. If such soil be left on the margin, its weight would tend 



to make the sides fall in, and the soil so left would crumble and be 



washed into the drains by heavy rains in a short time ; but by 



spreading it towards the middle, the centre is in a manner ridged 



up, and during heavy and continued rains (especially in tenacious 



land), the water, instead of remaining on the surface, at once flows 



towards the drains, and the roots of the plants are free from stagnant 



pools ; the ground is thus more dry after the trees have grown up, 



even should the clearing out of the drains be neglected. 



The distance between drains, whether open or covered, depends 

 upon circumstances. The nature of the soil and the depth of the 

 drains require to be considered, as the more open and porous the 

 soil is, and the deeper the drains are formed, the greater will be the 

 distance at which they may be made, and vice versa in stiff tenacious 

 soils with drains of less depth ; but it is seldom necessary to have 

 covered drains closer than 15 feet from one another, and open drains 

 24 feet apart between centres, or at greater distances from each 

 other than 40 feet. When open drains are closer than 24 feet at 2 

 feet deep, they become inconvenient, taking up much room, and 



