MUSCLE SHOALS, a name given to a section of the Ten nessee river, approximately 37 m. long, above Florence, Alabama. In this distance the river drops 132 ft. when it is discharging its average flow. The above section of the river is made up of rapids and connecting pools that collectively make navigation of the river in its natural state impossible. The first part of the name is probably the obsolete form of mussel, which is derived from Lat. musculus, dim. of mus, mouse.
The discharge of the Tennessee river in the Muscle Shoals section is produced by an average annual rainfall of about 45 in., falling on a catchment basin 30,80o sq.m. in area. The volume of water thus created, uninfluenced by,artificial storage, has varied from 5,00o cu.ft. per second to a maximum of 500,00o cu.ft. In the earlier colonial days the Tennessee river was considered of sufficient importance by the Federal Government to receive more or less continuous engineering study from the time of George Washington down to 1918, when President Wilson ordered the building on Muscle Shoals, near Florence, of the structures shown in the Plate as a war and national defence measure.
As a result of the various navigation surveys and studies of Muscle Shoals, made between 1828 and 1889, a small and incom plete set of lateral canals and locks were completed in 1890 by the Federal Government. These locks and canals proved of practically no value because of the absence of sufficient tonnage either up or down the river. In 1907 the Federal Government ordered the chief of army engineers to make a new examination of Muscle Shoals for the purpose of ascertaining its navigation and hydro-electric power possibilities. As a result of these examina tions and of succeeding official and private studies, sufficient engineering data of a reliable character had been assembled to warrant President Wilson in 1918 ordering the construction of what was then named dam No. 2 on the Tennessee river, as a part
of the general plan prepared by the U.S. army engineers for the improvement of the entire Muscle Shoals stretch of the river. Actual construction of dam and power-house No. 2 was begun by the war department in April, 1918, as an emergency war measure, to aid in the supply of nitric acid for war needs in lieu of Chilean nitrate of soda. The termination of the war in 1918 found the plant only about 3o% completed, and the question then arose as to whether to complete or abandon the power-plant and navigation work at Muscle Shoals. The plan to finish the structure prevailed, and the initial installation shown in the figure was placed in practical commission in Sept. 1925.
The entire length of dam and power-house is 4,86o ft., divided by expansion joints into 90 sections. Field measurements showed that the aggregate of the temperature and other changes in the lengths of these 90 sections was over 9 inches. The masonry crest of the dam is surmounted by flood gates, by the operation of which a uniform pool level can be maintained above the dam independent of the quantity of water flowing through the pool, and independent of the amount of water used for power purposes. The capacity of the flood gates is any discharge up to a maximum of one million cu.ft. per second, or three times the maximum dis charge of the St. Lawrence river in the International section.
Since 1933 these properties at Muscle Shoals have been oper ated by the Tennessee Valley Authority, a new Federal agency. After completion by that agency of its proposed ten-dam system on the Tennessee river and two of its tributaries, the productive capacity of the Government-built projects in the Tennessee valley will be more than 1,500,00o horse-power of primary and secondary hydroelectric power. See TENNESSEE RIVER.