Application of Gumbel Distribution Method on Rainfall Intensity Duration Frequency in Awka Metropolis, Nigeria

Abstract

The study investigates the rainfall intensity duration frequency relationship in Awka metropolis, Nigeria. From the raw data, the maximum precipitation and the statistical variables (mean and standard deviation) for each duration (5, 10, 15, 20, 25 and 30) were computed. The computed precipitation values and intensities for different durations. From the findings of the study, it was revealed that the coefficient of determination (R²) goodness of fit test gave a least of 75% correlation, which confirmed the appropriateness of the fitted distribution. Gumbel graphical plots showed that the Gumbel function fits well the set data for selected return periods (5, 10, 15, 20, 25 and 30 years) and durations (10, 15, 30, 60, 120 and 240 mins). From the conclusion the following recommendations were made that the rainfall intensity distribution curves established could be used by engineer and other specialist in urban design in making hydrological forecasting, the determination of parameters for planning, design and operation of engineering structures for the control and use of water in the area of study. Such Engineering structures include reservoirs used in irrigation or municipal water supply during draught, its effect on flood flows in stream; urban storm drainage system used in the collection of excess water from urban areas, irrigation works, open land and highways and discharge into stream or rivers, calculating point rainfall values which are needed in the design of water resources structures and environmental planning such as storm sewers in urban development, road and air drainage design.