I. OBJECTIVE

To use the principles of statistics and distribution analysis to produce an IDF curve.

II. EQUIPMENT

• Rainfall Data
• Distribution Analysis Software
• Regression Analysis Software
• Spreadsheet

The supplied data is compiled rainfall data (in inches) for a rainfall station. The data was compiled by determining the maximum amount of rainfall which occurred for a time period (1 hr, 2 hrs, etc...) during the year in question. We wish to use this data to develop an IDF (Intensity-Duration-Frequency) curve for the location. The IDF Curve should be for the 5, 10, 25, 50, and 100 year return periods.

• Each rainfall data value (given in inches) must be converted to an intensity (inches/hour).
• For each duration fit the annual maximum intensities to a distribution. To do this enter each of the annual maximum intensities for the duration in question into the DISTRIB program. After determining the best distribution, tabulate the intensities for the 5, 10, 25, 50, and 100 year return periods. The step is repeated for each duration of annual maximum intensities.
• Each set of intensities for a given return period must then be fit to a curve such that intenisty is expressed as a function of duration. The curve fit form usually used is;
i = a/(b + D)

where
i = rainfall intensity = volume/duration
a, b = coefficients
D = rainfall duration

However, you will need to determine if it is the best fit in this case. There will be a curve fit for each return period in question.

• Plot Intensity vs. Duration for each of the 5, 10, 25, 50, and 100 year return periods (frequencies) on one log-log plot. The log-log plot is the IDF (Intensity-Duration-Frequency) curve.

The report should contain the following;

• 1. A tabulation of the raw data.
• 2. A justification of the selected distribution with at least two plots showing the distribution fit.
• 3. A tabulation of the data predicted from the distribution fit.
• 4. A plot of Predicted vs. Duration values from the regression analysis for each of the return periods (Regress-generated plots are sufficient).
• 5. A tabulation of the coefficients and the r^2 values from the regression analysis.
• 6. A final plotted IDF curve using log-log scales (this should be a publishable-quality, fully-labeled plot; use the plotting software of your choice).

duration (hr)   1       2       4       6     10    12     24
1946            1.7    2.9    4.6    4.8    4.8    4.8    5.1
1947            1.9    2.6    2.6    3.0    3.7    3.7    4.8
1948            1.9    2.3    2.7    2.9    3.1    3.1    3.2
1949            1.9    2.4    2.8    4.0    4.7    4.9    5.7
1950            1.9    1.9    2.2    2.5    2.5    2.5    3.0
1951            2.1    2.4    3.0    3.5    4.0    4.2    5.1
1952            1.7    2.5    2.7    2.8    3.0    3.0    4.0
1953            1.7    3.6    3.6    3.6    4.3    4.3    4.7
1954            1.9    2.1    2.8    3.0    3.8    3.8    3.8
1955            2.4    3.7    4.5    4.5    4.6    4.6    5.4
1956            1.0    1.3    1.6    1.7    1.7    1.7    1.8
1957            2.7    2.8    3.2    3.7    3.7    3.8    4.4
1958            1.3    1.5    2.0    2.6    3.5    3.8    4.1
1959            2.8    3.2    3.4    4.1    5.2    5.7    6.0
1960            2.0    2.1    2.8    4.1    5.6    6.0    7.9
1961            1.8    2.7    2.8    2.8    2.8    2.8    2.8
1962            1.5    2.6    2.8    3.1    3.8    4.5    6.4
1963            1.4    2.5    3.1    3.7    4.2    4.3    4.5
1964            1.6    1.8    2.2    2.6    3.6    3.6    4.1
1965            1.2    1.7    2.4    2.7    3.0    3.1    3.3
1966            1.4    1.5    1.5    2.3    2.5    2.7    2.8
1967            1.7    1.8    2.4    2.7    2.9    2.9    4.4
1968            1.9    2.6    4.1    5.1    5.1    5.2    5.4
1969            1.8    3.2    3.8    3.9    3.9    3.9    3.9
1970            1.3    1.6    1.7    1.7    1.7    1.7    2.7
1971            1.8    2.1    3.3    3.4    3.7    4.2    4.9
1972            1.6    2.0    2.3    2.6    2.7    2.7    2.7
1973            1.9    2.8    2.8    2.9    2.9    2.9    2.9
1974            3.1    3.4    3.6    3.6    3.6    3.6    3.8
1975            1.5    1.6    2.1    2.9    3.6    3.6    4.2
1976            2.9    3.4    4.0    4.1    4.4    4.5    4.9
1977            1.4    2.5    2.8    2.8    2.8    2.8    2.9
1978            1.6    2.1    2.2    2.2    2.2    2.2    2.7
1979            2.2    2.3    4.5    5.2    7.6    7.7    7.8
1980            2.5    3.0    3.2    3.2    4.3    4.6    4.7
1981            2.1    3.0    3.1    3.1    3.1    3.1    5.0
1982            1.6    2.3    2.8    3.2    3.8    4.1    5.0
1983            1.2    1.8    2.1    2.5    2.5    2.5    2.6
1984            1.5    4.2    4.2    4.2    4.2    4.2    4.2
1985            1.7    2.7    2.7    2.7    2.8    2.9    3.5
1986            3.7    6.7    9.7   10.4   10.4   10.7   11.7
1987            2.7    4.8    4.8    4.8    6.2    6.2    6.7
1988            2.0    6.9    6.9    6.9    6.9    6.9   10.1
1989            1.9    2.9    3.0    3.0    3.0    3.0    3.2
1990            1.2    1.4    1.6    1.7    2.1    2.1    2.5