Page:The New International Encyclopædia 1st ed. v. 05.djvu/881

* DAMS AND RESERVOIKS. 763 DAMS AND RESERVOIKS. feet of water, which drownecl 143 persons and de- stroyed $1,000,000 worth of property. The most disastrous reservoir failure of the nineteenth century was the destruction of the South Fork Dam, which caused the famous Johnstown flood on June 1, 1889. That this disaster was due to an insufficient wasteway has been abundantly proved. The South Fork Dam was built on the lieadwaters of the Cone- niaugh River, about .'i miles al)ove .Tolmstouii. It was of earth, 70 feet in extreme height. The dam was built as far back as 1852, and, after various changes in ownership, the reservoir, in 1880, came into the possession of the South Fork Hunting and Fishing Club of Pittsburg, Pa. The original specifications for the dam required a waterway 1.50 feet wide. The waterway existing at the time of the disaster was 1.30 feet wide at its upper end, but was obstructed by a bridge and by screens to prevent the escape of fish. It extended across a channel 176 feet long, and at its lower end only 09 feet wide. In other words, the waste was only half that orig- inally contemplated, besides which a brick out- let culvert had been abandoned. Unusually heavy rains had been falling for several days, and for 3^,;; hours before the break occurred the water had been flowing over the entire length of the dam. When tlic dam was carried away, the reservoir emptied itself in about 45 minutes. Over 2000 lives were lost in this disaster, and between $3,000,000 and $4,000,000 worth of prop- erty. The Walnut Grove Dam, in Arizona, failed on February 22, 1890. It was one of the highest rock-fill dams ever built, having been 110 feet in height, about 10 feet thick at the top and 140 feet at the base, ^^■ith a top length of some 400 feet and a bottom length of 100 feet. Both faces were composed of granite blocks, laid by hand and derrick, these dry-face walls being 20 feet thick at the base and 5 feet thick at the top. It is supposed that a very heavy rainfall and an altogether inadequate spillway caused the destruction of the dam. which was over- topped for a number of hours. ^lanj' deaths re- sulted from the failure. The failure of the Puentes masonry dam, in Spain, in 1802, was due to defective foundation, the central part of the dam resting upon piles, instead of being carried down to bed rock. In the Ilabra masonry dam, in Algiers (see table), whose failure caused the drowning of 400 per- sons, the disaster was probablj' due to defective masonry work. The failure of the Bouzey ma- sonry dam, near Epinal, France, in 1895, was caused by defective construction between the base and the foundation, although in its dimen- sions the dam was, carried to the extreme of lightness. The failure of the dam on the Colo- rado River, at Austin, Tex., which occurred in April, 1900, was due to defective foundation, largely on account of the soft limestone rock on which the foundation was laid. The dam was 1090 feet long, 66 feet high above the founda- tion, and 60 feet above low water. The up- stream face of the dam was vertical, and the down-stream face was curved, giving a thickness of 66 feet at the base and 20 feet near the top. On April 7, 1900, after a heavy rainfall of sev- eral days, when the water was flowing over the crest of the dam to a depth of 11.07 feet, a por- tion some 500 feet in length was detached from Vol. v.— 19. (lie remainder of the dam, broke into two parts, and was carried down-stream. Two sections were left standing upriglit in the stream a few feet below tlic origjnal portion. One of these broke up in a few hours, but the other remained intact. When the dam broke, eight people in the power-house were drowiied by the sudden rush of water, and during the following night the power-house itself was jiartially destroyed. BESEKVOIRS. Reservoirs may be classified broadly into j»i- po-unding, sctlJiny, storage, and dixlrihtitimj res- ervoir-s, all of which, except inipovmding. may be covered or open, the latter being the general form, Inipouiidiiin reservoirs are fcu'med by throwing a dam across some stream and flood- ing the country aliove. Storage rcserroirs are often created in the same way ; or they may be formed more or less completely by embankments or excavation, or a combination of the two. Both impounding and storage reservoirs are designed to conseire a supply of water above the normal consumption, for times when either the natural yield is below the average or the consumption is unusually great. Impounding reservoirs are always for storage purposes, whether the capac- ity be for a few hours' supply or for a much longer period. The larger and more regular the daily yield of the stream or other source of supply, as compared with the consumption, the smaller need be the storage capacity. In some cases storage is required for months, or even for a year. The new Croton Dam will provide a storage of about 32,000.000,000 gallons, or near- ly enough to supply the whole of Greater Xew York (3,438,000 people in 1900) with 100 gal- lons each for 100 days. The Wachusett Dam, of the Metropolitan Water-Supply District (Bos- ton and vicinity), will retain about 63,000,000,- 000 gallons of water. It is located at Clinton, Mass., and ranks next to the new Croton Dam in height (see table of dams above for dimen- sions), but has almost double the storage capac- ity. The Periyar, or Periar, Dam in India (see table) forms a reservoir larger than either of the last two, having, as it does, a total capacity of about 100,000,000.000 gallons; but the outle't tunnel is at so high a level that only about one- half of this capacity can be utilized. Still great- er will be the capacity afforded by the great .s- suan Dam, now being liuilt (see table) across the Nile, .some 500 miles above Cairo, The stor- age here will be about 280,000,000,000 gallons, or sufficient to cover 6,400,000 acres of land to a depth of one foot. The Periyar and Assuan dams are for irrigation purposes. An important sanitary question involved in the construction of impounding and storage reservoirs for public water-supplies is the strip- ping of the sites, or flooded areas, of all heavy accumulations of organic matter which, either through their decay or through serving as a food- supply to low forms of life, would impart un- pleasant tastes an<l odors to the stored water. It is a common practice to remove .stumps and tim- ber and to burn over the site, where practicable, before filling such reservoirs; but outside of N'cw England very little more than this has been done toward stripping the sites of storage reser- voirs. The estimate for the Wachusett Reser- voir, mentioned above, included .•};2, 9 10.000. out of a total cost of $9,105,000, for stripping the reser'oir site. Aside from stripping and clear-