1st Annual Civil Engineering Conference University of Ilorin, Nigeria, 26-28 August 2009  CIVIL 2009 Civil Engineering Impact on National Development 32 INFLUENCE OF JEBBA HYDROPOWER DAM ON STATISTICAL DISTRIBUTION OF HYDRO-METEOROLOGICAL VARIABLES IN NIGER RIVER BASIN, NIGERIA 1 Yusuf, K.O and 2 Salami, A.W 1 Department of Agricultural and Biosystem Engineering University of Ilorin, P.M.B 1515. Ilorin, Nigeria. 2 Department of Civil Engineering, University of Ilorin, P.M.B 1515. Ilorin, Nigeria. Kamaru.yusuf@yahoo.com and awsalami2006@yahoo.co.uk ABSTRACT This report presents the evaluation of the effect of Jebba dam on hydro-meteorological variables within Niger River Basin. The study deal with time series analysis to depict the changes that occurred in the variables due to the existence of Jebba dam and the fitting of the variables with probability distribution models to select the best fit model for the purpose of prediction. The hydro-meteorological variables considered include; the reservoir inflow and outflow, rainfall, humidity, evaporation, temperature, sunshine and wind speed. The time series analysis indicated that there is positive correlation between the time and the variables considered. This implies that there would be an increase in those variables as a result of constructing the dam. Also, the Gumbel probability distribution models best fit Reservoir inflow, outflow and humidity at post dam stage. It was deduced that the maximum and minimum temperatures, evaporation and sunshine during dam construction and post dam stages were best fit by Gumbel. However, the Log-Pearson distribution model best fit rainfall and wind speed at both dam construction and post dam stages, while Log-Normal best fit humidity at dam construction stage. Keywords: Hydro-meteorological variables, Dam construction stage, Post dam stage, River basin, time series analysis and probability distribution models 1.0 INTRODUCTION River is a natural stream of water flowing in a channel to the sea or to the lake or joining another river, the area drained by a river and its tributaries is called river basin. There are two major rivers in Nigeria; the river Niger and river Benue. River Niger and its tributaries has great potential for the socio-economic transformation of the West African sub-region including Nigeria. Jebba hydropower dam is situated along the Niger River, a dam is a barrier built across a water body to hold back the flow of water, thereby creating a large body or pool of water called reservoir. Dams can be classified according to the purpose for which they are meant and also according to the materials used in constructing them, such as concrete, earth fill etc. The functions of dam include: regulation of the river flow, controlling of the water release in accordance to the electricity production or irrigation requirement. Despite the usefulness of dams, they usually have significant impact on economy, geology, environment, hydrology and meteorological variables.