Sept. 1906,] 271 Miscellaneous. 



Notes on Methods of Irrigation in Arizona. 



Bv J. H. W. Park. 



Although a good deal has been written concerning irrigation in the 

 Magazine of the Agricultural Society, nothing so far has appeared to indicate that 

 better methods of Irrigation than those now practised in Ceylon exist elsewhere. 

 As the writer believes that with proper methods of distribution of the water from 

 Irrigation Works and proper use of the distributed water in the fields, the 

 areas cultivated in the Island might easily be doubled without any great extension 

 of the works themselves, he trusts the following notes made in the course of a couple 

 of years' residence near Phoenix, Arizona, in the United States, may be of interest. 

 For the actual figures of results obtained he is indebted to the publications of the 

 United States Department of Agriculture. 



Climate.— The driest zone of the United States is practically represented 

 by the territory of Arizona. The average rainfall within the zone does not exceed 

 ten inches per annum, and the rainfall at Phoenix, which lies almost in its centre, 

 averages little over six inches per annum. The temperature is subject to extreme 

 variations. Frost is not uncommon in December and January, and temperatures 

 of between 100° F. and 120' F. in the shade are the rule rather than the exception 

 in the summer months. Under such circumstances the evaporation is very great 

 and averages close on 80 inches per annum, and excepting in bottom lands near the 

 streams or for a brief season after rain, or where irrigation is practised, nothing 

 except cactus and salt bush grows . 



The accompanying diagrams show the rainfall, relative humidity, evapor- 

 ation from a water surface and the mean temperature of Phoenix for each month of 

 the year. For comparison the same factors for the driest district in Ceylon — 

 Hambautota— are also shown. The evaporation from a water surface in Hambantota 

 I have not been able to ascertain, but I give that for the district near Giant's Tank 

 (as calculated by Mr. Parker) which probably is not very different from it. 



The want of rain, dryness of the atmosphere and rate of evaporation all 

 militate against the success of irrigation near Phoenix, but the variation in temper- 

 ature makes a great diversification of crops possible. The soil is a gravelly loam 

 underlaid by gravel and not specially retentive of moisture. 



In spite of these apparently unfavourable conditions, the town has become 

 the centre of a thriving agricultural district. This it owes to the waters of the 

 salt river, a perennial stream which, taking its rise on the western slopes of 

 the Southern Rockies, and fed partly by rain and more particularly by melted 

 snow, flows close to the town and joins the Gila River on its way to the Rio 

 Colorado and the Gulf of California a few miles below it. 



The Irrigation Works.— The waters of the salt river are diverted above 

 Phcenix, along both banks by a series of dams and canals, one of the chief of 

 which the "salt river canal" runs directly through the heart of the town. 

 During summer the bed of the river is entirely dry, the whole of the water being 

 taken for irrigation by the canals above, but below the town the river begins 

 again with the surplus water from the farms, and this is again diverted by 

 other canals and used for the production of further crops. The engineering 

 features of these works do not call for any special remark ; they are more or less of 

 the type used elsewhere, modified by American ingenuity to suit their surroundings. 

 The capacity of the works, the methods by which the water is distributed to the 

 various users, and the means by which the channels are maintained are of 

 more interest. 



