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3 is probable that in most localities the maximum storm has not taken place within the memory or records of man. Then, too, heavy storms are more or less limited in size, and seldom extend over all of a drainage area of moderate or large size. Once in a great while, however, a great storm does cover an unusually wide area, and then an extra bad flood sweeps down the river. There are other important factors affecting the intensity of floods. Deforestation, fanning methods, draining of swamps, channel constriction and the building of dams all tend to speed up and increase the heights of flood crests, as well as to enlarge the volume of the water to be handled. For these reasons, it 1s probable that the maximum flood has not yet been recorded, but it is obvious that it will take place, per- haps tomorrow, or perhaps at some more distant date. Of course it is necessary to design flood control works to meet such a catastrophe. By the study of stom and drainage area characteristics, it is poSSible to approximate what this maximum flood may be. The Amy Engineers call such a maximum super flood a SOO-year flood and design their structures to be safe against it. Chart I (see set of' charts following the text of' this paper) is a picture of a moderate-sized flood. The sketch shows an intense two-day rain f'~ing on the upper part of' a hypothetical drainage area. Part of the water soaks into the ground and the underground water channels. The remainder, generally the greater part of' the f'all, runs of'f' via gullies and small streams, to cause a f'lood in the tributaries and the main river. The flood situation at the end of five successive equal periods is shown by means of' five profiles of the same stretch of the main river. . The first period the flood is forming. By the next, a f'lood wave is moving down stream. By the third, the rain has ceased, the flood crest has reached its most destructive size, and has advanced