# The Travel Time of Floatable Litter of Different Densities Influenced by River Flow Velocity
## 3 Results and Discussion
### Relationship between Floatable Litter Density and Travel Time  
Figure 8 shows the scatterplot of FL travel time against FL density in three different river flow velocity conditions. The pattern of the change in FL density toward the change in travel time is observed.  
Preliminary analysis showed the relationship to be monotonic, as assessed by visual inspection of a scatter plot. A [PERSON]'s rank-order correlation analysis result shows there was no statistically significant correlation between the travel time and density of floatable litter (FL): rs = 0.098, \(\rho\) = 0.457. From the scatter plot, no distinguishable pattern of  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Condition** & **N** & **Mean** & **Minimum** & **Maximum** & **Standard Deviation** \\ \hline A & 20 & 51.48 & 43.93 & 82 & 8.87 \\ B & 20 & 97.56 & 71.95 & 204.9 & 28.82 \\ C & 20 & 85.3 & 57.65 & 186.75 & 27.46 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Descriptive statistics for the FL travel time in Condition A, B, and C.  
a relationship between density and travel time is observed for FL with \(\rho\) < 750 kg/m\({}^{3}\) in all conditions. However, a pattern starts to form when FL density \(\rho\) > 750 kg/m\({}^{3}\) where the FL travel time increases with density. This shows that FL travel time might change with FL density value--negatively correlated--when the density value is in the intermediate- to high-density class, \(\rho\) > 1000 kg/m\({}^{3}\). FL travel time is not influenced by the density factor when the FL has low-class density, \(\rho\) < 1000 kg/m\({}^{3}\). Moreover, according to [20], the horizontal transport of FL with a high density in rivers is dominant due to the higher current strength or turbulence in rivers. It causes the FL to remain buoyant and tend to transport horizontally rather than vertically.  
The correlation analysis result shows there is no relationship between the density factor and the travel time of FL. The negative correlation explains if there is any possibility for density to be affecting FL travel time, the higher FL density might result in a shorter travel time of FL migrating in rivers. The insignificant correlation between these variables might be caused by or influenced more by other factors. The overall findings from this FL travel time during different river flow velocity conditions were based on the real situation, where there are many other factors--both the litter's physical characteristics and environmental parameters--influencing the migration of FL through the migrating simulation, as explained in Section 3.3.  
In summary, the different density of FL does not explain the change in FL travel time because density value has more influence on the vertical transport of FL than horizontal transport of FL in rivers. While the majority of FL migration across the simulation distance is in horizontal transport mode. However, there seems to be a trade-off between vertical and horizontal transport of litter in which, during the low influence of vertical transport, the FL migration behavior is more influenced by horizontal transport. The density factor has no significant effect on FL horizontal transport; instead, other factors (e.g., wind, shape, turbulence) can influence the FL travel time more. Moreover, the density values of FL evaluated are very low which causes the tendency for horizontal transport to happen more.