AFFORESTATION OF CATCHMENT AREAS 75 
of water is not only a hygienic, but in some respects also an 
aesthetic one. People may drink turbid water and water 
with an unpleasant taste or smell for a time without 
perhaps any definite injury to health. The aim, however, 
must be always to secure a supply of drinking water that is 
not only free from infectious matter, but is also capable of 
being drunk with satisfaction. 
There is one means by which water catchment areas can 
be effectually guarded against pollution and at the same 
time be put to profitable use, and that is afforestation. In 
considering the advisability of afforesting a watershed, it 
need not be assumed that the entire area should be covered 
with trees. Questions of aspect, depth and nature of soil, 
shelter from wind or exposure, must be taken into account 
in determining where and what to plant. It is probable 
that the proportion of any gathering ground that can be 
planted with advantage will be found to vary from 10 to 
70 per cent of the total. It is well known that on sites 
above a certain altitude, varying with the latitude and with 
the exposure to the prevailing winds, and on undrained peat 
soil at any altitude, planting trees is always unprofitable 
and often impossible. Generally speaking, it may be laid 
down that on most catchment areas which attain over 1000 
feet elevation, a combination of grazing and forestry must be 
resorted to. Only the lower zone and the sites with favour- 
able soil are suitable for planting. The arguments for 
afforestation are cumulative. In an area planted with trees 
the water is conserved to a considerable extent. When 
heavy rain occurs, the run-off water is much lessened, as the 
rain, as fast as it falls, is absorbed and stored by the deep 
humus layer on the floor of the forest. A larger percentage 
of rain will reach the reservoirs from an area that has 
been afforested. The quality of the water will also be 
superior, as the soil on the hill slopes will be held together 
by the roots of the trees, and the destructive effects of 
heavy rains, in carrying down masses of clay and stones, 
will be prevented. Flood waters will also diminish to a 
great extent, and, in consequence, the reservoirs will not be 
