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<br />0"'" ,,,,, <br />u _ ..:... (~ '1 <br /> <br />KANSAS STREAMFLOW CHARACTERISTICS <br /> <br />PART 3 <br />FLOOD FREQUENCY <br /> <br />By Davis W. Ellis and George W. Edelen, Jr. <br /> <br />INTRODUC TION <br /> <br />Purpose and Scope <br /> <br />This report presents a comprehensive summary of past floods experienced <br />in Kansas and procedures for defining probable expectancy of future floods. <br />Such information is essential to the proper design of hydraulic structures <br />placed across or adjacent to streams, or to the design of other structures lo- <br />cated in flood plains. <br /> <br />Failure or overtopping of large dams and the destruction of other import- <br />ant structures has resulted in the loss of human life and in extensi ve property <br />damage. The "design flood" selected for such structures is usually one that <br />is not expected to be exceeded. Data on maximum known floods in Kansas are <br />included in this report. <br /> <br />An element of risk is involved if the "design flood" is less than the max- <br />imum expected. This risk may be justified for bridges and other structures <br />whose failure or overtopping results only in economic losses such as structural <br />damage or temporary loss of use and when human life is not a major consider- <br />ation. However, without a knowledge of expectancy of floods, the degree of <br />risk cannot be determined and the structure may be so underdesigned that it <br />suffers too frequent damage or even destruction; conversely, it may be so over- <br />designed that it is subject to damage only by floods with recurrence intervals <br />far greater than its probable useful life. The "design flood" used in planning <br />such structures is usually based on a definite frequency of recurrence deter- <br />mined by economic consideration or policy of the owner. An economical design <br />is one in which the cost of flood protection does not exceed the probable damage. <br />It is beyond the scope of this report to establish proper design criteria, but <br />procedures are included for defining the magnitude of floods for any selected <br />frequency up to 50 years. <br /> <br />All significant flood data collected in Kansas prior to Sept. 30, 1956, were <br />used to derive the flood-frequency relations described herein. The records <br />for each gaging station with five or more defined annual maximum floods were <br />adjusted to a common base period, 1921-56, historic data were added, and all <br /> <br />1 <br />