Of the various empirical formulae relating the flood peak to the catchment area,
Dickens formula is used in the Central and Northern parts of the country. Ryves formula is used in Tamil Nadu and parts of Karnataka and Andhra Pradesh. Inglish formula is used in Western Ghats in Maharashtra.
For an annual flood series arranged in decreasing order of magnitude, the return period for a magnitude listed at position m in a total of N entries is
The probability that a hundred year flood may not occur at all during the 50 year life of the project is
The general equation for hydrological frequency analysis states that xT = value of a variate with a return period of T years is given by xT =
For a return period of 100 years the Gumbel’s reduced variate yT is
An annual flood series contains 100 years of flood data. For a return period of 200 years the Gumbel’s reduced variate is
Gumbel’s reduced variate, yT,
To use Gumbel’s method to estimate the magnitude of a flood with a return period of T years, the following data pertaining to annual flood series are sufficient
To estimate the flood magnitude with a return period T by the log-Pearson Type III method, the following data pertaining to annual flood series are sufficient
To estimate the flood magnitude with a return period of T years by using log-normal distribution, the following statistics of data are absolutely necessary
The recurrence interval of an event is TA in annual series and Tp in partial-duration series, then
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