Sorting Skewness Grain size distribution .1 Mean grain size

3.3.2 Sorting

Sorting of the sediments reflects the overall size variation of the particles as influenced by the variation of the energy of the depositing medium.Analyses of the sorting distribution of the sediments Fig. 7­a revealed that majority of the sediment samples more than 85 were either poorly sorted sorting range between 1 and 2 phi; Folk, 1966 or moderately sorted sorting range between 0.7 phi and 1.0 phi; Folk, 1966, while 11.6 of the sediments were either moderately well sorted 8.3 or well sorted 3.3, with sorting ranges between 0.5 and 0.7 phi and 0.35 and 0.5 respectively. Furthermore, the results revealed that the sediments surrounding the western reef platform the reef platform off Mbegani as well as the most of the sediments on and adjacent to the northern tidal channel were relatively better sorted than the rest of the Lazy Lagoon sediments, These sediments were characterized by sorting value less than 1.0 phi, while the remaining parts of the sea bottom was characterized by poorly sorted sediments sorting value 1.0 phi.

3.3.3 Skewness

Skewness of the sediments is a measure of asymmetry of the sample distribution with respect to normal Folk, 1966. Analyses of the skewness of the sediments revealed that 43.3 of the sediments samples analysed had symmetrical skewness, with skewness value in the range between ­0,1 and +0.1, while 36.6 of the sample were either positively skewed18.3 or negatively skewed 18.3, with skewness value in the ranges of +0.1 to +0.3 or ­0.1 to ­0.3 respectively. Very negatively skewed sediments skewness value ­0.3 were also common with 15 of the 60 samples analysed but sediments with very positively skewness skewness 0.3 were relatively few. 9 a Sorting Poorly sorted 8.3 .3 3.3 60. 28 Moderately sorted Moderately well sorted Well sorted 496000 501000 9 2 8 2 5 9 2 8 5 5 1.0 1.0 0.8 0.8 1.2 0.8 1.0 1.2 1 .4 1 .6 1.2 4 Km Raised reef platforms with mangroves and other vegetations Raised reef platforms with mangroves Sandbanks Mangrove fringes Mbegani Mlingotini b Fig. 7: Lazy Lagoon sediments sorting; a Percentage of sorting classes from the 60 sediment samples analysed from Lazy Lagoon and b the contour map showing the distribution of sorting at Lazy Lagoon. 10 9 2 8 2 5 9 2 8 5 5 0.0 -0 .1 0.1 -0 .2 4 Km Raised reef platforms with mangroves and other vegetations Raised reef platforms with mangroves Sandbanks Mangrove fringes Mbegani Mlingotini -0 .1 -0 .2 .0 0.0 b 496000 501000 Fig. 8: Distribution of sediments skewness; a Percentage of skewness classes from the 60 sediment samples analysed at Lazy Lagoon and b the contour map showing the distribution of skewness at L:azy Lagoon. 11

3.4 Tidal currents