THE IRRIGATION AGE. 



895 



in the soil; thus the water drained from one farm may 

 used to irrigate and enrich another farm. 



A gravity system of drainage is naturally preferable 

 as its operation cost is practically nothing. There are how- 

 ever, localities where there is no natural drainage and in such 

 case the surplus water must be pumped. In such case the 

 cost of pumping must be considered, and if it can be worked 

 so as to store the water in a reservoir so as to use it when 

 the ground needs irrigation the pumps are doing double duty 

 as their work in draining the land is the first step toward 

 irrigation as well. 



It may be truly said that the arts of irrigation and drain- 

 age are just now beginning to be developed and that the next 

 decade will see a tremendous advance in this direction. 



The time will come when all the land that 

 Irrigation can be irrigated by a gravity plan will have 



by Pumps been taken up, and then the reclamation 



and Pipe of further land will necessarily depend on 



Lines. the ability of raising water from the deep. 



This will also include such lands as are 

 now watered by artesian wells which deliver water under a 

 head at present, but the time will come when the pressure 

 diminishes and that water will also have to be pumped. The 

 question whether it will pay to irrigate land by pumping the 

 necessary water will depend on a good many circumstances 

 which should be carefully considered. As a general proposi- 

 tion the government should be first consulted regarding the 

 geological formation, quantity and quality of ground water 

 supply in the region under consideration, next the condition 

 of the soil should be established, which is best done by taking 

 samples at different localities and depths and have them 

 analysed in the various experiment stations. From this in- 

 formation an approximate estimate of the cost of pumping 

 can be made. But the proposition is always one of more or 

 less uncertainty, as no one can definitely state whether a 

 subterranean water supply is permanent, like an underground 

 river or whether it is just a pocket. For this reason the 

 government should devote more work and money to the 

 establishment of hydraulic information in the various states, 

 especially in the arid and semi-arid regions. 



So much has been said and written about 

 The Roosevelt the Roosevelt Dam in Arizona recently that 

 Dam and it will not be amiss to briefly review the 



the Salt River work done by the government in con- 

 Project, structing one of the most gigantic irriga- 

 tion plants in the world. The purpose of 

 the dam is the impounding of the waters of Salt river for 

 the irrigation of the Salt River Valley in Arizona, reclaiming 

 about 250,000 acres of arid land. 



The dam is built square across the bed of the Salt River 

 between the mountains, forming the valley of the river, is 

 700 feet long, 280 feet high, 170 feet thick at the base and 

 16 feet wide on top; it is built of concrete and contains 344,- 

 000 cubic yards of masonry ; the 300,000 barrels of Portland 

 cement required for this structure were manufactured by the 

 government on the ground, thus not only saving about 600,- 

 000 dollars in the cost of the cement, but having positive as- 

 surance all the time that the material was reliable and avail- 

 able as required. The government likewise built a saw mill 

 in the nearby forrest for all the timber requirements of the 

 project. The reservoir thus formed covers an area of 16,300 

 acres and forms a lake 25 miles long by 7 miles wide in the 

 widest place. It is over 200 feet deep at the dam but the 

 average depth does not exceed 16 feet, and when the reser- 

 voir is full it contains 1,284,200 acre feet of water, which 



beis able to supply the 250,000 acres in the project something 

 like 60 inches per annum assuming that the reservoir just 

 fills once a year. 



These works do not only supply water for irrigation but 

 also hydro-electric power is developed to the tune of 12,000 

 horse power, which in the course of time can be increased 

 to 25,000 horse power. This power is carried a distance of 

 65 miles to the town of Phoenix where it is doing duty light- 

 ing the streets and propelling cars. There will no doubt be 

 a heavy demand for this source of power for the purpose of 

 pumping from wells in the Salt River Valley on lands which 

 are located too high to be served by gravity flow. 



Credit must be given to the government for carrying 

 through such a stupendous engineering feat under such diffi- 

 cult conditions, yet the terms under which the water is made 

 available to the settlers are very easy, as the payments are 

 from 4 to 6 dollars per acre per annum for ten years. 



There is perhaps one thing however which may cause 

 serious trouble in the near future and this is the fact that 

 strong leaks are developing in the cliffs which form the two 

 long sides of the reservoir. The dam built by the govern- 

 ment is in splendid condition and appears to be perfectly 

 water tight, but the walls which nature built are not proving 

 trustworthy and numerous miniature waterfalls appear on 

 the sides of the cliffs below the dam. This shows evidently 

 that the engineers in charge of the work should not have 

 taken it for granted that hills forming the sides of the pro- 

 posed reservoir were water tight ; they could have with reason- 

 able increased expenditures provided for a water tight con- 

 crete floor of the reservoir up to a certain height so that the 

 floor and sides subject to heavy pressure would be completely 

 protected. With a depth of water of 220 feet against the dam 

 it means a pressure of nearly 100 pounds, 94.6 pounds exactly, 

 per square inch and this means that if there is any chance 

 for the water to 'escape it will find it. Yet it is hard to fore- 

 cast whether the leaks that are showing now will become 

 worse or 'close up. It depends much on the nature of the 

 seam that the water is following through the hills whether 

 the leak will gradually be closed by the accretions of silt 

 or whether the water under its high pressure will enlarge 

 the crevices and increase the rippling stream to a raging 

 torrent carrying destruction down to the valley below. 



There is no doubt that the government engineers are 

 watching these leaks closely and taking all necessary precau- 

 tion for the protection of life and property. They can, how- 

 ever, not be too careful when the safety of thousands of peo- 

 ple may be threatened by great masses of impounded water at 

 a considerable elevation. 



Drainage 

 Problems 

 irr the 

 South. 



There is perhaps more land within the 

 boundaries of the United States in need of 

 drainage than in need of irrigation, or it 

 might be more appropriate to say that a 

 greater acreage of swamp lands can be 

 drained than there is arid land which can be 

 profitably irrigated. Hence drainage is at present receiving 

 considerable attention, especially in some of the southern 

 states, such as Louisiana, Florida and Texas. There are vast 

 tracts of partially submerged lands in the states of Arkansas 

 and Mississippi, which are in urgent need of drainage, and 

 which will form, when reclaimed, splendid land for all kinds 

 of crops. 



There are about four millions of acres of land in the 

 Yazoo Delta, in the state of Mississippi, of which only about 

 one-third is in cultivation. The remaining 2,600,000 acres can 

 be reclaimed by drainage and after clearing off the timber will 

 be capable of producing a very large revenue for the State. 



