Data Analysis

1. Sub Bottom Profile

Some results from the sub bottom profile along different survey lines are provided below.

(a) East of the exclosure

(b) West of the exclosure

(d) Outside the exclosure (parallel to the shore)

(e) Survey line from inside to outside the exclosure

From this data we can see that where there is vegetation, only one sediment layer is visible on the profile; however, where there is no vegetation there are two visible layers. For the two layer case it is suspected that the top layer is less dense material that may have been deposited from resuspended sediments. Within the exclosure there is more dense vegetation, and only one layer is visible on the profile, which indicates that the sediment near the surface is more stable and less likely to be resuspended.

2. Wave Climate

The wave climates inside and outside of the exclosure had very little noticeable difference. The wave height may have been slightly smaller inside the exclosure, but the difference was not substantial because the wind was mild.

(a) (b)

Figure 9. Wave observations (a) From inside of the exclosure looking out (b) From outside of the exclosure looking in.

3. Density and Water Content

(a)

(b) (c)

Figure 10. (a) The location of the samples that were used in density and water content analysis. The color of the location marker corresponds to that of the data plot. (b) Wet density of three samples as a function of depth. (c) Volumetric water content of three samples as a function of depth.

The density inside of the exclosure (Sample 1 and 3) is slightly greater than the density of the sample outside of the exclosure (Sample 11). From this density difference it can be assumed that the sediment inside the exclosure is more stable and would be less likely to be resuspended than that outside of the exclosure. The volumetric water content under saturation conditions is equal to the porosity of the sample. From previous studies, porosity is supposed to follow an exponential decay along with the depth. In our study, the sediment samples were not deep enough to obtain this trend. The other possible reason is that the soil samples have been disturbed under inappropriate preservation. The data shows that there is no noticeable difference between porosity inside and outside of the exclosure; therefore, no conclusions can be made about the consolidation (stability) difference inside and outside of the exclosure. This contradicts the conclusion made from the density analysis. The reason for this contradiction could be that the TDR analysis was performed before the density test, slightly disturbing the sample, or that the samples were analyzed two weeks after they were collected which may have led to errors in water content. From SBP data, we can find that for two layer cases, the thickness of the first layer is around 50 cm, exceeding the length of the Shelby tube; therefore, from density and volumetric water content analysis, there is no evidence showing the existence of the second layer.

4. Erosion Test

(a) (b)

Figure 11. (a) The location of the samples that were used in erosion analysis. The color of the location marker corresponds to that of the data plot. (b) Critical shear stress of two samples as a function of depth.

The critical shear stress for two samples inside the exclosure look roughly the same. However, sample 13 with more vegetation cover seems to have larger critical shear stress on the top, which indicate that it is harder to be eroded than sample 14 with less vegetation cover.

5. TDR Test

Figure 12. TDR result - Volumetric water content as a function of depth at Sample 3

From the TDR result, the volumetric water content as a function of depth was obtained, but it does not correspond to the results from density analysis. The reason for discrepancy may result from the metal Shelby tube, which conduct electromagnetic wave passing through it. Since the data is very different from the density analysis, it is believed that the TDR data is not accurate.