**2. Literature review**

This section provides a brief review of the relevant scientific state-of-the-art relating to morphological and hydrodynamic changes in lagoon systems. A coastal lagoon can be seen as a shallow water body that exists in the low-lying coastal plain, it always has a barrier island that separates it from the ocean and the system always has one or more connecting channel with the ocean, the connection that influences

the hydrological behaviour of the lagoon depending on the dimension of the channel's cross-sectional area [24, 25].

central mud basin. If we consider geological time scales, coastal lagoons like estuaries are short-lived coastal features of recent origin. They are formed during the eustatic (uniform worldwide change in sea level) rise of sea level between the times of the Wisconsin glaciation 18,000 years before present (BP) and stand the risk of being completely in-filled by sediments or closed off from the sea by littoral

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

Various authors with different studies on coastal lagoons have consensus agree-

However, being a shallow coastal feature, lagoons tend to be well-mixed (mainly by winds rather than by currents), and they vary from brackish to hyper-saline, depending on the geographic location which dictates the level of balance between evaporation, precipitation and river flow. In equatorial regions, lagoons can be hyper-saline during dry seasons as a result of low influx of fresh water and high intrusion of saline water. But the same lagoon may become entirely fresh during rainy seasons [49]. Even though lagoons are shallow water bodies, the Lagos Lagoon that is the lagoon for consideration in this chapter (our research) has some parts around the inlets that are deep (12–17 m) as a result of continuous dredging either for the purpose of sand mining and reclamation or for channel navigation. Likewise, it is considered too brackish during the dry season and a fresh water lagoon during

The fourth Intergovernmental Plan on Climate Change (IPCC) report (AR4) projected the estimate of sea level rise for this century that it could likely range from 18 to 59 cm [52]. However, the estimation of IPCC's AR4 did not include the contributions from Greenland and Antarctica [53]. Basically, the actual rise may be higher or lower than the projection of IPCC. Hence, there is uncertainty in the estimation of sea level rise; this dilemma in the rise projection could be as a result of variation in the greenhouse gas both now and in the future. Climate model of IPCC 2001 report indicates spontaneous rise in the annual global mean temperatures

Sea level is raised by warmer temperature that melts the glacier ice sheets, the melted ice sheet is discharged into the ocean and this in turn increases and expands the volume of the ocean water, which splits into the enclosed water bodies like the lagoons and the estuaries and increases the water level in the systems [53]. The effect of increasing sea level brings negative hazards for coastal areas, including increased erosion, increased flooding/submergence, increased salinisation and threats to coastal cities in terms of storm surges, and all these could create direct negative impact on the urban coastal communities, wetlands, coastal ecosystem and the various infrastructural development around the coast [56–59]. Due to the negative effect of sea level rise, scientists and coastal policy makers face the challenge of

ment on the depth of the lagoon all over the world, and they all affirmed that lagoons are generally shallow with a few metres depth [8, 9, 11, 24, 29, 30, 32, 44–46]. In terms of size, coastal lagoons can be features originating within a plain of beach ridges (good example is deltaic plain) or shallow basins existing in environments of over 10,000 square km [47, 48] partially blocked by a barrier

*2.1.3 Lagoon's definition in relation to depth and size*

*DOI: http://dx.doi.org/10.5772/intechopen.90189*

island (example is Lagoa dos Patos, Brazil).

*2.1.4 Lagoon stratification*

the raining season [50, 51].

[54, 55].

**83**

**2.2 The response of coastal lagoon to sea level rise (SLR)**

drift [24].
