52 IRRIGATION FARMING. 



down, with side ravines cutting into it and with many 

 laterals, and with a tra<5t of five or ten square miles 

 above, which a<5ls as a catchment area for waters which 

 run down in flood or storm times. 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. The great 

 storms w;ll 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 constru<5led 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, accu- 

 mulating 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 



