1 for instance, No. 3596 is prohibitively white alkaline and Nos. 5108, 5143, and 5163 are seriously white alkaline. Sometimes in irrigating with well waters it is possible to mix black alkaline and white alkaline waters in such a way that the resulting mixtur is harmless. In this conncetion, please see pages 698, 699, and 700 of our twenty-thir annual report, herewith sent you. Considered as a whole, the Casa Grande district and the Gila River district adjoining contain a great variety of well waters, some of them excessively black alkaline, others excessively white alkaline, but in many instances entirely acceptable for irrigating purposes, and in many more nstances not far from a point where their ultimate effects upon irrigated lands is somewhat debatable. It is to be remarked in this connection that the evidence is accumulating to indicate that deep wells in the district are likely to average better in quality than surface wells; for instance, compare Nos. 5143 and 5144. The first-named shallow well contains 354 parts of soluble solids. The second water stratum in the same well contained only 80 parts in 100,000. With reference to flood waters available from the Gila River, the Santa Cruz, and other tributary valleys, I will call attention to the character of these waters as shown in section 1, Table VIII, page 192, Bulletin 44, herewith sent you. As shown in this table the flood waters of the Gila River (and the same is true of Salt River and I think of floods generally in Arizona) are black alkaline in character. In the table flood waters for six weeks during the period of observation contained 3.66 to 6.66 parts of black alkali in 100,000 of water. This is not a prohibitive amount, but when added to a soil of black alkaline in character might, in some cases, aggravate an existing tendency. In other cases where soils contain an excess of while alkali, as is shown in several instances on the sheets submitted, the excess of calcium sulphate in the soil and the black alkali in the flood water would neutralize each other. The practical outcome, however, of the use of these flood waters in the district would not be injurious, for the reason that their abundance would result in so flooding and draining the soil as in the average instance to benefit rather than harm it in so far as the black alkali content mentioned is concerned. With reference to reservoir waters, I will again call attention to section 1, Table VIII,2 in Bulletin 44, in which you will see that the low waters of the Gila River contain an excess of calcium sulphate. In a reservoir the black alkali of the flood waters would be neutralized by the calcium sulphate of the low waters and the character of the general river flow thereby be improved for irrigation. This is supported by observations made on the Salt River which, as shown in section 1, Table IV, page 174, Bulletin 44, is also black alkaline in flood, although in the case of that table the floods and the low waters were not so sharply divided as in the case of the Gila. In October, 1911, a sample of the mixed waters of the Salt River, as obtained from the irrigating outlet of Roosevelt Reservoir, contained an excess of 1.6 parts in 100,000 of calcium sulphate. Inasmuch as the Salt and Gila Rivers are similar in their chemical composition, there is reason to believe that a large reservoir upon the Gila River would have similar effect upon irrigating waters contained. Summing up, therefore: 1. The soils of the Casa Grande Valley are physically desirable, but, generally speaking, contain noticeable, and sometimes serious, amounts of black alkali which it would be well to consider in general measures affecting the welfare of the district. 2. The well waters vary greatly in character, those along the Gila River being for the most part white alkaline in character, while those at a distance from the Gila River are for the most part black alkaline in character. A number of instances are observed where either black or white alkalies are contained in injurious excess; in other cases they are contained in dubious amount, and in yet other cases they are not contained in any damaging quantity. In cases of a large general development of the ground waters of the district through single or harmonious agencies, these waters should be so combined in irrigating that sodium carbonate and calcium sulphate contained may react in a manner improving the quality of the water. 3. In the case of river waters, the black alkaline flood waters and the calcium sulphate low flow, more especially of the Gila River, will unquestionably benefit by mixture in a storage reservoir. 4. Aside from discussions more or less theoretical in character, the history of the district for the last 20 years shows that for the most part wherever abundant irrigating water is available large and profitable crops may be grown. I hope these statements will prove sufficient for your purpose, and remain, Very respectfully, R. H. FORBES, Director. 1 Extracts referred to, marked "Inclosure No. 5," follow this letter. |