LETTER OF MR. JOHN MEIGS, JR., INSPECTOR.

WASHINGTON, D. C., February 27, 1901. COLONEL: The recent examination of the piers of the Aqueduct Bridge by diver developed the fact that some of them are in very bad condition, and the advisability of early repairs to them is apparent.

The cavities, in themselves, are not large enough at present to endanger the actual stability of the piers, but the extent to which and the rapidity with which they may enlarge under the eroding influence of any flood, it is impossible to predict.

These cavities are none of them of very large size, as compared with those repaired in 1894, the largest being of less than 10 cubic yards in content, but the masonry overhanging them is in a decidedly precarious position, the strength of the mortar and the interlocking of the stones with each other alone keeping them in place, and unless some steps are taken to prevent the progress of this undermining process, it may extend indefinitely.

The only practicable way of filling in these holes is by the usual method of concrete in bags placed by a diver and built up by him into a rough semblance of

masonry.

The larger cavities, which may be filled in in this way, were found in piers 6 and 8, with smaller ones in piers 1 and 5, the total contents of them being nearly 25 cubic yards.

In the case of pier 5, and in lesser degree pier 8, it is not so much the actual amount of the missing masonry to be considered as it is the general bad condition and apparent looseness of it which is alarming.

It is difficult to see how this condition can be remedied at this late date in any way except by entire reconstruction.

Had the piers been thoroughly riprapped at the time of their construction, it might possibly have prevented the erosion of mortar from the joints, assuming that they were originally full, but at the present time to do this as a protective measure would be of very doubtful utility.

To adequately riprap pier 5, for instance, would require from 800 to 1,000 cubic yards of stone. This method would be deplorable, if followed for all of the piers, in the first place because of the consequent reduction of the already too small cross section of the river at this point, and secondly, as adding considerably to the difficulties of the future repair work which will inevitably have to be done in time.

I would therefore recommend that the cavities in the piers large enough to be treated in this way be filled in with concrete in bags and that only as much riprap as is necessary to cover these repairs be placed around them.

As nearly as I can estimate, this would require about 25 cubic yards of concrete and 125 cubic yards of riprap.

Very respectfully,

Lieut. Col. CHAS. J. ALLEN,

JOHN MEIGS, Jr., Inspector.

Corps of Engineers, U. S. A.

BBB 2.

MEMORIAL BRIDGE ACROSS POTOMAC RIVER AT WASHINGTON, DISTRICT OF COLUMBIA.

There are no operations to report for the year ended June 30, 1901, construction of the bridge not having as yet been authorized by Con

gress.

The specifications and estimates accompanying the competitive design which was selected as the most suitable (Design No. 2, by Mr. Burr are full, explicit, and clear. The estimate is as close as can be expected of an advance estimate for a large work of that kind. The plans, sec tions, profiles, and details (twelve in number) are in good shape for In case of an appropriation for this much-needed bridge, there will be nothing, so far as known, to prevent a prompt commencement

use.

of the work, including the preparation of materials, special detail drawings, such borings at the precise sites for piers and abutments as a prudent constructor would make, notwithstanding that a full survey, including borings, had previously been made, etc.

Money statement.

July 1, 1900, balance unexpended

June 30, 1901, amount expended during fiscal year

July 1, 1901, balance unexpended

ENG 1901-229

$227.24

6.54

220.70

APPENDIX C C c.

WASHINGTON AQUEDUCT, INCREASING THE WATER SUPPLY OF WASHINGTON, D. C., AND WASHINGTON AQUEDUCT, D. C., FILTRATION PLANT.

REPORT OF LIEUT. COL. A. M. MILLER, CORPS OF ENGINEERS, OFFICER IN CHARGE, FOR THE FISCAL YEAR ENDING JUNE 30, 1901.

OFFICE OF THE WASHINGTON AQUEDUCT,

Washington, D. C., July 20, 1901. GENERAL: I have the honor to forward herewith the annual reports for Washington Aqueduct, increasing the water supply of Washing ton, D. C., and Washington Aqueduct, D. C., filtration plant. Very respectfully, your obedient servant,

A. M. MILLER,

Lieut. Col., Corps of Engineers.

CCC I.

WASHINGTON AQUEDUCT.

Appropriations for the Washington Aqueduct are applied to the improvement, maintenance, and repair of all of those parts of the water supply that have been placed under the supervision of the Chief of Engineers, except the new reservoir near Howard University and the tunnel connecting it with the distributing reservoir. These are the masonry dam across the Potomac at Great Falls, the works there for regulating the supply to the conduit, the Conduit road from Great Falls to Washington, a distance of about 14 miles, the conduit from Great Falls to the distributing reservoir, the three reservoirs for supplying the city, the mains for delivering water from the reservoirs into the city's distributing system, and the two bridges for carrying the mains across Rock Creek.

The water supply is taken from the Potomac River at Great Falls, about 14 miles above the city.

At this point a masonry dam extends across the river from the Maryland to the Virginia shore. Its total length is 2,877 feet, and the width of its crest in the Virginia channel and across Conns Island is 8 feet 3 inches and in the Maryland channel 7 feet 9 inches. In 1895-96 the crest of the dam was raised from a reference of 148 feet above mean

tide at the Washington Navy-Yard to 150.5 feet above the same datum plane.

The top of the mouth of the feeder of the conduit at Great Falls is at a reference of 149 feet and the bottom at a reference of 139.5 feet. The water passes from the feeder through the gatehouse and into the conduit, which at this point has a reference of 152 feet at the interior surface of the crown of the arch.

The slope of the conduit is uniform between the gatehouse at Great Falls and the distributing reservoir and is 9 inches in 5,000 feet.

The conduit is circular in cross section, and for the greater part of its entire length is 9 feet in diameter and composed either of rubble masonry plastered or of three rings of brick, but where the soil in which it was built was considered particularly good the inner ring of brick was omitted and the diameter is 9 feet 9 inches. Where the conduit passes as an unlined tunnel through rock, the excavation was sufficient to contain an inscribed circle 11 feet in diameter.

The lengths of the conduit and its connections are as follows:
Length of feeder at Great Falls, 256 feet.

Area of cross section at mouth, 157.45 square feet.

Length of conduit between gatehouse at Great Falls and north connection of Dalecarlia Reservoir, 47,896.5 feet; least diameter, 9 feet. Length of by-conduit around Dalecarlia Reservoir, 2,730.5 feet; diameter for 625 feet, 8 feet; for rest of distance, 9 feet.

Length of conduit between south connection of the Dalecarlia Reservoir and north connection of the distributing reservoir, 10,149.87 feet; diameter of conduit, 9 feet.

Length of by-conduit around the distributing reservoir, 2,274.35 feet; diameter, 7 feet.

At the distributing reservoir the water passes into 4 cast-iron mains 48 inches, 36 inches, 30 inches, and 12 inches in diameter, respectively. The Dalecarlia Reservoir has a storage capacity of about 150,000,000 gallons, is practically without paved slope wall, is perfectly protected against pollution from the drainage of the surrounding country, and is provided with a spillway, the reference of the bottom of which is 146.5 feet. The reference of the interior surface of the crown of the arch of the conduit at the north connection of this reservoir is 143.77 feet and at the south connection 143.39 feet. The distance between these points, measured along the line of flow of the water across the reservoir, is about 3,550 feet.

The distributing reservoir has a storage capacity of about 150,850,000 gallons and is divided by a puddled and paved wall, through which is a passageway which can be closed with stop planks, into two sections, containing 97,600,000 and 53,250,000 gallons, respectively.

The interior surface of the crown of the arch of the conduit at the north connection of this reservoir has a reference of 141.87 feet.

The Georgetown high-service reservoir is circular in plan and has an available capacity of about 1,500,000 gallons. The reference of its water surface when the reservoir is full is 220.5 feet. Although this reservoir is under the charge of this office, the duty of keeping it filled by pumping devolved upon the water department of the District of Columbia until it was taken out of service, November 17, 1897, at the request of the Commissioners of the District of Columbia, the Fort Reno reservoir and the pumping service having rendered its further use inadvisable except in case of emergency.