*4.3.3 South to north profiles*

Furthermore, four profile lines (**Table 7**) were created in a longitudinal direction to investigate the changes on the lagoon along the direction west to east. The choice of this transect lines was based on the fact that human activities and urban development are more pronounced in the western part of the lagoon than what goes on in the eastern region, hence the reason for investigating the trend of changes on the lagoon water bed moving from west to east on its water bed. Likewise, some places of significant human activities were identified where a possibility for a high erosion and siltation rate on the lagoon bed could be feasible. A good example of such is the profile HH<sup>0</sup> (**Figure 3**) constructed from the southwestern region of the lagoon outlet around Carter Bridge. This region is known for heavy traffic: ferries and other human activities such as local sand mining. The position of profiles I-I<sup>0</sup> and J-J<sup>0</sup> was strategically chosen because a lot of dredging activities are going on in the area due to increased urban development and a struggle for space around the lagoon coast. It was assumed that accretion due to sediment transport from the uplands would be more pronounced in the western part than in the eastern side of the lagoon; this is assuming there is no dredging activity going on in the lagoon.

means of the two samples. The analysis presents (**Table 7** and **Figures 11** and **13**) a result of statistically significant differences existing along the profiles and the extent of change along each profile is presented graphically (**Figures 14–17**) and as

*Multiple comparisons mean plot with 95.0 percent LSD intervals for south-north direction profile.*

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

From the statistical tests of the four south-north directional profiles, the values of t-statistics and p-value are calculated for individual profile section at 95% confidence level. Other statistical tests were performed for further comparison of the individual data files that were involved in constructing each of the profiles. Further tests, F-test, ANOVA, multiple range and variable check (**Tables 7**–**9**), were constructed to further examine the result of the t-test and confirm the scientific evidence of the statistic tests. The F-test in ANOVA table, the statistically significant difference of the data means and the expression of the multiple range test show a p-value of 0.000037848; hence, there is a significant difference between the 2008

result of the F-test, the procedure of the multiple sample comparison compares 8 columns of data to reveal the overall changes between the two data sets in south-

*Accretion and erosion on Lagos Lagoon water bed between 2008 and 2014. Accretion is shown in red as*

*sediment net gain, while erosion is in blue colour as sediment net loss.*

. Consequent upon the

and 2014 bathymetric data around the region of profile H-H<sup>0</sup>

results from ArcGIS (**Figure 12**).

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

north directions.

**Figure 12.**

**97**

**Figure 11.**

Thus, this analysis investigates if there is a significant change on each of the established profile lines of 2008 and 2014 bathymetric datasets along south/north direction. Therefore, the hypothesis is set as follows:


In testing the hypothesis in this section, the research carried out a t-test to test the significant variation of the depth dynamic of the two repeated bathymetric data (2008 and 2014). The test constructs confidence intervals for each mean and for the difference between the means. It also compares the actual difference between the


*Morphodynamics in a Tropical Shallow Lagoon: Observation and Inferences of Change DOI: http://dx.doi.org/10.5772/intechopen.90189*

**Figure 11.**

with all the transect lines of C to F0

direction at different spatial location.

*4.3.3 South to north profiles*

significant variation with transects AA<sup>0</sup> and FF<sup>0</sup>

*Lagoon Environments Around the World - A Scientific Perspective*

direction. Therefore, the hypothesis is set as follows:

lagoon bed along the easting direction.

*\**

**96**

**Table 7.**

*South to north profiles.*

*denotes a statistically significant difference.*

the 2014 bathymetric data along the easting direction.

those of C to F0

, so also does transect A. This indicates that there

. It can be concluded that significant

is a statistically significant difference in the depth values of transect lines AA<sup>0</sup> and

changes have taken place between and within the transect line at varying degrees. Interestingly, it is evident in the results of **Figures 4**–**9** that erosion, shoaling, channel migration, channel movement and accretion take place along a west-east

Furthermore, four profile lines (**Table 7**) were created in a longitudinal direction to investigate the changes on the lagoon along the direction west to east. The choice of this transect lines was based on the fact that human activities and urban development are more pronounced in the western part of the lagoon than what goes on in the eastern region, hence the reason for investigating the trend of changes on the lagoon water bed moving from west to east on its water bed. Likewise, some places of significant human activities were identified where a possibility for a high erosion and siltation rate on the lagoon bed could be feasible. A good example of such is the profile HH<sup>0</sup> (**Figure 3**) constructed from the southwestern region of the lagoon outlet around Carter Bridge. This region is known for heavy traffic: ferries and other human activities such as local sand mining. The position of profiles I-I<sup>0</sup> and J-J<sup>0</sup> was strategically chosen because a lot of dredging activities are going on in the area due to increased urban development and a struggle for space around the lagoon coast. It was assumed that accretion due to sediment transport from the uplands would be more pronounced in the western part than in the eastern side of the lagoon; this is assuming there is no dredging activity going on in the lagoon. Thus, this analysis investigates if there is a significant change on each of the established profile lines of 2008 and 2014 bathymetric datasets along south/north

1.*H*<sup>0</sup> : There is no significant difference between the 2008 bathymetric data sample and the 2014 bathymetric data sample in predicting changes in the

2.*H*<sup>1</sup> : There is significant difference in the 2008 bathymetric data sample and

In testing the hypothesis in this section, the research carried out a t-test to test the significant variation of the depth dynamic of the two repeated bathymetric data (2008 and 2014). The test constructs confidence intervals for each mean and for the difference between the means. It also compares the actual difference between the

**Profile t-Statistic p-Value** Profile G-G<sup>0</sup> 0.348271 0.727964 Profile H-H<sup>0</sup> 4.1955 0.000037848\* Profile I-I<sup>0</sup> �1.71216 0.090557 Profile J-J<sup>0</sup> 1.30189 0.199436

. However, transect CC0 shows no difference at all but does show

*Multiple comparisons mean plot with 95.0 percent LSD intervals for south-north direction profile.*

means of the two samples. The analysis presents (**Table 7** and **Figures 11** and **13**) a result of statistically significant differences existing along the profiles and the extent of change along each profile is presented graphically (**Figures 14–17**) and as results from ArcGIS (**Figure 12**).

From the statistical tests of the four south-north directional profiles, the values of t-statistics and p-value are calculated for individual profile section at 95% confidence level. Other statistical tests were performed for further comparison of the individual data files that were involved in constructing each of the profiles. Further tests, F-test, ANOVA, multiple range and variable check (**Tables 7**–**9**), were constructed to further examine the result of the t-test and confirm the scientific evidence of the statistic tests. The F-test in ANOVA table, the statistically significant difference of the data means and the expression of the multiple range test show a p-value of 0.000037848; hence, there is a significant difference between the 2008 and 2014 bathymetric data around the region of profile H-H<sup>0</sup> . Consequent upon the result of the F-test, the procedure of the multiple sample comparison compares 8 columns of data to reveal the overall changes between the two data sets in southnorth directions.

#### **Figure 12.**

*Accretion and erosion on Lagos Lagoon water bed between 2008 and 2014. Accretion is shown in red as sediment net gain, while erosion is in blue colour as sediment net loss.*

*.*

as a variable so as to determine which of the profile depth mean (average) is

(that is sediment gain) was shown from the region of profile H<sup>0</sup> to profile J.

*Profile section H-H*<sup>0</sup> *showing degree of variation in the depths of the lagoon repeated bathymetric data.*

From the table of results on multiple range tests, six contrasts show a result that is significantly different, which implies significant variations in the depth of the 2008 and 2014 data sets. Further confirmation of the change is graphically

**Source Sum of squares Df Mean square F-Ratio P-Value** Between groups 56.9298 7 8.13284 9.18 **0.0000**

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

**Contrast Sig. Difference** �**Limits** G 2008-H 2014 **\* 0.782877** 0.238985 G 2014-H 2014 **\* 0.75562** 0.238985 G 2014-I 2008 **\* 0.505063** 0.33051 H 2008-H 2014 **\* 0.614762** 0.232394 H 2014-J 2008 **\*** �**0.928135** 0.410819 H2014-J 2014 **\*** �**0.603552** 0.410819

Within groups 534.972 604 0.885715

Total (corr.) 591.902 611

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

. It could be inferred from **Figure 15** that a mean depth of 3.1 m in 2014 against the mean depth of 2.5 m in 2008 shows erosion (whether by dredging or

, I-I<sup>0</sup>

. On the contrary, accretion

displayed in **Figure 15**. The difference in the mean of the dataset on line H-H<sup>0</sup> that was overlaid on each other shows a wide variation. The variations in the mean values of the two datasets on the same profiles are very visible on profiles H-H<sup>0</sup>

significantly different from the other (**Table 9**).

*\*denotes a statistically significant difference.*

naturally) around and along the profile section H-H<sup>0</sup>

and J-J<sup>0</sup>

**Figure 15.**

**99**

**Table 9.** *Multiple range test.*

**Table 8.** *ANOVA table.*

**Figure 13.** *Analysis of mean for all changes in depths from profile A-A*<sup>0</sup> *to J-J*<sup>0</sup>

**Figure 14.** *Profile section G-G*<sup>0</sup> *showing degree of variation in the depths of the lagoon repeated bathymetric data.*
