26 A MANUAL OP FORESTRY. 



portion of the area for ditches does not reduce the 

 returns. 



There may be three kinds of ditches : 



(a.) The collecting ditches, or feeders ; 

 (#.) The connecting ditches, or leaders ; 

 (c.) The main drain. 

 See Fig. 12. 



The feeders receive the water from the soil and con- 

 duct it to the leaders, whence it is taken into the main 

 drain. In some cases the feeders fall directly into the 

 main drain. 



The first step in proceeding to drain an area is to 

 take levels, so as to ascertain accurately the fall of the 

 locality ; if the area is of some extent, a map showing 

 contour lines should be constructed. Unless this is 

 done mistakes are likely to occur in laying out the 

 system of drains. 



The second step is to lay out the main drain, if 

 possible along the natural line of drainage ; in other 

 words, along the lowest part of the area. According to 

 the natural fall of the land, the gradient of the main 

 drain may have to be increased by cuttings, or reduced 

 by giving it a winding course, so as to secure a suitable 

 faU. 



The third step is to lay out a system of feeders, more 

 or less parallel to each other, at a suitable angle with 

 the general slope of the country, and to connect them at 

 an acute angle with the main drain, either directly or 

 through a leader, which is similarly connected with the 

 main drain. 



In laying out such a system of drains, the gradient, 



