THE IRRIGATION AGE. 



901 



and auxiliary walls. Perhaps a better way to figure the 

 factor of safety of the buttresses is as follows : 



The water pressure acts in a horizontal line inducing 

 shear strain. The strength of concrete in shear is one-half 

 what it is in compression. 



Owing to the fact that these buttresses are tightly held on 

 both sides by the auxiliary walls and the earth filling, they 

 cannot yield by buckling and if they yield at all, it must be 

 by shear or crushing. We may, therefore, double all the 

 horizontal pressure and add to it all the vertical pressure 

 and if the wall is sufficiently strong in compression it surely 

 will be in shear. When considered in this way, however, it 

 is proper to consider all the material that will be in shear. 

 This includes a segment of the face wall 20 ft. wide, and a 

 similar segment of all the auxiliary walls. There will be a 

 total of 910 sq. ft. of reinforced concrete to resist the shear 

 and pressure. This material, disregarding the reinforcement, 

 is capable of standing a pressure of 910 X 440,000 = 400,- 

 400,000. 



The total pressure is as follows: 

 Double the water pressure as given above. .. .42,665,400 Ibs. 



Weight of aux. walls 3,150,000 Ibs. 



Weight of buttresses 3.073,750 Ibs. 



Weight of earth above sill-floor 2,002,000 Ibs. 



Weight of face wall 2,760,000 Ibs. 



55,641,190 Ibs. 



As the power of resistance is 400,400.000 Ibs., and the 

 maximum strain 55,641,190 Ibs., it is plain that we have a 

 factor of safety of 7.1, which will be much increased when 

 the reinforcement of the concrete and the resistance of the 

 earth filling are considered. 



Thus it will be seen that the lower section of the dam 

 as designed is amply strong. In the same way each section 

 taken at 5, 20 and 40 foot intervals, has been checked and the 

 dam is abundantly strong on each section. 



The arched floor is calculated as a horiontal slab which 

 must be able to carry the dirt filling. Taking a 1 ft. segment, 

 the load will be 



1 X 20 X 80 X HO = 176,000 Ibs., 

 and its own weight == 20 X 1 X 1 X 150 = 3,000. 



The total weight upon the slab is 179,000 Ibs. With a 

 safety factor of 4, the ultimate load will be 

 4 X 179,000 = 716,000 Ibs. 



To compute the required thickness of the arched floor, 

 the same notation as above is used. 



And from the above formula, 

 Mo=p b d S (d Y), we deduce, 



Assuming that P = \% and d = 12, we find from equa- 

 tion (6) Webb and Gibson that Y = .357 Kd. From table on 

 page 61 we find K = 422, so Y = .161d and d x = .849d. 



As Mo = 716.000 Ibs., we obtain 



\/ .0121X12X55,OOOX-849 V 710,000 



d = - - = V 118 = 11" 



716,000 6780 



The sill-floor, then, will be 1 ft. thick, assuming that the 

 reinforcing is l" from the surface. It will also be arched 

 to increase its strength. 



The reinforcing for each part of the dam has been figured 

 out, as given above for the face wall. Although there w^s 

 some variation in results it was not sufficient to adopt differ- 

 ent percentages for different parts of the dam, and 1% is a 

 good average reinforcement for all parts, but the face wall 

 which will be 1.2% on each side or 2.4% altogether. 



From the foregoing calculations, I believe this type of 

 dam is thoroughly strong and safe. 



In the particular instance given above, a solid concrete 

 dam will require 300,000 cu. yds. of concrete. The cellular 

 dam will require 300,000 cu. yds. of dirt filling and 50,000 cu. 

 yds. of reinforced concrete. 

 300,000 cu. yds. concrete at $5.00 = $1,500,000. 

 300,000 cu. yds. dirt at 20c = $60,000. 

 50,000 cu. yds. reinforced 



concrete at $12.00 = $600,000. 

 Total $660,000 



While the above figures would vary with each individual 

 case, it can readily be seen that there is great economy in the 

 use of this dam, if no unforseen conditions may arise which 

 render it inapplicable. I shall welcome criticisms of the 

 structure. 



Mr. W. A. Homan, of my office, assisted me in working 

 out the design. 



The computations were then gone over and checked by 

 Mr. J. E. Payne, engineer for the Corrugated Bar Company 

 of St. Louis. Mr. Payne's great experience in reinforced 

 concrete enabled him to make some valuable suggestions 

 which were adopted. 



A great many power and irrigation projects come to my 

 attention, and to the attention of other engineers, which would 

 be very _ desirable indeed were it not for the great expense 

 of building a thoroughly substantial dam. This is particularly 

 true with regard to projects involving the use of mountain 

 meadows for reservoir sites. -In such instances it is gener- 

 ally unwise to use an earthen dam because of the violent 

 floods which characterize the mountain streams and a ma- 

 sonry or monolithic concrete dam is so expensive that the 

 project is impracticable. It is most important to the Rocky 

 Mountain States that the storing of water be made as cheap 

 as possible. The most efficient way to use our waters is to 

 develop power in the mountain canons and then use the water 

 for irrigation on the plains and valleys below. To do this 

 requires double storage. The power user wants water in a 

 continuous and regulated flow the year round. The farmer 

 wants all his water during three months in the summer. Na- 

 ture, on the other hand, pleases neither the power man nor 

 the farmer, for she furnishes a flow which varies from year 

 to year and season to season. It will readily be seen, I think, 

 what a very important matter it is if a good dam can be built 

 at half the present cost of masonry dam construction. 



LARGER AREA OF LAND LEFT OPEN IN COLO- 

 RADO THAN IN OTHER STATES, 

 BARRING TWO. 



The annual report of the United States land office, just 

 issued, gives to this state 19,432,000 acres of surveyed lands 

 not homesteaded, a larger area than that left open in any 

 commonwealth in the union, barring Wyoming and Nevada. 

 This land, according to the officers of the land department 

 in Denver, does not include any within the forest reserves. 



The total acreage, surveyed and unsurveyed in the state, 

 is 21,726,192. A majority of this land is fine for agricultural 

 purposes, though much of it is of a mountainous, grazing 

 or mineral nature. 



In the Denver district alone, including the counties of 

 Adams. Arapahoe, Boulder, Clear Creek, Douglas, Eagle, El- 

 bert, Gilpin, Grand, Jackson, Jefferson, Larimer, Morgan, 

 Routt, Summit and Weld, there is a total of 1,237,040 acres 

 of surveyed lands. 



The largest district in the state is the Glenwood Springs 

 section, with 4,593,668 acres. This district contains Routt 

 county, with 1,869,036 acres. Las Animas county, in the 

 Pueblo district, has 1,521,524 acres. 



Del Norte district contains 644,433 acres; Durango, 982,- 

 170; Montrose, 3,946,703; Pueblo, 4,106,118; Hugo, 124,530; 

 Lamar, 2,170,640; Leadville, 534,073; Sterling, 1,092,634. 



Those interested in securing government lands should 

 have a copy of "The Settler's Hand Book," which contains 

 maps showing the location of the different lands and just 

 the information that the homeseeker requires. These books 

 can be had from Ranch and Range. 



ANOTHER IRRIGATION ENTERPRISE FOR 

 COLORADO. 



The neighborhood of Pueblo is to be the scene of effort 

 of another large irrigation concern. The new concern has 

 filed incorporation papers here, the capital being given at 

 $50,000, which is 50,000 shares of stock at $1 each. 



However, it is understood that this is only the pre- 

 liminary capitalization, and that the company will later in- 

 crease its capital to a considerable extent. The incorporators 

 are L. A. May, E. T. May, Denver; and Kurt Grunwald. 

 formerly of Pueblo, but now of Denver. 



Four large reservoirs are planned by the new concern, 

 the water supply to be derived from the flood waters of 

 the Fountain river and the Chico creek. The land is lo- 

 cated northeast of Pueblo and consists of approximately 

 25,000 acres. The directors of the company are E. T. May, 

 L. A. May, Kurt Grunwald, R. W- Rose and H. S. Hopkins. 

 Their attorney is former Attorney General John T. Barnett. 



The principal office will be in Pueblo, and it is expected 

 that this office will be opened in the near future. A branch 

 office will be maintained in Denver. 



