Abstract
Rainfall Intensity-Duration-Frequency (IDF) relationship remains one of the mostly used tools in hydrology and water resources engineering, especially for planning, design and operations of water resource projects. IDF relationship can provide adequate information about the intensity of rainfall at different duration for various return periods. The focus of this research was to develop IDF curves for the prediction of rainfall intensity within the middle Niger River Basin (Lokoja and Ilorin) using annual maximum daily rainfall data. Forty (40) year’s annual maximum rainfall data ranging from 1974 to 2013 was employed for the study. To ascertain the data quality, selected preliminary analysis technique including; descriptive statistics, test of homogeneity and outlier detection test were employed. To compute the three hours rainfall intensity, the ratio of rainfall amount and duration was used while the popular Gumbel probability distribution model was employed to calculate the rainfall frequency factor. To assess the best fit model that can be employed to predict rainfall intensity for various return periods at ungauged locations, four empirical IDF equations, namely; Talbot, Bernard, Kimijima and Sherman equations were employed. The model with the least calculated sum of minimized root mean square error (RMSE) was adopted as the best fit empirical model. Results obtained revealed that the Talbot model was the best fit model for Ilorin and Lokoja with calculated sum of minimized error of 1.32170E-07 and 8.953636E-08. This model was thereafter employed to predict the rainfall intensity for different durations at 2, 5, 10, 25, 50 and 100yrs return periods respectively.
Highlights
Knowledge of intense rainfall characteristics is a useful asset in Engineering application especially for dams dimensioning and design of hydraulic projects (Pruski et al, 2002)
Descriptive statistics of annual maximum daily rainfall data employed for this analysis is presented in Tables 1 and 2 respectively
The data used in this study represent annual daily rainfall data obtained from Nigerian Meteorological Agency, Nigeria Meteorological Agency (NIMET)
Summary
Knowledge of intense rainfall characteristics is a useful asset in Engineering application especially for dams dimensioning and design of hydraulic projects (Pruski et al, 2002). Generation of intensity duration frequency curves for flood prediction within the Niger River Basin has become imperative owing to the recent devastations caused by flood in various parts within that zone; perhaps being due to the lack of rainfall data and the subsequent design of most drainage structures without appropriate rainfall intensity values (Antigha and Ogharekpe, 2013). Nigerian Journal of Environmental Sciences and Technology (NIJEST) Vol 4, No 2 October 2020, pp 382 - 397 runoff estimation formulas such, as the rational method, in order to predict the peak runoff flow from exact point of basin These are used in certain aspects of hydraulic structures design such as size of pipes and culvert (Dupont and Allen, 2000). An attempt was made to develop intensity duration frequency curves for Lokaja and Ilorin and generate models that can be employed to predict the intensity of rainfall for ungauged sites within the study area
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