The improvement in the drainage districts provided for in this chapter may consist solely, if so desired by those concerned, in the changing in whole or in part of the course or channel of a natural watercourse, or in straightening, as far as practicable, such watercourse and cleaning out so much of its natural channel as it is desired to utilize; or the improvement in such drainage district may, in addition to the main ditch, or drain, or channel, include such other lateral and other ditches and levees as may be deemed proper or necessary.