| OCR Text |
Date Flood height reduction by storage Estimated prevention of damage by flood storage Mar. 29, 1936............. Apr. 9,1936............... June 4, 1937............... Dec. 30, 1942.............. Feb. 19, 1944.............. Mar. 30, 1944............. Jan. 9, 1946............... Feb. 11, 1946.............. Jan. 21, 1947.............. Feb. 14, 1948.............. Nov. 29, 19-48.............. Jan. 6, 1949............... Feb. 2, 195O............... Mar. 15, 1950............. Feet 4.2 3.4 2.5 3.9 11.6 6.1 10.1 7.1 12.7 10.5 6.7 6.8 11.2 5.8 $1, 930, 000 679, 000 19, 000 1,065, 000 8,000 325, 000 11,800,000 415,000 11,495,000 12, 940, 000 360, 000 500,000 3, 400, 000 30,000 Total................ 44, 966,000 Source: Tennessee Valley Authority. Effect of the Tennessee on Mississippi River Floods The great floodways of the central United States are concentrated in the Mississippi Valley, from Cairo to th.e Gulf. Here also is the Nation's great- est single flood problem. The Mississippi has periodically flooded its vast plain far back into the geologic psLst. The volumes of water in these floods are illustrated in the 1929 flood, not a disastrous one. The total flood volume passing Cairo in the four months from March to June was 305 million acre-feet. The fertility of the valley, its use for important transportation arteries, and the tendency in modern times to settle in floodways have made floods a huge economic problem. Many millions of dollars of damage has been suffered in these floods, hundreds of communities have been disrupted, and hundreds of lives have been lost. The traditional method of controlling Mississippi floods has been by levees and local works. Levees now confine the Mississippi on the west from Gape Girardeau to the Gulf, and on the east from Cairo to Vicksburg, and Baton Rouge to the Gulf. Be- hind these levees lie some of the major railroads and highways of the country, and more than 20 million acres of agricultural land. Although the levees have contained the greatest floods of record, it will be necessary, by means of storage reservoirs, to reduce the peaks of still greater floods that may be expected, so as to keep the flow line within the established levee grades. Because the Tennessee is an important contribu- tor to many Mississippi floods, flood water storage in the Tennessee is essential to adequate control on the Mississippi. During the 1937 flood, the Ten- nessee discharged about 1,740,000 acre-feet into the Ohio at the time of the peak of the flood on the Ohio. In the control of Mississippi floods Kentucky Dam and Reservoir on the Tennessee is a key unit. The flood storage depth of 21 feet provides space for impounding 4 million acre-feet of flood waters. Upstream dams at Pickwick Landing, Wheeler, and Guntersville also provide helpful storage space for flood regulation on the Ohio and Mississippi systems, as to a lesser, but still significant degree, do all of the other upstream dams. Controlled flow on the Tennessee is of major value with respect to Mississippi River floods at Cairo and below because: the Ohio River is an important contributor to floods on the lower Mississippi; the Tennessee is the largest tributary of the Ohio; the confluence of the Tennessee and Ohio is less than 50 miles from the confluence of the Ohio and Mississippi; Kentucky Dam, with its large flood control storage, is within 22 miles of the Ohio, and regulates the flow from the entire Tennessee Basin; Kentucky Dam, about 1 day's water travel from Cairo, can be regulated far more closely to meet Cairo's requirements than any other project proposed within the Mississippi Basin. Contribution of Tennessee River flow to flood peaks in four major Mississippi floods is indicated by the following figures: [Cubic feet per second] Date Mississippi River discharge Tennessee River discharge Tennessee discharge as percent of Mississippi discharge April 1912........ April 1913........ April 1927........ February 1937 2,015,000 2,015,000 1, 765, 000 2, 010, 000 272,000 213,000 205,000 238,000 13.5 10.6 11.6 11.8 722 |
