THE WASHINGTON AQUEDUCT.

THE WASHINGTON AQUEDUCT.

Captain Gaillard, of the United States Engineers, the officer in charge of the Washington aqueduct, has reported on the project for increasing the water supply of the District of Columbia by raising the height of the dam at Great Falls. This dam extends from the Virginia to the Maryland shore of the Potomac, crossing Conn’s Island. The reference of the crest of the original dam was 148 feet. It has been raised to a reference of 150.3 feet. The project of improvement involved removing the old coping stones, raising the height of the body of the dam two and one-half feet and resetting and bolting in place the coping stones; also strengthening the conduit to withstand the increased pressure caused by raising the dam. The stage of the river was so high that it was impossible to begin to begin laying the stone until April 20 last. Even then the depth of water pouring over the crest of the dam was over two feet. By the use of horizontal movable shutters and sand bags and by caulking to prevent the smaller leaks a cheap and efficient cofferdam was devised, by means of which the stone was finally laid against a head of over five feet on the dam. Riprap revetment was laid on the up stream side of the dam as a protection against ice. and about 199 cubic yards of this riprap were carried over the dam during the flood of October last.

To strengthen the conduit against the increased pressure which may be developed on account of raising the dam, the embankments in which the conduit rests were widened. In this work 9,780 cubic yards of material were put in place. The work of raising the dam and strengthening the conduit has been completed at a cost much below the original estimate. Capt. Gaillard says that, when all the outstanding liabilities have been settled, including the award to the Chesapeake and Ohio Canal Company, there will remain a surplus of about $23,000. The amount expended to the end of the last fiscal year was $52,266, leaving a balance available of $72,734, of which amount there has been since expended $33,340, leaving a balance on hand January 1, 1897, $39,394, against which there are outstanding liabilities of $15,475 leaving an unexpended balance of $23,919 January 1, out of the appropriation of $125,000 made by the act approved March 2, 1895.

Baltimore, Md., last year consumed water, as registered by meters and indicators, 2,201,725,200 gallons. Beer breweries used 441,907,000 gallons through meters; elevators, 710,606,000, whiskey distilleries, 48,945; hotels. 86,722. The rents for 1,220 meters and 410 indicators was $185,000; the total receipts from all sources aggregating $836,893.

The Washington Aqueduct.

The Washington Aqueduct.

The annual report of Col. G. H. Elliott to the chief engineer in charge of Washington city aqueduct, D. C., contains some interesting facts. It states that no damage was experienced during the past year to the masonry dam at Great Falls. Some of the rip rap back of the dam that was carried away by ice in previous years has not been replaced owing to inadequate appropriation for preservation and repairs of the rip rap, but a portion of the conduit was flushed several times during the year. An estimate of $14,000 was included in the last annual report of estimates for removing thirty years’ accumulation of deposits in the conduit, which was found on inspection in September, 1891, to be about 15,000 cubic yards, but this estimate has not yet been acted upon by Congress.

The deposits in tunnel No. 4 and the nine-foot by-conduit at the Dalecarlia reservoir have been pretty well cleaned out during the last two years by means of the small appropriations for repairs, but these appropriations are barely sufficient for the most urgent work required for controlling the supply of water to the city and the maintenance of the aqueduct system, including the conduit, the reservoirs and twenty-one miles of forty-eight-inch and other mains in the city. These appropriations cannot be relied on to complete the expensive work of removing the deposits by hand, and all that can be accomplished until a further appropriation be granted is by means of flushing to prevent further accumulation. This, however, requires the wastage of a large quantity of water that during the low stages of the river cannot be spared. . . .

The amount of water consumed and wasted in the city was measured at the distributing reservoir and found to be 38,853,529 gallons, or at the rate of 60,114 cubic feet per second. The sectional area of the nine-foot conduit is 63,617 feet. Experiments made May 1 show the mean velocity to have been .94489 foot per second. Then as the value of R for the Washington aqueduct is 2.25 feet, we find (according to the Chezy formula) we have C — 82.812. This experiment was made again June 20. The weather was very hot, and the consumption and waste in the city had increased to 46,727,108 gallons in twenty-four hours. By reason of Jhis heavy draft on the distributing reservoir its surface had fallen to 144.73 feet above datum. The slope of the water in the conduit had increased to .00006218, and the velocity through the conduit had increased to 1.14 feet per second. The value of C had therefore increased to 96.13. This and the result of the former experiment are much smaller than was anticipated, but after a careful leveling and horizontal measurement between the ends of the section of the tonduit under trial they appear to be correct. . . .

The repairs on the conduit road are the most extensive had for many years. It is to be regretted that the annual appropriation for the aqueduct does not permit greater expenditures for this purpose. On September 27, 1892, the consumption of water was 44,582,627 gallons. This was the largest measurement of the daily supply to Washington and Georgetown ever made, and it was accounted for by the extra flushing of the street mains by the district authorities on account of the cholera excitement and the presence in the city of the Grand Army of the Republic, but the measurement of the day ending at 8 A. M. June 22 of this year exceeded it, and was 46,727,30S gallons. The dates for measuring consumption and waste of water were quite irregular. . .

No complaints as to condition of the water except its turbidity. From 1874 to 1893 inclusive the daily consumption during the month of June in each year, was as follows: 1874, 17,555,848 gallons ; 1875,21,000,00c; 1876,24,177,797; 1877, 22,252 932; 1878, 24 885,945; 1879, 25,947,642; 1880, 25,740,138; 1881, 26,525,991; 1882. 29,727,864; 1883, 24,314.715; 1884, 24,827,118; 18S5. 25,219,194; 18S6, 25,542,476; 1887, 26,898,424; 1888, 29,115,774; 1889, 27,708,779; 1890,35,541,545 (in this year a 48-inch water main was added to distribution); 1891, 38,594,741; 1892, 41,161,780; 1893, 46,727,108.

Towards improving the receiving reservoir by works required for cutting off the drainage into it of polluted waters and sewage from the surrounding country. . . . To exclude from the reservoir all the drainage water that now runs into it from three streams, known as East creek, Mill creek and Little Falls branch, and the water that flows into the reservoir from the land lying contiguous and between those streams. . , . The combined area of the three water sheds, the drainage from which is to be provided for in the works contemplated, is assumed to be 3822 acres. . . . According to rainfall tables it is estimated that the discharge from the total areas of the three water sheds may be x 122 cubic feet per second. . . .

It is proposed to construct dams across East and Mill creeks and Little Falls branch, and open a paved channel from East creek around the reservoir to a point on Mill creek, around to the mouth of a short tunnel that will carry into Little Falls branch above the dam the combined waters of East and Mill creek, as well as the surface drainage contiguous to the reservoir and located between Mill creek and the efflux of the tunnel. A special provision is to be made for diverting from the reservoir by means of small paved ditches the water discharged from all that part of the little peninsula lying between the lower end of the reservoir and the Little Falls branch, that is outside the portion of the peninsula that must be purchased or condemned. . . .

The receiving shaft, or well, that is to receive all the drainage of the water shed is to be on the right bank of Little Falls branch, above the dam. . . . It is to be ten feet in diameter and fifty-six feet in depth, to be lined with brick, backed by concre;e. From above the water cushion at the bottom of the well there will be run under Dalecarlia Hill and below the Washington aqueduct, a tunnel that will conduct the drainage into an open channel, thence to the lower portion of Little Falls branch. A brick circular conduit will be built in the tunnel seven feet in diameter, having a grade of thirty-one feet in 100 feet. Two reasons have governed the engineer in fixing this grade. It will pass the drainage tunnel as far under aqueduct tunnel No. 4 as practicable. From the north connection, for a distance of 163 feet, aqueduct tunnel No. 4 is lined with brick, and for a further distance of thirty one feet it is lined with rubble stone ef not very good quality, but from here, from within a few feet of the point of crossing below the aqueduct tunnel of the line of the drainage tunnel, the aqueduct tunnel is not lined. It is a great misfortune that General Meigs did not completely line aqueduct tunnel No. 4, for although the rock is fairly good, I found when I emptied the conduit between Great Falls and the distributing reservoirs and inspected it in September, 1891, that there had been several slides from the roof and sides of the tunnel. A serious one, if it ever occurs, will block up the tunnel and cut off the supply of water to the city, but it is too late to line it now. . . .

The excavation of the drainage tunnel through Dalecarlia Hill and under the aqueduct, will be a delicate operation. The blasting out of the former in such a manner as not to pro* duce shocks and jars on the unsupportable rock of the latter, will have to be done with the greatest care and caution on the part of all concerned. . .

With a grade of .0031 the velocity of the water in the conduit when full will be ten feet per second. This will be the condition of the conduit when the discharge from the entire water shed will be 385 cubic feet per second. A careful estimate of the cost of the receiving shaft of well, the drainage conduit and the open cut at its mouth, allowing two per centum for contingencies, gives $50,686.

The remainder of the $60,000 appropriated by the act of March 3, 1893, will be required for the purchase or condemnation of six small parcels of land and the purchase of machinery necessary for the work. . . .

Should it be decided at some time in the future to follow the examples presented by the large cities of Europe to filter the Potomac river, it will be indispensable in order to save a great part of the cost of maintenance of the filters to “settle” the water as much as possible before it enters the filters, and the receiving reservoir will then be available and even necessary for this purpose, for the reason that the filtration works must be at or near the lower (distributing) reservoir, and there is no place other than the receiving reservoir that is suitable for the settling basins, which must, of course, be above the filtration works.