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<br />002101
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<br />Water Resources Development
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<br />25
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<br />The Lebo Storm
<br />
<br />An examination of the records of ~torms which have occurred in
<br />this part of the United States since about 1900 shows that the one
<br />which centered around Lebo in November, 1928, was one of the
<br />largest of record, Precipitation occurred over a period of four days
<br />and extended over an area of 23,060 ~quare miles in Kansas and
<br />Mii'souri to amounts ranging from 5 to 11% inches. The area af-
<br />fected and distribution of the rainfall are shown on the map in
<br />Figure 4.
<br />The drainage b:lsin boundaries of the Marais des Cygnes and
<br />Neosho rivers are sketched on the map for reference. It is apparent
<br />that the heaviest precipitation occurred over the Marais des Cygnes
<br />basin. A complete record of the resulting flood on this stream was
<br />obtained .at the gaging station maintained by this department at
<br />Trading Post near the state line in Linn county. A hydrograph of
<br />the discharge at this point is shown in Figure 5. The flood reached
<br />a crest of 120,000 cubic feet per second and involved a total runoff
<br />of 1',087,700 acre-feet.
<br />No gaging stMion is maintained on the Neosho river in the vicinity
<br />of the Strawn dam site. Consequently, there is no actual record of
<br />the flood discharge at. thllt location in November, 1928, although an
<br />estimate of it can be computed. It was obviously a good deal less
<br />than at Trading Post, since the rainfall over the area above Strawn
<br />was less.
<br />There is a striking similarity in size and shape of the drainage
<br />basins of the Marais des Cygnes river above Trading Post and the
<br />Neosho river above Strawn. At these points the Marais de~ Cygnes
<br />drains 3,210 square miles and the Neosho, 2,915 square miles. They
<br />are also similar in topography and geology. It is thus logical to
<br />conclude that under the same conditions of rainfall the two areas
<br />could produce similar flood discharges. Thus, a flood of the char-
<br />acter shown by the hydrograph for Trading Post in November, 1928,
<br />can reasonably be expected to occur at Strawn. It is estimated that
<br />floods of this magnitude have a probable frequency of occurrence of
<br />only once in more than 100 years. Such a flood is not the greatest
<br />which can possibly occur, although it is twice as great as any flood
<br />on the Neosho of which there is record. It is not necessarily the
<br />flood against which protection should be provided unless such a de-
<br />gree of control is found justified. For the purpose of the studies
<br />which are being made, this flood is taken as the measure by means
<br />of which the relative effectiveness of various plans will be deter-
<br />mined.
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