*4.5.2 Evidence base*

If the yearly average accretion (0.026 m/year) persists in the lagoon without any dredging/other removal, the study area of the lagoon will have gained a sediment height of 1.3 m in 50 years. Kjerfve and Magill [9] confirm that lagoons are net material sinks and that they are often subject to rapid sedimentation and will transform into other types of environments through sediment infilling and land-use activities. Hence, its time scale of transition since it is geologically rapid can occur within decades to centuries, and the Lagos Lagoon, as is the case with any other lagoon, is susceptible to disappearing after some decades. Kjerfve and Magill [9] use a systematic review approach and concluded that lagoons will quickly transform into other types of coastal environment without using any data to substantiate their inference. However, this aspect of the research has been able to confirm with scientific evidence that the Lagos Lagoon is a net material sinks, subject to rapid sedimentation, and can easily transform or go into extinction.

The spatial variability of erosion and accretion on the lagoon bed (**Figures 18** and **19**) shows that a large area of about 70,944,744 m2 was submerged into accretion with approximately 54,148,636 m<sup>3</sup> volume of sediment gained around the area. This large sediment deposition gives an indication that change in the lagoon bed is evident, that sediment is drifting constantly into the lagoon through erosion reducing the depth of the lagoon very fast despite the fact that there local dredging is going on within the system.
