CHAPTER II. 

 CHARACTERISTICS OF RIVERS. 



Physical Features. Under similar conditions the same laws apply to all natural 

 watercourses, regardless of size. The smallest creek is characterized by its sinuosities, 

 eddies, bars, caving banks, and overflows exactly as is the greatest river. There is but 

 little definitely known concerning the complicated laws governing these phenomena, but 

 it is of course necessary to take cognizance of this knowledge, scant though it be, in 

 projecting works of amelioration. 



The physical features of a country may be resolved into a series of inclined basins 

 or valleys, each drained in its lowest portion by a stream, each stream flowing toward 

 some other watercourse or body of water. Each of these valleys is subdivided into 

 smaller basins, and these again subdivided in the same manner, until the little springs 

 or rivulets at the source are reached. Thus the smaller valleys all lead to a great central 

 valley through which flows a stream of greater or less magnitude, dependent upon the 

 amount of rainfall and the character of the material upon which it is precipitated. 



Rainfall. The cooling of layers of air charged with moisture produces rain or 

 snow, and the presence of forests, mountains, and valleys will also influence the tem- 

 perature and cause precipitation. The quantity of rainfall in any one locality varies 

 greatly from year to year, and is also much greater at some points than at others, usually 

 diminishing as the distance from the sea or other place of great evaporation is increased. 

 Thus in Ixmdon, England, the mean annual rainfall is about 23 inches, while in certain 

 districts in India, as shown by the records of the Royal Engineers, the rainfall has reached 

 as much as 600 inches in one year. 



Upon reaching the earth the rain-water is either taken up by the soil and vegetation, 

 or runs off into the streams. That portion of the rainfall which runs off and immediately 

 finds its way into thV streams causes freshets and floods. Its proportion will vary, like 

 the portion infiltrated, with the character of the material upon which it falls, and the 

 amount of vegetation present. Torelli has stated that a wooded mountain will retain 

 four-fifths of the rainfall, and that the same mountain if denuded will retain but one- 

 fifth, but this is disputed by others. Time is required for the absorption, and this time 

 is furnished where timber covers the ground. Water falling on the foliage is distributed, 

 and upon reaching the earth is held a longer time by the vegetation of various kinds 

 and the fallen leaves. In penetrating the earth it meets conduits through which it is 



