# The Travel Time of Floatable Litter of Different Densities Influenced by River Flow Velocity
## 2 Materials and Methods
### Measuring River Flow Velocity  
The river chosen for the simulation medium was Sg. Berkelah, Pahang as shown in Figure 3. It is about 31-35 km away from Kuantan City in the direction of Maran. The part of Sg. Berkelah used for field testing is located in Hulu Lepar, Malaysia Gambang; 41.6 km west of the nearest estuary, 5.38 km south of the Sg. Berkelah Waterfall landmark. The coordinates are 3.705124 N, 102.980644 E. Figure 3A-C is pictures showing the location of Sg. Berkelah and the selected river section.  
Figure 2: Water displacement method. Source: Author.  
River flow velocity is the measure of the speed of river water flows. The method used is extrapolated from the float method suggested by [9]. The float method is a simple method for measuring the flow rate of a river with an open channel and is suitable for rivers with small to large water flow and calm waters. River flow velocity was determined using the general formula of velocity, which the formula is part of the float method equation. The parameters are measured to calculate flow velocity using the general velocity formula as in Equation (5).  
Flow velocity, \(v=(\Delta s/\Delta t)\times\) correction factor  
Figure 3: The pictures to show the location of Sg. Berkelah. (**A**) Map of Malaysia. (**B**) Location of selected Sg. Berkelah river section. (**C**) The picture of the exact river section of Sg. Berkelah. Source: Google Map.  
where v is river flow velocity (m/s), As is the distance between two points (m), \(\Delta\)t is the time taken for the float bottle to travel between 2 points (s), and correction factor = 0.85.  
Firstly, for a 5 m float distance, m was measured and two points were marked along the channel. The minimum float distance required is 3 m. The average width and depth of the river were measured for information on the river's physical characteristics. River depth was measured at three points across the channel's cross-section; which are at the west riverbank, middle of the river, and east riverbank. Then, the average of the depths was calculated. River depth was recorded for Condition A, B, and C of river flow velocity. This is by assuming that river widths are the same along the river section. Figure 4 shows the selected river section of Sg. Berkelah has a straight riverbank.  
A bottle was used as the float bottle. The bottle was partially filled with water. The floating bottle was tossed from upstream at Point A of the river channel and the timer started. When the bottle reached Point B downstream, the timer was stopped. The floating bottle was tossed in the middle of the river channel. The floating bottle tossing process was repeated three times and the average of the time taken, s, was calculated. This float method was conducted in three river flow conditions--Condition A, Condition B, and Condition C--and the tossing of the float bottle was at the same place for all conditions, which was at the middle of the river channel. The river flow velocity was calculated using Equation (5) after all data required were measured.  
Three conditions for measurements were made, which were: (1) Three hours after rainfall on the day of heavy rainfall (three days straight rain) (Condition A); (2) Three hours after rainfall on the day of light rainfall (Condition B); (3) A sunny day (Condition C). Wind and turbulence conditions for each condition were observed.