Greatest Dam in the World.

Progress, Volume II, Issue 2, 1 December 1906, Page 47

Greatest Dam in the World.

Fifteen years ago the highest dam in existence was the Furens dam (in France), the total height of which was 170 feet. Since then three very much larger dams have been built in the United States. These are the Croton dam in New York, the Clinton waterworks dam at Boston, and the waterworks dam at Denver, on the South Fork of South Platte river. Each of these at present holds the record in one respect or another : the Denver dam is the highest in the world ; the Clinton impounds the largest amount of water ; and the Croton dam contains the largest mass of masonry. But the Salt river dam, when finished, will exceed each of these in its own speciality ; it will be higher than Denver ; will exceed the Croton dam in masonry ; and will impound twice as much water as all three dams put together. It will be 270 feet high from foundation to parapet, will contain 300,000 cubic yards of masonry, and will impound more than a million acre-feet of water — that is, more than enough to cover a million acres (1,500 square miles) to a depth of one foot. It will form a lake 25 miles long and one to two miles wide, covering an area of 14,000 acres. Its cost, with maintenance for ten years, will be about The dam will be thrown across a gorge — 300,000 cubic yards of solid masonry, to be laid in Portlandcement mortar in a wedge-shaped section, 16 feet wide at top and 165 feet wide at bottom. It will tower 230 feet above the level of the present river bed, and penetrate 40 feet beneath it, giving it a total height of 270 feet. Two gigantic spillways, each 100 feet wide, sunk 20 feet below the crest of the dam, will provide an outlet for floods too great to be risked against the mam body of the dam. When fully opened, these spillways will discharge 10,000 cubic feet of water per second — an enormous flow, but none too great, for these arid-land rivers, when they come down in their might, rival even the Mississippi in their volume. In 1891 Salt river discharged for a few days the almost incredible amount of 300,000 cubic feet per second enough to fill the entire reservoir in one day. Only about half of this, however, came from the watershed behind the Salt river reservoir, the other half coming from tributaries entering below the dam site. The reservoir behind the dam extends up both Salt river and Tonto creek, and can be made to hold almost any amount of water that is desired. Exhaustive surveys were made to determine its capacity, as few things are so deceptive to the eye as the area of a reservoir before it is filled. The three power sites of the Salt river project are expected to develop power, which, when transmitted by electric cable to the proper places, will pump enough to irrigate some 50,000 acres of land. This, with 150,000, or more, acres supplied direct from the stored water behind the great dam, will make up the entire irrigable land of the Salt river project — an area equivalent to one-third of that of the entire state of Rhode Island. We are indebted to the Technical World Magazine for the illustrations of this great undertaking.

The Trinity House authorities are placing a new foghorn signal at the Needles Lighthouse. It is a reed trumpet worked by compressed air, and will be heaid eight or ten miles from the lighthouse.