200 IRRIGATION IN THE SOUTHWEST. 



irrigation is really superior in point of convenience, certainty, rel- 

 iability to that which depends upon the caprice of the summer rainfall 

 for the nourishment of crops. There is every incentive, therefore, for 

 the fullest development of all the water which the mountains will 

 yield and its conversion to useful purposes. 



FORMATION OF IRRIGATION DISTRICTS. 

 The beginning of every Irrigation district Is naturally made by 

 the construction of canals and the diversion of the flowing streams. 

 At the outset the water so diverted performs a limited duty, as the 

 thirsty lands absorb it greedily, and a large stream will wet but a small 

 proportion of what it will ultimately water when the subsoil becomes 

 saturated and the water plane rises nearer and nearer to the sur- 

 face with each successive year. Gradually the stream Is able to 

 care for more land, cultivation is extended, additional canals are 

 made possible, and the irrigated settlements grow in extent and 

 area of cultivation. Occasionally there will come a season when 

 the rainfall is below the normal, and the run-off of the streams, 

 which in the rainy season may still be abundant, will, in the 

 months of greatest need, be so far short of the usual flow as to 

 cause serious inconvenience and emphasize the need of storage reser- 

 voirs. This is the stage of progression which is everywhere reached 

 in course of time. The third stage after the reservoir period is that 

 which implies the development of underground waters by wells and 

 pumps. In some sections of the country where the streams are quite 

 irtermittent, and only flow during the rainy season, development 

 must begin with the storage of water. In other sections, where reser- 

 voir sites are scarce and dams expensive to build, irrigation begins with 

 wells and pumps, to be followed later by the more costly works. The 

 final stage is that where a water supply can only be obtained by works 

 that are beyond the reach of private capital or individual effort by 

 reason of their magnitude, and where government aid must be invoked. 

 Over a large portion of the arid West it is believed that this stage has 

 been reached, and further progress can only be attained by inaugurating 

 a liberal policy of governmental control and construction of storage 

 reservoirs, and there is a growing sentiment in favor of such a policy. 



THE TONTO BASIN RESERVOIR. 

 In the great Salt River valley of Arizona, the natural stream flow 

 has been utilized in the cultivation of some 250,000 acres of land, whose 

 fertility and productiveness form the basis of the agricultural wealth 



