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Abstract of proposals for reconstruction of Pier No. 4 of the Aqueduct Bridge, District of Columbia, opened by Lieut. Col. Chas. J. Allen, Corps of Engineers, April 30, 1897.

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NOTE.-The bid of R. H. Hood was not made in accordance with printed form.

The contract was awarded to the Houston Construction Company, the lowest bidder. Date of contract, May 17; approved May 28, 1897. Date of commencement, on or before May 30; date of completion November 1, 1897.

APPENDIX A A A.

WASHINGTON AQUEDUCT AND INCREASING THE WATER SUPPLY OF WASHINGTON, DISTRICT OF COLUMBIA.

REPORT OF CAPT. D. D. GAILLARD, Corps of ENGINEERS, OFFICER IN CHARGE, FOR THE FISCAL YEAR ENDING JUNE 30, 1897.

1. Washington Aqueduct.

2. Increasing the water supply of Washington, D. C.

OFFICE OF THE WASHINGTON AQUEDUCT,

Washington, D. C., July 17, 1897.

GENERAL: I have the honor to forward herewith the annual reports for Washington Aqueduct and increasing the water supply of Washington, D. Č., for the fiscal year ending June 30, 1897,

Very respectfully, your obedient servant,

Brig. Gen. JOHN M. WILSON,

D. D. GAILLARD, Captain, Corps of Engineers.

Chief of Engineers, U. S. A.

A A A 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 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

3991

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 3 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 devolves upon the water department of the District of Columbia.

In addition to the three reservoirs already mentioned, which form a part of the aqueduct system, there is another reservoir, built and con

trolled by the Commissioners of the District of Columbia, called the Fort Reno reservoir, with a capacity of about 4,500,000 gallons, the reference of its water surface when the reservoir is full being about 420 feet.

This reservoir, like the high-service reservoir in Georgetown, is supplied with water taken from the supply mains by the U street pump.

The Dalecarlia and distributing reservoirs supply this station and that part of the District which lies below 100 feet above datum. The areas lying between the levels of 100 and 210 feet above datum are supplied by pumping from the U street station directly into the distributing mains, the Georgetown high-service reservoir being held as a reserve supply. The areas having a greater elevation than 210 feet above datum are supplied from the Fort Reno reservoir.

It will be observed, therefore, that the total present storage capacity of all reservoirs is a little less than 307,000,000 gallons, or about seven days' normal supply.

Until the average daily consumption of water becomes considerably greater than at present, the reference of the surface of the water at the lowest stage of the Potomac will be about 151 feet at the mouth of the feeder at Great Falls, about 146.75 feet at the Dalecarlia reservoir, and 146 feet at the distributing reservoir.

From August 17 to November 16, 1896, Maj. Charles J. Allen, Corps of Engineers, was in temporary charge of the Washington Aqueduct and its accessory structures during my absence on duty in Alaska.

The following statement shows the operations upon the aqueduct and its accessory works during the fiscal year and their condition at its close:

GATEHOUSES, WATCHMEN'S QUARTERS, AND OTHER BUILDINGS.

The watchman's house at the Dalecarlia Reservoir was furnished with a new roof and a complete set of new window shutters. The laborer's house at the same reservoir was extensively repaired throughout. The engine house on the Virginia shore at Great Falls was provided with a new felt roof.

The four gatehouses at the Dalecarlia and distributing reservoirs, and the house over the entrance to the valve chamber at the latter, which had become much discolored and weather-stained, were covered with a wash of Portland cement, which greatly improved their appearance. All other buildings were repainted or whitewashed, and such minor repairs as were necessary for their proper preservation were made.

THE RESERVOIRS.

The improvement of the Dalecarlia Reservoir was completed under the supervision of Col. George H. Elliot, United States Corps of Engineers, retired, on November 15, 1895, with the exception of the acquirement by condemnation of a small piece of land, four hundred and eight one-thousandths of an acre, the property of John P. Hickey, proceedings for the acquirement of which were in progress at the close of the last fiscal year. These proceedings were completed early in the present fiscal year and the award was paid to Mr. Hickey on September 5, 1896.

The works were designed to divert from the reservoir the drainage from a watershed of about 3,825 acres, which drainage had so polluted its waters as to cause the reservoir to be thrown out of service in the spring of 1888.

This drainage formerly entered the reservoir by three streams, Little Falls Branch, Mill Creek, and East Creek, with drainage areas of about 2,700, 900, and 225 acres, respectively.

The plan of improvement adopted consisted in constructing dams across these streams just above their mouths, and carrying the waters of East Creek by an open intercepting channel around the margin of the reservoir into Mill Creek above its dam, from which point by a similar and proportionally longer channel around the reservoir and a short tunnel through a hill the drainage of the two streams and the slopes adjacent to the open channels were carried into Little Falls Branch above its dam.

The drainage of the entire watershed, thus collected, was carried into a shaft 51 feet deep, excavated in the bed of the latter stream. From the bottom of this shaft a tunnel 1,000 feet long and 7 feet in diameter carries the water under Dalecarlia Hill to its former course leading into the Potomac River.

These works are in excellent condition, are very sightly in appearance, and effect perfectly the object for which they were designed.

A large number of trees blown down in the storm of September 29, 1896, near the northwest shore of this reservoir were cut up and removed, and the underbrush, leaves, and straw around the borders of the reservoir have been burned or carted away. Some of the more irregular banks of this reservoir were graded and the excess of materials used in filling the few shallow, marshy portions of the reservoir.

The unsightly spillway was extensively repaired and its appearance much improved thereby. A gauging weir for computing the overflow of the spillway was constructed in the channel beneath the wooden bridge. A boathouse in course of construction near the south connection of the reservoir will afford much needed protection for the boat used in operating the works at this reservoir.

An iron hand rail was placed around the shaft at the Dalecarlia Reservoir as a measure of precaution against accidents.

About 800 feet of the wooden fence around the distributing reservoir damaged by the storm of September 29, 1896, was repaired, and a number of ornamental plants and grasses were set out around the borders of the reservoir.

During the past three months the fences around both reservoirs have been extensively repaired and all of them have been whitewashed.

All cracks in the bottom and along the sides of the high-service reservoir in Georgetown were plastered up, and the interior surface was carefully covered with several washes of Portland cement to prevent exfiltration. The exterior was much improved in appearance by two washes of Portland cement over all masonry and two coats of paint on all ironwork of the reservoir and on the iron fence surrounding it.

During the past year, not including the few. occasions when the water was lowered by the supply being shut off for the purpose of repairs or of removing deposits from the conduit, the extreme fluctuations of the level of the water in the distributing reservoir had a range of but 1 foot as against 1.80 feet for the preceding year and 4.1 feet in 1894-95, the corresponding heights being as follows:

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