W ATE It SUPPLY. 39 



Now, if we attempt to catch the waters in the main 

 channel, the works must be strong enough to hold and 

 control all the water which may ever flow there. Tlu 

 great storms will only come once in a while, say five, ten, 

 twenty, thirty or forty years apart, but when they come 

 they will sweep everything before them, unless enormous 

 works are constructed which are unnecessary to hold the 

 waters of ordinary years. In taking water from streams 

 build cheap diverting dams with a few sand bags or 

 something of that sort, to keep the water back and turn 

 it out into a side channel. It is the result of experience 

 in Mexico, Spain and India that the storm waters, when 

 stored, must be impounded in the lateral basins. 



Mud and Silt in Reservoirs. There is another 

 difficulty about the storage of storm waters, which can be 

 avoided by the plan suggested. Storm waters are always 

 more or less impregnated with mud, and if these roily 

 waters are stored in the main channels, the reservoirs will 

 soon fill up and destroy the catchment by the mud and silt, 

 brought down from above, accumulating in the bed'; but 

 if the water is diverted into a lateral or supply channel, 

 the flow can be checked, by methods which are well 

 known, so as to deposit the mud and silt largely, and 

 carry the purer waters around into the reservoir. These 

 conditions must be carefully observed if success is to be 

 attained in the storage of storm waters. Experience 

 shows that it is more economic, and that a greater area 

 of the world is irrigated by the storage of storm waters 

 than is irrigated by well waters. Storm waters are very 

 rich, carrying with them many elements of fertilization, 

 and are very valuable. 



Underflow, Phreatic and Artesian. These are 

 iill definitions of subterranean waters. Underflow waters 

 may consist of either the phreatic those waters under- 

 neath that have come from the surface or the artesian, 

 whi"h are almost invariably deep-founded, and owe their 



