RIVERS IN DRY CLIMATES 341 



river has accomplished its life work, it has borne to the 

 sea all the burden it has to bear, its labors are ended, it 

 has reached old age. It has reduced its drainage area to 

 a base level of erosion. When a river has thus done all 

 the wearing down of which it is capable it is said to have 

 completed a cycle of erosion. 



159, Rivers in Dry Climates. In a region where the 

 climate is very dry, rivers are often intermittent in their 



RESULTS OF A SUDDEN FLOOD. 



flow. They contain water only after rains. Such rivers 

 may dry up before they reach any other body of water, 

 their water entirely evaporating or sinking into the dry 

 soil. Their development is therefore somewhat irregular. 

 If the slopes are steep and there is little vegetation to 

 protect them and hinder the quick run-off of the water, 

 rivers flood very rapidly, eroding their channels and wash- 

 ing away their banks. Where they descend upon level 

 ground they silt up their old courses and acquire new 

 channels. Thus a river which for the larger part of the 



