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PLAT SHOWING PAWNEE PASS RESERVOIR PROJECT, COLORADO, AND EXISTING CANALS AND RESERVOIRS.

of "silting" this portion of the canal will have to be resorted to, but the cost of doing this has not been included in this estimate. Through this light material a slope of 2 to 1 has been used.

From the twelfth to the thirty-fourth mile, inclusive, the soil is composed of sand, but apparently much heavier and more compact than that above mentioned. There is also more vegetation, consisting of blue stem, buffalo grass, dwarf sagebrush, and cactus, though these are seldom all found in one place. In making the estimates over this portion of the line a slope of 14 to 1 has been used.

From the thirty-fifth mile to the end of the present location the soil is a bluish clay and sand, with here and there outcropping ledges of broken lime rock. The general slope used on these sections has been

1 to 1.

In making this location the canal has been put in "excavation" as much as possible, the constant effort being to have a cut of from 2 to 3 feet on the lower side. It has, however, been found necessary to use embankments in a few places, notably in crossing the head of Sanborn Draw on the eighteenth mile. As this piece of work lies along the crest of a ridge frequently swept by terrific northwest winds, and ast the embankments will be made of a sandy soil, it is thought that it will be necessary to cover them with a layer of clay to protect them from the action of the wind. Clay for this purpose can be had in Sanborn Draw, about 24 miles to the south. The cost of thus protecting these embankments has not been included in this estimate.

As near as can be ascertained the prices used in making this estimate are those now prevailing in Colorado on large contracts.

COST OF DAM AND CANALS.

Estimate of cost of Paunee Pass project with a dam 100 feet in height.

[blocks in formation]

2,315,000 cubic yards embankment, at $0.30 per cubic yard .......
58,300 cubic yards riprap, at $1.25 per cubic yard..........
6,820 cubic yards concrete, at $7.50 per cubic yard..........
Tower, gatehouse, and gates

694,500

72,875

51, 150

13,500

832, 025

[blocks in formation]

Grading 5,820,400 cubic yards earth, at $0.14 per cubic yard.......... 814,856
Grading 162,100 cubic yards loose rock, at $0.35 per cubic yard.
Grading 33,600 cubic yards solid rock, at $1 per cubic yard.....

56, 735.

33, 600

941, 791

Total......

1,786, 316

Estimate of cost of Pawnee Pass project with a dam 125 feet in height.

[blocks in formation]

4,400,000 cubic yards embankment, at $0.30 per cubic yard.... 1,320,000
81,600 cubic yards riprap, at $1.25 per cubic yard.
8,600 cubic yards concrete, at $7.50 per cubic yard.
Tower, gatehouse, and gates

180 feet fluming, at $1.50 per foot.... 385 feet bridging, at $6 per foot............ 32,600 feet sand fence, at $0.20 per foot

11 sand gates, at $2,500 each

CANAL.

Grading 5,820,400 cubic yards earth, at $0.14 per cubic yard......
Grading 162,100 cubic yards loose rock, at $0.35 per cubic yard.
Grading 33,600 cubic yards solid rock, at $1 per cubic yard..........

Total......

102,000

64, 500

15,000

1,501, 500

270

2,310

6,520

27,500

814, 856

56, 735

33, 600

941, 791

2,455, 791

The foregoing estimates are based upon the most simple forms of construction and do not include rights of way, head-gates, sluice gates, wasteways, spill boxes, drops, etc., nor the necessity for covering considerable portions of the canal with clay. These items would increase the estimate by probably not less than $150,000.

The necessary reinforcement of the dam by trenching, the construction of a puddled core, and the necessary distributing system, which would consist approximately of 60 miles of canal, at an average cost of not less than $5,000 per mile, would certainly increase the cost of construction at least another $350,000, so that the total cost on the basis of a 125-foot dam, which the officers of the South Platte Land, Reservoir and Irrigation Company state to be necessary to permit the storage of 284,696 acre-feet, would certainly be not less than $3,000,000, and if there is added to this 20 per cent for engineering and contingencies, the total estimated cost is approximately $3,600,000. These estimates are necessarily rough, and it is probable that the cost would exceed this amount rather than fall short of it. It is interesting to note, in this connection, that the estimate for the construction of the dam of loose rock, made by L. G. Carpenter, an engineer employed by the above-named company, was $2.500,000. His estimate would increase the total cost by at least another million, raising it to $4,600,000.

SANBORN DRAW.

A reconnaissance survey was made of Sanborn Draw by running an assumed high-water line around its sides as far as possible, and then following the high ridges where any proposed dam would prob

ably be constructed to connect the extremities of this high-water line. Stations 500 feet apart were used. Points are established at various places along these lines for plane-table work, it being understood at the time that such a survey was to be made.

Owing to the very uneven surface of this basin any estimate of its storage capacity based upon anything but a careful and detailed survey would be of little value. A large amount of grading would be required to connect the various depressions which collectively constitute Sanborn Draw, as well as to provide a suitable outlet. The greatest depth of water would be about 45 feet, and to procure this a dam 4 miles long, averaging 30 feet high, would have to be constructed. The outlines of Sanborn Draw reservoir, as determined by the reconnaissance survey, are shown upon the map submitted with the estimates to which this is attached.

This reservoir site has been filed upon by private parties, who are now constructing a ditch to it from South Platte River.

DUTY OF WATER.

Whenever any irrigation project for the reclamation of arid lands is being investigated, one of the most important of the many problems to be solved, after the undertaking is found to be feasible from a physical standpoint, is that of arriving at a definite conclusion as to the amount of water needed per acre, or, in other words, the answer to the question, What is the duty of the water? There is, perhaps, no other subject relating to irrigation concerning which more has been written and less can be determined. The extent and nature of the country traversed, altitude, temperature, precipitation, wind, protection, or lack of same, soils, channels, depth of water carried, and many other factors, so enter into the consideration of this problem that it is most difficult to arrive at a satisfactory conclusion in any given case, and yet the necessity for determining the specific duty for each project considered is so great that it may be regarded as absolute.

It is clear that conclusions concerning any given project can never be entirely applicable to any other. The amount of water required for the most advantageous use will vary in different localities and under different conditions to such an extent that no hard-and-fast rule can be made, even for the amount actually to be used on the land. In Wyoming, for example, the duty is very much greater than in Arizona, even when conditions are as nearly equal as possible, and the more diverse the conditions the greater will be the difficulty in arriving at any satisfactory basis of comparison.

It is clear, moreover, that even upon one system widely differing values may be given to the duty of water, the differences depending upon where the discharge measurements are made, as well as upon the conditions mentioned above. If, as in this case, for example, an

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