Morphodynamics in a Tropical Shallow Lagoon: Observation and Inferences of Change

Abstract

The Lagos Lagoon system and its adjacent tidal basins exhibit dynamics that are significantly different on both spatial and temporal scales. As urbanisation and human activities around the lagoon have intensified, the volume of sediment deposited into the basin is increasing on a daily basis. Changes on the lagoon bed over a 6-year time scale using repeated bathymetric data (2008, 2014) are presented, and the related data acquisition technique is explained. Data reduction is followed by analysis of the lagoon water bed dynamics using abstracted profile lines from the bathymetric data within a GIS environment. The results of the significant accretion and erosion within the lagoon system were analyzed spatially to quantify the volume of sediment gain or loss on the lagoon bed. The findings partly show that over 6 years, an average height of 0.16 m was gained by the lagoon. This amount translates into an annual accretion rate of 0.026 m. These findings enhance the prospect of verifying in the long term whether the Lagos Lagoon is gradually disappearing. To the best of the author's knowledge, this research reveals for the first time the complex evolutionary changes (channel movement, accretion, erosion, infill and movement of shoal) on the Lagos Lagoon bed.