UM-32 : Power transformation technique in basic for flood frequency analysis

Abstract

Flood frequency analysis is a very useful technique for the estimation of design flood corresponding to a specified recurrence interval from the limited data. Generally, sample data is fit to several frequency distributions and then a suitable distribution is considered for estimating the floods of required recurrence intervals. Instead of fitting a probability distribution to raw data, sometimes the data is transformed, so that it conforms to a particular distribution of known characteristics for the purpose of flood frequency analysis. Power transformation (Box and Cox) is one of the powerful techniques for transforming any data series to near normal series.

The present user' s manual describes the power transformation technique in details and the computer programme transforms the given series of annual maximum peak flood to near normal distribution using power trans- formation. It then performs the flood frequency analysis on this transformed series using the method of moments for estimating 50,100,200,500,1000 and 10,000 years return period floods using two approaches based on the criteria that (1) coefficient of skewness is nearly zero and (ii) coefficient of skewness is nearly zero and coefficient of Kurtosis nearly equal to 3. 0

The programme of this user s manual is usable both on VAX-11/780 computer system as well as on IBM compatible Personal Computer with minor changes, which has been described in the programme itself. This user's manual also lists the sample input and corresponding generated output of one example.