24 A MANUAL OF FORESTRY. 



the continuous flow of water in the ordinary water 

 channels, or even the amount of rain and dew in the 

 neighbourhood. In this manner, existing woods, which 

 have become accustomed to a certain degree of moisture, 

 may be seriously injured.* 



If, after full consideration, it has been decided to 

 remove the excess water, this can be done either by 

 diverting the water before it reaches the swampy ground, 

 or by draining the latter. 



a. Diversion of Excess Water. 



This is done by embankments in the case of inundation 

 water coming from rivers in low lands, or by ditches in 

 the case of spring water or surface drainage coming from 

 higher ground. 



Inundation water moving over the surface of the land 

 may be kept out of a certain locality by a surface em- 

 bankment ; if the water moves underground, it can only 

 be stopped by a substantial underground embankment, 

 such as a stone or concrete wall. 



Spring water and surface drainage in hilly ground is 

 caught and diverted by running a ditch of suitable 

 dimensions along the slope of the hill just above the 

 swampy ground. The ditch intercepts the water and 

 leads it past the swamp. In some cases the mouth of 

 the spring is situated in the swampy ground itself, when 

 only draining can meet the evil. 



* It is believed that some of the Elms in the Long Walk, Great Windsor 

 Park, died in consequence of drainage carried out some years ago ; after 

 these drains had, in consequence, been blocked again, the remaining trees 

 recovered. 



