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Show Chapter 2 The River and Its Tributaries The Tennessee River is formed by the junction of the French Broad and Holston Rivers just above the city of Knoxville, and flows 652 miles to its mouth at the Ohio. Its fall in that distance is about 500 feet. The total distance from the source of its longest tributary to the Ohio is approximately 900 miles. In that distance it falls from an eleva- tion of more than 3,000 feet to about 300 feet. The streams which feed the Tennessee from the north rise on the eastern slopes of the Cumberland Mountains in southeastern Kentucky and south- western Virginia. Those from the South originate high in the Unaka and Smoky Mountains, which rise to more than 6,500 feet. The river flows generally southwest to Chattanooga, where it turns west for about 160 miles and then north across Tennessee and Kentucky to join the Ohio. The Tennessee Valley is well watered. In some places on the eastern rim of the basin, at the summit of the Smoky Mountains^ average annual rainfall is 75 to 85 inches, with maximums well in excess of 100 inches. The 60-year average for the basin above Chattanooga is 51 inches. The wettest year of record was 1901, with a rainfall of 63 inches; the driest years were 1925 and 1930 with 37 inches. September, October, and November are the months of lowest rainfall with an average of approximately 3 inches for the season, while the season from December through March and April brings monthly rainfall of approximately 4.5 inches. Occasional tropical storms from the Gulf reach into the headwater areas with as much as 22 inches of rain in a 24-hour period, and as much as 35 inches in a single month. The average annual runoff is 21.9 inches at the mouth of the Tennessee River and 23.8 inches at Chattanooga, the area of greatest flood hazard. At Kentucky Dam, 22 miles from the mouth of the river, the average flow of the river from 1889 to 1943 is estimated to be 65,000 cubic feet per second. Maximum flow of about 500,000 cubic feet per second occurred during the 1897 flood. It is estimated that the minimum daily natural flow is 4,500 cubic feet per second. The average flow of the river at Chickamauga (1874 to 1943) was 36,500 cubic feet per second. Maximum flow of 459,000 cubic feet per second occurred in the great flood of 1867; the minimum daily natural flow at Chickamauga was recorded in 1925 with 3,200 cubic feet per second. The distribution of floods on the Tennessee River has been concentrated in the period from January 1 to April 30. Since flood recording began in 1867, the river has been at flood stage at Johnsonville 100 times during these months; in the other 8 months it has reached flood stage 13 times. It has never been above the discharge rate of 280,000 cubic feet per second during the last 8 months of the year but it has surpassed this rate 33 times in the first 4 months of the year. At Chattanooga the flood stage (30 feet) has been passed more than 60 times since 1867, during the period from December 15 to April 15. There is no record of any flood waters above the 34-foot stage at Chattanooga between April 15 and Decem- ber 15. The principal tributaries of the Tennessee are the Clinch, French Broad, Hiwassee, Holston, and Little Tennessee, all of which rise in the mountains or higher elevations to the east and north, and all of which enter the main stream above Chatta- nooga. The French Broad is the largest of these streams in water contribution to the main stream, although all make important contributions to the flow of the Tennessee. (See table 1.) 711 |