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OPERATIONS IN IDAHO.

By D. W. Ross.

GENERAL CONDITIONS.

The construction work which was begun in December, 1904, on the Minidoka project has been steadily prosecuted during the season of 1905. In addition to the work in progress on the dam and spillway, contracts were let during July and August, 1905, for the construction of the main canals and distributing system; also for the construction of a telephone system. Work under these contracts is now in progress, provisions being made in the specifications for the completion of the entire gravity system of canals, which will irrigate about 80,000 acres of land, by June 1, 1906.

On February 15, 1905, a project board met at Boise for the consideration of plans and estimates in connection with the Payette-Boise project. Recommendations favoring the early construction of a portion of this project were made to the chief engineer, and in March, a favorable report having been made to the Secretary of the Interior, an allotment from the reclamation fund of $1,300,000 was ordered for the construction of a part of the Boise Valley division of this enterprise. During the present field season surveys of this portion of the project have been in progress, and plans and estimates are now being made preparatory to the letting of contracts at an early date. Negotiations for the use and control by the United States of the New York canal, which is to be enlarged and extended to form the main canal on the south side of Boise Valley, have been very satisfactorily concluded by the Reclamation Service. The Payette-Boise Water Users' Association has appraised the lands needed for right of way for the Deer Flat reservoir, and many contracts have been made by the owners for the sale of lands to the United States.

♦ A general reconnaissance covering practically all the minor streams of the arid portion of the State has been concluded, and it is now thought that fairly accurate estimates can be made of the irrigation possibilities of practically every stream system.

The Second Annual Report of the Reclamation Service contained preliminary estimates of several projects in Idaho. In the case of the Minidoka project the probable cost of reclamation is fairly indicated by contract prices, only a comparatively small amount of work remaining to be done outside of these contracts. Detailed surveys lately made of the Payette-Boise project have suggested many changes in the plans originally proposed, and have led to an increase in the estimated cost of construction. Preliminary surveys and reconnaissance to determine the feasibility of storage works on the headwaters of Snake River were completed during the latter part of the field season of 1904. In some cases these conditions are almost ideal, but in others there will undoubtedly be found many difficult features. The great development now in progress in the Snake River Valley will lead to a demand for the construction of works to regulate the flow of this stream at an early date-much earlier than has generally been estimated.

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B. ROCK FILL AND CORE WALL FROM NORTH BANK, MINIDOKA DAM, MINIDOKA
PROJECT, IDAHO.

MINIDOKA PROJECT.

DAM AND SPILLWAY.

The contract entered into by the Bates & Rogers Construction Company, dated September 17, 1904, provides for the construction of a dam in Snake River, spillway, head gates, and forebay canal, the work to be completed by December 17, 1905. The lowest bidder for this work having failed to comply with the requirements of the specifications, it became necessary to let the contract to the above-named company, whose bid was second in amount. Considerable delay occurred before the matter was finally adjusted, and owing to this and to delay in receiving the shipment of the construction plant and equipment the winter season was well advanced before work was fairly under headway, little work having been done before January, 1905. Since that time the work has been vigorously prosecuted, but owing to the fact that the work had to be carried forward in a certain sequence, and that in constructing certain portions only a comparatively small number of men could be employed, progress seemed at times to be slow. This was particularly noticeable when the core wall was being laid across the deep, narrow portion of the river channel; also when it became necessary to concentrate on the excavation of the narrow diversion channel. Owing to these causes it will not be possible for the contractors to finish this work within the time specified in their contract.

The dam, when completed, will consist of a heavy rock fill with a concrete core wall, faced on the upstream side with a heavy earth embankment. A spillway (Pl. XV, A), provided on the left bank of the river, is of ample capacity to carry the greatest possible flow of flood water without danger of overtopping the dam. The total length of the entire structure is 4,412 feet.

The rock fill (Pl. XV, B) is constructed of lava rocks ranging in size from a few cubic inches to 4 cubic yards or more in volume. The smaller ones fill the interstices between the larger ones, and in turn the interstices between the smaller rocks are sluiced full of gravel and sand, thus making the structure tight and securing the maximum weight. In filling the deep channel stones of not less than 2 tons in weight were used until the velocity of the water was checked, after which smaller ones were filled in. The stones decrease in size toward the upstream face of the rock fill, where small ones are used. The earth embankment joins the upstream face of the rock fill, and is composed of gravel and sand and faced with earth containing from 35 to 50 per cent of clay.

A concrete core wall extends across the river upstream from and parallel to the axis of the dam. This wall is founded on the solid rock bed of the river and serves as a cut-off to water that would otherwise follow along the bed of the river underneath the structure. The spillway (Pl. XV, A) is constructed of concrete on a solid rock foundation, with an earth embankment along the upper face.

Around the northern end of the dam a channel is cut through a rock point to divert the entire flow of the river during the construction of the southern end of the dam. In this channel there is a concrete dam with regulating devices, below which it is proposed to build a water-power plant for the purpose of generating electric power to be used for pumping water onto tracts of land that lie above the gravity canal in Cassia County.

On beginning excavation here it was found that the cofferdam as constructed was totally inefficient in itself, and it became necessary to build a secondary cofferdam, inclosing an area just sufficient for the construction of the wall. Much difficulty was experienced in getting this one built, as water broke through a number of times, but finally this secondary cofferdam was made tight and the construction of this section of the core wall proceeded without serious interruption and was completed June 30. Owing to the loss of time in awarding the contract during the summer of 1904 this work was carried on during the highwater period, which rendered it more hazardous and difficult than it otherwise would have been, inasmuch as the difference between the high and low water discharge of the river was about 11,000 cubic feet per second.

Efforts are being concentrated toward the completion of the diversion channel and the concrete dam with regulating devices, as the early completion of the rock fill is dependent on this. Work is being vigorously prosecuted night and day. Cement for this work, all machinery, and supplies are hauled by teams from Minidoka, a distance of 6 miles.

MAIN CANALS AND DISTRIBUTING SYSTEM.

BIDS AND CONTRACTS.

A project board, consisting of the governor and state engineer of Idaho and engineers of the Reclamation Service, met at Boise February 15, 1905, and recommended that contracts be let for the immediate construction of the north side canal and lateral system. In view of the fact that the Reclamation Service had decided not to install a pumping system for the irrigation of the lands on the south side of the river for perhaps several years yet, it was recommended that a small canal be constructed on the south side of the river with a view to providing at once for the irrigation of the lands which could be reached by gravity. This recommendation was approved, and on April 20, 1905, bids were invited for the construction of a main canal and branches and distributaries on the north side of the Snake River, and of a canal on the south side; also for the construction of a telephone system. In letting these contracts the work was divided into eight parts. Schedule 1 consisted of the north side main canal, which contained practically all the rockwork on the north side of the river; schedule 2 covered the canal on the south side; schedules 3, 4, and 5 covered divisions of the branch canals and distributaries on the north side; schedule 6 covered the waste canal on the north side; schedule 7, the head gates, turnouts, and bridges and other structures; while schedule 8 covered the gates and lifting devices.

The following table shows the bids received and the amounts for each bid:
Bids received on schedule 1, distribution system, Minidoka project, Idaho.

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