DISTRIBUTION OF WATER. 41 



equable and continuous, has become fitful and uncertain. 

 Floods and drouth alternating clearly indicate that the natural 

 physical conditions 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 prop- 

 erty." 



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 under- 

 ground run-off or percolation. The former is likely to do 

 injury by eroding the soil, while the latter is generally beneficial 

 to vegetation in the formation of springs and in raising the 

 water level in the soil. It is evident that the less surface drain- 

 age and the more underground drainage the greater the spring- 

 water supply and vice versa. We are, therefore, interested in 

 determining the factors that increase underground drainage and 

 reduce the surface flow. 



It is plain that whatever retards the flow of water over the 

 land aids it in sinking into the soil. We find this exemplified 

 in swamps, where the soft, rough ground retards the surface 

 flow, and in forests, where the foliage checks the water in its 

 descent to the ground and the forest floor retards the surface 

 run-off. Theoretically such a cover should promote the flow 

 of springs and maintain the height of water in wells, and in 

 practice we find that this is often the case. In some cases 

 springs had entirely disappeared after the clearing of near-by 

 forests, but have commenced their regular flow since the trees 

 have been allowed to grow again. Springs in turn influence 

 the flow of water in rivers, so that forests about the headwaters 

 of streams often have a most potent effect in maintaining their 

 flow. There is in fact no influence of the forest that is of 

 greater importance in the distribution of water supplies than 

 its effect in retarding the run-off, even though its effect in pre- 

 venting evaporation is very important. 



