ELEMENTS OF DISSIPATION. 33 



our forests will come a much more rigorous climate and a 

 decrease in rainfall. But the records of the weather bureau 

 do not show that there is any connection between the two or 

 that there has been any apparent change in the general climate 

 or amount of rainfall due to the removal of our forests. The 

 flow of water in most of our rivers, and in many cases the flow of 

 water from springs, and the height of the water table in the land, 

 have been most seriously affected by the removal of our forests 

 and should be regarded as the ways by which our water supply 

 is to suffer most severely from deforestation.] 



DISPOSAL OF WATER SUPPLIES. 



"Given a certain amount of precipitation in rain or snow over 

 a certain area, the disposal of the water after it has fallen, and 

 the influence of the forest cover on its disposal, require our 

 attention. For the sake of convenience we can divide the ele- 

 ments which need consideration in this discussion into elements 

 of dissipation, elements of conservation, elements of distribu- 

 tion. 



"The difference in effect between the first two classes of ele- 

 ments will give us an idea of the amount of available water sup- 

 ply or run-off resulting from precipitation, while the third class 

 bears upon the methods of distributing the available water sup- 

 ply. 



ELEMENTS OF DISSIPATION 



"Elements of dissipation are those which diminish the avail- 

 able water supplies; they are represented in the quantity of 

 water which is prevented by interception from reaching the 

 ground, in the quantity dissipated by evaporation, in the quan- 

 tity used by plants in their growth, and in that used by trans- 

 piration during the process of growing. 



Interception. The amount of rainfall and snow* which is 

 prevented by a forest from reaching the soil varies considerably 

 according to the nature of the precipitation and to the kind of 

 trees which form the forest, as well as the density and age of the 

 growth. 



"A light drizzling rain of short duration may be almost 

 entirely intercepted by the foliage and at once returned to the 

 atmosphere by evaporation; if, however, the rain continues, 

 3 



