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Show Chapter 10 Flood Management HOWEVER BIG FLOODS GET, there will al- ways be a bigger one coming. So says one theory of extremes, and experience suggests it is true. The country spends hundreds of millions on flood control, increasing its expenditures every year, yet each year brings headlines of new "worst" floods, new damage, new loss of life. As the country becomes more thickly settled, more rather than less flood damage is incurred in many areas, even with floods of the size already encountered. It becomes necessary, then, to re- examine our whole theory of flood control, to improve its effectiveness and to make sure that the large sums being appropriated are spent wisely. This Commission can offer no ready-made so- lutions, but it can perhaps offer suggestions as to the lines which river basin investigations might follow in the future. The Value of Floods Scientific use and management of floodwaters is a fundamental part of multiple-purpose water resources development. Where rainfall is mea- ger, man's ability to maintain himself in arid regions may depend upon his husbanding of flood- waters. Where rainfall is more plentiful, con- servation of floods provides water for cities and energy for industries and farms. The great civilization of Egypt was based, in part, on the fertile sediment which the flooding Nile each year poured over the fields. Manage- ment was simple, consisting merely of recognition of the necessity for moving out of the flood plain each year, then moving back to crop the land as the floods receded. Flood management in this country in early days consisted largely of building dikes or levees to protect farm land against rising floodwaters, or later of building channels to carry the waters to the sea. But modern engineering has made it possible to store and use floodwaters for many purposes. Where conservation storage is feasible, the single- purpose flood detention reservoir, which treats floodwaters simply as a menace, has come to be recognized as an unforgivable waste. Modern flood management includes scientific management of the watersheds as well as the con- struction of reservoirs to catch the excess runoff from the soil and hold the floodwaters for con- trolled release. Release from such reservoirs is timed to serve the purposes of domestic and industrial water supply, irrigation, navigation, power, and regulation of stream flow. These reservoirs are built as high up on the river system as possible, in order to avoid unnecessary flooding of valuable agricultural lands in the lower valley and to multiply the hydroelectric power which can be developed at each fall on the way to the sea. Falling water represents energy equivalent to that which can be derived from such mineral fuels as coal and oil. But the energy available from falling water is renewed each year by the water cycle, while the energy from coal and oil, once used, is gone. If all floodwaters in the United States for which development is feasible 141 |