Grain Size Analysis of the Sediments from Ogun River, South Western Nigeria

The grain size analysis for thirty-two sediment samples from Ogun River was carried out. Mechanical sieving method using a Ro-tap shaker was chosen for the analysis. The cumulative frequency curve is obtained by plotting grain size (in phi scale) versus cumulative percent using the Probability paper. The phi values of the percentiles 5%, 16%, 25%, 50%, 75%, 84% and 95% were read off from the ogive curve that was plotted. These were used to calculate the statistical parameters of standard deviation, skewness, kurtosis and mean. 2.1 is the mean value for the grain size distribution within the analysed sediments with a graphic mean distribution for these sediments ranging from 1.09 to 2.90 phi, indicative of fine to medium grained sand. The standard deviation (sorting) shows a spread of of 0.54 to 1.42 phi and a mean value of 0.81. Most of the samples are moderate to poorly sorted with only a few being moderately well sorted. The skewness values of the samples ranged from -0.25 to 0.53, thus indicating the presence of fine fraction and coarse fraction in the particle population. The kurtosis is between 0.58 and 4.5, indicating that 38% of the samples are leptokurtic, 41% are very leptokurtic, 6% are mesokurtic and 15% is very platykurtic.