# The Travel Time of Floatable Litter of Different Densities Influenced by River Flow Velocity
###### Abstract  
Rivers are a source of life. However, these past years, the sustainability of rivers around the world has been threatened by urbanization, industrialization, and rapid development. These activities put pressure on waterway systems and rivers, leading to the emergence of riverine litter. The lack of understanding of the migration of litter in rivers can affect the decision-making efficiency of policymakers when it comes to riverine litter management. Therefore, the primary objective of this study is to evaluate the travel time for different densities of Floatable Litter (FL) in rivers influenced by river flow velocity. The density of the selected FL was manually determined by assessing litter characteristics of mass, volume, and size. The Sg. Berkelah river in Pahang, Malaysia was used as the simulation medium for the sampling of FL travel time utilizing the extrapolation of the Time of Travel (ToT) approach. The ToT technique utilizes a 30 m distance. The sampling was done under three different river flow velocity conditions. In this study, a correlation analysis between these two variables was carried out and evaluated. The results revealed that magazine papers possess the fastest FL travel time, with T = 43.9 s when v = 0.230 m/s, while cloth possesses the slowest FL travel time, with T = 204.90 s when v = 0.167 m/s. The travel time of FL is not influenced by low-class density, \(p<1000\) kg/m\({}^{3}\), but by other factors that have a stronger influence on the travel time of horizontally migrated litter. This study provides a basic understanding and overview of FL migrating characteristics in rivers for further reference by local authorities for litter monitoring and also future riverine litter studies. floatable litter; riverine litter; migration; density; travel time +
Footnote †: journal: Applied Sciences  
Riverine litter is the solid waste that is disposed of in the river, i.e., the riverbed and riverbanks [3]. Riverine trash pollution is a growing environmental concern around the world because it has the potential to harm aquatic species' survival, river ecosystems' optimal functioning, and local economies [4]. The study of quantifying and estimating the abundance and composition of riverine floatable litter (FL) getting into the ocean is quite popular. However, the transport of litter in rivers is rarely studied. Moreover, the specification of litter characteristics that will likely affect the migration of litter is not given much attention. Litter characteristics such as mass, shape, and density influence litter movements [5]. The physical characteristics of litter affect the extent of litter transportation and distribution patterns in aquatic environments. The density factor is directly related to buoyancy which will determine the persistence of litter in the river by affecting either litter's migration rate or its sinking to the river bottom. Assessing the migration behavior and transport pathway of riverine litter is important as it fills the 'knowledge gap' between marine litter and riverine litter studies by understanding the migration of FL in rivers before it gets into the ocean. The dynamics of litter migration behavior in rivers are caused by many factors linked together. However, there are still few studies on the factors, either individually or collectively. For instance, flow rate determines the fluxes of pollutants in rivers [6; 7; 8], and flow velocity is a component in determining flow rate where the higher river flow rate results in higher flow velocity. However, the effect of a river flow velocity as a factor influencing the litter flux and its migration is still understudied. An extrapolated methodology for the study of riverine litter is outlined and can easily be adapted as it does not cost much.