Research article

Rainfall- Intensity- Duration- Frequency Models for selected Cities in Southern Nigeria

¹Itolima Ologhadien and *²Ify L. Nwaogazie

¹Department of Civil Engineering, University of Science and Technology, PMB 5080, Nkpolu Port Harcourt, Nigeria

²Department of Civil and Environmental Engineering, University of Port Harcourt, Uniport Box 156, Choba, Nigeria

*Corresponding Author E-mail:  ify.nwaogazie@cohseuniport.com, itolima2000@yahoo.com

Accepted 12 October 2014

Abstract

Rainfall-Intensity-Duration-Frequency (IDF) models for five selected cities in Southern Nigeria were developed using standard statistical bivariant analyses. The Gumbel Extreme Type 1 distribution was applied to estimate 5-, 10-,15-,20-,25-,35- and 40-year return period maximum values for durations of 0.083 to 24hrs. Two-parameter models (Types-1 and 2), three-parameter model (Type-3) and four-parameter (general) models (Type-5) were developed for each station; thus, giving rise to four IDF models per station. The coefficients of variation (r²) for the two-parameter models range between 0.6 and 1.0; three-parameter models range between 0.915 and 1.0 while those of the four-parameter models range between 0.645 and 1.0, respectively. Based on the high magnitude of r², the IDF models developed are useful and programmable tools for hydrologic design of structures for control of storm runoff and flooding.

Keywords: Rainfall, Intensity, Duration, Frequency models, design, runoff structures.