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<br />2 <br /> <br />As might be expected, each flood is different from any of its <br />predecessors. This is due to variations in the intensi~ of rainfall, <br />its distribution over the watershed, the direction and type of the <br />storm, the condition of the soil and such factors as size, shape, eleva- <br />tion, topography, geology and location of the watershed. <br /> <br />Some areas have a "flood season," during which most of the <br />major floods occur. In others, a flood may happen during any season of <br />the year. Quite often, especially on drainage areas of moderate size, <br />a severe flood may be followed by another witAin a few days. The 1943 <br />catastrophe in Oklahoma and Arkansas was such a double flood. It was <br />very destructive. <br /> <br />In duration, floods range from the great Ohio and Mi~sissippi <br />floods prevailing for many weeks, to the localized cloudbursts which, <br />although highly destructive, are over in a few hours. In general, the <br />height of the flood, rather than its duration, causes the greatest loss <br />of life and the major part of the destruction of property. A long- <br />continued high water may, however, be costly because. of the length of <br />the disruption of communications and other essential services, and the <br />suspension of industrial end farm production. <br /> <br />It is poSSible, through knowledge of conditions in a watershed, <br />to recognize that the stage is set for a flood. But it is impossible to <br />forecast when the right combination of setting end storm will take place <br />to produce a destructive flood. Once the critical storm has hit and its <br />intensity is known, some advance notice, ranging from a few hours on a <br />small watershed to a considerably longer period of time on streams like <br />the Mississippi, cm be given as to the time end approximate height of <br />the crest. <br /> <br />Past floods are not reliable guides to the height of future <br />floods. Water records in t.'1.is country cover only a short span of years. <br />It is known that weather end rainfall follow cycles of great length,some of which are estimated to be as long as 1500 years. Therefore, it <br />