Simplicity.

It flows.
 It crashes.

It employs only 
 as much effort as
  conditions dictate.

It does not rush
 in a panic.

While straight,
 its movements seem
  whip-like.

When possible,
 it moves straight,

But it rolls around or over
 any obstacle. 

If follows the course,
 but also carves
  the course.

Its movement, inexorable.