# Flood Flow Frequency Analysis 1-6-2009

OS : Windows / Linux / Mac OS / Solaris

Script Licensing : Other Free / Open Source License

Created : Jan 23, 2009

Downloads : 25

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## It uses a Log Pearson Type-3 distribution for ...

It uses a Log Pearson Type-3 distribution for estimating quantiles.

NaN need to be removed in the dataset. If any years have missing data, it will still assume to include that year as part of the sample size-- as stipulated in 17B guidelines. An exmaple MAT file is provided for the user to test.

A nice enhancement to this function is a plot of the analyses. It is plotted in probability space-- SKEWED probability space! Because data may not be normally distributed, plotting in skewed space maintains a straight line for the final frequency curve.

[dataout skews pp XS SS hp] = b17(datain, gg, imgfile)

datain(:, 1) = year or datenum

datain(:, 2) = peak annual flow rate

gg = a generalized weighted skew

imgfile = full path and file name to export the figure

dataout(:, 1) = Return Period (in years)

dataout(:, 2) = Probability

dataout(:, 3) = Final Frequency curve

dataout(:, 4) = upper CI frequency curve

dataout(:, 5) = lower CI frequency curve

dataout(:, 6) = Expected Probability (N-1)

skews(1) = Station Skew

skews(2) = Station Skew outliers, zero removed

skews(3) = Synthetic Skew

skews(4) = Weight adjusted skew

pp(:, 1) = gringorten plotting position

pp(:, 2) = weibull plotting position

pp(:, 3) = observations

XS = mean of Log10(Flow rates)

SS = standard deviation Log10(flow rates)

hp = historically adjusted weibull plotting position where historical peaks our high outliers are ranked in integer values (e. g. 1, 2, 3, etc. ) and systematic observations are adjusted.

• confidence intervals (95%) for the final frequency

• expected frequency curve based on an adjusted conditional probability

• observed data with computed plotting positions using Gringorten and Weibull techniques

• various Skews

• mean of log10(Q)

• standard deviation of log10(Q)

• a probability plot that does not require a toolbox to create, but also plots the probability space using the computed weighted skew and not just the normal probability

NaN need to be removed in the dataset. If any years have missing data, it will still assume to include that year as part of the sample size-- as stipulated in 17B guidelines. An exmaple MAT file is provided for the user to test.

A nice enhancement to this function is a plot of the analyses. It is plotted in probability space-- SKEWED probability space! Because data may not be normally distributed, plotting in skewed space maintains a straight line for the final frequency curve.

*Usage**Syntax:*[dataout skews pp XS SS hp] = b17(datain, gg, imgfile)

**datain = Nx2 double**

*Input:*datain(:, 1) = year or datenum

datain(:, 2) = peak annual flow rate

gg = a generalized weighted skew

imgfile = full path and file name to export the figure

**(is in the form of a N x 6 double, and all flows are in Log10)**

*Output:*dataout(:, 1) = Return Period (in years)

dataout(:, 2) = Probability

dataout(:, 3) = Final Frequency curve

dataout(:, 4) = upper CI frequency curve

dataout(:, 5) = lower CI frequency curve

dataout(:, 6) = Expected Probability (N-1)

skews(1) = Station Skew

skews(2) = Station Skew outliers, zero removed

skews(3) = Synthetic Skew

skews(4) = Weight adjusted skew

pp(:, 1) = gringorten plotting position

pp(:, 2) = weibull plotting position

pp(:, 3) = observations

XS = mean of Log10(Flow rates)

SS = standard deviation Log10(flow rates)

hp = historically adjusted weibull plotting position where historical peaks our high outliers are ranked in integer values (e. g. 1, 2, 3, etc. ) and systematic observations are adjusted.

**• estimates of a final frequency (based on a weighted skew)**

**Most important functions of Flood Flow Frequency Analysis by Jeff Burkey:**• confidence intervals (95%) for the final frequency

• expected frequency curve based on an adjusted conditional probability

• observed data with computed plotting positions using Gringorten and Weibull techniques

• various Skews

• mean of log10(Q)

• standard deviation of log10(Q)

• a probability plot that does not require a toolbox to create, but also plots the probability space using the computed weighted skew and not just the normal probability

**• MATLAB 7. 7 (R2008b)**

**Demands:****Flood Flow Frequency Analysis 1-6-2009 scripting tags:**annual extremes, flood frequency, curve, flow estimation, probability, flood flow frequency analysis, skews, dataout, space, plotting.

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