Spatial Assessment of the Textural Characteristics and Sorting of Beach Deposits on the Barrier Lagoon Coastal Complex, Lagos Nigeria

Abstract

The textural characteristics and sorting of the beach deposits on the Lagos barrier lagoon coastal complex was determined using grain size analysis of sediments. Fifty sediment samples were collected from five beaches namely Seme, Yovoyan, Lekki, Okun-Ajah and Orimedu. Inclusive mean and the inclusive standard deviation (sorting) were used to spatially assess the textural characteristics and sorting of sediment grain size so as to determine the prevailing wave energy level traversing the beaches and their significant variations at each beach using analysis of variance. The textural characteristics for the beaches showed dominantly coarse sands, moderately sorted sediments along the waterline, while medium sands, moderately well sorted sediments were found at the berm of the five beaches. The cross-shore profile of the beaches gave a dynamic system with moderately high wave energy between the waterline and the berm which affects the swash and backwash sediment grain size. Analysis of variance and post-hoc multiple comparisons according to Tukey-Kramer critical value was adopted to assess the spatial variations of the descriptive statistics and consequently, the wave energy level. The inclusive mean and the inclusive standard deviation were significantly different between the pairs of Seme and Okun-Ajah beaches in terms of textural characteristics and between the pairs of Seme and Yovoyan beaches in terms of sorting, accounting for the spatial variation in the descriptive statistics and thus the wave energy level between the beaches showing greater impacts with high wave energy level on Yovoyan and Okun-Ajah beaches than Seme beach due to their textural compositions. However, the hydrodynamic forces of the ocean were responsible for the moderately high wave energy level that traverses the beaches, making it unequivocal that the beaches on this barrier lagoon coastal complex are susceptible to coastal erosion.