A log is floating downstream. How would you calculate the drag force acting on it?

Assumption:
Assume that the log and the water move downstream together with the same acceleration.
To calculate the drag force acting on the log floating downstream, first calculate the theoretical value of the acceleration it must have under the action of gravitational force and the frictional forces.
Assuming that the angle of inclination of the slope from which the log falls is ∅ , the gravitational force pulling the log downward is:
F = mg sin ∅
Here m is the mass of the log, g is the acceleration due to gravity, and ∅ is angle of inclination of slope.
The acceleration of the log because of the action of gravitational force is:

Now experimentally observe the acceleration of the log using change in its position vector, and determine its magnitude.
Calculate the acceleration due to drag force by subtracting the theoretical value of acceleration and the one experimentally observed. Multiplying this acceleration with the mass of the log gives the magnitude of the drag force on the log.
It is important to note that the above calculation would give an approximate value of the drag force because the assumptions taken under consideration do not represent real conditions. For example, the effect of buoyancy and smoothness of the plane are not considered in above calculations while in reality they bring considerable changes in the net acceleration of the log.