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Flood Frequency Analysis The magnitude of flooding on the White River has decreased significantly since the mid-1960s (Figure A-7). The average peak flood at the Watson gage between 1923 and 1965 was 4,300 cfs. The average peak flood magnitude between 1965 and the construction of Taylor Draw Dam in 1984 was 3,470 cfs. After the completion of the dam, peak floods have changed little. The average peak flood for the period between completion of dam in 1984 and 1997 was 3,437 cfs. Peak floods from these three time periods were compared using a series oft-tests. Test results (Table A-I) show that at a 95% confidence interval, the average peak flows between 1923 and 1964 are significantly different from peaks both before (1965 and 1983) and after the completion of Taylor Draw Dam (1984 and 1997). The average peak flows for the two time periods since 1965 are not significantly different. Thus, the decreased peak flow magnitudes which have occurred since the mid-1960s were not due to the construction of Taylor Draw Dam because the decrease occurred before the dam was built. Regional climate changes may be responsible for this shift. Partial-duration series analyses for these same three time periods yields a slightly different perspective about the differences among these periods. The magnitude of high recurrence floods (1.25 - 2 year recurrence interval) has decreased in the post-Taylor Draw Dam period, while the magnitude of larger floods (5 - 10 year recurrence interval) may have increased (Figure A-8) (Table A-2). This may be due to the small storage capacity of Kenney Reservoir, and also to climatic changes during the period after completion of the dam. The small reservoir can store a portion of the inflow of small floods, but cannot control larger magnitude floods. 18