CHAPTER VII. 

 DRAINAGE. 



\Yi; will, for our purpose, suppose that the area to be 

 drained is practically level, and that the outfall cannot 

 be determined with sufficient accuracy by the eye. 

 If the land is undulating in character it is often easy 

 at a glance to determine the exact spot for the outlet, 

 and also the precise direction for the main drain or 

 drains. We use the term drains because it is often 

 necessary to make several, both on account of undula- 

 tions and extent of area. On fairly level ground one 

 sub-main may be sufficient for (say) 15 acres; if the 

 area is greater than this it is usually better to make 

 two or more. It is impossible to lay down any rule as 

 to the number required when the land undulates ; but 

 the same rule may apply, viz., that 15 acres, if 

 obtainable, may be made to flow into one drain ; but 

 this must be left to the discretion of the forester. 



We must also at the outset draw attention to tin- 

 fact that great care must be exercised in determining 

 the amount of drainage required, both as to depth 

 and frequency of the drains ; because the removal of 

 unnecessary earth increases needlessly the cost of 

 drainage, which ought instead to be reduced to a 

 minimum, bearing in mind efficacy. Often too many 



