UM-24 : Technique for flood frequency analysis

Abstract

This user's manual gives the details of eight computer programmes to carry out flood frequency analysis. These programmes are for fitting of

1 Lognormal two parameter,

2. Lognormal three parameter,

3. Extreme value type 1

4. Pearson type III

5. Log Pearson type III distributions, and for

6. Computation of standard errors,

7. Best fit distribution using normalization procedures and ch square criterion and

8. Flood frequency analysis using power transformation method.

These programmes are written in FORTRAN language. The programmes listed 1 to 6 have been adopted from Kite (1977) and implemented and tested on VAX-11/780 Computer System of National Institute of Hydrology, Roorkee. While the programmes 7 to 8 have been developed and tested on the computer system of the Institute.

The programmes 1 to 5 compute the floods of 2, 5, 10,20, 50, and 100 years recurrence interval only. The parameters are estimated by method of moments and method of maximum likelihood.

The programme 6, computes standard errors of events computed from normal, 2 parameter log normal, 3 parameter log normal, EV-1, Pearson type III and log Pearson type III distributions compared to the observed event magnitudes.

Various normalization procedures used in the programme 7, include inverse Pearson type III transformation, lognormal transformation for which the parameters are estimated on the basis of theoretical relationships, log transformation, inverse log Pearson type III transformation and square root transformation.

Programme 8 estimates 50, 100, 200, 500, 1000 and 10,000 years return period floods using power transformation method to normalize the data.

All these programmes could be run on micro computers also with minor modifications on to suit particular system. This user's manual provides useful information for application by field engineers for hydrologic analysis and design. The results obtained by these programmes are subject to assumptions and limitation of flood frequency analysis approach