Relationship between extreme daily rainfall and maximum daily river discharge within Lagos metropolis

Abstract

Many research works emphasized on rainfall pattern and urban flooding while others examined the relationship between extreme rainfall and its implication for flood frequency with little attempt to establish relationship between extreme rainfall and maximum river discharge. This study therefore, draws interconnection between extreme daily rainfall and maximum daily river discharge within Lagos metropolis. Data on rainfall were collected from Ikeja and Lagos Roof weather stations within the Yewa Basin in Lagos. Also, data on river discharge for Yewa River were obtained from Ogun-Oshun River Basin Development Authority, Abeokuta. Pearson Product Moment Correlation Coefficient (PPMC) was employed to assess the relationship between extreme daily rainfall and maximum daily river discharge at 95% confidence level. Analysis of Variance (ANOVA) employed was used to test for the variability in the means of extreme daily rainfall events across the two weather stations. The result showed that there is a significant relationship between extreme daily rainfall events and maximum daily river discharge for Ikeja station (t_value = 2.60, Cv= 2.18, P≤0.05) while no significant relationship was shown in Lagos Roof (t_value = 1.60, Cv= 2.18, P≥0.05). It was also revealed that that there are no significant differences in the mean values of extreme daily rainfall across the stations (F¹₃₀=2.086, P≥0.05).Therefore, this work has been able to show that the relationship between extreme rainfall and maximum river discharge is not always significant due to several factors such as distance from the sea (continentally) and variation in rainfall across the weather stations.

Keywords: Extreme Rainfall, Maximum River Discharge, Ogun-Osun, Flood Frequency