RESERVOIRS 303 



and the fact that silt is liable ultimately to fill up the depression 

 are great disadvantages in the use of this type of reservoir. To 

 avoid the accumulating of silt in the reservoir a second reservoir, 

 smaller than the main one, may be constructed above the one 

 to be used chiefly for watering the livestock. All of the water 

 drains into it; naturally the silt collects here; and the water is 



{Forest Service.) 

 Fig. 113. — an EARTH RESERVOIR IN NORTHERN ARIZONA BUILT TO COLLECT 

 AND CONSERVE FLOOD WATER FOR WATERING SHEEP. 



left reasonably clear as it reaches the second or main reservoir. 



A heavy clay or adobe soil is the best type for the construction 

 of reservoirs. The passing of horses to and fro as the reservoir 

 is being built does much to settle the banks. The best way to 

 make the bottom and sides impervious to water is to place salt 

 in the reservoir so that the grazing animals will do the packing 

 themselves. This plan, as shown in Figure 113, is effective 

 where the soil contains suflScient moisture to cause it to puddle. 



The cost of building a reservoir is seldom high if the additional 

 forage made available and the benefits derived by the stock are 

 considered. The cost will be determined largely by the char- 

 acter of the soil and the way it can be handled. Barnes ^ has 



1 Barnes, Will C, "Stock-Watering Places on Western Grazing Lands." U. S. 

 Dept. of Agr. Fanners Bui. 592, p. 15, 1914. 



