It is therefore important that we give attention to wise 

 use and conservation of soil and water resources; observe how 

 they have been brought into a relationship in which each 

 makes the other more useful; consider whether we are impair- 

 ing this relationship; and if we are, take steps to correct any 

 serious harm we may be doing to basic arrangements and 

 therefore to our civilization. 



The waters to which we shall here give attention are little 

 waters rainfall, water in the soil, rivulets that flow off the 

 land, creeks and other headwater streams, ponds, and small 

 lakes not great rivers and their major tributaries. A river 

 system is like a tree with its trunk, large branches, small 

 branches, smallest branches, twigs, and leaves. It is with 

 the leaves, twigs, and smallest branches of a river system 

 that we are here concerned. 



In the aggregate these little waters are of immense impor- 

 tance. They create the big rivers and lakes. As they are 

 controlled and made to behave, so in considerable measure 

 will the tributaries of big rivers be controlled and made to 

 behave. 



1. THE NATURAL CIRCULATION OF WATERS 



THE TOTAL quantity of water in, on, and about the earth is 

 believed to be fairly constant, but it exists in various forms 

 and places; as liquid or ice in the oceans, lakes, rivers, and 

 other surface waters; as liquid or frost in ground and under- 

 ground storage; as clouds, fogs, mists, and vapors in suspen- 

 sion in the atmosphere. It changes from one to another of 

 these forms and moves from one to another of these places. 



In their major aspect earth waters have a natural circula- 

 tion (the hydrologic cycle), in bare outline essentially as fol- 

 lows: 



a. The atmosphere absorbs water from oceans, lakes, riv- 

 ers, the land, and other exposed surfaces even from falling 

 raindrops (evaporation), and also that drawn from ground 

 storage and exhaled by the leaves of trees and other vegeta- 

 tion (transpiration). Few people know what quantities of 

 water are transported by evaporation and transpiration. 



