OCR Text |
Show (2) By administration: The TVA Board offi- cially has delegated the operation of its reservoirs to the chief engineer. He is held responsible for results of multiple-purpose operation; his office de- fines the broad seasonal rules as well as the day-to- day requirements within which the manager of power controls the storage and release of water. The TVA dams and reservoirs now built pro- vide a total useful storage capacity of 14,535,560 acre-feet. Of this, 11,738,400 acre-feet are avail- able for flood storage on January 1; 10,380,800 acre-feet on March 15; and 9,078,100 acre-feet on April 1. The storage provided on March 15 is sufficient to control the design flood to the degree planned. There is year-round reservation of 2,489,400 acre-feet. A greater volume of flood control storage is provided on January 1 than on March 15 so that in the event of two successive major floods in the same season there would be less difficulty in drawing the reservoirs back to required levels following the first flood. The most critical situation, with respect to flood hazards, on the Tennessee River is at Chattanooga, Tenn., where the maximum flood of record in 1867 reached a stage of 57.9 feet. This stage under present-day development would have caused dam- age estimated at 100 million dollars. Recurrence of such a flood with the reservoir control now in effect would result in a stage not exceeding 44 feet. The resulting damage under present-day condi- tions would be not over 12 million dollars. The unregulated maximum flood would reach a stage of 77.0 feet at Chattanooga. The reservoirs upstream now in existence will lower such a flood to a stage not exceeding 60 feet. To protect the city from floods at this stage, it will be necessary to supplement the reservoirs with levees. Both the Corps of Engineers and TVA have reported on a plan for these levees and Congress has authorized their construction by the Corps of Engineers. Levees for protection from flood-water levels in excess of 60 feet are not physically feasible because of local limitations, and levees would not be prac- ticable without the reduction of high stages afforded by the reservoirs. The March 15 flood control storage space of 5,388,700 acre-feet in the reservoirs above Chat- tanooga is used primarily for reduction of stages at that point. This operation affords optimum bene- fits to agricultural lands and other communities above Chattanooga and assists in control of floods on the lower river. The reservoirs below Chattanooga provide 4,992,- 100 acre-feet of flood control storage, including 4,010,800 acre-feet in Kentucky Reservoir near the mouth of the river. This storage was designed and has been operated primarily to reduce flood crests on the lower Ohio and Mississippi Rivers; Kentucky Reservoir is particularly valuable for this purpose. The Flood Control Act of 1944 formalized previous informal cooperation between TVA and the Corps of Engineers by specifying that TVA control re- leases from the Tennessee during danger from floods on the Ohio and Mississippi in accordance with in- structions by the Corps of Engineers. Flood control storage on the Tennessee is oper- ated on the theory that during the major flood sea- son any flood may become a design flood; and hence, storage must always be held in reserve for a major flood. Consequently, peaks of many moderate sized floods are not reduced as much as they might be. If weather forecasting afforded complete knowledge of the size and duration of storms in advance, such precaution would not be necessary. The following reductions in natural stage have been obtained in the major floods since 1946 when most of the reservoirs in the TVA system became available. Year Chattanooga Cairo 1946.................. Feet 10.1 Feet 1.4 1947.................. 12.7 .9 1948.................. 10.5 1.8 1949.................. 6.8 .7 1950.................. 11.2 1.9 The average annual direct flood control benefits from the reservoirs in the Tennessee River system are estimated to be $11,145,000 on the basis of 1948 values. TVA now has installed in its own hydroelectric plants a total name-plate rating capacity of 2,136,- 000 kilowatts in 23 major plants and a number of small installations. The average annual energy generated by this system is about 14 billion kilowatt- hours per annum. This generation is possible with- out infringing on flood control storage reservations. Conclusions Multiple-purpose projects in which a consider- able portion of the storage volume in reservoirs is 769 |