Abstract:
Nigeria has witnessed diverse flood events in the past years, but the year 2012 was a year that went
down in the history of Nigeria pertaining to flooding.
The 2012 Nigeria climate Review showed very interesting features in the variability of
atmospheric elements compared to their long term averages. Notable amongst these observed
features was the positive rainfall anomaly recorded in most parts of the country including the
northeast zones. This anomaly gave rise to severe flooding which caused widespread devastation
to both lives and properties. Areas affected included Lokoja , Benue and Adamawa states amongst
others.
This study is to analyzed rainfall pattern and characteristics in Lokoja, determined the discharge
characteristics and established a relationship between rainfall amount and flood occurrence in the
study area.
The data used for the purpose of this study was the thirty years of annual peak flows and annual
rainfall data spanning the period 1983-2012. The data was sourced from the archives of the
Nigerian Hydrological Storms Agency (NIHSA) and Nigerian Meteorological Agency (NIMET),
Abuja. Thirty years (1983-2012) of annual rainfall data and annual peak flow was collected from
Nigerian Hydrological and Storms Agency (NIHSA), and the Nigerian Meteorological Agency
(NIMET), Abuja. The data covered the synoptic meteorological station and Hydrological stations
over Lokoja .
Annual rainfall and discharge data was analyzed using Gumbel distribution techniques,
Regression models was employed to estimate the annual Rainfall and the coefficient of
determination (R2). In determining the best plotting formula for the best probability distribution
v
used for the study, the results obtained from this study proved that Gumbel distribution technique
when matched with Weibull plotting position is the best method to employ when attempting to
predict return periods of floods statistically in the study area. While Hazen plotting position
matched with Gumbel distribution should be used for future analysis of rainfall data in the study
area.
