tion. It will only be practicable to use masonry for the piers and abutments of a truss bridge. A wooden bridge is objectionable for many reasons. It would not be durable, and in spite of any protection from the weather would require frequent renewal and almost constant expenditure. In a few years the spans would have to be replaced, as has been found necessary on the Long Bridge. It would be liable to be burned at any time, and this danger will be increased from the proximity of the railroad. The Government is now replacing the wooden superstructure of the Aqueduct Bridge with iron at an expense of about $100,000, and this would appear to be a good reason why it should not undertake the construction of a wooden bridge across the Eastern Branch. An iron bridge resting on masonry piers possesses the essential requisites of durability and strength, and will be found in the end the most economical bridge that can be constructed. Such a bridge will meet all the public needs, will be creditable to the city as an engineering structure, and is recommended as the most approved and satisfactory form of construction that can be employed.

WIDTH OF BRIDGE.

The great increase of travel on the Navy-Yard Bridge within the past few years indicates that a similar increase may be expected on a bridge built at Pennsylvania avenue. The cost of the bridge, however, increases very rapidly when the width is increased. Pennsylvania avenue is 160 feet wide, and the bridge ought to have a width which is in some degree commensurate with the character and dignity of such a thoroughfare; but this is impossible with the means at hand. It only remains to ascertain the least width which will accommodate travel in the immediate future. An ordinary carriage-way on a bridge should be from 8 to 9 feet wide; 18 feet between sideguard timbers is considered ample for two lines of ordinary travel. Where one sidewalk is used the width should be 6 feet. This gives a minimum width of 24 feet, and estimates on this basis have been made. It is not probable, however, that such a narrow bridge would meet the public needs. The roadway should be at least 24 feet wide to allow at times three lines of ordinary vehicles to be abreast, to allow room for passing loads of hay and wide vehicles used in this vicinity for the transportation of farm products, and also to give room for the management of horses who may be frightened by trains on the Baltimore and Potomac Railroad. A single sidewalk is objectionable, as pedestrians moving in one direction are inconvenienced by turning out for those moving in the opposite direction. Two narrower sidewalks, each 4 feet wide, would better accommodate travel. This would give a total width of 32 feet, and is believed to be as narrow a bridge as it would be advisable to construct.

COMPARISON OF THE SEVERAL LINES.

Pennsylvania avenue extended.

Line 4.-The length of this line, measured from the center of the circle on the Washington side to high-water mark on the eastern side, is 2,145 feet. The line crosses the stream diagonally, making an angle of about 46 degrees with the general direction of the stream. A skew bridge would therefore be required. The length over the channel is 450 feet. This line is the longest of the four surveyed and will be the most expensive. The principal objection to it lies in the fact that on the eastern side it soon runs into low and swampy ground, forming the valley of a small stream. The road leading from the bridge would be costly in construction, and the ground on either side could not be utilized for any purpose until the higher levels were reached. Other things being equal, it is undoubtedly desirable that the continuity of Pennsylvania avenue should be preserved. But, on the other hand, it may be stated that the avenue has already three different directions and a fourth would not be a serious matter if the change be made at a circle. Furthermore, it will undoubtedly be necessary to modify the line of the avenue in continuing it up the valley to the Bowen Road, as proposed, and in this event a change of direction at the circle would not be objectionable.

Line B.-This line bisects the angle of Pennsylvania and Kentucky avenues extended. Its length from the initial point to high-water mark on the eastern side of the river is 1,860 feet, which is about the same as line D. It does not cross the stream at right angles, and the skew is such as would make the cost per foot of an iron bridge greater than on any of the other lines. It appears to be the least desirable line, and no estimates for it have been made.

Line C.-This is the extension of Kentucky avenue, and crosses the Eastern Branch at right angles a short distance above the site of the old "Burnt Bridge," the piles of which may still be seen at low tide. In point of facility and economy of construction alone it is the best line that can be adopted. The piers and abutments would not need to be so long as for a skew bridge, the truss would be of the simplest construction,

and the length is of course less than on any other line, being 1,770 feet. It has, ho ever, these objections: The ground at the eastern approach is low. The Baltime and Ohio Railroad is about 160 feet from the end of the bridge, at a grade of 15.4 The railroad can be crossed at this level, with a slight modification in the graded the causeway of the bridge. For an over-grade crossing an expensive embankme will be required on the roadway and also for the bridge causeway. Moreover de direction of the bridge is not such as seems generally desired by the people ou the country side of the branch. Estimates for a bridge on this line have, however, beei prepared and are submitted below.

Line D.-This line is the one marked by a row of piles driven a year or two sin It deflects about six degrees to the south from the line of Pennsylvania avenue 6tended, and is the line on which citizens interested have requested by a petition th the bridge may be built. The ground for the eastern approach is more favorable thi on any of the other lines, involving less expense for the connecting road and pe mitting an over-grade crossing of the Baltimore and Ohio Railroad at the minica cost. A bridge built on this line would be a skew bridge, but the skew is such th the construction of an iron bridge of the spans required would not be unusually a pensive. The piers and abutments being on a skew will cost more than on line C. T length of this line (between the center of the Pennsylvania Avenue Circle and hi water mark on the southeastern side of the branch) is 1,910 feet. It seems to bea the whole the most favorable line for the bridge.

GENERAL PLAN OF BRIDGE.

The general plan of bridge on which the estimates are based is an iron Pratt trus deck-bridge, resting on masonry piers, with approaches of earthen embankment either end. The masonry abutments are designed to act as retaining-walls for th embankments, and are to be built on a pile and grillage foundation. The piers are s be of masonry, finished with a coping. Their widths vary with the length of ser and the skew, the minimum top width being 5 feet. They rest on a pile and grillag foundations (at low-water level) protected from scour by riprap.

With this arrangement the low-tide section on line C is reduced from 5,864 squar feet to 4,429 square feet, and the high-tide section from 10,388 square feet to 7,54% reduction of about 25 per cent. As the velocity of the current will be considera increased in the channel, an estimate has been made for building the channel-pel. which carries heavy 150-foot spans, by means of a coffer-dam, the pile and grill foundation being at the level of the bottom. Should a draw be built hereafter, to method of constructing the pier will be necessary. The trusses have been estima to carry a live load of 100 pounds per square foot for the spans of 100 feet or less, a 90 pounds per square foot for 150-foot spans.

The floor system is designed to carry a steam road-roller of 15 tons weight. A able iron railing is provided for.

ESTIMATE OF THE COST OF A BRIDGE THIRTY-TWO FEET WIDE ON LINE D, DEFLECTIS SIX DEGREES SOUTH FROM PENNSYLVANIA AVENUE EXTENDED.

Retaining-wall, western approach

Embankment, 2,000 cubic yards, at 25 cents.

Span over Baltimore and Potomac Railroad

Three 85-foot spans, at $3,600

Three piers, at $3,100.

Two piers, at $3,500

One channel-pier, at $9,000

Two 150-foot spans, at $9,000.

Seven piers, at $3,100..

Eight 100-foot spans, at $4,400.

Retaining-wall, eastern approach.

37,000 cubic yards embankment, at 30 cents

1,200 square yards slope paving, at $1.25

Contingencies, 10 per cent......

Total....

$12,00

10,

7,0

18.0

21,7

35.2

20.9

11.1

1,3

157,9

15,7

173,

ESTIMATE OF THE COST OF A BRIDGE TWENTY-FOUR FEET WIDE ON LINE D, EIGHTEE

FOOT ROADWAY, ONE SIX-FOOT SIDEWALK.

Retaining-wall and abutment, western approach..

Embankment, 2,000 cubic yards, at 25 cents..
Span over Baltimore and Potomac Railroad
Three piers, at $3,100.

$125

1,4

ESTIMATE OF THE COST OF A BRIDGE THIRTY-TWO FEET WIDE ON LINE C (KEN

If the channel-pier is built on piles and grillage at low water, the above estimates will be reduced about $4,000. The estimates are based on the prices of iron at this date. Any advance in the price of iron would increase the cost of the bridge. The cost of earth work is based on the price at which persons interested in the bridge state that they will do this part of the work.

Respectfully submitted,

Ccl. PETER C. HAINS,

JOHN B. DUNCKLEE,
Assistant Engineer.

Corps of Engineers, U. S. A.

PROCEEDINGS AND REPORT OF THE BOARD OF ENGINEERS CONVENED BY SPECIAL ORDER NO. 61, HEADQUARTERS CORPS OF ENGINEERS, U. S. A., WASHINGTON, D. C., JUNE 6, 1887, TO CONSIDER THE SUBJECT OF BRIDGING THE EASTERN BRANCH OF THE POTOMAC AT WASHINGTON, DISTRICT OF COLUMBIA.

The Board met at the office of Lieutenant-Colonel Hains, Corps of Engineers, June 10, when the letter of instructions from the Chief of Engineers, dated June 6, 1887, was read, and also report of Colonel Hains, with accompanying papers, covering the questions of survey, location, plans, and cost of the proposed structure. On the following day the Board reassembled and visited the site of the contemplated bridge, and on the second day thereafter, Sunday intervening, it again met in session, when, after a full discussion, the conclusions and recommendation set forth in the following report were agreed upon. At the several meetings all the members and the recorder were present. C. McD. TOWNSEND, Lieutenant, Corps of Engineers, Recorder.

JOHN M. WILSON,
Lieut. Col. Eng's, Col., U. B. A.,
Senior Member of the Board.

REPORT.

WASHINGTON, D. C., June 15, 1887.

The Board, having given most careful consideration to the subject, has the honor to submit the following report:

The act under which the work is to be done directs the Secretary of War to cause the construction of a wooden, iron, or masonry bridge, with necessary approaches, at a cost not to exceed $110,000, after making a survey to determine the length, width, and height of said bridge.

The location of the proposed bridge recommended by LieutenantColonel Hains, in his report to the Chief of Engineers, dated May 31, 1887, is approved by the Board. The axis of the bridge so located will make an angle of about six degrees to the southward with the line of Pennsylvania avenue extended; will be 1,705 feet long between highwater lines, with approaches about 530 feet long; making the total length of the bridge and approaches about 2,235 feet.

The Board also concurs with Colonel Hains in the opinion that the width of the bridge should not be less than 32 feet.

The height of bridge recommended by the officer in charge of the work places the roadway at an elevation of 35 feet above mean low tide, in order to make sufficient head-room for an over-grade crossing of the Baltimore and Potomac Railroad. The Board approves of this height for the further reason that the necessary height of piers and truss would place the roadway of a deck-bridge at substantially that eleva tion.

Colonel Hains in his report raises the question whether the expense of crossing the tracks of the Baltimore and Potomac Railroad should not be borne in whole or part by the railroad company. Considered only as a legal question, this Board is not qualified to give an opinion, but must leave its determination for the consideration of the proper legal officer or tribunal, if such determination be deemed necessary, but the Board would remark that this crossing is a part of the neces sary approaches to the bridge, and that Congress included the cost of these approaches in the act of appropriation; further, it is very doubtful whether the charter restriction, which forbids the obstruction of any "established road, street, or other way" in the construction of the railroad, has any application in this case, for it is not at all clear that Pennsylvania avenue at the point of crossing was in fact an “estab lished way "when the road was constructed.

The Board has no detailed plan of bridge before it for consideration, nor does it understand that it can fix upon any particular plan, inasmuch as the law requires that after determining the "length, width, and height" of the proposed bridge, the Secretary of War shall there upon advertise for plans and prices" for its construction. The Board is of the opinion, based on estimates submitted in Colonel Hains's report, that advertisement for the construction of a bridge (located on the proposed line), in which the material of the frame and its supports shall be iron and stone, the clear width of structure not less than 32 feet and height of roadway above low water 35 feet, will bring out bids for the work within the limits of the appropriation.

In accordance with the foregoing views the Board has the honor to recommend that advertisment for plans and prices of a bridge that shall conform to the general requirements indicated above be now

prepared and published, as required by the act approved February 23, 1887.

JOHN M. WILSON,

Lt. Col. Engineers, Col. U. S. Army.

G. J. LYDECKER, Major Engineers, U. S. A.

I concur fully in the above report, but I recommend that the question whether the Baltimore and Potomac Railroad Company can be required to pay all or part of the expense of crossing that road be submitted to the law officers of the Government. There may be laws of Congress bearing on the subject of which I have no knowledge.

To the CHIEF OF ENGINEERS, U. S. A.

PETER C. HAINS, Lieut. Col. of Engineers.

J 5.

IMPROVEMENT OF SHENANDOAH RIVER, WEST VIRGINIA.

Congress, by act of June 14, 1880, made an appropriation of $15,000 for improving the Shenandoah River, West Virginia. By act of March 3, 1881, an additional appropriation of $2,500 was made for the same object. A proviso was added to the latter act, to the effect that neither of these appropriations shall be expended "until any corporate rights or franchises that may exist over said river shall have been relinquished to the United States, to the satisfaction of the Secretary of War." This condition has been complied with.

The project for the improvement has for its object the rebuilding of the locks, dams, and chutes of the navigation company, so as to secure a down-stream navigation of about 18 inches. At the present time there is practically no commerce to be benefited by this improvement, and whether any would be built up by it is a question. Congress, by act of July 4, 1884, sold the sites of the lower docks that would be needed in this improvement, and with them all the water privileges at Harper's Ferry.

No work has been done during the past year and it seems questionable whether any should be undertaken. In my last annual report the attention of Congress was called to the necessity of further legislation, if the work is to be done.

July 1, 1886, amount available
July 1, 1887, amount available..

Money statement.

$16, 083. 40 16,083.40