tion season, giving a relief of only 11 feet. In the preparation of these plans, however, and in determining the strains upon the gate, a possible maximum relief of 16 feet has been assumed.

Upon the foundation just described rests an iron framework consisting of two parts, MLNOPD and DEFG, which, with the concrete mass HIJK, forms the fixed weir. The arrangement of these frames is shown in detail in the drawings. The frames DEFG occur every 5 feet. The frames LMNOPD occur every 2 feet.

The frame LMNOPD forms the lower wall of the chamber AZQ and sustains the pressure on the concave surface D'Q. It also supports the upper end of the apron RR'; and, when the gate is closed for repairs, it supports also a part of the weight of the gate and the pressure on the bulkhead VWX.

The frame DEFG supports the movable part of the dam and forms the upper wall of the chamber. The wooden partitions D'Q and E'Z are water-tight.

The concrete mass HIJK forms the impervious barrier of the fixed weir and supplies the weight necessary to the stability of the whole structure.

The apron of the dam, like the main structure, rests upon piles, and is not liable to undermining from the agitation of the water below the dam. Its construction is fully illustrated by the drawings. The space beneath it is left vacant, except as filled with backwater from below, or with the sediment that may collect there. The escape of water from the chamber at Q and from the interior of gate at B passes into this space. The superstructure, or movable portion of the dam, is a sector of a circle in cross section. The arc subtended is 67° 30'. It consists of an interior iron framework A' B' C', with a wooden exterior ABC. The upper face AB is air-tight, the lower face is water-tight, and the cylindrical face is air-tight about two-fifths of the distance from C to B. The ends of each section of the gate are closed and air-tight from C down to a line shown in fig. 2, Pl. XIV. The gate is held by the hinge A, of which a full-sized drawing is given on Pl. IX. When the gate is in operation it is supported by water pressure and by the pin A. When not in operation it falls into the chamber AZQ and rests against the stop Z. The other details of the structure are readily understood from the drawings.

The triangular space DEH is a longitudinal culvert by which water is conveyed to or from the chamber AZQ. In order that the pressure of the water may be applied to or withdrawn from the face AB of the gate uniformly throughout its entire length, the connection between the chamber AZQ and the culvert DEH consists of a narrow opening, ZQ', extending the entire length of the gate. Its entire area slightly exceeds that of DEH.

The piers (Pl. XI) separating the sections contain the culverts and valves by which the supply of water to the chamber AZQ is controlled. A rectangular culvert 3 by 4 feet enters centrally from the upper end of each pier and passes out at the lower end. It is intersected at the center of the pier by a cross culvert of trapezoidal cross section, but of the same area. A heavy iron girder, embedded in concrete at the ends, cuts both culverts in two diagonally at their junction, so as to restrict communication through the upstream culvert to the chamber to the right of the pier, and that through the downstream culvert to the chamber to the left of the pier. The culverts are closed by sliding valves operated by oil cylinders actuated from shore.

The operation of the gate is as follows: The outlet valve being closed,

the inlet valve is opened. The head of the upper pool is brought to bear on the lower surface AB of the gate. As shown in the discussion on the strains in the gate, there is always a sufficient head to raise the gate except in a certain contingency to be considered further on. As the gate rises and approaches its normal position when up, it is not brought to rest by a stop, but by closing the inlet valves, or, automatically, by the escape of water at Q. RQ is a gate 24 feet long. (Pl. X.) There are seven of these to each section. Their combined free space for the flow of water is about 10 square feet. The area of the inlet culvert is 12 square feet. When Q' passes above Q, water begins to escape, and the outflow increases the farther the gate rises. By the time Q'reaches R the outflow through the gate, with the leakage at other points, will fully equal the inflow, and the gate will cease to rise. By gradually closing the inlet valve the gate will settle back to its normal position when Q' is just below Q. The valve is then left in this position, and the friction of the gate will preserve a balance of forces. Ordinarily the gate would be stopped by the operator when it has reached its normal height, but in case of inadvertence or carelessness no harm can result, for the gate will come automatically to rest without shock or sudden stop, as just explained.

The contingency already referred to, when there will not be sufficient. initial head to raise the gate, is fully considered in the discussion on the strains in the gate. The air necessary for the expulsion of sufficient water from the interior of the gate to give it the requisite buoyancy to rise in still water is supplied through a 2-inch pipe leading from each section to an air pump on shore. These pipes, with those conveying oil to the valve cylinders, are buried in the concrete mass, as shown in the drawings. The operating room, or house to cover the air and oil pumps, will be located close to the head walls of the lock on the shore side.

For the purpose of making repairs to any section, the bulkhead VWX (Pl. VIII) may be erected, supported by the frame DEFG and by the gate through the struts CX and SW. The gate is supported at A and by braces resting on the apron and against the circumference of the gate. By closing the upper valve and opening the lower, the structure is uncovered down to the level of the lower pool. By closing the lower culvert also and applying a pump, the entire structure is rendered accessible.

The gate will never be kept up after the upper pool reaches stage 120 feet. The piers will not form obstructions to drift, as drift does not begin to run in the river until they are entirely submerged. At such times their location will be marked by buoys for the information of pilots.

The cost of the dam, with a liberal allowance for every item, is a trifle under $120,000, or $140 per linear foot.

For a comparison of the probable cost of this form of gate with that of other forms, the following examples are cited:

Dam at Lock No. 7, Great Kanawha River.-(Authority, Col. Peter C. Hains, Corps of Engineers.) Elevation of bed of river, 535 feet; low water, 539.6 feet; crest of dam, 550.5 feet; type, Chanoine wicket; cost, $270 per linear foot. The relief of this dam, both above low water and above the bed of the river, is very nearly the same as at Lock No. 1, Osage River.

Lumbermen's dam in Minnesota.-(Authority, A. O. Powell, United States assistant engineer, who prepared the estimates.) Common bear

trap type; head of dam, 10 feet. Estimated cost, $280 per linear foot. Big Sandy River, Kentucky.(Authority, Board of Engineer Officers-Craighill, Lockwood, Turtle.) Type, Poiree needles; length of dam about 300 feet; clear height of crest above sill of navigable pass, 13 feet; estimated cost, $93,029.25. (Annual Report Chief of Engin eers, 1892, p. 2108); cost per linear foot, $310.

HIRAM M. CHittenden,

Captain of Engineers.

REPORT OF THE BOARD OF ENGINEERS.

THE BOARD OF ENGINEERS,
New York City, June 23, 1897.

GENERAL: In reply to your indorsement of May 24, 1897, The Board of Engineers has the honor to state that it has examined the project submitted by Capt. H. M. Chittenden, Corps of Engineers, for the construction of Lock and Dam No. 1, Osage River. This project was forwarded with request for your approval by Lieut. Col. Amos Stickney, Corps of Engineers, president of the Missouri River Commission, with the statement that the Commission had approved it in all of its general features.

In examining the project and making its recommendations The Board of Engineers has acted with the understanding that its opinion has been requested solely upon the novel features of the dam proposed and not upon the question whether the improvement as a whole is a desirable one, nor upon points of foundations, levels, material, etc., upon all of which no opinion can be formed without a personal knowledge of the locality. From the action of the Missouri River Commission it may safely be assumed that the constructive details are suited to local requirements.

As stated in the memoir descriptive of this project (see page 3949), a dam 16 feet in height above extreme low water in the lower pool is necessary in order to pool the water to the required distance upstream. A fixed dam is not regarded as desirable since it would unduly raise the flood level above. On this account Captain Chittenden recommends a dam consisting of a fixed concrete portion 9 feet high supporting a movable portion which can be raised by the hydrostatic head to the full height of 16 feet above extreme low water below. The movable portion is a novel modification of the drum weir. A detailed description is given in the memoir and the accompanying illustrative plate (see page 3947). The whole dam relies for its stability mainly upon the concrete mass of the fixed portion, which rests upon a flooring supported by piles and grillage. With proper care in construction to insure no leakage between the concrete and floor, this part of the dam possesses ample stability against overturning. Proper precautions against sliding can readily be taken.

The movable dam is built in lengths of 75 feet, separated by piers in which the valves of the operating culverts are placed. Captain Chittenden states that it can be raised by a head which is normally obtainable at times of low water, and estimates that it will respond to a pressure of less than 1 foot. In the unusual case of its being drowned by backwater from the Missouri at times when the discharge of the Osage is small, provision has been made to raise it mechanically by pumping air into the drum. The pipe through which the air is pumped

has a diameter of 2 inches, and must serve not only to convey the air under pressure to raise the drum, but to relieve the internal pressures by letting air in and out when the gate is worked by the hydrostatic head. It is believed that there is but one such pipe for each section of the dam 75 feet long. It is possible that freer communication for the air should be provided in order to allow sufficiently quick and easy operation. This fact will be developed in the experiments which are proposed.

Captain Chittenden states that a model on a scale of one-third natural size has already been built, and has worked satisfactorily. He states further that should his plans meet with approval a short section of full size will be built at the sight of the dam to develop any latent defects in the design. The Board of Engineers considers the dam sound in principle and especially well adapted to a locality where it may be placed on the crest of a fixed weir to increase the height of the latter. For such service it preserves to a great degree the advantages of the drum weir while avoiding its one notable disadvantage, that of the deep and expensive foundation usually necessary. Accepting Captain Chittenden's estimate of say $140 per linear foot as accurate, the cost of the dam as proposed will not be greatly in excess of a reasonable estimate for a fixed dam of similar relief and foundation, while much below the ordinary cost of a movable dam.

The Board recommends the design of the dam for approval, and considers it advisable that experiments should be made with a full-sized model, as proposed by Captain Chittenden, before undertaking the final construction.

Respectfully submitted.

Brig. Gen. JOHN M. WILSON,

Chief of Engineers, U. S. A.

HENRY M. ROBERT, Colonel, Corps of Engineers.

G. L. GILLESPIE,

Colonel, Corps of Engineers.
H. M. ADAMS,

Major, Corps of Engineers.
JOHN G. D. KNIGHT,
Major, Corps of Engineers.
H. F. HODGES,

Captain, Corps of Engineers.

NOTE. The project as recommended by the Missouri River Commission and by the Board of Engineers was approved by letter of the Chiet of Engineers, dated June 29, 1897, with the understanding that experiments will be made with a full-sized model before final construction is undertaken.

ESTIMATES.

REVIEW OF PREVIOUS ESTIMATES AND TABULATED STATEMENT UPON WHICH PRESENT ESTIMATE IS BASED.

Inasmuch as the final estimate of the cost of Lock and Dam No. 1, Osage River, as submitted with the present revised project, is apparently largely in excess of previous estimates, it will be of interest to present a condensed summary of the earlier estimates.

ENG 97-248

The first of these estimates appears in Major Miller's project dated May 14, 1891. Lock.-Length over all, 339 feet 6 inches; length between quoins, 275 feet; width, 50 feet; lift, 8 feet 6 inches

Dam.-A timber and rock structure of 11.5-feet lift.

Cost of lock and dam, $187,244.

This project was modified somewhat on the recommendation of General Comstock, and the above estimate was increased to $200,000 (Annual Report Chief of Engineers, 1892, p. 1742).

The first important revision of this estimate occurred in 1894, when the whole subject of the Osage lock and dam was exhaustively reviewed by a committee of the Missouri River Commission, consisting of Major Allen, Corps of Engineers, and Mr. R. S. Berlin, in a report to the Commission dated September 22, 1894. (Published in minutes of Commission meeting of November 28, 1894).

The lock considered was to be of the following description:

A needle dam was also provided for. The following extract from the committees report will show their estimate of the cost of this work:

Estimated cost of the lock, including lock keeper's dwelling, etc., according to best information at present attainable, $216,000.

"The cost of the dam has not yet been figured, but it seems safe to assume that it will be sufficient to bring the total cost of lock and dam and appurtenances to about $300,000, though these figures may be modified one way or the other after proposals are received for building the lock."

This estimate does not seem to have been adopted by the Commission, because in the Annual Report the probable cost of the lock and dam is thus stated:

"Based on such data as we now have, it appears that the probable total cost of the lock and accessories will be about $190,000, and of the dam about $75,000, or a total of $265,000 as against the estimate of $200,000 submitted in 1892. For reasons above given this latter estimate could only be regarded as approximate."

The "reasons" here referred to relate to a preceding paragraph in the same report, viz:

"In November, 1894, a plane-table survey was made from the site selected for the lock and dam to a point about 30 miles above to ascertain the additional amount of land that would be overflowed, due to a stationary dam of 10.5-feet lift, should the river reach the highest recorded flood stage. The results of this survey showed that such a dam would, at the above stage, cause an additional overflow of 636 acres within the limits of the survey, or an increase of about 20 per cent in area of land flooded. In view of these results, the Commission decided, February 11, that a modification of the plans of the dam to provide for a stationary dam of less lift than 10.5 feet, and upon this a low, movable dam to bring the lift to 10.5 feet when raised, would be advisable. It is proposed during the current season to make a complete examination of the site of the dam, and to prepare new plans and estimates of cost in accordance with the above decision."

The dam provided for in the above $75,000 estimate was for a movable crest of only 24 feet lift, estimated to cost only about $11,000, and was in no sense a comprehensive project such as was contemplated in the report of the committee above referred to.

In January, 1895, an additional estimate was prepared for a movable dam, the type considered being the Chanoine wicket. This estimate was $182,500. Substituting this figure for $75,000 would give, as the estimated cost of the lock and a movable dam, $372,500. It will thus be seen that no estimate for a lock and a movable dam of any comprehensive pattern has ever been below $300,000. None of these estimates, however, were ever acted upon.

Subsequent to the date of the Annual Report for 1895 it developed that the foundation of the lock would have to be lowered about 5 feet for reasons fully explained in the present revised project and accompanying papers. As nearly as can be determined from the correspondence on the subject, an estimate of the additional cost which this change of plan would involve was about $45,000. With this additional cost the foregoing estimates of $300,000 and $372,500 would become $345,000 and $417,500, respectively.

The changes authorized in the partial project approved by the Chief of Engineers November 23, 1896, viz, a diminution of the size of the lock and a substitution of concrete for rock masonry in its construction, as well as the proposed adoption of a less expensive type of dam, will materially reduce the above estimated cost. The