Woods and Water Supplies. 



393 



of the water reaches the ground through the leafy canopy of a 

 dense forest. Then, again, much depends on the kind of tree, 

 evergreens intercepting more water throughout a year than de- 

 ciduous trees ; and a larger proportion of the rainfall is evapo- 

 rated from the leaves and branches in summer than in winter. 



But although less rain-water reaches the soil of a wood than 

 finds its way to the ground in the open country, the moisture in 

 the soil is much better conserved in the former than in the latter 

 case. This is due partly to the exclusion of the sun's rays by 

 the foliage, partly to the absorbent and retentive character of the 

 decaying vegetable matter that covers the ground of a dense 

 and well-managed wood, and partly to the air in a forest being 

 more humid, and thus better fitted to discourage evaporation. 

 The lace-work of tree roots, too, that occupy the soil of a 

 forest, offers mechanical resistance to the rapid surface-flow and 

 percolation of water. It is also to be noted that roots penetrate 

 to great depths, and when they die they leave holes through 

 which water readily penetrates from the surface. The friable 

 condition of the soil of a wood, too, permits ready percolation of 

 water, whereas in the open country the denser character of the 

 surface of the ground is less favourable to the entrance of 

 water. The consequence is that streams in a wooded country 

 are not so subject to rapid rises and falls, the flow being main- 

 tained more equably throughout the year. 



Where water-supply for domestic or industrial purposes is 

 concerned the avoidance of violent freshets on the one hand 

 and scanty flow on the other is alike desirable. Not only may 

 the water of sudden and heavy floods be lost owing to the 

 incapacity of the reservoir to contain it, but such floods have 

 also the disadvantage of carrying much mud and similar 

 material in suspension, and this gradually silts up reservoirs, 

 besides entailing increased expenditure in filtering. 



It may be pointed out that the water of a reservoir surrounded 

 by well-stocked woodland is not subjected to the same amount 

 of violent agitation during gales as is the case where such 

 sheltering agency is absent. The mud and silt deposited on the 

 bottom, and especially along the margin, is, consequently, left 

 comparatively undisturbed, with corresponding advantages in 

 the matter of purity. 



