AFFOEESTATION OF CATCHMENT AEEAS 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 



