LAND WATERS STREAMS Ifd 



each is less than that of the original stream. (3) Still again, many 

 streams, especially in arid regions, have much of their water with- 

 drawn for 'purposes of irrigation. Many streams in the west are 

 made smaller in this way. (4) Streams decrease in volume as 

 their floods decline, and so deposit in their channels during low 

 water, where they eroded during high water. 



Location of Alluvial Deposits and their Topographic Forms 

 1. At the bases of steep slopes. Every shower washes fine 

 sediment down the slopes of the hills, and much of it is left at their 



Fig. 147 An alluvial cone. (U. S. Geol. Surv.) 



bases. Its lodgment is sometimes shown by the fact that fences 

 in such situations are in places buried by the mud lodged against 

 them. Temporary streams, bred of showers, sometimes flow 

 down steep slopes, and are. suddenly checked at their bases. Such 

 streams gather much debris from the steep slopes, but abandon it 

 where their velocity is suddenly checked. Thus, at the lower end 

 of the new-made gully on the hillside there is commonly a mass of 

 debris which was washed out of the gully itself (Figs. 72 and 147). 

 Material in such positions accumulates in the form of a partial cone, 

 known as an alluvial cone. Alluvial cones have much in common 

 with cones of talus; but in the latter, gravity brings the material 

 down without the aid of water, or with but little help from it. Be- 



