Suitable rainfall­Intensity­Duration­Frequency (IDF) models for Uyo City were developed using the statistical method of least­squares for non PDF and optimization solver for PDF models. A total of 20 rainfall models were developed based on 10 years rainfall data. These models are categorically grouped into three sets. The first set contains 10 rainfall models which represent inverse relationship between rainfall intensities and duration for specified frequencies called Intensity­Duration ­ Models. The second set contains 8 rainfall models which represent rainfall intensities and frequencies for specified duration called Intensity­Frequency Model.  The third set has two general models of Log Pearson Type –3 [LPT­3] and Gumbel Extreme Value Type – 3 (GEVT­3) based on modified Sherman’s empirical equation of intensity as a function of duration and frequency. The three sets of models developed in this study recorded high and positive values of coefficient of correlation, an indication of good curve fitting with values of Intensity­Duration Models ranging from 0.948 to 0.977; intensity frequency model ranging from 0.641 to 0.938 and the general models from 0.8619 – 0.905. The graphical comparisons of developed models at frequencies of 5.5 and 11 years confirmed LPT­3 to predict highest intensity values at short durations of 50 minutes or less, followed by the Quotient model (i.e intensity­duration model) and lastly by GEVT­3. For longer durations greater than 50 minutes, the Quotient models gave best performance prediction­wise. These set of models developed will serve as valuable tools for predicting rainfall events in Uyo City as well as for use in the design of hydraulic structures, urban drainage and flood control.

Author(s) Details

Professor Ify L. Nwaogazie
Department of Civil and Environmental Engineering, University of Port Harcourt, Nigeria.

Martin C. Ekwueme
Department of Civil and Environmental Engineering, University of Port Harcourt, Nigeria.

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