‘The ideal river, which would have a uniform flow, does not exist in nature.‘ (Mississippi Valley Committee Report, 2d ed., p. 3, 1934.)
From time immemorial floods have transformed beneficent river waters into a menace to humanity. ManTs progress toward economic stability has been repeatedly halted or even thrown backward by the interruption of his efforts to make effective use of rivers and of valley lands. This handicap is not imposed by the destructiven&ss of large rivers alone, or of rivers in widely separated areas, for there are few if any streams, brooks, or rivulets that are not subject to flows beyond their channel capacities. Yet, though man for ages has suffered seriously from recurring floods, he has not been deterred from continuing to extend his activities in areas that are virtually foredoomed to flood damage.
Today in the United states serious floods may occur in any section in any year, and even, in some regions, several times a year. Many of these floods leave behind them the tragedy of death and disease and of property irreparably damaged. The aggregate direct property damage caused by floods in this country has been estimated roughly to average $35,000,000 a year. In addition there are serious indirect and intangible losses of great but not precisely calculable magnitude.
The persistent recurrence of flood damages in our country, and, indeed, their tendency to increase, have given birth to the mistaken notion that floods are increasing in size and frequency. The rising damage totals are not attributable to greater or more frequent floods, however; rather they are the result of increasing occupation of river banks and river valleys by cities, towns, industrial plants, bridges, railroads, and highways and the increasing use of rivers as a source of water supplies for municipalities and industries and for power, irrigation, navigation, and recreation.
Safety of life and reduction of both direct and indirect losses from floods may be promoted by the adoption of measures for protection and control. It should be borne clearly in mind, however, that probably no single method of flood control will insure the protection of a large drainage basin. ‘The improvement of natural channels; the building of reservoirs - sometimes well adapted for purposes of irrigation and power; the construction of levees, such as now exist along the lower Mississippi; reforestation and a Change in certain areas from tilled crops to grass crops, may all playa part in slowing down the rush of water to the sea, or in keeping it away from cities, towns, and valuable lands.‘ (Mississippi Valley Committee Report, 2d ed., p. 3, 1934.)
‘Consideration of a national flood-control policy must necessarily recognize that the flood-control aspects of a project, be it a major purpose or an incidental one, must be evaluated in the light of a broad study which takes into account all other purposes or possibilities involved. Among such other purposes may be power, navigation, irrigation; may be low-water control, water supply, sewage, or waste disposal. Wherever more than one purpose is indicated, each must be considered in its full relation to all the others. Only by such procedure can a well-coordinated project be evolved.‘ (Idem, p. 27.)
In planning public works for the con trol of floods, and in relating such works to effective utilization of river waters for the various purposes enumerated above, two basic requirements are (1) accurate and reliable records of the stage and discharge of past floods, and (2) development of methods for the analysis of such data, to determine the frequency of floods heretofore experienced and to estimate the magnitude and frequency of future floods. It is the purpose of this study to present for certain rivers in the United States much of the basic information of this sort now available. Engineers generally agree that a large part of the flood destruction in this country could have been pre