FENCING AND DRAINING 185 



Before draining a large area the consequences must be 

 carefully considered, as otherwise unlooked-for results may be 

 obtained. For instance, the drainage of an extensive swamp 

 at a high elevation may reduce the water level of a large tract 

 of lower lying country, and may thus do damage to agricultural 

 land, and brooks and streams may dry up. For these reasons 

 the woodman should only drain small local swamps unless 

 expert advice is first obtained. Drainage should be done 

 while land is bare of trees, as if it is carried out in existing 

 woods, the water level being reduced, the standing trees may 

 die. The best time to drain land used for forest purposes is 

 about three years before planting, as the ground then settles, 

 and the new water level finds its place, before the trees are 

 planted. 



In forestry, open ditches are used, because pipes would soon 

 be choked up by the roots, and because ditches are cheaper. 

 Where drainage has been decided on, ditches are dug at from 

 16 to 22 yards apart according to the soil; the stiffer this is 

 the nearer must be the drains. The depth may vary from 

 4 feet on very stiff soil down to about 2 feet on lighter land. 

 The width depends on depth, the general rule on the lighter 

 soils being to make the width of the top of the drain one-third 

 wider than the depth ; thus a drain 3 feet deep should be 

 4 feet wide at the top, the sides being given a suitable slope 

 to prevent the soil falling in. On stiff soil the width may be 

 about equal to the depth, and the sides can be almost vertical. 

 The bottom of the smallest drain made should be a little wider 

 than a spade, so as to enable it to be easily cleaned out. 



In laying out a drainage system a main drain should be 

 made along the line of lowest level, and this should terminate 

 in a stream or existing large ditch. From this, other large 

 drains, called leaders, are made along the lowest depressions 

 to all parts of the area, and from these the feeder drains are 

 laid out. All ditches should fall into the larger drains in such 

 a way that the water will not scour away the sides. The 



