Development of Intensity Duration Frequency Curves for Accra

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May, 2016
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The research work is about the development of Intensity-Duration-Frequency curves for Accra. The IDF relationships is a mathematical relationships between the rainfall intensity, duration and frequency. It is a hydrologic statistical tool that is commonly used by engineers during planning and designing of hydraulic infrastructures such as drainage system and water storage facilities for urban and rural areas. Maximum rainfall depths of nine different durations for 28 years (1971 to 2006) were obtained from the Ghana Meteorological Agency. Regression analysis were used to fill in the missing gaps found in the data. Various literatures reviewed to find the probability distribution that best fitted the acquired data chose the Gumbel Extreme Value Type I (EVI) and the Log-Pearson Type III distributions. The Goodness of fit tests (Kolmogorov-Smirnov Anderson - Darling and the Chi-Square) using the aid of the Easy fit software finally selected and confirmed the Gumbel EVI as the best fit distribution function for the analysis of the data. For each duration: (0.2hr, 0.4hr, 0.7hr, 1.0hr, 2.0hrs, 3.0hrs, 6.0hrs, 12.0hrs, and 24.0hrs) sample characteristics were analyzed and used to determine the population parameters, which aided in finding the frequency of the rainfall depths and intensities for the construction of the IDF curves for Accra. Comparison made between the existing and the new intensities showed more than 20% average increase in value over J. B. Dankwa’s from shorter to longer durations (i.e. 0.2hr to 24.0hrs) and selected return periods (i.e. 5 to 100 years). This implies that the rainfall intensities for Accra has changed as a result of climate variability. Therefore, the relevant institution must begin to update the IDF curves for the various regions in Ghana. Besides, the responsible institution should commence an IDF curves development projects for those areas that presently lack the curves to guide planners and engineers during the design of hydraulic infrastructures.
A thesis submitted to the Department of Civil Engineering, College of Engineering in Partial Fulfilment of the requirements for the degree of Master of Science, Water Resources Engineering and Management.