Well this is just my opinion but I think because all the plants were gone they cant stop mud from rolling into it. Also when it rains the trees wont suck up the water, that will make it over flow and release into the land or dirt on the outsides of it. Mixing those two gives mud and it can potentially flow back in the river in largeish masses causing the river to mix with the mud makinging it more muddy. Hope this helps :D
Answer:

Explanation:
The acceleration of an object is equal to the change in velocity of the object divided by the time taken for the object to change the velocity:

where:
u is the initial velocity
v is the final velocity
t is the time taken for the velocity to change from u to v
For Ms Jackson in this problem, we have:
u = 6 m/s (initial velocity)
v = 0 m/s (final velocity)
t = 4 s (time elapsed)
Substituting into the equation, we find the acceleration:

And the negative sign indicates that the direction of the acceleration is opposite to the direction of motion.