36 PKINCIPLES OF AMERICAN^ FORESTRY. 



sota and Wisconsin, where the land is more nearly level. 

 Where streams have their sources in mountains, as those 

 of Colorado and other Rocky Mountain States, the cutting 

 away of the forests causes a heavy flow of water early in 

 the spring and little water in the summer, when it is most 

 needed for irrigation purposes. This has become so evi- 

 dent that the Chamber of Commerce of Denver, Colorado, 

 recently petitioned the President of the United States to 

 reserve such land in forests and administer it at public 

 expense, and in their petition used in part the following 

 language : 



"The streams upon which the irrigation system of Colo- 

 rado depends are fed by the springs, rivulets, and melting 

 snows of the mountains, which in turn are nourished and 

 protected by the native forests. Where the forests have 

 been destroyed and the mountain slopes laid bare, most 

 unfavorable conditions prevail. The springs and the rivu- 

 lets have disappeared, the winter snow melts prematurely, 

 and the flow of the streams, formerly equable and continu- 

 ous, has become fitful and uncertain. Floods and drought, 

 alternating clearly, indicate that the natural physical condi- 

 tions of the region have been unduly disturbed. In winter 

 and early spring, when heavy masses of snow have been 

 accumulated on treeless precipitous slopes, snow- and land- 

 slides frequently occur with disastrous result to life and 

 property.'' 



THE DISTRIBUTION OF WATER. 



The distribution or ''run-off" of the water is often a 

 more important factor in its economy than the quantity 

 available. It is influenced by the surface conditions of the 

 soil cover, by the porosity and structure of the soil, and by 

 the slope. There are two kinds of run-off — the surface 

 run-off and the underground run-off or percolation. The 

 former is likely to do injury by eroding the soil, while the 



