The EPA SYNOP program (Environmental Protection Agency, 1976; Hydroscience, 1979; SWMM4 Ra...

The EPA SYNOP program (Environmental Protection Agency, 1976; Hydroscience, 1979; SWMM4 Rain block—Huber and Dickinson, 1988) has been run for hourly rainfall data for Houston for the period 1948-1979. A minimum interevent time of 16 hr was used to separate independent storm events, giving the following results:

(a) Perform a log Pearson type 3 frequency analysis (Chapter 3) to determine the storm volume magnitudes corresponding to return periods of 2, 5, 10, 25, 50, and 100 yr. Use the method-of-moments fit.

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(b) Compare the volumes of part (a) with the 24-hr volumes indicated on the Houston IDF curve shown in Figure. The fair agreement between the LP3-fitted storm event depths and the 24-hr IDF depths indicates that the IDF curves were probably derived from these very same data, extracting the largest 24-hr depth out of a much longer storm event (see the durations listed in the preceding table).

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(c) Plot storm event depths vs. storm event durations. Compute the coefficient of determination (R2). The linear relationship between event depths and event durations is very poor and is not significant at the 95% level.

Figure

Intensity-duration frequency curves for Houston, TX.