**6. Summary and recommendations**

to calculate erosion rates and sedimentation. Sources of error and uncertainty are due mainly as a result of the surveying techniques used [81], the density of depth sampling points [82], interpolation and averaging [83] during compilation. The error and uncertainty due to survey methods and density of depth sampling are cared for during the survey exercise, while the careful choice of the interpolation method helps to reduce the uncertainty that could result from interpolation. Documentation on the sea bed morphological development of a lagoon is often needed to support its management, such as navigation, flood defence and habitat preservation, and the effects of changes in natural forcing factors (sea level rise) on the lagoon ecosystem. The present rate of change in the lagoon sea floor must be made a baseline for assessing historic evolution in order to understand and predict its sea bed dynamic trend. However, this demands both reliable data and consistent effec-

Numerous possible responses to sea level rise abound among which are inundation and flooding [55, 58, 84–86]. Prospective studies that focus on identifying the complex nature of the changes along the Nigeria coast should precede assessment of sea level; hence, the two combined can be evaluated to see the effect of sea level rise on the lagoon and other lagoons bounded along the Nigerian coastline. This is because the same rate of sea level rise scenario could bring different degrees of

From all the results presented in this study, changes exist on the lagoon bed, which are deemed highly significant. Therefore, it is recommended for any future studies that there is a need for consistent bathymetric data and that it is acquired with a high level of accuracy. This will help in measuring and monitoring the consistent change on the lagoon bed and also facilitate decision-making for better

On the basis of the foregoing evidence from the result in this chapter, it can be concluded that the lagoon bed sediment is appreciating gradually over years. If proper caution is not taken to monitor the diversion of effluent, erosion and runoff into the lagoon, in the next few decades, the entire lagoon may have reduced greatly both in plane and depth. With this conclusion, the lagoon can be managed and sustained from immediate future disappearance by employing consistent maintenance dredging on the system. Conversely, the cost of doing such consistent maintenance dredging might be too high for the government and hence a pro-active sustainable management of the lagoon and its ecosystem is the unique solution to

Although the results of this methodology address a particular lagoon, however, it can be adapted to lagoons and estuaries globally since in the global context, many lagoons and estuaries are faced with increased urbanisation around their ecosystem and the same forcing conditions are responsible for the changes in the systems. This section has been able to provide a synthesis that can be used globally for sustainable

This chapter has been able to use repeated bathymetric measurements to assess the dynamics of the Lagos Lagoon bed. The assessment revealed that a constant change mostly in terms of accretion takes place on the system's bed. However, there are other sections of the lagoon bed that experience erosion. The study achieves a

monitoring of the lagoon system in any region of the world.

tive survey methods.

**5.4 Concluding remarks**

management of the system.

the problem.

**108**

**5.3 Sea-level rise and its impact on the coastal lagoon**

*Lagoon Environments Around the World - A Scientific Perspective*

impact on different spatial locations on the coastline.

This chapter has been able to sum up its findings in this research that Lagos Lagoon is highly vulnerable to morphodynamic changes, and these changes include, as investigated in this research, interaction and the adjustment of its floor topography, and sequences of change involving the lagoon spatial sediment. Hence, it has been discovered from the research finding that the lagoon faces the challenge of sustainability and extinction due to poor planning across its ecosystem.

Mitigating the potential effects of morphological and hydrodynamic changes on a lagoon is a controversial issue, with many unanswered questions and a great portion of uncertainty.

The use of a functional mechanism to build a model for detecting the coastline changes of the lagoon was made possible with the application of ArcGIS 10.1. The model derived has been useful to ascertain the degree of transgression and regression of the lagoon coastline. From literature, it was discovered in 2010 that the lagoon surface area was 208 km<sup>2</sup> . However, the results of the model revealed the present surface area to be approximately 204 km<sup>2</sup> . Hence, the lagoon is gradually disappearing. Likewise, in the lagoon seafloor, specifically in the region used as a case study, the depth has decreased by an average of 0.16 m (0.026 m/year). By implication, without any dredging, the study area will have gained 1.3 m of sediment during a 50-year period.

For better management and sustainability of the lagoon, consistent measurement should go on henceforth especially measurement regarding bathymetry survey, flow and mixing in the lagoon.
