fully met by a steel-truss bridge resting on masonry piers, the bridge to be a deck bridge, except where it crosses the Baltimore and Potomac Railroad, where a through span will be required.

Plans are submitted for such a bridge, with fixed spans and having a total length, including approaches, of 2,517 feet, and width of 52 feet between railings, and the cost of its construction is estimated to be $441,208. The plans provide accommodations for ordinary highway traffic and for street-car tracks, as required by the law; also for the construction of a draw, should one be required in the future.

The estimated cost of a bridge with a draw (swing span on a pivot pier) is $476,843, but the necessity for a draw is not now apparent. Very respectfully, your obedient servant,

JOHN M. WILSON,

Brig. Gen., Chief of Engineers,
U. S. Army.

Hon. R. A. ALGER,

Secretary of War.

REPORT OF LIEUT. COL. CHAS. J. ALLEN, CORPS OF ENGINEERS.

UNITED STATES ENGINEER OFFICE, Washington, D. C., November 29, 1897. GENERAL: I have the honor to submit the following report upon a survey, plan, and estimate of cost of a bridge across the Eastern Branch of the Potomac River, in line with Massachusetts avenue extended eastward, made in accordance with the provisions of act of Congress of February 17, 1897. The act in full is as follows:

[Public-No. 70.]

AN ACT to authorize a survey for construction of a bridge across the Eastern Branch of the Potomac River, in line with Massachusetts avenue extended eastward.

Be it enacted by the Senate and House of Representatives of the United States of America in Congress assembled, That the Secretary of War be, and he is hereby, authorized and directed to cause to be made, as soon as practicable, a survey, plan, and estimate of the cost of constructing a substantial wooden, iron, steel, or masonry bridge across the Eastern Branch of the Potomac River, in the District of Columbia, and the necessary approaches thereto, such bridge to begin for its westward end at a suitable point on the Government reservation in line with Massachusetts avenue extended eastward, and extending thence across the said river to a suitable point in the line of Massachusetts avenue extended, for its eastern end, such bridge when constructed to be maintained as a free bridge for travel, and to be of such strength and dimensions as to accommodate the ordinary traffic which passes over an ordinary highway, and also the tracks and traffic of any street railway or railways employing horses or electric or mechanical motors (not steam-operated motors) for the propulsion of its cars, which may hereafter be granted the right to cross such bridge by the authorities vested with such power, and to report thereon to the Congress of the United States on the first Monday of December, eighteen hundred and ninety-seven; and that the sum of three thousand dollars be, and the same is hereby, appropriated, out of any money in the Treasury not otherwise appropriated, for such survey, plan, and estimate, and such contingencies as are necessarily incident thereto, such sum of money to be immediately available upon the passage of this act. Approved, February 17, 1897.

The act fixes the line of the proposed bridge.

The duty of making the survey, plan, and estimate provided for by the act was assigned to my charge by letter of March 9, 1897, from the Chief of Engineers.

LOCALITY.

The existing eastern terminus of Massachusetts avenue is at Nineteenth street east, at the western boundary of reservation 13, which is

occupied by the District jail, almshouse, workhouse, etc. The line of the avenue extended eastward would pass through this reservation, and in crossing the Eastern Branch (Anacostia River) would also cross the trestle bridge of the Baltimore and Potomac Railroad near the southern end of the yard known as Bennings Railroad Yard. The line, as it crosses the river, is about 3,200 feet above the Pennsylvania Avenue Bridge aud about 6,200 feet below Bennings Bridge, both of which are highway bridges, the former, built in 1889, having a superstructure of wrought iron, and the latter, built about 1892, having a steel superstructure.

The length of the Eastern Branch from its mouth to Bennings Bridge, which is at the eastern boundary of the city, is 4 miles. About 2 miles above the mouth the river is spanned by the Navy-Yard Bridge, which has a draw about 30 feet wide. There are at present, then, four bridges spanning the river within the limits of the city, but one of which has anything like a draw.

SURVEY.

The field work of the survey was commenced early in June. The center line of Massachusetts avenue was run between Nineteenth street east and the Anacostia road, on the east side of the river. Stations were established on this survey line at intervals of 100 feet. The various buildings on the Workhouse reservation and near the line of survey were located and noted on the general map accompanying this report. The shore lines of the river were located above and below the line of survey for a total distance of about 1,100 feet. The distance across the river on the line of survey was determined by triangulation and checked. The intersection of the survey line with the center line of the Baltimore and Potomac Railroad, and the direction of that road and the location of the trestle bridge and embankment on which it crosses the river were determined, as were also the intersection of the survey line with the Sheperds Branch of the Baltimore and Ohio Railroad. Levels were taken along the line of survey, on both sides of the river, at intervals of 100 feet and at intermediate points wherever additional levels were needed to show the configuration of the ground. These levels were referred to the established datum of mean low tide in the Potomac River, and are shown on the profile accompanying this report.

Cross sections were taken to the right and left of the center line, to supply the data needed for estimates of the amount of embankment required for approaches to the proposed bridge.

Soundings were taken of the river along the survey line and also on additional cross lines within limits of about 500 feet above and about 500 feet below the center line of the avenue, in order to ascertain the existing depths in the channel and determine its contours and direction, as well as to ascertain the depths on the flats bordering the channel. These soundings were reduced to the same datum of mean low tide in the Potomac River. A part of the soundings taken are shown on the accompanying general map, the scale of the map limiting the number which could be plotted.

TEST BORINGS.

In order to determine the character, depth, and thickness of the strata underlying the river bed, a series of test borings was made. This work was done by contract.

Eight borings were made along the center line of Massachusetts avenue extended, within the proposed limits of the bridge. On the

westerly side of the Baltimore and Potomac Railroad test borings were made at intervals of 150 feet. On the east side of the railroad the interval was somewhat greater, but did not exceed 250 feet. The depth of the borings ranged from 47.5 to 72.4 feet, the total depths of borings being as follows:

The stratum first underlying the river bed was in all cases soft river mud, which varied from 16 to 30 feet in thickness. Beneath the mud, gravel, sand, and clay were found in strata of varying thickness. At depths of from 37 to 52 feet a stratum of compact red clay was found which will afford bearing ground for piles and in which most of the borings were terminated. The results of the test borings are shown graphically in a longitudinal section of the channel on the general elevation of the proposed bridge, and are also given in detail in the following statement:

Record of boring made for proposed bridge across the Eastern Branch on line of Massachusetts avenue extended.

[On survey line of center of Massachusetts avenue.]

FUTURE IMPROVEMENT OF THE EASTERN BRANCH (ANACOSTIA RIVER). Congress has by affirmative legislation in previous years provided for examinations and surveys of this river with a view to improvement for navigation as well as for reclamation of its flats. The river and harbor act of September 19, 1890, contained an allotment of $20,000 for improvement of the river, which sum was applied to dredging channels 20 feet deep and about 200 feet wide through shoals near the foot of South Capitol street and off Greenleaf or Arsenal Point.

This legislation would seem to indicate that Congress had in contemplation, more or less, the subject of improvement of this stream.

It hardly seems probable that that portion of the river above the bridge of the Baltimore and Potomac Railroad Company will need improvement of its navigation for many years to come, but when the demand is made for it there will be a necessity for a suitable draw in this bridge, as well as in all the other bridges, Bennings Bridge probably excepted.

Under the provisions of the act of September 19, 1890, harbor lines were established in 1892 by the Secretary of War between the mouth of the Eastern Branch and the Pennsylvania Avenue Bridge, about 23 miles above the mouth. The established width between the bulkhead lines, above the Navy-Yard Bridge, is 900 feet, the distance between the wharf lines being 700 feet.

Consideration has been given to the location and direction of harbor lines between the Pennsylvania Avenue Bridge and Bennings Bridge with reference to the most desirable position for such lines at the crossing of Massachusetts avenue. It seems practicable to give the lines at this locality a direction normal to the line of the bridge, substantially as indicated on the general map. The distance between bulkhead lines is assumed at 900 feet, the same width as that provided between the Pennsylvania Avenue and the Navy Yard bridges, as all considerations point to the desirability of contracting the space for tidal flow as little as possible.

CHARACTER OF BRIDGE.

The general character of the bridge structure which, with due regard to considerations of utility and economy, seems to be required at this site, is determined largely by the existing local conditions to be met. The ground on the west side of the river is high, while on the east side, although of less elevation, it rises gradually toward the high ridge which bounds the Anacostia Valley on the east. The tracks of the Baltimore and Potomac Railroad must be crossed by the proposed bridge over grade, in order to avoid danger and liability to accidents. From an examination of the profile accompanying this report it will be evident that the grade of the roadway of the bridge must be at a considerable elevation above the surface of the river.

In case of future improvement of the river at the site of the bridge, to afford depths sufficient for large vessels, a draw of sufficient capacity will be needed in the bridge, and provision should therefore be made or indicated for one in planning the structure.

If, however, the navigation of the river at the bridge is to be limited to flatboats or other small craft, the proposed elevation of the bottom chord of the structure and the clear widths between piers provided in the plan herewith will doubtless suffice.

In view of the fact that the Pennsylvania Avenue Bridge and the greater length of the trestle bridge of the Baltimore and Potomac Railroad, both below the line of Massachusetts avenue extended eastward, are without draws, and that Bennings Bridge, above the line of Massa

chusetts avenue, is also without a draw, the question may be asked why a draw should enter into the consideration of the plan for the proposed bridge.

If the bridge above and the bridges immediately below the proposed structure are to remain without draws, then, of course, it would be useless to provide for a draw for the proposed bridge.

It is understood that it was the desire at the time the Pennsylvania Avenue Bridge was built to provide a draw for that bridge, but that the funds available were not sufficient to admit of constructing one.

While the trestle of the Baltimore and Potomac Railroad has no draw, an opening of 35.5 feet in width has been left in it, and apparently with a view to one in case it should ever be required.

As to the material for the bridge, large wooden bridges have so passed out of use in all except remoter sections of the country where timber is still abundant and cheap, and are so liable to destruction by fire, and so lacking in the important element of durability, that the construction of such a bridge at this date for the Eastern Branch of the Potomac River can not be recommended.

A masonry bridge at this point would necessarily be an arched structure, and would admit of the consideration of architectural effect, but it would involve increased elevation for roadway, due to crossing the line of the Baltimore and Potomac Railroad, and would be more expensive than a steel truss bridge, and without compensating advantages. In addition, its piers would contract the area of waterway more than would the piers for a steel truss bridge, and should a draw ever be required it would, of course, have to be of material different from the rest of the bridge.

Wrought iron is now but little used for structural purposes; for bridges it has given way to steel.

The use of steel arched girders enables a combination of substantial results with pleasing architectural features, but they would not be as economical in the present case as a truss with horizontal bottom chord, and the introduction of a draw (swing) in such a bridge would call for the construction of heavy abutments on each side of the pivot pier. The swing is here mentioned for the reason that it is the usual form of draw in bridges.

The site of the proposed bridge, however, is not such as to demand extensive outlay with a view to architectural effect. The bridge should be suited to the service demanded of it. It will be essentially a traffic bridge.

In view of the foregoing, it is believed that the conditions of the locality and the requirements of the act will be most fully met by a steel truss bridge resting on masonry piers, the bridge to be a deck bridge, excepting where it crosses the Baltimore and Potomac Railroad, where a through span will be required. The general features of the proposed bridge as designed by this office are as follows:

SPANS.

The deck spans and the through spans are to be each 144 feet long from centers of end pins, excepting that one span, capable of being converted into a drawspan when necessary, is to have a length of 180 feet between centers of end pins.

WIDTH.

The act requires that provision be made for a street railway, and, as the electric street railway with an underground or subway conduit is the most perfect system yet devised for running electric street railway