A GLANCE AT DAM WORK.
Address of President W. R. Hill at the Chicago Convention.
Chief Engineer W. R. Hill, of the Croton aqueduct commission. New York city, in his opening address as president before the convention of the American Water Works association, claimed the hydraulic engineer as the pioneer engineer in the history of the world, because “man first exercised his constructive skill in the art of procuring water.” “In history we read of many notable aqueducts and reservoirs that excite our admiration and astonishment, and today we are laboring to make more perfect methods that were established centuries ago.” Mr. Hill then pointed out that it was no such simple task to build a waterworks system, as Nature herself seemed to “rebel against the attempts of man to convert its beautiful waters and landscapes into artificial lakes or reservoirs, as is manifested by many unsuccessful efforts.” These failures, according to Mr. Hill, have been due to the following causes:
(I) “Insufficient spillways, thus causing the water to rise in the reservoirs and to flow over and wash away the embankments. The Walnut Grove dam on the Hassayampa river, Arizona, failed on February 22, 1890. It was no feet high from the rock foundation to the coping, 400 feet long, 140 feet thick at the base and 10 feet at the top. It was a rock-filled dam with walls on both faces made of large granite blocks of dry masonry, with a timber lining on the water side. The walls were twenty feet thick at the bottom and five feet at the top. The waste weir was only twenty-six feet wide, while the area of the watershed was about 500 square miles. The reservoir had an area of about 1,000 acres. The cause of the failure was supposed to be water flowing over the crest of the dam. About 150 lives were lost and the damage to the dam and the property destroyed was estimated to be about $800,000. The dam across the south fork of the substantially-built Conemaugh river, above Johnstown, Pa., built in 1852, as feeder for the Pennsylvania canal, was abandoned in 1857, and in July, 1862, a culvert in the embankment gave way, owing to an imperfect foundation. Thirty-two feet of water leaked out slowly and the damage was small. It remained empty till 1880, when a fishing club reconstructed it to a height two to three feet lower than originally. However, a fatal mistake was made in leaving a low place or sag in the middle of the dam. Another mistake was the obstruction of the spillway with an iron grating placed to retain the fish in the reservoir. The spillway should have heen lowered because of the lowering of the crest of th dam, and enlarged because of the obstruction. On the fatal day the water rose and flowed over the crest of the dam because the spillway was too small to discharge the water, and in a short time 400 feet of the dam washed away. I he loss of life was far up in the thousands; the property loss was about $9,000,000. The reservoir had an area of about 400 acres, an average depth of thirty feet, and a capacity of about 5,000,000,000 gallons. The area of the watershed was about sixty square miles. The dam was constructed entirely of clayey earth seventy-two feet high, twenty feet wide on the top with an inside slope of two to one, and an outside slope of one and one-half to one. The inside slope was protected with a light riprap.
(3) Water leaking along pipes laid through embankment, but not in ruffle or concrete masonry surrounded with puddle. This was the cause at Portland, Me., where a fouryear-old 20,000,000-gallon distributing reservoir, whose embankment, ten feet wide at top, forty-five feet high, with slopes one and one-half to one on each side and six feet of the inner slope of puddled clay and six inches of broken stone, having granite paving blocks eight inches thick laid on, burst. Four lives were lost. A drain pipe through, and one overflow pipe sloping downwards and through the embankment allowed the water to leak through and caused the trouble. The dam of the Soring lake reservoir, near Fishville, R. I., is another case in point. It failed on August 25, 1889. The reservoir had a capacity of 35,000,000 gallons. The dam was made of clay and gravel and was 825 feet long, eighteen feet high, eight feet wide on the top and thirty-five feet wide on the bottom. The outside slope was retained by a stone wall and the inner slope was paved with stone. The portion washed away was just above the waste pipe. Property valued at about $25,000 was destroyed and three lives were lost.
(3) The tendency of water to follow along masonry laid in one embankment, as was shown in 1876 by the Lynde brook reservoir embankment at Worcester, Mass. It was of earth paved on the inside with rubble masonry on a slope of two to one. It was 287 feet long, twenty-seven feet high and twentyfive feet wide on top. The embankment was originally built in 1854, was enlarged and modified in 1870, when it was made nineteen feet higher, and a heavy face wall of masonry was added. The reservoir had a capacity of 776,000,000 gallons. Water leaked around a culvert that passed through the base of the embankment, making a breach 200 feet long and destroying property valued at nearly $1,000,000. Great precautions should be taken to see that culverts or masonry laid through an embankment are on a firm foundation and well surrounded with puddle.
(4) The breaking or settling of the bottoms of reservoirs, due to the weight of the water, thus giving it an opportunity to escape through the loose underlying material. To obviate this difficulty the outer walls of the reservoirs should be carried down to solid rock, if possible, or to some other stable impervious material. If such material cannot be found, the greatest care should be exercised in lining both the bottom and the sides of the reservoir. Among the instances quoted by Mr. Hill are the Milburn storage reservoir of Brooklyn, New York, which was completed in 1893 and has never been in use. In August of that year 43,500,000 gallons of water leaked out in ten days. The material used for the puddle bottom was good enough; but it was improperly put in. The whole forty-tour-acre bottom must be repuddled. Philadelphia has been peculiarly unlucky in this respect. One basin of the. Roxborough reservoir leaked in 1894 after a year s service. A depression was found in the embankment, about three feet above the bottom. The day had been washed away underneath the brick lining, and below was a six-inch to ten-inch wide fissure in the rock, through which the water came to the surface 1,200 feet away. When the water was first pumped into this reservoir on September 21, 1893, and it had been filled to a depth of twenty feet, an increased flow was detected in a nearby stream, but the leak was not detected for nearly a year afterwards. .It took $140,000 to reconstruct the interior lining. The Queen Lane reservoir, also, was practically completed on October 1, 1894. On being filled to a depth of ten feet many leaks were discovered. The bottom was lined with _____our inches of concrete and upon a layer of clay puddle two feet in thickness built up in layers, rolled, and watered. The underhung rock is gneiss and mica, whose upper portion is more or less disintegrated. It cost about $275,000 to reconstruct the interior lining. The Housatonic masonry, near Birmingham, Conn., failed in January, 1891. It cost $264,000 and twenty-two years before, while under construction, 160 feet of the partly finished work was carried away by a freshet and a cavity twenty feet deep was scoured out in the river bed. This was filled in with loose rock, and a timber apron. Twenty-two years afterwards the loose rock under the timber apron was undermined, and 250 feet of the dam was swept away. A quicksand beneath the foundation caused a large part of the bank of the 140,000,000-gallon reservoir at Dallas, Tex., to sink vertically. The settlement was over 300 feet in length and extended from the outer slope to within five feet of the top of the inner slope. The earthen dam of the mill reservoir at Williamsburgh, Mass., which had a masonry core wall two feet thick at top and five feet nine inches at bottom. The area of the reservoir was 114 acres and the average depth twenty feet. The dam was 600 feet long, forty-three feet high, and sixteen feet wide on top, with sides of one and one-half to one on both sides. Water found its way under the core wall and destroyed the embankment. The water rushed down into the narrow valley, and caused a loss of 140 lives and some $1,000,000. The Angel’s dam, Calaveras county, Cal., was undermined on April 10, 1895. It cost $52,000, and was of rubble stone masonry, 400 feet long and fiftytwo feet high. It was thirty-five feet thick at the base, and at a height of twenty feet the thickness was abruptly reduced from twenty-one to thirteen feet. At the top it was three feet thick. The upstream face of the dam was vertical. During the time of construction workmen were engaged digging a hole near the wall, and the foreman said “they were trying to dig out a cottonwood stump, but the blamed roots ran clear under the wall and he could not get them out.” One life was lost by the flood, and a coroner’s jury, after investigating the case, returned a verdict of “accidental death,” and, by implication, censured the victim for carelessness in being in his garden where the flood could reach him.
(5) Poor workmanship or faulty designs often developed by ice-pressure. The Mud Pond dam, near East Lee, Mass., was of earth, with a dry boulder wall on the downstream side. It was 325 inches long, fifteen feet high, twenty-eight feet thick at base, and six feet at top. Seven lives were lost and damage to the amount of $250,000 was done. In 1896 a 42,000,000-gallon reservoir at Montreal Quc., leaked at the rate of 350,000 gallons a day. The leakage is believed to have been caused by the ice near the high water line. The reservoir was formed by a masonry wall, backed first with puddle and then with an earth and stone embankment. Icepressure caused $25,000 damage to the upper dam of the St. Anthony’s Falls Waterpower company at Minneapolis, Minn. It was of coursed ashlar sandstone masonry, 530 feet long, eighteen feet high, twelve feet thick at base, and five feet one inch and a half at top. Ice-pressure and the sudden drawing off of the water caused the Kinsman street reservoir at Cleveland. Ohio, to fail in December, 1856. Faulty construction, not ice-pressure, caused the failure of a wall of asphalt concrete built round the 100-foot square reservoir on Vernon Heights, Oakland, Cal., to increase its capacity. The wall was eight feet high and only two feet thick at the base and one foot at the top. It had no depth in the soil, and was built partly on made ground.
(6)Unknown causes. A masonry dam in the Colorado river at Austin, Tex., which had cost $1,400,000, failed on April 7, 1890. It was 1,275 feet long and sixty-six feet thick at base. A freshet and great depth of water flowing over the crest forced 500 feet of the dam down the river, with a damage amounting to about $500,000. The bursting of the dam of the lake at the fair grounds at Staunton, Va., on September 30, 1896, due to. high water, caused the loss of five lives and much property. One railroad and two highway bridges were destroyed by the sudden liberation of 50,000,000 gallons of water from two of the reservoir dams on Beaver brook, destroyed on March 26, 1884, $250,000 worth of damage resulting. President Hill tells of several other cases coming under the above heads, and refers, besides, to forty eight other similar failures which have come to his notice, but unfortunately without any record of the accompanying conditions and circumstances. He concludes by expressing the hope that all who become acquainted with failures of dams or reservoirs will impart such knowledge to the association, as well as to the technical press, whose columns contain many object lessons for the guidance and education of waterworks men.